virus-induced immunopathology cell mediated immunopathology antibody-mediated immunopathology...
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Virus-Induced Immunopathology
Cell mediated Immunopathology Antibody-mediated Immunopathology Virus-initiated Immunopathology
Cell mediated immunopathology Contact between CTL (CD8+) and
target TCR recognizes cognate peptide
presented by MHC I Activation of CTL; release of
membrane granules with perforin and granzyme
Perforin: Pore formation in target cells resuting in cytolysis
Granzyme B: induction of apoptosis
Release of Inflammatory cytokines (TNF-, IFN-, ILs)
CD4+ T cells can enhance CD8-mediated immunopathology
NK Cell Non-specific of “non-self” ADCC
CTL
MHC Class I
Viral antigen
Effector Cell
Target Cell
TCR
MHC Class I
Viral antigen
Infected Choriodal Cells
Inflammatory Cytokines
Inflammatory Macrophageat
tract
ion
NOS
Nitric Oxide
Convulsions (?)
CTL
Effector Cell
TCR
Cytopathic attack on choriodal cells can damage meninges
Cell-mediated Immunpathology: LCMV, an experimental model
Cell-mediated Immunpathology: LCMV, an experimental model
Lymphocytic Choriomeningitis Virus causes fatal choriomeningitis (inflammation of meninges) in immunocompetent mice, but not in immunosuppressed mice
Intracerebral Innoculation
e.g. via Cyclophosphamide Rx,or irradiation
Adoptive Transfer:Syngeneic normal mice “immunized” IP with LCMV. Anti-serum or lymphocytes then adoptively transferred
CTL activity is required for LCMV immunopathology
A: Perforin is required for CTL effector function
B: Perforin, hence CTL function, is required for virus clearance (IV challenge)
C: Perforin, CTL activity, mediates fatal choriomeningitis (IC infection)
D: CTL is also involved in hepatopathology (liver damage) by hepatotropic LCMV
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Immune mediated disease: Tissue destruction in addition to
inflammation Hepatotropic LCMV
Liver destruction Cerebellar involution in newborn rats
Pathogenic consequences: severe ataxia
Immunosuppressed Non-Immunosuppressed
CD4+ T cells can enhance immune pathology
Immunization(day 0)
Depletiondays 18, 20, 23
IntranasalRSV infection
day 21
Alveolitis(% lung area)
day 25
Formalin-inactivatedRSV(all groups)
NoneCD8CD4
CD8 + CD4
YESYESYESYES
9.6%3.9%0.5%0.3%
Respiratory Syncytial Virus: virus induced immunopathology (bronchioaveolitis) is more dependent on CD4 T lymphocytes
Passsive transfer of antibodies (from RSV infected animals) cannot re-produce aveolitisConclusion: alveolitis is mediated mainly by CD4+ effector cells
(N.B. in the book, should be RSV should be Respiratory Syncytial Virus, NOT Rous Sarcoma Virus)
Depletion is usually accomplished by infusingmice with antibodies (complement-fixing) against the specific cell-surface molecule
IgG3>IgG1>IgG3>>>(IgG4)(neg.)
Complement Fixation
Cell-mediated Immunopathology:Human disease
Hepatitis B Virus infection Clinical disease associated
with development of high-titer antibodies
Presence of high titer virus (viremia) in the absence of clinical disease (hepatitis) suggest that the disease is not caused by infection per se
Anti-HBsAg may contribute to transient acute hepatitis, but may synergize with CTL mediated clerance of virus from hepatocytes
CTL response itself can result in acute hepatitis
% M
ax
imu
m%
Ma
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~45 nm “Dane”particles(infectious)
~20 nM spheresHBsAg (major) and middle proteins and host lipids;No nucleic acid, non-infectiousPresent in 103 to 106 fold excess over Dane particlesCan reach 1012 particles/ml in infected patientsHighly immunogenic, original source of 1st generation HBV vaccine
~20 nM in diameter filaments(contains the L protein, but lack nucleic acids; Non-infectious)
HBVAll three particles contain HBsAg (also known as the major protein)The L(large) and M(middle) are also contained in the Dane particlesThe L protein when expressed alone gets trapped in ER
Cell-mediated Immunopathology:Human disease
Evidence from mice model Transgenic mice can be made to express large, middle or major
envelope proteins Wt. Mice can be vaccinated with envelope proteins and Ag-specific
CTL clones can be made directed against specific epitopes in large, middle or major envelope proteins
System allows dissection of which immune response, targeted against which epitope, that is responsible for the immunopathology
Cell-mediated Immunopathology:Human disease
Evidence from mice model Transgenic mice expressing HbsAg
Adoptive transfer of CTL specific for a HepB envelope protein results in acute hepatitis
Direct cytotoxic effects of CTLs is limited to small numbers of hepatocytes (why? If all liver cells express the HBsAg)
However, IFN secreted by CTLs can attract other WBCs (phagocytes, PMNs) leading to necroinflammatory foci
However, these cytokines are also involved in viral clearance; down regulates viral transcription
Transgenic mice expressing large Hep B envelope protein (intracellular accumulation)
Adoptive transfer of CTL specific for a HepB large envelope protein results in progessive inflammation and liver necrosis
ER accumulation of L protein may be cytotoxic resulting in activation of liver macrophages (Kupffer cells)
Antibody-mediated Immunopathology
Ab-Ag complex formation during viremic infections
Deposition of immune complex in glomerulus can initiate complement cascade and cause inflammation, scarring and eventual kidney failure
Large complexes get trapped at the basement membrane
Mesangial cells enlarge into the subepithelial (mesangial) space in an attempt to remove accumulating immune complexes
Long term: glomerular capillary gets constricted foot processes of podocytes (glomerular endothelial cells) get fused; basement membrane gets leaky but filtering is blocked
Result: Impaired glomerular function, kidney failure (no urine production)
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Antibody-mediated Immunopathology
Ab-Ag complex formation during viremic infections
Deposition of immune complex in glomerulus can initiate complement cascade and cause inflammation, scarring and
eventual kidney failure
YY
YY
YY
Y
Y= anti-LCMV
= anti-mouse IgG
virus
Infectious Ab-Ag complex Can be demonstrated by
reduction in infectious titer using antibodies against
mouse IgG
Treatment of seraFrom mice persistentlyinfected with LCMV
LCMV titer(log10 LD50 per 0.02 ml)
Anti-mouse immunoglobulin
ControlsNormal rabbit serumAnti-mouse albumin
<1.0
3.73.5
Antibody-Mediated Immunopathology: Human Disease
Dengue hemorrhagic fever Dengue virus, flavivirus transmittted by mosquitoes 4 serotypes (1-4) Disease is usually self-limiting but small percentage
develop hemorrhagic fever and shock DHF/DSS occurs most commonly in
children previously infected with a different serotype infants with primary infection but with maternal anti-dengue
antibodies against another serotype Abs against one serotype can enhance infection by second
serotype (Antibody-Dependent Enhancement)
monocyte
Fc Receptor
(Heterotypic anti-Dengue Ab)
YY
Y
Y
Enhancement is dependent on Fc portion of Abs(Fab fragments from immune sera do not have Enhancing ability)
Y YTotal IgG F(ab)2
ADE +++ -
Enhancement is dependent on the titer of the Abs
Enhancement is dependent on the titer of the Abs
At high concentrations of virus-specific Ab (low Ab dilution), percent occupancy of antibody binding sites is sufficiently high to inhibit critical steps in the viral life cycle
As antibody becomes more dilute, its inhibitory activity becomes attentuated, at some point below the neutralization end-point, antibody binding at subneutralizaing concentrations (High Ab dilution) enhances viral infectivity
Neutralization end-point
monocyte
Fc Receptor
(Heterotypic anti-Dengue Ab)
Y
Y
Y
(Heterotypic anti-Dengue Ab)
YY
Y
Y
YYY
Y
Y
Y Y
monocyte
Fc Receptor
No free envelope spikes to mediate fusion
Enhanced attachment, free envelope spikes available to mediate fusion
Enhancement is dependent on Fc portion of Abs(Fab fragments from immune sera do not have Enhancing ability)
Y YTotal IgG F(ab)2
ADE +++ -
Enhancement is dependent on the titer of the Abs
[+anti-F(ab)2]+++ADE
YYY Fc
How does ADE in secondary Dengue virus infection lead to DHF/DSS?
Increased entry/replication in target cells (Monocytes/Macrophages) results in secretion of inflamatory cytokines (TNF-, IFN and IL-2) that also have vasoactive properties
In 2º Dengue infection, pre-existing Ag-specific CD8 and CD4 T cells are activated, and also secrete similar vasoactive cytokines
Resulting “cytokine” storm can capillary fragility (associated with hemorrhage) and permeability (associated with shock--loss of intravascular osmotic pressure)
Anti-viral antibodies: the good, the bad, and the useless
LCMV immunopathogenesis: Virus infected meningeal cells become target for CTLs--
resulting in choriomeningitis CTLs are made due to hematogenous spread to spleen
and other lymphoid tissues Too high a level of viral replication in lymphoid tissue
can lead to immune exhaustion: activation induced apoptosis of Ag-specific CTLs
A: Slowly replicating Armstrong strain Ab slows hematogenous spread of LCMV, and
prevents robust CTL response; protects animals against CTL mediated choriomeningitis
B: Intermediate replicating WE strain Ab did not slow spread of LCMV sufficiently to
affect disease outcome C: High replicating strain
Usually causes immune exhaustion (“high-dose paralysis”); Ab slows down virus enough for robust CTL response, which results in fatal choriomeningitis
Virus-initiated autoimmunity:Molecular mimicry
Immune response against a viral antigen cross-reacts with a host protein
Cross-reactivity doesn’t necessarily result in autoimmune disease
Experimental Allergic Encephalitis (EAE)
Myelin Basic Protein immunization results in EAE (demyelination); “encephalitogenic” epitope confined to 10 amino-acid stretch in MBP
HBV polymerase contains similar 10 aa stretch; immunization with this peptide can cause encephalitis in rabbits
P R O TE I N S E Q U E NCE
I M MUN O L OGI CAL
CR OSS
RE A CTI V IT Y
DE MO NS T RAT E D
P ol i ov i r us V P 2
Ace t y l c h o lin e r ece pt or
STTKESRGTT
TVIKESRGTK
YE S
P ap illo m a v ir us E2
Insu lin rece pt or
SLHLESLKDS
VYGLESLKDL
YE S
Ra bi esv ir u s g lyco p ro te in
Insu lin rece pt or
TKESLVIIS
NKESLVISE
YE S
H IV p 24
Ig G co n sta n t reg io n
GVETTTPS
GVETTTPS
YE S
Mea sles v ir u s P3
Cor tico tro p h in
LECIRALK
LECIRACK
N O