Negative regulation of immune responses by various mechanisms

ITAM-ITIM

ITIM- mediated inhibition

ITIM recruited phosphatases inhibit the ITAM-induced kinase cascade

B cell regulation CD22

Sialic acid

Phosphorilated ITIM motifs on FcγRIIbrecruits phosphatases to interfere signal

transduction

Inhibition of the signal transduction of B cell receptor

B cell

Ag Ag

B cell

FcγRII mediated B cell feedback regulation

FcγRIIbFcγRIIb

B cell regulation FcγRIIb

T cell regulation CTLA4, PD-1(ITIM Like)

NK cell regulation MHCI

2B4/CD244/SLAMF4 ILT7/CD85g BLAME/SLAMF8 ILT11/LILRA5 BTLA Immunoreceptor Array Kit CD3 Integrin alpha 2b beta 3 CD3 epsilon Integrin beta 3/CD61 CD5 KIR/CD158 CD6 KIR2DL1/CD158a CD23/Fc epsilon RII KIR2DL2/CD158b1 CD28 KIR2DL3/CD158b2 CD31/PECAM-1 KIR2DL4/CD158d CD72 KIR2DL5/CD158f CD84/SLAMF5 KIR2DS1/CD158h CD229/SLAMF3 KIR2DS4/CD158i CD300a/LMIR1 KIR2DS5/CD158g CD300b/LMIR5 KIR3DL1 CD300c/LMIR2 KIR3DL2/CD158k CD300e/LMIR6 KIR3DL3/CD158z CD300f/LMIR3 KIR3DS1/CD158e2 CEACAM-1/CD66a KLRG1 CEACAM-3/CD66d LAIR1 CLEC-1 LAIR2 CLEC-2 LIR-8/CD85c CLEC-2A MDL-1/CLEC5A CRACC/SLAMF7 MICL/CLEC12A CTLA-4 NFAM1 DCAR/CLEC4B NKp30/NCR3 DCIR/CLEC4A NKp44/NCR2 Dectin-1/CLEC7A NKp46/NCR1 DNAM-1/CD226 NKp80/KLRF1 Fc epsilon RI alpha NTB-A/SLAMF6Fc epsilon RI beta/MS4A2 PD-1 Fc gamma RIII (CD16) PDCD6 FCAR/CD89 PILR-alphaFc gamma RI/CD64 Siglec-2/CD22 Fc gamma RII/CD32 Siglec-3/CD33 Fc gamma RII/RIII (CD32/CD16) Siglec-5/CD170 Fc gamma RIIA/CD32a Siglec-5/Siglec-14 Fc gamma RIIB/CD32b Siglec-6/CD327 Fc gamma RIIB/C (CD32b/c) Siglec-7/CD328 Fc gamma RIIC/CD32c Siglec-8 Fc gamma RIIIA/CD16a Siglec-9 Fc gamma RIIIB/CD16bSiglec-10 FCRL1/FcRH1 Siglec-11 FCRL2/FcRH2 Siglec-14 FCRL3/FcRH3 Siglec-16FCRL4/FcRH4 Siglec-E FCRL5/FcRH5 Siglec-F FCRL5/FCRL3 Siglec-G FCRL6/FcRH6Siglec-H G6b SIRP beta 1/CD172b ILT2/CD85j SLAM/CD150 ILT3/CD85k TIGIT ILT4/CD85d TREM-3 ILT5/CD85a TREML1/TLT-1 ILT6/CD85e TREML2/TLT-2

ITAM and/or ITIM containing receptors

ITAM/ITIM-mediated regulation is a general process

Immune Tolerance

Central and Peripherial tolerance

Central tolerance

++

1. The primary T cell pool is biased to MHC-specificity (V genes) 1-2% for one allotype

2. Focusing the T cell pool to self MHC recognition (+)

3. Elimination of useless and self agressive clones (-)

4. CENTRAL TOLERANCE

5. Focusing the T cell repertoire for recognition of non self

6. CD4+ and CD8+ T cell use the same TCR repertoire

7. Individualized T cell repertoire available in the periphery

8. CD4 and CD8 co-stimulatory molecules are involved in positive selection

αβTCR αβTCRCD4+ CD8+

SELECTION OF T LYMPHOCYTES IN THE THYMUS

UNDER THE CAPSULE

CORTEX

CORTEX/MEDULLA

IL-7-dependent proliferation

β+preTαCD4-CD8-

DN

CD4+CD8+DP

MEDULLA

TCRαβ

TCR(-) sMHC+sP sMHC+fP fMHC+fP

selection

– selection

–AICD

NO

PERIPHERAL TOLERANCE

AICD – Activation Induced Apoptosis

POSITIVE SELECTION – Thymic education (no instruction for specificity)Low avidity interaction of MHC - self peptide - TCR Thymic epithelial cellsSelf peptide composition and concentration (foreign peptides are not present)Low peptide dose induces positive selection – special ligands80-90% of DN (CD4-CD8-) T cells is NOT positively selected PASSIVE CELL DEATH BY NEGLECTION

NEGATIVE SELECTION – Central self toleranceHigh avidity of MHC - self peptide - TCR interactionUbiquitous and abundant self antigens are present in the thymusHigh peptide dose induces negative selectionAny thymic antigen presenting cell: epithelial cells, bone marrow-derived macrophages, dendritic cells

THE GENERATION OF SELF MHC + FOREIGN PEPTIDE SPECIFIC T CELLS REQUIRES WEAK INTERACTION WITH SELF MHC + SELF PEPTIDE

SELF RESTRICTED AND TOLERANT PERIPHERAL T CELL REPERTOIREPHYSIOLOGICAL TRESHOLD

NOT COMPLETE

SELECTION OF THE T CELL REPERTOIRE – CENTRAL TOLERANCE

tissues are represented promiscuous gene expression in thymic epithelial cells

AIRE transcription factor

autoimmune regulator (AIRE) protein. Mutations in the AIRE gene are the cause of a multiorgan autoimmune disease called the autoimmune polyendocrine syndrome (APS).

Peripherial tolerance

Peripherial tolerance

deletion, apoptosis

Activation induced cell death

NEGATIVE REGULATION OF T CELL RESPONSES

Days5 10 15 20 25 30

Naive lymphocytes

Number of antigen specific cells

Primary effectors

Secondary effectors

Memory

DIFFERENTIATION

AICD

EXPANSION

AICD

MEMORY

AICDActivation Induced Cell Death

Signaling Pathways of AICD

Ligand binding to TNFR1 és TNFR2 receptors triggers pro- and anti-apoptotic signalling pathways

Elimination of effector T cells at the end of the immune response

Activation-induced cell death (AICD)

Sustained T cell activation induces pro-apoptotic signals

Expression of Fas, FasL, Bad, Bax is increased – CELL DEATHExpression of Bcl-2, FLIP is decreased – SURVIVAL decreased

repeated stimulation of T cells by persistent antigens leads to the coexpression of the two molecules, a death- inducing receptor called Fas(CD95) and its ligand, Fas ligand(FasL)

C D 8 + Tc

F a s

C D 4 + T h 1

F a s L

C D 4 +

T h 1

A P C

B

THE ROLE OF CD4+ T CELLS IN APOPTOSISFas receptor – Fas ligand interactions

T CELL HOMEOSTASIS SHUT OFF IMMUNE RESPONSES

Anergy

A B7 : CD28 receptor family

ABBAS MIT 2013 Pécs

The activation of naiv T cell requires costimultaionCostimulatory molecules are expressed only in professional antigen presenting cells

Anergy

Absence of costimulation

or

Negative signal

TCR activation in the absence of costimulation results in the degradation of key moleclues in TCR signaling

B71/2

TAPC

CD28 activation

CTLA-4

ITIM

NEGATIVE REGULATION OF T CELL ACTIVATION BY CTLA-4

LATE EXPRESSION

CTLA4 has HIGHER AFFINITY TO B7 THAN TO CD28, but the amount of it is limited

CTLA4 1. Inhibition of ITAM signaling

2. Competition with CD28

In general the activation of naiv T cells requires DC-mediated antigen presentation

Normal tissue cells do not express MHC class IINO SIGNAL 1. for CD4+ Th activation

Normal tissue cells do not express co-stimulatory molecules and do not produce T cell differentiating cytokinesNO SIGNAL 2. for CD4+ Th activation

Migration of naive T lymphocytes to normal tissues is limitedAntigen presenting cells are not activated in normal tissues

NO SIGNAL 3. for CD4+ Th activation

PERIPHERAL TISSUES TOLERIZE THEMSELVES

PERIPHERAL TOLERANCEIMMUNE RESPONSES ARE NOT INITIATED IN THE PERIPHERY

NEGATIVE REGULATION OF IMMUNE RESPONSES BY REGULATORY T CELLS

The main role of regulatory T cells

ABBAS MIT 2013 Pécs

Sakaguchi 2008

FUNCTIONS OF REGULATORY T CELLS

• Maintenance of peripheral tolerance

• Prevention of autoimmunity

• Limiting inflammatory processes (asthma, inflammatory bowel diseases)

• Inhibit protection against infectious diseases

• Limit immune responses to tumors

MECHANISM

Intrinsic and extrinsic regulation

Various inhibitory mechanisms

Cell contacts – Cytokines

Interaction with the target effector T cells

Regulatory T cells are normal T cells!MHC/peptide recognition--- self peptides!clonal proliferation, activation...mostly 95% CD4+ helper T cells

Natural regulatory T cell

Development of the CD25+CD4+ regulatory T cell lineage

TCR as polymorphic as for CD25- cellsSpecific to self antigens, MHC II restrictedRequires IL-2, Co-stimulation, CD28, B7

Foxp3 is a master regulatortransforms CD25 status

SchwartzNat Immunol 2005

EFFECTOR CD4+ HELPER T LYMPHOCYTES SECRETE DIFFERENT CYTOKINES

Inflammatory cytokines

CELLULAR IMMUNE RESPONSE

Anti-inflammatory cytokines

HUMORAL IMMUNE RESPONSE

IFNγ, IL-2, TNF-β/LT

Th1 Th0

IL-4, IL-5, IL-10

Th2IL-4IFNγ

Inducible Treg cells

Sakaguchi 2008

InducibleTreg requires TGF-β, IL2

TGF-β or blocking of TGF-β signals in T cells leads to a systemic inflammatory disease IL-2 receptor is knocked out develop autoimmunity

The dependence of Treg cells on IL-2, which they cannot produce themselves but instead receive from conventional T cells, provides a negative feedback loop through which the ratio between Treg cells and conventional T cellsis controlled

Mechanisms of Action of Regulatory T Cells

1. produce IL-10 and TGF-bTGF-β • inhibits the proliferation and effector functions of T cells and the activation of

macrophages, neutrophils and endothelial cells• inhibits development of TH1 and TH2 subsets • promotes the development of the TH17 subset (in the presence of other cytokines)• stimulates production of IgA antibodies • promotes tissue repair IL10• inhibits the expression of costimulators and class II MHC molecules on

dendritic cells and macrophages • inhibits the production of IL-12 by activated dendritic cells and macrophages • inhibits macrophage and dendritic cell functions

2. inhibit the ability of APCs to stimulate T cells (binds to B7 molecules on APCs and either blocks these molecules or removes them by

internalizing them )

3. consume of IL-2

4. metabolism

5. cytolitic processes

MECHANISMS RELATED TO REGULATORY T LYMPHOCYTE FUNCTIONS

IL-35

Inhibitory cytokines

TGFβ

IL-10

Cytolysis

Metabolic disturbance Inhibition of T cell proliferation

Reduced cytokine production (IL-2)Peri-cellular adenosine

cAMP transfer

Indolamine-2,3 dioxigenaseLAG-3 – CD4 homologue

CELL SURFACE ENZYMES OF REGULATORY T CELLS PRODUCE EXTRACELLULAR NUCLEOTIDES

Ectonucleoside triphosphate diphosphohydrolase (E-NTPDase

Ecto-5’-nucleotidase

EBI3Ebstein-Barr virus induced gene 3

IL-27 and IL-35

Naiv T sejtek toborzása, aktiválása, polarizálása

CD4+CD25- effektor sejtek A2A receptort fejeznek ki

Peri-cellular/Szupresszív

Treg constitutively downregulates the self presenting DC

Possible Mechanisms of Treg-Mediated Suppression

Sakaguchi 2008

ABBAS MIT 2013 Pécs

ABBAS MIT 2013 Pécs

A regulátor T-sejtek különálló fejlődési vonalat képviselnek és gátolják az autoreaktív T-sejtek aktivációját

CD25+ FoxP3+ sejtek

FoxP3-hiány: autoimmun betegség

IPEX: immune dysregulation polyendocrinopathy, enteropathy, X-linked syndrome

Summary of peripherial tolerance:

B cells tolerance

B-sejt tolerancia

The absence of T cell help / Treg cell siganal

Peripherial tolerance

deletion, apoptosis