review immune mechanisms in the pathogenesis of …...(mhc) class i transgene [3]. these non-immune...
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Available online http://arthritis-research.com/content/9/2/208
AbstractIdiopathic inflammatory myopathies (IIMs), comprising polymyositis,dermatomyositis, and inclusion-body myositis, are characterized byinflammatory cell infiltrates in skeletal muscle tissue, muscleweakness, and muscle fatigue. The cellular infiltrates often consistof T lymphocytes and macrophages but also, in some cases,B lymphocytes. Emerging data have led to improved phenotypiccharacterization of the inflammatory cells, including their effectormolecules, in skeletal muscle, peripheral blood, and other organsthat are frequently involved, such as skin and lungs. In this reviewwe summarize the latest findings concerning the role ofT lymphocytes, B lymphocytes, dendritic cells, and other antigen-presenting cells in the pathophysiology of IIMs.
IntroductionIdiopathic inflammatory myopathies (IIMs) are characterizedby mononuclear inflammatory cell infiltrates in skeletal muscletissue, by muscle weakness, and by muscle fatigue. They areoften subclassified into three major groups on the basis ofclinical and histopathological differences: polymyositis,dermatomyositis, and inclusion-body myositis. The cellularinfiltrates in muscle tissue are mainly composed of T lympho-cytes and macrophages but also, in some cases, B lympho-cytes. This observation, together with frequently detectedautoantibodies particularly in polymyositis and dermato-myositis, suggests that the inflammatory myopathies areimmune-mediated; they are believed to be triggered byenvironmental factors in genetically susceptible individuals.The varying clinical features and the different predominatinghistopathological features such as localization andphenotypes of inflammatory infiltrates, or rimmed vacuoles asseen in inclusion-body myositis, suggest that there aredifferent pathophysiological mechanisms leading to myositis.Despite these differences the inflammatory moleculesproduced in muscle tissue are highly similar in chronic
inflammatory myopathies, suggesting that some molecularpathways are shared between the subsets of inflammatorymyopathies.
In the inflammatory myopathies there are also signs ofmicrovascular involvement. The involvement of microvesselswas first reported in patients with dermatomyositis ascapillary loss and recognized by the presence of themembrane attack complex (MAC) [1,2]. Later, activatedcapillaries with increased expression of adhesion molecules(intercellular cell-adhesion molecule-1 and/or vascular cell-adhesion molecule-1) and IL-1α were also seen in patientswithout skin rash, in polymyositis and inclusion-body myositis.Damage or activation of blood vessels could indicate that themicrovessels are targets of the immune reaction in somesubsets of patients with IIM.
It has long been recognized that the inflammatory cellinfiltrates and muscle fiber damage are patchy and aresometimes not detected in muscle biopsies. This is a clinicalproblem in the diagnostic procedure. Moreover, the lack ofcorrelation between the degree of inflammatory infiltrates andmuscle weakness has led to a search for mechanisms otherthan immune-mediated muscle fiber damage that could causemuscle weakness. One such non-immune mechanism,endoplasmic reticulum stress, has been proposed, on thebasis of observations both from human studies and from ananimal model for myositis, the major histocompatibility complex(MHC) class I transgene [3]. These non-immune mechanismshave been addressed in a recent review paper [4].
New data are constantly emerging, leading to improvedcharacterization of the phenotypes of the inflammatory cellsand their effector molecules that are expressed in IIMs, not
ReviewImmune mechanisms in the pathogenesis of idiopathicinflammatory myopathiesCecilia Grundtman, Vivianne Malmström and Ingrid E Lundberg
Rheumatology Unit, Department of Medicine, Karolinska University Hospital Solna, Karolinska Institutet, SE-171 76 Stockholm, Sweden
Corresponding author: Cecilia Grundtman, [email protected]
Published: 26 March 2007 Arthritis Research & Therapy 2007, 9:208 (doi:10.1186/ar2139)This article is online at http://arthritis-research.com/content/9/2/208© 2007 BioMed Central Ltd
APC = antigen-presenting cell; DC = dendritic cell; ICOS = inducible co-stimulator; ICOS-L = ICOS ligand; IFN = interferon; IIM = idiopathicinflammatory myopathy; IL = interleukin; ILD = interstitial lung disease; MAC = membrane attack complex; MHC = major histocompatibility complex.
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Arthritis Research & Therapy Vol 9 No 2 Grundtman et al.
only in the major target organ, the skeletal muscle, but also inperipheral blood and in other organs that are frequentlyinvolved, such as skin and lungs. This increasing knowledgehas a great potential to improve our understanding of the roleof these inflammatory cells in disease mechanisms in IIMs. Inthis review we summarize the latest findings concerning therole of T lymphocytes, B lymphocytes, dendritic cells, andother antigen-presenting cells (APCs) in the pathophysiologyof IIMs.
T lymphocytesT lymphocyte functionT lymphocytes recognize antigens on APCs through theT-cell antigen receptor in a MHC-restricted fashion. Peptidesfrom intracellular pathogens proliferating in the cytoplasm arecarried to the cell surface by MHC class I molecules andpresented to cytotoxic (CD8+) T lymphocytes, which oncefully activated have the capacity to lyse infected target cells.In contrast, peptide antigens from pathogens in intracellularvesicles, and those derived from ingested extracellularbacteria and toxins, are carried to the cell surface by MHCclass II molecules and presented to CD4+ T helper cells.These can then differentiate into effector cells, such as TH1,TH2, and TH17 cells [5]. Pathogens that accumulate insidemacrophages and dendritic cells (DCs) tend to stimulate thedifferentiation of TH1 cells and the production of IgGantibodies by B lymphocytes. Conversely, extracellularantigens tend to stimulate the production of TH2, which cansubsequently stimulate the production of IgA and IgE. TH17 isa recently described effector T lineage that has beensuggested to contribute to chronic inflammatory settings.CD8+ T lymphocytes do not have as distinct sublineages andare cytotoxic cells working in a perforin/granzyme-dependentmanner; interestingly, CD4+ lymphocytes can sometimes alsodisplay cytotoxic effector functions.
T lymphocytes in idiopathic inflammatory myopathiesAlthough prominent T lymphocyte infiltrates are not alwaysfound in muscle biopsies, two types of cellular infiltrate havebeen recognized in IIMs, one being endomysial inflammatoryinfiltrates consisting mainly of CD8+ T lymphocytes andmacrophages invading non-necrotic muscle fibers expressingMHC class I antigens [6-8]. These are typically, but notexclusively, found in inclusion-body myositis and polymyositis.The other type of mononuclear cell infiltration isperivascular/perimysial and has become a characteristic ofdermatomyositis; it consists predominantly of CD4+ Tlymphocytes, occasionally together with B lymphocytes andmacrophages [6,9]. The deposition of complementcomponents is also mainly localized to the perivascularregions of muscular or cutaneous lesions. However, the‘classical’ T lymphocyte picture in IIM is, as the authors say,much more complex and an oversimplification of reality [6,9].Independent of T lymphocyte localization, their presencesuggests an involvement of the adaptive immune system inthese disorders (Figures 1 and 2).
Cytotoxic CD8+ T lymphocytes can release three differentcytotoxic proteins: perforin, granzyme, and granulysin. It isknown from earlier studies that in polymyositis and inclusion-body myositis, CD8+ T lymphocytes and macrophagessurrounding the non-necrotic muscle fibers expressing MHCclass I antigen do express perforin. Perforin may cause a leakin the sarcolemmal surface through which granzymes couldinvade the sarcoplasm to initiate muscle fiber necrosis [10-12]. Recently, granulysin has also been demonstrated in bothpolymyositis and inclusion-body myositis [13]. The presenceof granulysin-expressing CD8+ T lymphocytes tended tocorrelate with steroid resistance in polymyositis [13].Interestingly, perforin/granzyme-expressing CD4+ T lympho-cytes have also been demonstrated [10,14]. A schematicsummary of the potential role of different immune cells in thecontext of chronic muscle inflammation is presented inFigure 3.
The T lymphocyte repertoire in blood seems to differ betweenpolymyositis and dermatomyositis [15]. In peripheral blood ofactive dermatomyositis, a decreased percentage of CD3+
and CD8+ T lymphocytes and decreased IFN-γ expression byCD4+ and CD8+ T lymphocytes but an increase in B lympho-cytes and IL-4-producing CD4+ T lymphocyte frequencieswere found. These features were not seen in the inactive formof the disease. In patients with polymyositis with relapsingdisease, markedly perturbed T cell repertoires were seen. Theexpanded T lymphocytes clonally displayed a memoryphenotype, expressed intracellular perforin, and responded tostimulation by IL-2, which indicates that they have thepotential for reactivation under appropriate conditions [16].This suggests that a continuous autoantigen-driven processmight be prominent in this disease and that in patients withpolymyositis a relapse would more probably be associatedwith the reactivation of clones, which are present at diseaseonset, rather than with the emergence of new ones. Theconcept that clonally expanded muscle-infiltrating CD8+
T lymphocytes could recirculate into the blood is true not onlyfor patients with polymyositis but also for those withinclusion-body myositis [17]. Another possibility for therecirculation of T lymphocytes seen in polymyositis andinclusion-body myositis might be that the same antigen, forexample a virus, could independently induce the sameexpansion in the blood and in the muscle tissue if the antigenis present at both sites.
In patients with IIMs, T lymphocytes are found not only ininflammatory muscle tissues or blood but also in lungs inpatients with interstitial lung disease (ILD), which is afrequent manifestation in patients with polymyositis anddermatomyositis; this was found in up to 60 to 70% of suchpatients when sensitive techniques such as high-resolutioncomputed tomography and pulmonary function tests wereemployed [18]. ILD seems to be less common in patientswith inclusion-body myositis, although no reports are availablein which newly diagnosed patients have been investigated for
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lung involvement with these techniques. In the lungs CD8+ Tlymphocytes were distributed both in and around lymphoidfollicles and in the walls of normal-appearing alveoli, whereasCD4+ T lymphocytes and B lymphocytes were seen inassociation with lymphoid follicles. CD4+ T lymphocytes havealso been demonstrated in reconstructed thick alveolar walls[19]. The CD4+/CD8+ ratio in bronchoalveolar lavage fluidwas low [20,21]; most of the CD8+ T lymphocytes were ofHLA-DR+ [21] and CD25+ [22] types, suggesting that theywere activated. In a small study [23], a low CD4+/CD8+ ratiowas seen in bronchoalveolar lavage fluids in all patients withradiographic signs of ILD early in the disease course ofpatients with polymyositis or dermatomyositis. The function ofthese T lymphocytes is not known. It can only be speculatedthat they might interact with antigens (from viruses or othersources) expressed in various pulmonary cells (Figure 3). It isinteresting in this context that there is a reported tissuevariation of histidyl-tRNA synthetases with a higherexpression in normal lungs than in other organs, and thatpatients with autoantibodies against histidyl-tRNA synthetase– anti-Jo-1 antibodies – have ILD in close to 100% of cases.
Furthermore, a restricted accumulation of T lymphocytesexpressing selected T-cell antigen receptor V-gene segmentswas recorded in skeletal muscle and lung but not in peripheralblood, which suggests a common target antigen in theseorgans [23]. Moreover, a role for histidyl-tRNA synthetase inthe disease mechanism is supported by the observation thatthis antigen can serve as a chemokine for DCs and Tlymphocytes when cleaved by certain proteases [24].
Even though the histopathological picture in polymyositis anddermatomyositis is often different, a similar clonal expansionof T lymphocytes is seen in bronchoalveolar lavage fluid [25].In addition, T lymphocytes have been extracted from muscletissue of these patients. The established T cell lines showed avariable proportion of CD4+ and CD8+ T lymphocytes, whichdid not correlate with diagnosis [26]. Examples of CD4+ andCD8+ T lymphocyte localization in polymyositis, dermato-myositis, and inclusion-body myositis are shown in Figures 1and 2. As demonstrated here, a similar pattern with a mixtureof cell populations and both endomysial and perimysiallocalization may be found despite the diagnosis of myositis.
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Figure 1
Endomysial localization of CD4+ and CD8+ T lymphocytes. Immunohistochemical staining of samples from patients with polymyositis (PM) (a–c),dermatomyositis (DM) (d–f), and inclusion-body myositis (IBM) (g–i). (a) Hematoxylin and eosin (H&E) staining to localize inflammatory cellinfiltrates in a patient with polymyositis. (b) CD4+ T lymphocytes stained with a monoclonal SK3 mouse IgG1 antibody (Becton Dickinson, SanJose, CA, USA) in the same area as in (a) but further down in the biopsy. (c) CD8+ T lymphocytes stained with a monoclonal SK1 mouse IgG1antibody (Becton Dickinson) in a consecutive section to that in (b). (d) H&E staining to localize inflammatory cell infiltrates in a patient withdermatomyositis. (e) CD4+ T lymphocytes stained with a monoclonal SK3 mouse IgG1 antibody in the same area as in (d) but further down in thebiopsy. (f) CD8+ T lymphocytes stained with a monoclonal SK1 mouse IgG1 antibody in a consecutive section to that in (e). (g) H&E staining tolocalize inflammatory cell infiltrates in a patient with inclusion-body myositis. (h) CD4+ T lymphocytes stained with a monoclonal SK3 mouse IgG1antibody in the same area as in (g) but further down in the biopsy. (i) CD8+ T lymphocytes stained with a monoclonal SK1 mouse IgG1 antibody ina consecutive section to that in (h). Original magnifications: ×250 (a–f) and ×312.5 (g–i).
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When evaluating the presence of CD8+ T lymphocytes inbiopsies it is important to consider which reagents have beenused. Although the CD8 molecule is the classic lineagemarker for cytotoxic T lymphocytes, this is only true if the CD8molecule consists of an α and a β subunit (CD8αβ) and not ifit is a CD8αα homodimer. The homodimer can sometimes befound on activated CD4+ T lymphocytes [27], especially inthe gastrointestinal tract. Thus if the reagent used to detectCD8+ T lymphocytes is an antibody against the α subunit itcould detect both classical CD8+ T lymphocytes but alsoactivated CD4+ T lymphocytes. This information was notalways available when immunophenotyping of lymphocytes inmuscle tissue was presented. However, if the analysisincludes the detection of a cytotoxic agent this caveat ispartly avoided. A summary of selected T lymphocyte studiesin IIMs is presented in Table 1.
A role of T lymphocytes in polymyositis and dermatomyositisis further supported by the clinical improvement aftertreatment with immunosuppressive drugs that are known toaffect T lymphocytes. In contrast, patients with inclusion-bodymyositis rarely display improved muscle function after
treatment with immunosuppressive drugs, which is why therole of T lymphocytes in disease mechanisms is morequestionable in this form of myositis. Therapeutic agents thatdo not solely target T lymphocytes, but in all mentionedexamples affect T lymphocyte populations, have been shownto be effective in polymyositis and dermatomyositis; these aremethotrexate, cyclosporin A, tacrolimus, and anti-thymocyteglobulin. Methotrexate is one of the most commonly usedsecond-line immunosuppressive drugs given to patients withIIM. It is known to be well tolerated and effective inpolymyositis and dermatomyositis, although no placebo-controlled trials have yet been performed [28]. There are alsocase series showing beneficial effects of tacrolimus and anti-thymocyte globulin [29,30]. In addition, topical cutaneoustacrolimus therapy has also effectively been applied to skinlesions in patients with dermatomyositis [31]. Although theclinical improvement with these drugs could indicate that Tlymphocytes have a role in polymyositis and dermatomyositis,there are no data available to show that these therapies haveeffects on inflammatory cell infiltrates or molecular expressionin muscle tissue that correlate with the clinical effects, whichwould strengthen such a hypothesis.
Arthritis Research & Therapy Vol 9 No 2 Grundtman et al.
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Figure 2
Perivascular localization of CD4+ and CD8+ T lymphocytes. Immunohistochemical staining of samples from patients with polymyositis (PM) (a–c),dermatomyositis (DM) (d–f), and inclusion-body myositis (IBM) (g–i). (a) Hematoxylin and eosin (H&E) staining to localize inflammatory cellinfiltrates in a patient with polymyositis. (b) CD4+ T lymphocytes stained with a monoclonal SK3 mouse IgG1 antibody in the same area as in (a)but further down in the biopsy. (c) CD8+ T lymphocytes stained with a monoclonal SK1 mouse IgG1 antibody in a consecutive section to that in(b). (d) H&E staining to localize inflammatory cell infiltrates in a patient with dermatomyositis. (e) CD4+ T lymphocytes stained with a monoclonalSK3 mouse IgG1 antibody in the same area as in (d) but further down in the biopsy. (f) CD8+ T lymphocytes stained with a monoclonal SK1 mouseIgG1 antibody in a consecutive section to that in (e). (g) H&E staining to localize inflammatory cell infiltrates in a patient with inclusion-bodymyositis. (h) CD4+ T lymphocytes stained with a monoclonal SK3 mouse IgG1 antibody in the same area as in (g) but further down in the biopsy.(i) CD8+ T lymphocytes stained with a monoclonal SK1 mouse IgG1 antibody in a consecutive section to that in (h). Original magnifications:×312.5 (a–c, g–i) and ×250 (d–f).
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B lymphocytesB lymphocyte functionB lymphocytes have a major role in the immunological patho-genesis of autoimmune diseases. Not only can theirdifferentiated progeny, plasma cells [32,33], synthesize andsecret large quantities of immunoglobulins, they could alsoregulate other cell types, secrete cytokines, and presentantigens. B lymphocyte activation requires both binding of anantigen by surface immunoglobulin – the B-cell receptor –and an interaction with antigen-specific T lymphocytes(CD4+). CD4+ T lymphocytes then can induce vigorous Blymphocyte proliferation and direct the differentiation of theclonally expanded progeny of naïve B lymphocytes into eitherplasma cells or memory B lymphocytes. Both cytokines
released by CD4+ T lymphocytes and somatic hypermutationof V-region genes can influence antibody isotype switching orthe antigen-binding properties of the antibody, respectively,resulting in the production of antibodies of various isotypesthat can be distributed to various body compartments.
B lymphocytes in idiopathic inflammatory myopathiesIn 1984 and 1990, Arahata and Engel showed that B lympho-cytes were more frequent in perivascular sites than in endo-mysial sites [6,9]. Furthermore, B lymphocytes were morecommon in muscle tissue from patients with dermatomyositisthan from those with polymyositis or inclusion-body myositis.This observation was further supported by another study inwhich perivascular B lymphocytes were only found in patients
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Figure 3
Hypothetical involvement of T lymphocytes, B lymphocytes, and dendritic cells (DCs) in idiopathic inflammatory myopathies. (1) An unknown trigger(for example viral infection or ultraviolet radiation) in the respiratory tract or through the skin leads to the cleavage of histidyl-tRNA synthetase bygranzyme B through antiviral CD8+ T lymphocytes in the lungs. (2) Immature DCs carry receptors on its surface that recognize common features ofmany pathogens. When a DC takes up a pathogen in infected tissue it becomes activated and migrates to the lymph node. (3) Upon activation, theDC matures into a highly effective antigen-presenting cell (APC) and undergoes changes that enable it to activate pathogen-specific lymphocytesin the lymph node. T lymphocytes become activated and B lymphocytes, with active help from CD4+ T lymphocytes, proliferate and differentiateinto plasma cells. (4) Activated DCs, T lymphocytes, and B lymphocytes could release cytokines into the bloodstream. (5) The activated Tlymphocyte, on which the DC-MHC–antigen complex is bound, itself binds to specialized endothelial cells called high endothelial venules (HEV).For this purpose it uses the VLA-4 (very late activation antigen-4) and LFA-1 (lymphocyte function associated antigen-1) molecules on its surface tointeract with adhesion molecules (vascular cell-adhesion molecule-1 (VCAM-1) and intercellular cell-adhesion molecule-1 (ICAM-1)) on HEVs,where they can penetrate into peripheral lymphoid tissues. (6,7) Naïve T lymphocytes and B lymphocytes that have not yet encountered theirspecific antigen circulate continuously from the blood into the peripheral lymphoid tissues. (8,9) Various cytokines from the bloodstream orproduced locally could affect the muscle tissue or cell in many different ways. However, it is not clear whether the muscle cell itself could produceand release cytokines. (10-12) DCs, macrophages (Mφ), and B lymphocytes can interact with T lymphocytes in various ways. T lymphocytes couldpossibly also bind to muscle cells through inducible co-stimulators (ICOS), CD40 ligand (CD40-L), CD28, and CTLA-4 (CD152) on T lymphocytesto ICOS ligand (ICOS-L), CD40, and BB-1 antigen on the muscle cell. In that fashion, the muscle cell would function as an APC. (13) Plasma cells(CD138+) can be found in the muscle tissue of certain subgroups of patients with idiopathic inflammatory myopathy, but whether these cells couldproduce autoantibodies locally is not yet known. (14) T lymphocytes have been shown to bind in close contact with muscle cells and to releaseperforin, granzyme A, and granulysin, which may cause necrosis of muscle tissue or cells.
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Tab
le 1
Sel
ecte
d a
rtic
les
on
imm
un
oh
isto
chem
ical
loca
lizat
ion
of
infl
amm
ato
ry c
ells
in id
iop
ath
ic in
flam
mat
ory
myo
pat
hie
s
Ref
eren
ceP
olym
yosi
tisD
erm
atom
yosi
tisIn
clus
ion-
body
myo
sitis
T ly
mph
ocyt
es[9
]53
pat
ient
s. T
lym
phoc
ytes
wer
e le
ast a
bund
ant a
t 31
pat
ient
s. T
he p
ropo
rtio
n of
T ly
mph
ocyt
es w
as
48 p
atie
nts.
T ly
mph
ocyt
es w
ere
leas
t abu
ndan
t at
periv
ascu
lar a
nd m
ost a
bund
ant a
t end
omys
ial s
ites.
The
lo
wes
t at p
eriv
ascu
lar s
ites
and
high
est a
t pe
rivas
cula
r site
s an
d m
ost a
bund
ant a
t end
omys
ial
CD
4/C
D8
ratio
was
hig
hest
at p
eriv
ascu
lar s
ites
and
low
est
endo
mys
ial s
ites.
The
CD
4/C
D8
ratio
was
hig
hest
si
tes.
CD
4/C
D8
ratio
was
hig
hest
at p
eriv
ascu
lar
at e
ndom
ysia
l site
s. T
he p
ropo
rtio
n of
T ly
mph
ocyt
es
at p
eriv
ascu
lar s
ites
and
low
est a
t end
omys
ial s
ites.
si
tes
and
low
est a
t end
omys
ial s
ites.
The
pro
port
ion
estim
ated
to b
e Ia
+, o
r act
ivat
ed, w
as n
early
twic
e as
hig
h at
M
any
infla
mm
ator
y ce
lls d
ispl
ay th
e Ia
mar
ker,
but
of T
lym
phoc
ytes
est
imat
ed to
be
Ia+, o
r act
ivat
ed,
endo
mys
ial s
ites
as a
t per
ivas
cula
r site
son
ly o
ne-s
ixth
of p
eriv
ascu
lar l
ymph
ocyt
es a
nd
was
nea
rly tw
ice
as h
igh
at e
ndom
ysia
l site
s as
at
one-
fifth
of e
ndom
ysia
l T ly
mph
ocyt
es w
as Ia
+, o
r pe
rivas
cula
r site
sac
tivat
ed
[8]
7 pa
tient
s. E
ndom
ysia
l inf
iltra
tes
of T
lym
phoc
ytes
wer
e 21
pat
ient
s. S
ever
e m
uscl
e fib
er n
ecro
sis,
–
pred
omin
ant.
Par
tly in
vade
d no
n-ne
crot
ic c
ells
wer
e al
so
pred
omin
ant p
eriv
ascu
lar T
lym
phoc
yte
infil
trat
es,
seen
; som
e of
thes
e fib
ers
also
exp
ress
ed M
HC
cla
ss I
fibro
sis
and
perif
asci
cula
r atr
ophy
. MH
C c
lass
I w
ere
loca
lized
to p
erifa
scic
ular
fibe
rs
[11]
5 pa
tient
s. P
erfo
rin w
as c
o-lo
caliz
ed w
ith g
ranz
yme
A a
nd
5 pa
tient
s. T
here
wer
e ve
ry fe
w p
erfo
rin+
and
2 pa
tient
s. P
erfo
rin w
as c
o-lo
caliz
ed w
ith g
ranz
yme
occa
sion
ally
inva
ded
non-
necr
otic
mus
cle
fiber
s. T
he
gran
zym
e A
-pos
itive
cel
ls in
DM
A a
nd o
ccas
iona
lly in
vade
d no
n-ne
crot
ic m
uscl
e pe
rcen
tage
of p
erfo
rin+
cells
am
ong
the
endo
mys
ial C
D8+
fiber
s. T
he p
erce
ntag
e of
per
forin
+ce
lls a
mon
g th
e ce
ll po
pula
tion
was
9.9
%en
dom
ysia
l CD
8+ce
ll po
pula
tion
was
12.
5%
[10]
5 pa
tient
s. C
o-lo
caliz
atio
n of
per
forin
with
CD
8, C
D4,
4
patie
nts.
Co-
loca
lizat
ion
of p
erfo
rin w
ith C
D8,
–
CD
3, a
nd C
D2
was
ana
lyze
d. T
he g
ener
al d
istr
ibut
ion
of
CD
4, C
D3,
and
CD
2 w
as a
naly
zed.
The
gen
eral
in
flam
mat
ory
cells
was
end
omys
ial.
The
over
all C
D4/
CD
8 di
strib
utio
n of
infla
mm
ator
y ce
lls w
as p
eriv
ascu
lar
ratio
was
1.1
and
the
tota
l num
ber o
f CD
8+in
flam
mat
ory
and
perim
ysia
l. Th
e ov
eral
l CD
4/C
D8
ratio
was
1.2
ce
lls in
9 ra
ndom
mic
rosc
opic
fiel
ds w
as 2
36. M
ore
than
90%
an
d th
e to
tal n
umbe
r of C
D8+
infla
mm
ator
y ce
lls in
of
per
forin
+ce
lls w
ere
CD
2+C
D3+
, and
per
forin
was
exp
ress
ed
9 ra
ndom
mic
rosc
opic
fiel
ds w
as 1
67. M
ore
than
bo
th in
non
-inva
sive
inte
rstit
ial T
lym
phoc
ytes
and
in a
utoi
nvas
ive
90%
of p
erfo
rin+
cells
wer
e C
D2+
CD
3+, a
nd 5
0% o
f C
D8+
T ly
mph
ocyt
es. O
f all
perfo
rin+
cells
, 60%
wer
e C
D8+
and
all p
erfo
rin+
cells
wer
e C
D4+
and
50%
wer
e C
D8+
. 40
% C
D4+
. Con
vers
ely,
75%
of t
he C
D8+
cells
and
50%
of t
he
Con
vers
ely,
80%
of t
he C
D4+
cells
and
90%
of t
he
CD
4+ce
lls w
ere
perfo
rin+. 4
3% o
f the
CD
8+T
lym
phoc
ytes
C
D8+
cells
wer
e pe
rforin
+. P
erfo
rin w
as d
istr
ibut
ed
that
con
tact
ed a
mus
cle
fiber
exp
ress
ed p
erfo
rin v
ecto
rially
ra
ndom
ly in
the
cyto
plas
m o
f the
infla
mm
ator
y to
war
d th
e ta
rget
mus
cle
fiber
T ly
mph
ocyt
es
[13]
17 p
atie
nts.
The
num
bers
of C
D4,
CD
8, a
nd C
D56
cel
ls p
er
–7
patie
nts.
The
num
bers
of C
D4,
CD
8, a
nd C
D56
1,
000
mus
cle
fiber
s at
end
omys
ial s
ites
wer
e 27
5 ±
140
, ce
lls p
er 1
,000
mus
cle
fiber
s at
end
omys
ial s
ites
355
± 1
50, a
nd 2
5 ±
13
(mea
ns ±
SD
) in
all c
ases
. Gra
nuly
sin
wer
e 25
0 ±
120
, 330
± 2
00, a
nd 3
1 ±
16
was
exp
ress
ed in
the
cyto
plas
m o
f inf
iltra
ting
cells
, mos
tly
(mea
ns ±
SD
) in
all c
ases
. Gra
nuly
sin
was
C
D4+
and
CD
8+ce
lls, o
nly
a fe
w C
D56
+ce
lls a
t a h
ighe
r ex
pres
sed
in th
e cy
topl
asm
of i
nfilt
ratin
g ce
lls, m
ostly
le
vel i
n en
dom
ysia
l site
s th
an in
per
ivas
cula
r site
s. N
otab
ly,
CD
4 an
d C
D8+
cells
, onl
y a
few
CD
56+
cells
at a
st
eroi
d-re
sist
ant p
atie
nts
with
PM
had
a h
ighe
r fre
quen
cy o
f hi
gher
leve
l at e
ndom
ysia
l site
s th
an a
t per
ivas
cula
r do
uble
-pos
itive
CD
8 an
d gr
anul
ysin
at e
ndom
ysia
l site
s th
an
site
sst
eroi
d-re
sist
ant p
atie
nts
with
IBM
[61]
2 pa
tient
s. C
D8+
T ly
mph
ocyt
es w
ere
foun
d to
inva
de m
uscl
e 2
patie
nts.
Mos
t IC
OS
and
ICO
S-L
pos
itive
cel
ls
20 p
atie
nts.
CD
8+T
lym
phoc
ytes
wer
e fo
und
to
fiber
s co
-exp
ress
ing
ICO
S-L
and
MH
C c
lass
I. T
he e
ndom
ysia
l w
ere
loca
lized
to th
e pe
rimys
ial r
egio
ns a
nd
inva
de IC
OS
-L a
nd M
HC
cla
ss I
co-e
xpre
ssin
g IC
OS
-pos
itive
CD
8+an
d C
D4+
T ly
mph
ocyt
es w
ere
seen
at a
co
nnec
tive
tissu
e. IC
OS
-exp
ress
ing
CD
4+an
d m
uscl
e fib
ers.
ICO
S-L
exp
ress
ion
was
foun
d on
the
sim
ilar f
requ
ency
and
ratio
to th
ose
in p
atie
nts
with
IBM
CD
8+T
lym
phoc
ytes
wer
e in
frequ
ent a
nd p
rese
nt
surfa
ce o
f alm
ost a
ll fib
ers,
incl
udin
g he
alth
y on
ly in
the
perim
ysiu
m a
nd a
roun
d bl
ood
vess
els,
m
yofib
ers
away
from
infla
mm
atio
n. 1
/20
or 2
/20
but n
ot a
mon
g au
toin
vasi
ve T
lym
phoc
ytes
auto
inva
sive
CD
8+T
lym
phoc
ytes
wer
e do
uble
-po
sitiv
e fo
r IC
OS
and
CD
8. A
sim
ilar p
erce
ntag
e of
C
D4+
T ly
mph
ocyt
es, p
artly
foun
d in
clo
se c
onta
ct
with
CD
8+T
lym
phoc
ytes
, als
o sh
owed
ICO
S
doub
le im
mun
orea
ctiv
ity
Con
tinue
d
-
Available online http://arthritis-research.com/content/9/2/208
Page 7 of 12(page number not for citation purposes)
Tab
le 1
(co
nti
nu
ed)
Ref
eren
ceP
olym
yosi
tisD
erm
atom
yosi
tisIn
clus
ion-
body
myo
sitis
B ly
mph
ocyt
es
[9]
53 p
atie
nts.
B ly
mph
ocyt
es w
ere
mos
t abu
ndan
t at
31 p
atie
nts.
B ly
mph
ocyt
es w
ere
mos
t abu
ndan
t 48
pat
ient
s. B
lym
phoc
ytes
wer
e m
ost a
bund
ant a
t pe
rivas
cula
r site
s an
d le
ast a
bund
ant a
t end
omys
ial
at p
eriv
ascu
lar s
ites
and
leas
t abu
ndan
t at
periv
ascu
lar s
ites
and
leas
t abu
ndan
t at e
ndom
ysia
l si
tes;
how
ever
, onl
y fe
w B
lym
phoc
ytes
wer
e ex
pres
sed
endo
mys
ial s
ites
site
s; h
owev
er, o
nly
few
B ly
mph
ocyt
es w
ere
expr
esse
d in
com
paris
on w
ith p
atie
nts
with
der
mat
omyo
sitis
com
pare
d w
ith d
erm
atom
yosi
tis
Pol
ymyo
sitis
, 3
patie
nts.
Occ
asio
nal s
catte
red
B ly
mph
ocyt
es (C
D19
and
N
o da
ta w
ere
give
n fo
r 5 p
atie
nts
with
16
pat
ient
s. O
ccas
iona
l sca
ttere
d B
lym
phoc
ytes
de
rmat
o-C
D20
) with
a m
ean
dens
ity o
f 2.8
cel
ls/m
m2
wer
e se
en.
derm
atom
yosi
tis w
ho w
ere
inve
stig
ated
for
(CD
19 a
nd C
D20
) with
a m
ean
dens
ity o
f m
yosi
tis, a
nd
Pla
sma
cells
(CD
138)
sho
wed
a m
ean
dens
ity o
f B
lym
phoc
ytes
(CD
19 a
nd C
D20
) and
pla
sma
4.2
cells
/mm
2w
ere
seen
. Pla
sma
cells
(CD
138)
in
clus
ion-
body
11
.0 c
ells
/mm
2 . C
D13
8+ce
lls w
ere
loca
ted
pred
omin
antly
ce
lls (C
D13
8). H
owev
er, a
com
paris
on w
as d
one
show
ed a
mea
n de
nsity
of 1
7.2
cells
/mm
2 . C
D13
8+
myo
sitis
, [34
]; in
the
endo
mys
ium
. The
re w
ere
3.9-
fold
mor
e pl
asm
a ce
lls
with
ano
ther
stu
dy in
whi
ch it
was
sho
wn
that
IBM
ce
lls w
ere
loca
ted
pred
omin
antly
in th
e en
dom
ysiu
m.
derm
ato-
than
B ly
mph
ocyt
esm
uscl
e tis
sue
had
0.84
-fold
B ly
mph
ocyt
es a
nd
Ther
e w
ere
4.1-
fold
mor
e pl
asm
a ce
lls th
an
myo
sitis
, [49
]4.
3-fo
ld p
lasm
a ce
llsB
lym
phoc
ytes
Den
driti
c ce
lls
Pol
ymyo
sitis
10
pat
ient
s. C
olle
ctio
ns o
f mye
loid
DC
s (B
DC
A-1
+) w
ere
14 p
atie
nts.
Pla
smac
ytoi
d D
Cs
(BD
CA
-2+) w
ere
20 p
atie
nts
with
IBM
wer
e in
vest
igat
ed. C
olle
ctio
ns
and
incl
usio
n-pr
esen
t in
90%
, wid
ely
dist
ribut
ed a
cros
s th
e se
ctio
n w
ith
seen
in 1
0/14
pat
ient
s an
d w
ere
mai
nly
loca
lized
of
mye
loid
DC
s (B
DC
A-1
+) w
ere
pres
ent i
n 17
/20
body
myo
sitis
, ad
ditio
nal h
igh-
dens
ity a
ccum
ulat
ions
. Hig
h-de
nsity
to
end
omys
ial a
nd p
reiv
ascu
lar l
ocat
ions
patie
nts
wid
ely
dist
ribut
ed a
cros
s th
e se
ctio
n w
ith
[48]
; der
mat
o-ac
cum
ulat
ions
wer
e ty
pica
lly e
ndom
ysia
l and
eith
er
addi
tiona
l hig
h-de
nsity
acc
umul
atio
ns. T
hese
hig
h-m
yosi
tis, [
49]
surr
ound
ed m
yofib
ers
and
som
etim
es in
vade
d ap
pare
ntly
de
nsity
acc
umul
atio
ns w
ere
typi
cally
end
omys
ial a
nd
non-
necr
otic
myo
fiber
s. T
hey
wer
e al
so e
xpre
ssed
in d
ense
ei
ther
sur
roun
ded
myo
fiber
s an
d so
met
imes
inva
ded
colle
ctio
ns o
f cel
ls (a
lway
s so
me
CD
3+ce
lls in
thes
e de
nse
appa
rent
ly n
on-n
ecro
tic m
yofib
ers.
The
y co
uld
also
co
llect
ions
) bet
wee
n m
yofib
ers.
Har
dly
any
plas
mac
ytoi
d be
exp
ress
ed in
den
se c
olle
ctio
ns o
f cel
ls (a
lway
s D
Cs
(BD
CA
-2+) w
ere
seen
som
e C
D3+
cells
in th
ese
dens
e co
llect
ions
) be
twee
n m
yofib
ers.
Har
dly
any
plas
mac
ytoi
d D
Cs
(BD
CA
-2+) w
ere
seen
Der
mat
o-–
14 p
atie
nts.
MxA
was
exp
ress
ed in
per
ifasc
icul
ar
20 p
atie
nts.
A q
uant
itativ
e st
udy
has
been
don
e m
yosi
tis, [
49];
area
s. E
ight
pat
ient
s sh
owed
MxA
exp
ress
ion
betw
een
patie
nts
with
IBM
and
DM
who
had
not
in
clus
ion-
body
by
myo
fiber
s in
a p
refe
rent
ially
per
ifasc
ular
re
ceiv
ed im
mun
osup
pres
sive
trea
tmen
t. Th
e m
yosi
tis, [
48,4
9]di
strib
utio
n in
bot
h at
roph
ic a
nd n
orm
al-s
ized
nu
mbe
rs o
f mye
loid
and
pla
smac
ytoi
d D
Cs
wer
e fib
ers
but a
lso
in c
apill
arie
s an
d ot
her b
lood
si
mila
r in
periv
ascu
lar a
nd p
erim
ysia
l are
as in
IBM
. ve
ssel
s in
13/
14 p
atie
nts.
In re
gion
s of
H
owev
er, t
he e
ndom
ysia
l loc
atio
ns o
f mye
loid
DC
pe
rifas
cicu
lar a
trop
hy a
ll m
yofib
ers
wer
e po
sitiv
enu
mbe
rs w
ere
a m
ean
of 3
-fold
hig
her t
han
thos
e of
pl
asm
acyt
oid
DC
s. In
con
tras
t, in
DM
ther
e w
ere
16-fo
ld a
nd 3
-fold
mor
e pl
asm
acyt
oid
DC
s th
an
mye
loid
DC
s in
end
omys
ial a
nd p
eriv
ascu
lar s
ites,
re
spec
tivel
y
[47]
6 pa
tient
s. Im
mat
ure
DC
s (C
D1a
) wer
e m
ainl
y fo
und
in
6 pa
tient
s. Im
mat
ure
DC
s (C
D1a
) wer
e m
ainl
y –
lym
phoc
ytic
infil
trat
es in
all
patie
nts.
Mat
ure
DC
s fo
und
in ly
mph
ocyt
ic in
filtr
ates
in a
ll pa
tient
s.
(DC
-LA
MP
/CD
83) w
ere
loca
lized
to p
eriv
ascu
lar i
nfilt
rate
s M
atur
e D
Cs
(DC
-LA
MP
/CD
83) w
ere
loca
lized
to
surr
ound
ing
mus
cle
fiber
spe
rivas
cula
r inf
iltra
tes
surr
ound
ing
mus
cle
fiber
s
The
refe
renc
es w
ere
sele
cted
acc
ordi
ng to
imm
unoh
isto
chem
ical
dat
a of
loca
lizat
ion
of T
lym
phoc
ytes
, B ly
mph
ocyt
es, a
nd d
endr
itic
cells
(DC
s) in
ske
leta
l mus
cle
tissu
e of
pat
ient
s w
ith p
olym
yosi
tis (P
M),
derm
atom
yosi
tis (D
M),
and
incl
usio
n-bo
dy m
yosi
tis (I
BM
). M
HC
, maj
or h
isto
com
patib
ility
com
plex
; IC
OS
, ind
ucib
le c
o-st
imul
ator
; IC
OS
-L, I
CO
S li
gand
.
-
with dermatomyositis but not in patients with polymyositis orinclusion-body myositis [8]. In contrast, a recent study byGreenberg and colleagues [34] demonstrated the presenceof differentiated B lymphocytes in the form of CD138+ plasmacells predominantly in the endomysium of muscle tissue ofpatients with polymyositis and inclusion-body myositis (nopatients with dermatomyositis were included in this study). Alocal antigen-driven response has been shown to be present ininflammatory myopathies. Clonal expansion, class-switchedsignificant somatic mutation, and variation of local Blymphocyte and plasma cell maturation could occur within theskeletal muscle [35]. These characteristics are hallmarks of anantigen-driven response, which would mean that T lympho-cytes are not the only cell that could drive an intramuscularantigen-specific autoimmunity in inflammatory myopathies.
In peripheral blood, activated B lymphocytes (RP105-negative B cells) were distinctly increased in patients withdermatomyositis in comparison with those with polymyositis[36]. In another study, peripheral blood mononuclear cellsfrom patients with dermatomyositis, but not from those withwith polymyositis, produced significant amounts ofimmunoglobulins in vitro [37].
Thus, earlier studies based on cellular expression in muscletissue and, to some extent, the investigations of peripheralblood suggest that B lymphocytes are important indermatomyositis but may have a less important role inpolymyositis. However, more recent data using stainingmarkers to detect plasma cells indicated a role of Blymphocytes in polymyositis and inclusion-body myositis aswell [34]. Autoantibodies are present in 60 to 70% ofpatients with polymyositis or dermatomyositis, supporting arole for B lymphocytes in these disease entities, but lessoften in patients with inclusion-body myositis. Someautoantibodies found in patients with myositis, such as anti-Ro/SSA, anti-La/SSB, anti-Scl-70, and anti-U1 ribonucleo-protein, are also found in other autoimmune diseases,whereas others, especially anti-synthetase antibodies (forexample anti-histidyl-tRNA synthetase or anti-Jo-1), anti-Mi2,and anti-signal-recognition particle are more specific formyositis. The myositis-specific autoantibodies are oftenassociated with distinct clinical manifestations, such as theanti-synthetase syndrome characterized by myositis, ILD,arthritis, Raynaud’s phenomenon, and skin changes called‘mechanic’s hands’. The most frequent myositis-specificautoantibody is anti-Jo-1, which is more common in patientswith polymyositis but may also be present in patients withdermatomyositis [38,39]. The newly discovered autoantibodyanti-p155 seems to be associated more often withdermatomyositis and para-neoplastic dermatomyositis, and itsfrequency is similarly high in children (29%) and adults (21%)(with para-neoplasy the frequency is 75%) [40].
There are also reports on autoantibodies in patients withinclusion-body myositis. In one of these, an increased
frequency of serum monoclonal antibodies reactive to amuscle constituent was demonstrated [41].
The functional role of plasma cells in muscle in polymyositis andinclusion-body myositis is not yet fully elucidated. B lymphocytesand plasma cells could, beside antibody secretion or their roleas APCs, function as stimulatory cells for other immune cells. Indermatomyositis, CD4+ T lymphocytes could release IL-17 andIFN-γ after both polyclonal and oligoclonal activation to acquirea plasma cell-like morphology that is associated with a highsecretory activity, similar to that of plasma cells secretingimmunoglobulins [42]. The different role of immune cells in thecontext of muscle inflammation is presented in Figure 3.
More recent support for a role of B lymphocytes is the goodclinical effect seen with B cell depletion. This was firstreported in a pilot study that included patients withcorticosteroid-refractory dermatomyositis who were treatedwith rituximab (Rituxan®), an anti-CD20 monoclonal antibodythat is approved for treatment of some rheumatic diseases[43]. Later short-term beneficial effects with rituximab werealso demonstrated in a case report of two patients withrefractory polymyositis and one with dermatomyositis [44].
So far, only few studies have investigated and furtheraddressed the roles of B lymphocytes and plasma cells inmyositis. It is, however, certain that further research focusingon the functional role of B lymphocytes and specificautoantibodies in IIMs is warranted; this could provide pivotalinsights in the disease mechanisms for a possible futurespecific targeted treatment strategy. A comparison ofexpression in B lymphocytes in IIMs is presented in Table 1.
Dendritic cells and other antigen-presenting cellsDendritic cell functionTissue DCs that have internalized particulate and solubleantigens at the site of inflammation are induced to mature,and an innate immune response is triggered. These cells areactivated through receptors that signal the presence ofpathogen components or cytokines. DCs are also respon-sible for T lymphocyte activation by migrating to the lymphnode and providing both antigen presentation and co-stimulation. After maturation, DCs lose their ability to capturenew antigens and thus there is a continuous flow of DCs fromtissue to draining secondary lymphoid organs after challengewith antigen. In their mature activated form, DCs are the mostpotent APCs for naïve T lymphocytes. Both macrophagesand B lymphocytes also have the capacity to function asAPCs, but the ability of DCs to take up, process, and presenta variety of pathogens and antigens makes them the mostimportant activators of naïve T lymphocytes.
Dendritic cells and other antigen-presenting cells inidiopathic inflammatory myopathiesThe presence of T lymphocytes in all subsets of IIMsindicates a permanent immune response that requires the
Arthritis Research & Therapy Vol 9 No 2 Grundtman et al.
Page 8 of 12(page number not for citation purposes)
-
presence of APCs. DCs are central to the development ofinnate and adaptive immune responses. Two main classes ofDC have been classified, myeloid and plasmacytoid DCs.Myeloid DCs are potent APCs and have a function in theadaptive immune system. They are capable of capturing,processing, and presenting antigens and thereby stimulatinglymphocytes to a specific immune response. In contrast,plasmacytoid DCs are important in the innate immune systemand can produce large amounts of IFN-α and IFN-β, both ofwhich have several functions including the stimulation of cellsto produce specialized protein as a defense againstpathogens. IFN-α can transform healthy monocytes into cellswith properties of DCs; this was shown in sera from patientswith active systemic lupus erythematosus [45]. IFN-α canalso contribute to plasma cell differentiation and couldtherefore be important in the generation and sustenance ofantibody responses [46].
Until recently, only few data were available on DCs in IIMs, butthe results of some very recent studies have partly revealedimportant insights on this issue. Physiologically, DCs do notappear in normal muscle tissue, whereas the use of newmarkers for immature and mature DCs (CD1a and DC-LAMP/CD83, respectively) enabled the immature DCs to bedetected in lymphocytic infiltrates in both polymyositis anddermatomyositis muscle tissue samples [47]. Local DCs haverecently been demonstrated in all subsets of IIMs [48]: inmuscle specimens from patients with inclusion-body myositisand patients with polymyositis, myeloid DCs were present insubstantial numbers, frequently surrounding and sometimesinvading intact myofibers. They were part of a dense collectionof cells that also included T lymphocytes. In dermatomyositismuscles, an increased number of plasmacytoid DCs wasfound in comparison with the amount of myeloid DCs [48].The importance of the plasmacytoid DCs in activating the typeI interferon system in dermatomyositis was suggested by itsassociation with the transcriptional response of the IFN-α andIFN-β inducible genes and by the fact that the interferon-induced MxA protein was expressed in muscle tissue of thesepatients [49]. MxA expression was demonstrated in capillariesand in perifascicular myofibers, which are characteristic sitesof dermatomyositis pathology [49].
We have also found MxA expression in muscle tissue indermatomyositis, but also in polymyositis and inclusion-bodymyositis, supporting a role of the type 1 interferon in allsubsets of myositis. We therefore could not confirm aspecific MxA staining pattern able to be used as a diagnostictool that then could distinguish dermatomyositis from theother subsets of myositides, as suggested by Greenberg andcolleagues [34]; this therefore needs to be pursued further. Acomparison between expression patterns of DCs in IIMs ispresented in Table 1.
However, the detailed function of both myeloid andplasmacytoid DCs in IIMs has still not been fully clarified.
Greenberg and colleagues [34] proposed two hypotheses:first, the presence of myeloid DCs invading the non-necrotic-seeming myofiber regions suggests the occurrence of activephagocytosis, endocytosis, pinocytosis, or receptor-mediateduptake of antigen, activities for which these cells arespecialized; and second, that some of these cells are activelypresenting antigen and activating T lymphocytes locally withinmuscle tissue rather than in the lymph node [48].
In addition, there is some evidence that chemokine receptorson DCs can promote autoimmune reactions. This issupported by the observation mentioned above that someautoantigens, such as aminoacyl tRNA synthetases, mayexhibit chemotactic properties for activated monocytes,T lymphocytes, and immature DCs (not mature DCs). Theycould therefore have a capacity to attract inflammatory cells,including immature DCs, to infiltrate affected muscle cells.Taken together, these results suggest that antigens deliveredto receptors on immature DCs are potent immunogenscapable of breaking self-tolerance and able to induceautoimmune diseases [24,50].
As mentioned above, macrophages and B lymphocytes canalso function as APCs. In addition to those, other cell typescan acquire this function, although usually without reachingthe same efficacy as a ‘professional’ APC [51]. Emergingevidence from experiments in vitro and in vivo suggests thatmuscle fibers could function as antigen-specific cells [52-54].A schematic summary of the different roles of immune cells inthe context of muscle inflammation is presented in Figure 3.
Whether muscle cells actually do function as APCs stillremains uncertain. Muscle fibers are incapable of expressingthe ‘classical’ co-stimulatory molecules B7-1 and B7-2, butsome studies indicate that skeletal muscle cells and humanmyoblasts still have the possibility of acting as APCs with acell-to-cell contact between BB-1 antigen on the one hand,and CD28 and CTLA-4 on CD4+ or CD8+ T lymphocytes onthe other [53-55]. However, whether muscle cells that expressBB-1 simultaneously could express MHC class I and/or classII antigens is still not clarified. Furthermore, cDNA for the BB-1antigen has not been isolated. BB-1 is selectively induced bytreatment of myoblasts with pro-inflammatory cytokines suchas IFN-γ or tumor necrosis factor [55]. As both thesecytokines have been detected in muscle tissue from patientswith IIM [56-58], the muscle environment in the inflamedmuscle could possibly provide the necessary signals onmuscle fibers for an antigen presentation to T lymphocytes.
Once a naïve T lymphocyte has been activated, it expressesseveral proteins to sustain or modify the co-stimulatory signalfor the clonal expansion and differentiation of T lymphocytes.Several co-stimulatory signal systems have been identified inmuscle tissue from patients with IIM, such as CD40–CD40ligand (CD40-L), inducible co-stimulator (ICOS)–ICOS ligand(ICOS-L), B7RP-1, B7h, and B7-H2. When a co-stimulatory
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receptor is bound by its ligand, an activating signal istransmitted to the T lymphocyte. This also activates the APCto express B7 molecules, which further stimulate Tlymphocyte proliferation. Interestingly, muscle cells andmyofibers have been shown to express some of these co-stimulatory signals, namely CD40-L and ICOS-L (ICOS-Lboth expressed and functional [59]) during pathologicalconditions [59,60]. Schmidt and colleagues [61] demon-strated that muscle fibers expressing MHC class I, taken frompatients with inclusion-body myositis, caused an upregulationof ICOS–ICOS-L molecules in association with enhancedperforin expression by autoinvasive CD8+ T lymphocytes,which could exert a cytotoxic effect. This further supports thehypothesis that muscle fibers could work as APCs.
ConclusionThe molecular basis of IIMs in humans, as in many otherautoimmune rheumatic diseases, is heterogeneous, involvingseveral complex cellular components that probably contributeto differences in disease susceptibility, clinical and histopatho-logical phenotype, and severity. Although this heterogeneitymakes the study of the pathogenesis of IIMs extraordinarilycomplex, it might also provide distinct avenues for noveltherapeutic interventions. Controlling the immune response isas complex as its launching. An essential feature ofphysiological immune response is its self-limitation, by which itis attenuated by several mechanisms. We have only juststarted to understand the orchestrated life of T lymphocytes, Blymphocytes, and DCs in IIMs, but there are still manyunanswered questions about how this usually effective systemcan go awry and result in false immune-mediated reactions.
On the basis of detailed immunohistochemical studies onmuscle biopsies, two major types of inflammatory infiltratewere observed: endomysial and perivascular/perimysial. Inendomysial infiltrates there was a striking dominance of CD8+
T lymphocytes, which could even be the predominatinginfiltrating cell type, followed by macrophages and CD4+
T lymphocytes. These infiltrates often surrounded non-necrotic fibers and sometimes seemed to invade the fibers(Figure 1). This observation suggests an immune reactionthat targets muscle fibers. The perivascular infiltrates, incontrast, were dominated by CD4+ T lymphocytes andmacrophages, and sometimes the presence of B lympho-cytes suggested an immune reaction that targets micro-vessels (Figure 2). A role for B lymphocytes as well as one forCD4+ T lymphocytes in the pathogenesis of IIMs is supportedby frequently detected autoantibodies in polymyositis anddermatomyositis but less often in inclusion-body myositis.These autoantibodies are both non-specific (frequently alsobeing found in other autoimmune disease) and myositis-specific [38,39]. A role for CD4+ T lymphocytes in thedisease mechanism is further supported by the geneticassociation with HLA-DRB1*0301, DQA1*0501, andDQB1*0201, which was particularly seen for subgroups ofpatients with autoantibodies.
The endomysial infiltrates were reported to be characteristicfeatures of polymyositis and inclusion-body myositis, whereasthe perivascular infiltrates were associated with patients withdermatomyositis. However, there are cases with a less distinctlocalization of infiltrates or with combined endomysial andperivascular cellular infiltrates [3,6]. Moreover, in some casesthe inflammatory cell infiltrates are diffusely spread in thetissue, whereas in other cases the infiltrates are very small orare not found at all. In addition, the perivascular changes maybe seen in patients without a skin rash, whereas endomysialinfiltrates are occasionally seen in cases with a skin rash.
Taken together, these results indicate that there may be twomajor pathways: one leading to cellular infiltrates withpredominating endomysial localization, and another with apredominantly perivascular localization often with microvesselinvolvement and capillary loss. The latter is more often seen inpatients with a skin rash and dermatomyositis, but thereseems to be an overlap between clinical phenotypes, histo-pathology, and immunotypes. These observations suggestthat there might be more than just one factor that determinesthe histopathological and clinical phenotypes, for examplegenes and environment.
During the past few years, the results of several advancedhistopathological, molecular, functional, and medical studieshave provided new data that could be of importance inunderstanding the immune mechanisms in IIMs. Takentogether, they demonstrate the complexity of involvement ofthe immune system in these diseases and suggest that boththe innate and adaptive immune systems are involved indermatomyositis, polymyositis, and inclusion-body myositis.This complexity of T lymphocyte populations in muscle tissuein clinical subsets of myositis was demonstrated in the originalobservations of different cellular subsets in muscle tissue byArahata and Engel [6,7,9] and is exemplified in Figures 1 and2. These observations make it necessary to revise the ‘oldhistorical’ hypothesis on the pathogenesis of IIMs. Recently adispute over the most appropriate and accurate diagnosticcriteria has erupted, including the importance of thehistopathological picture and the localization of immune cells[62]. Other phenotypes such as autoantibody may also beimportant for the classification of disease subsets that will helpto enhance our understanding of disease mechanisms andthereby improve the treatment and prognosis for thesepatients. A revision of classification criteria has recently beenstarted in an international interdisciplinary collaboration thatwe believe will facilitate these efforts.
Competing interestsThe authors declare that they have no competing interests.
References1. Whitaker JN, Engel WK: Vascular deposits of immunoglobulin
and complement in idiopathic inflammatory myopathy. N EnglJ Med 1972, 286:333-338.
Arthritis Research & Therapy Vol 9 No 2 Grundtman et al.
Page 10 of 12(page number not for citation purposes)
-
2. Emslie-Smith AM, Engel AG: Microvascular changes in earlyand advanced dermatomyositis: a quantitative study. AnnNeurol 1990, 27:343-356.
3. Nagaraju K, Casciola-Rosen L, Lundberg I, Rawat R, Cutting S,Thapliyal R, Chang J, Dwivedi S, Mitsak M, Chen YW, et al.:Activation of the endoplasmic reticulum stress response inautoimmune myositis: potential role in muscle fiberdamage and dysfunction. Arthritis Rheum 2005, 52:1824-1835.
4. Grundtman C, Lundberg IE: Pathogenesis of idiopathic inflam-matory myopathies. Curr Rheumatol Rep 2006, 8:188-195.
5. Weaver CT, Hatton RD, Mangan PR, Harrington LE: IL-17 familycytokines and the expanding diversity of effector T cell lin-eages. Annu Rev Immunol, in press.
6. Arahata K, Engel AG: Monoclonal antibody analysis of mono-nuclear cells in myopathies. I: Quantitation of subsets accord-ing to diagnosis and sites of accumulation and demonstrationand counts of muscle fibers invaded by T cells. Ann Neurol1984, 16:193-208.
7. Emslie-Smith AM, Arahata K, Engel AG: Major histocompatibilitycomplex class I antigen expression, immunolocalization ofinterferon subtypes, and T cell-mediated cytotoxicity inmyopathies. Hum Pathol 1989, 20:224-231.
8. Pedrol E, Grau JM, Casademont J, Cid MC, Masanes F, Fernan-dez-Sola J, Urbano-Marquez A: Idiopathic inflammatorymyopathies. Immunohistochemical analysis of the major his-tocompatibility complex antigen expression, inflammatoryinfiltrate phenotype and activation cell markers. Clin Neu-ropathol 1995, 14:179-184.
9. Engel AG, Arahata K, Emslie-Smith A: Immune effector mecha-nisms in inflammatory myopathies. Res Publ Assoc Res NervMent Dis 1990, 68:141-157.
10. Goebels N, Michaelis D, Engelhardt M, Huber S, Bender A, Pon-gratz D, Johnson MA, Wekerle H, Tschopp J, Jenne D: Differen-tial expression of perforin in muscle-infiltrating T cells inpolymyositis and dermatomyositis. J Clin Invest 1996, 97:2905-2910.
11. Orimo S, Koga R, Goto K, Nakamura K, Arai M, Tamaki M, SugitaH, Nonaka I, Arahata K: Immunohistochemical analysis of per-forin and granzyme A in inflammatory myopathies. Neuromus-cul Disord 1994, 4:219-226.
12. Dalakas MC, Hohlfeld R: Polymyositis and dermatomyositis.Lancet 2003, 362:971-982.
13. Ikezoe K, Ohshima S, Osoegawa M, Tanaka M, Ogawa K, NagataK, Kira JI: Expression of granulysin in polymyositis and inclu-sion-body myositis. J Neurol Neurosurg Psychiatry 2006, 77:1187-1190.
14. Hombach A, Kohler H, Rappl G, Abken H: Human CD4+ T cellslyse target cells via granzyme/perforin upon circumvention ofMHC class II restriction by an antibody-like immunoreceptor. JImmunol 2006, 177:5668-5675.
15. Benveniste O, Cherin P, Maisonobe T, Merat R, Chosidow O,Mouthon L, Guillevin L, Flahault A, Burland MC, Klatzmann D, etal.: Severe perturbations of the blood T cell repertoire inpolymyositis, but not dermatomyositis patients. J Immunol2001, 167:3521-3529.
16. Benveniste O, Herson S, Salomon B, Dimitri D, Trebeden-NegreH, Jean L, Bon-Durand V, Antonelli D, Klatzmann D, Boyer O:Long-term persistence of clonally expanded T cells in patientswith polymyositis. Ann Neurol 2004, 56:867-872.
17. Dimitri D, Benveniste O, Dubourg O, Maisonobe T, Eymard B,Amoura Z, Jean L, Tiev K, Piette JC, Klatzmann D, et al.: Sharedblood and muscle CD8+ T-cell expansions in inclusion bodymyositis. Brain 2006, 129:986-995.
18. Fathi M, Dastmalchi M, Rasmussen E, Lundberg IE, Tornling G:Interstitial lung disease, a common manifestation of newlydiagnosed polymyositis and dermatomyositis. Ann Rheum Dis2004, 63:297-301.
19. Yamadori I, Fujita J, Kajitani H, Bandoh S, Tokuda M, Ohtsuki Y,Yoshinouchi T, Okahara M, Yamaji Y, Tanimoto Y, et al.: Lympho-cyte subsets in lung tissues of interstitial pneumonia associ-ated with untreated polymyositis/dermatomyositis. RheumatolInt 2001, 21:89-93.
20. Sauty A, Rochat T, Schoch OD, Hamacher J, Kurt AM, Dayer JM,Nicod LP: Pulmonary fibrosis with predominant CD8 lympho-cytic alveolitis and anti-Jo-1 antibodies. Eur Respir J 1997, 10:2907-2912.
21. Kourakata H, Takada T, Suzuki E, Enomoto K, Saito I, Taguchi Y,Tsukada H, Nakano M, Arakawa M: Flowcytometric analysis ofbronchoalveolar lavage fluid cells in polymyositis/dermato-myositis with interstitial pneumonia. Respirology 1999, 4:223-228.
22. Kurasawa K, Nawata Y, Takabayashi K, Kumano K, Kita Y,Takiguchi Y, Kuriyama T, Sueishi M, Saito Y, Iwamoto I: Activationof pulmonary T cells in corticosteroid-resistant and -sensitiveinterstitial pneumonitis in dermatomyositis/polymyositis. ClinExp Immunol 2002, 129:541-548.
23. Englund P WJ, Fathi M, Rasmussen E, Grunewald J, Tornling G,Lundberg IE: Restricted TCR BV gene usage in lungs andmuscle tissue of patients with idiopathic inflammatorymyopathies. Arthrithis Rheum 2007, 56:372-383.
24. Howard OM, Dong HF, Yang D, Raben N, Nagaraju K, Rosen A,Casciola-Rosen L, Hartlein M, Kron M, Yang D, et al.: Histidyl-tRNA synthetase and asparaginyl-tRNA synthetase, autoanti-gens in myositis, activate chemokine receptors on Tlymphocytes and immature dendritic cells. J Exp Med 2002,196:781-791.
25. Chino Y, Murata H, Goto D, Matsumoto I, Tsutsumi A, SakamotoT, Ohtsuka M, Sekisawa K, Ito S, Sumida T: T cell receptor BVgene repertoire of lymphocytes in bronchoalveolar lavagefluid of polymyositis/dermatomyositis patients with interstitialpneumonitis. Int J Mol Med 2006, 17:101-109.
26. Hohlfeld R, Engel AG: Coculture with autologous myotubes ofcytotoxic T cells isolated from muscle in inflammatorymyopathies. Ann Neurol 1991, 29:498-507.
27. O'Donovan MR, Jones DR, Robins RA, Li KF, Shim HK, Zheng Z,Arlett CF, Capulas E, Cole J: Co-cultivation of CD4+ and CD8+human T-cells leads to the appearance of CD4 cells express-ing CD8 through de novo synthesis of the CD8 αα-subunit.Hum Immunol 1999, 60:1018-1027.
28. Vencovsky J, Jarosova K, Machacek S, Studynkova J, Kafkova J,Bartunkova J, Nemcova D, Charvat F: Cyclosporine A versusmethotrexate in the treatment of polymyositis and dermato-myositis. Scand J Rheumatol 2000, 29:95-102.
29. Ochi S, Nanki T, Takada K, Suzuki F, Komano Y, Kubota T,Miyasaka N: Favorable outcomes with tacrolimus in twopatients with refractory interstitial lung disease associatedwith polymyositis/dermatomyositis. Clin Exp Rheumatol 2005,23:707-710.
30. Mitsui T, Kuroda Y, Kunishige M, Matsumoto T: Successful treat-ment with tacrolimus in a case of refractory dermatomyositis.Intern Med 2005, 44:1197-1199.
31. Lampropoulos CE, DP DC: Topical tacrolimus treatment in apatient with dermatomyositis. Ann Rheum Dis 2005, 64:1376-1377.
32. Stashenko P, Nadler LM, Hardy R, Schlossman SF: Expressionof cell surface markers after human B lymphocyte activation.Proc Natl Acad Sci USA 1981, 78:3848-3852.
33. Anderson KC, Bates MP, Slaughenhoupt BL, Pinkus GS,Schlossman SF, Nadler LM: Expression of human B cell-asso-ciated antigens on leukemias and lymphomas: a model ofhuman B cell differentiation. Blood 1984, 63:1424-1433.
34. Greenberg SA, Bradshaw EM, Pinkus JL, Pinkus GS, Burleson T,Due B, Bregoli L, O'Connor KC, Amato AA: Plasma cells inmuscle in inclusion body myositis and polymyositis. Neurology2005, 65:1782-1787.
35. Bradshaw EM, Orihuela A, McArdel SL, Salajegheh M, Amato AA,Hafler DA, Greenberg SA, O'Connor KC: A local antigen-drivenhumoral response is present in the inflammatory myopathies.J Immunol 2007, 178:547-556.
36. Kikuchi Y, Koarada S, Tada Y, Ushiyama O, Morito F, Suzuki N,Ohta A, Horiuchi T, Miyake K, Nagasawa K: Difference in B cellactivation between dermatomyositis and polymyositis: analy-sis of the expression of RP105 on peripheral blood B cells.Ann Rheum Dis 2001, 60:1137-1140.
37. Cambridge G, Faith A, Saunders C, Dubowitz V: A comparativestudy of in vitro proliferative responses to mitogens andimmunoglobulin production in patients with inflammatorymuscle disease. Clin Exp Rheumatol 1989, 7:27-33.
38. Love LA, Leff RL, Fraser DD, Targoff IN, Dalakas M, Plotz PH,Miller FW: A new approach to the classification of idiopathicinflammatory myopathy: myositis-specific autoantibodiesdefine useful homogeneous patient groups. Medicine (Balti-more) 1991, 70:360-374.
Available online http://arthritis-research.com/content/9/2/208
Page 11 of 12(page number not for citation purposes)
-
39. Brouwer R, Hengstman GJ, Vree Egberts W, Ehrfeld H, Bozic B,Ghirardello A, Grondal G, Hietarinta M, Isenberg D, Kalden JR, etal.: Autoantibody profiles in the sera of European patientswith myositis. Ann Rheum Dis 2001, 60:116-123.
40. Targoff IN, Mamyrova G, Trieu EP, Perurena O, Koneru B, O'Han-lon TP, Miller FW, Rider LG; Childhood Myositis HeterogeneityStudy Group; International Myositis Collaborative Study Group: Anovel autoantibody to a 155-kd protein is associated with der-matomyositis. Arthritis Rheum 2006, 54:3682-3689.
41. Dalakas MC, Illa I, Gallardo E, Juarez C: Inclusion body myositisand paraproteinemia: incidence and immunopathologic corre-lations. Ann Neurol 1997, 41:100-104.
42. Page G, Sattler A, Kersten S, Thiel A, Radbruch A, Miossec P:Plasma cell-like morphology of Th1-cytokine-producing cellsassociated with the loss of CD3 expression. Am J Pathol 2004,164:409-417.
43. Levine TD: Rituximab in the treatment of dermatomyositis: anopen-label pilot study. Arthritis Rheum 2005, 52:601-607.
44. Noss EH, Hausner-Sypek DL, Weinblatt ME: Rituximab astherapy for refractory polymyositis and dermatomyositis. JRheumatol 2006, 33:1021-1026.
45. Blanco P, Palucka AK, Gill M, Pascual V, Banchereau J: Inductionof dendritic cell differentiation by IFN-alpha in systemic lupuserythematosus. Science 2001, 294:1540-1543.
46. Jego G, Palucka AK, Blanck JP, Chalouni C, Pascual V,Banchereau J: Plasmacytoid dendritic cells induce plasma celldifferentiation through type I interferon and interleukin 6.Immunity 2003, 19:225-234.
47. Page G, Chevrel G, Miossec P: Anatomic localization of imma-ture and mature dendritic cell subsets in dermatomyositisand polymyositis: interaction with chemokines and Th1cytokine-producing cells. Arthritis Rheum 2004, 50:199-208.
48. Greenberg SA, Pinkus GS, Amato AA, Pinkus JL: Myeloid den-dritic cells in inclusion-body myositis and polymyositis.Muscle Nerve 2007, 35:17-23.
49. Greenberg SA, Pinkus JL, Pinkus GS, Burleson T, Sanoudou D,Tawil R, Barohn RJ, Saperstein DS, Briemberg HR, Ericsson M, etal.: Interferon-αα/ββ-mediated innate immune mechanisms indermatomyositis. Ann Neurol 2005, 57:664-678.
50. Oppenheim JJ, Yang D, Biragyn A, Howard OM, Plotz P:Chemokine receptors on dendritic cells promote autoimmunereactions. Arthritis Res 2002, 4(Suppl 3):S183-188.
51. Steinman RM: The dendritic cell system and its role inimmunogenicity. Annu Rev Immunol 1991, 9:271-296.
52. Curnow SJ, Willcox N, Vincent A: Induction of primary immuneresponses by allogeneic human myoblasts: dissection of thecell types required for proliferation, IFNγγ secretion and cyto-toxicity. J Neuroimmunol 1998, 86:53-62.
53. Murata K, Dalakas MC: Expression of the costimulatory mole-cule BB-1, the ligands CTLA-4 and CD28, and their mRNA ininflammatory myopathies. Am J Pathol 1999, 155:453-460.
54. Murata KY, Sugie K, Takamure M, Ueno S: Expression of thecostimulatory molecule BB-1 and its receptors in patientswith scleroderma–polymyositis overlap syndrome. J NeurolSci 2002, 205:65-70.
55. Behrens L, Kerschensteiner M, Misgeld T, Goebels N, Wekerle H,Hohlfeld R: Human muscle cells express a functional costimu-latory molecule distinct from B7.1 (CD80) and B7.2 (CD86) invitro and in inflammatory lesions. J Immunol 1998, 161:5943-5951.
56. Lundberg I, Brengman JM, Engel AG: Analysis of cytokineexpression in muscle in inflammatory myopathies, Duchennedystrophy, and non-weak controls. J Neuroimmunol 1995, 63:9-16.
57. Dalakas MC: Molecular immunology and genetics of inflam-matory muscle diseases. Arch Neurol 1998, 55:1509-1512.
58. Lundberg I, Ulfgren AK, Nyberg P, Andersson U, Klareskog L:Cytokine production in muscle tissue of patients with idio-pathic inflammatory myopathies. Arthritis Rheum 1997, 40:865-874.
59. Wiendl H, Mitsdoerffer M, Schneider D, Melms A, Lochmuller H,Hohlfeld R, Weller M: Muscle fibres and cultured muscle cellsexpress the B7.1/2-related inducible co-stimulatory molecule,ICOSL: implications for the pathogenesis of inflammatorymyopathies. Brain 2003, 126:1026-1035.
60. Sugiura T, Kawaguchi Y, Harigai M, Takagi K, Ohta S, FukasawaC, Hara M, Kamatani N, et al.: Increased CD40 expression on
muscle cells of polymyositis and dermatomyositis: role ofCD40–CD40 ligand interaction in IL-6, IL-8, IL-15, and mono-cyte chemoattractant protein-1 production. J Immunol 2000,164:6593-6600.
61. Schmidt J, Rakocevic G, Raju R, Dalakas MC: Upregulatedinducible co-stimulator (ICOS) and ICOS-ligand in inclusionbody myositis muscle: significance for CD8+ T cell cytotoxic-ity. Brain 2004, 127:1182-1190.
62. Hengstman GJ, van Engelen BG: Polymyositis, invasion of non-necrotic muscle fibres, and the art of repetition. BMJ 2004,329:1464-1467.
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AbstractIntroductionT lymphocytesT lymphocyte functionT lymphocytes in idiopathic inflammatory myopathies
Dendritic cells and other antigen-presenting cellsDendritic cell functionDendritic cells and other antigen-presenting cells in idiopathic inflammatory myopathies
B lymphocytesB lymphocyte functionB lymphocytes in idiopathic inflammatory myopathies
ConclusionCompeting interestsReferences