Cellule souche Un double système,cellulaire et moléculaire de reconnaissance de l’antigène Bourse de Fabricius Ou moelle osseuse Organe de différenciation thymus B cell CD3 T cell TCR BcR = immunoglobulines Récepteurs clonaux Peptide issu de l’antigène MHC Antigène entier Antigène (protéine bactérienne)

La bonne coopération T – B requiert que les 2 partenaires : Pour fabriquer des quantités optimales d’Ac affins, Les cellules B doivent avoir coopérer directement Avec les cellules T Cellule B CelluleT La bonne coopération T – B requiert que les 2 partenaires : Développent des contacts directs Soient spécifiques du même Ag aient été préactivés par un 3° partenaire cellulaire

La coopération cellules T- cellules B, Un long ballet avec de nombreux partenaires 50 années de coopération T – B : La question du pont antigènique 2. Les évènements cellulaires ; la réaction du centre germinatif. 3. Les évènements moléculaires : récepteurs de surface et ligands. Cytokines chimiokines et leurs récepteurs

La coopération T – B l’effet haptène-porteur (Ovary et Benacerraf, 1963) porteurs NIP OVA BSA BSA NIP OVA NIP BSA B cells BSA T cells Réponse Ac secondaire Intense À NIP-BSA

La coopération T-B Le modèle du pont Antigénique NIP OVA BSA Recognition phase Production phase Activation phase : + proliferation + differentiation B cell BcR cooperation Ag Bridge model TcR T cell Antibody production

T-cells must be activated by Ag Presenting cells to cooperate with B cells (3 cells partnership) Activation phase : + proliferation + differentiation Primed B cell BcR cooperation TcR Activ T cell APC cooperation

La Restriction allogénique : La présentation de l’Ag au TCR est restreinte par le MHC (Doherty et Zinkernagel, 1975) MHC classe II T cell TCR CD3 Cellule dendritique B cell

TcR ne peuvent reconnaître leurs epitopes qu’en association avec molecules MHC :La version moderne du pont antigénique Ag B cell BcR Primed B cell Endocytosis Ag digestion T epitopes Transfert on Class II Export to the membrane B epitopes Activ.T cell cooperation DC

La coopération cellules T- cellules B, Un long ballet avec de nombreux partenaires 1. 50 années de coopération T – B : La question du pont antigènique 2. Les évènements cellulaires ; la réaction du centre germinatif. 3. Les évènements moléculaires : récepteurs de surface et ligands. Cytokines chimiokines et leurs récepteurs

T – B Cooperation : a cascade of synapses (#1 & 2) Naive T cell Soluble Ag T cell Zone Day Day 1 Synapse 3 Synapse 1 Synapse 2 Activated DC Naive B cell Soluble Ag Cell bound Ag Primary follicle DC Secondary follicle Secondary follicle B CXCL13 B Th Th CXCR5 B B B Short lived plasma cells (No somatic hypermutation) Day 7

T et B se rencontrent :une question d’équilibres De parfums B Ag Naive B cell CXCL13 CXCL13 CXCR5 CXCL13 B Th Activ B CXCR5 CCR7 CCL19 CCL21 Naive T cell CCL19 CCL21 CCL19 CCL21 CCL19 CCL21 T cell Zone CCR7 CCL19 CCL21

T – B Cooperation :The GC deadly ballroom Bone marrow Long lived plasmocytes Germinal center Follicular dendritic cells Ag B B death + select. Centrocytes selection Memory B cells B B B T cell Zone Th B B Synapse 3 B Somatic hypermutations B B Light zone Clonal proliferation B B B B B Dark zone B B B B B Proliferation B B B B B B B B B B B B Day 14

T – B Cooperation : Old B cells remember with the help of old T cells years Recall Ag Recall Ag mB mB mB mB mB mB mB mB mTh mB mTh mB mB Memory T helper B220- memory B B220+ memory B B220- CD136+ plasmocytes.

Diagram of T – B cooperation in B cell differentiation/activation follicle Germinal center B1 or MZ B cells B2 cells Th cells Long lived plasmocytes Long term memory B 3 4.. Somatic Hypermutation & selection. 1 Ag contact Ag contact 2 Class Switch Recombin. DC Shorted lived plasmocytes 1 Memory Th Memory Th

La coopération cellules T- cellules B, Un long ballet avec de nombreux partenaires 1. 50 années de coopération T – B : La question du pont antigènique 2. Les évènements cellulaires ; la réaction du centre germinatif. 3. Les évènements moléculaires

The molecular events : surface receptors & ligands First signals : Ag recognition and initiation of the synapse Coactivation signals : crucial cosignals modulating signals Regulatory & inhibitory signals

First signal, 2d part : initiating the synapse Class II signals Proliferation & differentiation Both early & late events CD3 ZAP70 Synergy with BCR & CD40 signals Associate with CD19 22 & CD40 (?) p56lck CD18 icam icam CD18

The synapse in T-B cooperation Cell division & differentiation Early S meeting scanning Late synapse B 5 – 30 min. 12 – 24 hours B B B B B B Th Th Th Th Th Th Th

Ag recognitions during T-B cooperation a splited first signal B cell BcR B cell Ag B cell Activ.T cell cooperation

The molecular events : surface receptors & ligands First signals : Ag recognition and initiation of the synapse Coactivation signals : a) crucial signals b) modulating signals c) negative signals Depends mainly upon : Ig superfamily, partic. The CD28 family TNF/TNFR family members others : CD72 – CD100

The CD28/B7 families of coreceptors Inhibitors / activators (Ig like superfamily) Receptor ligand CD28 CD86 CD80 CTLA-4 ICOS ICOS-L (B7RP1) PD1 PDL-1 PDL2 BTLA B7x TIM-3 ? Inhibitors / activators

The molecular events : surface receptors & ligands First signals : Ag recognition and initiation of the synapse Coactivation signals : a) crucial signals CD28 – CD86/CD80 CD154 – CD4O ICOS – ICOSL CD100 – CD72

CD40 – CD154 The central pathway for T-B cooperation Activated Tcell CD154 (CD4OL) inducible CD40 signal Synergy with the BCR signal B cell Increase adhesion And signal. mol. (CD80, 86, class II CD 95) IL-6, TNF, IL-10 & 12 LT, Ig, chemok. Clonal Proliferation Differentiation & Ab production germinal centers development Memory Bcells Isotype switching Humoral memory

The CD28 pathway is started by the CD40 pathway 5 6 CD86 2d signal CD3 TCR 3 1 1st signal CD4O CD40L 2

ICOS-/- mice have + no GC + a low Ig production,part. IgE. Constitutive surf. Molecule Inducible surf. Molecule B7RP-1 Ag CD40 B7RP-1 CD86+CD80 CD28 ICOS Class II TcR Tc in GC CD40 CD154 CD28 CD40 CD154 1 2 3 CD86+CD80 ICOS TCR IL-4 & 13 Recept. IL-4 & 13 B cell prolif & differentiation

CD72 : stimulates B cell prolif., survival, MHC ClII expression Potentializes MHC ClII and CD40 signals Required for diff. Of B-1 B cells, high affinity Ig responses to T dep. Ags CD100 CD72 TcR Class II Tc in GC CD40 CD154

The molecular events : surface receptors & ligands First signals : Ag recognition and initiation of the synapse Coactivation signals : a) crucial signals b) modulating signals c) negative signals CD134 – 134L (OX40 - OX40L) CD137 – CD137 L (4-1BB – 4-1BBL) CD27 – CD70 BCMA - TACI

Prolonging and modulating B cell coactivation 1 : Once the CD40 and CD28 pathway fully works The CD134 (0X40) & 137 (4-BB1) pathways Help B cell proliferation deficient Ig switch (KO mice) IgM production normal GC OK CXCR5 CD134L CD134 Strong Coactivation signal Enhance B-cell prolif to anti µ, yet no effect Of humoral response In KO mice CD137L CD137 TCR CD28 CD4O CD154

Prolonging and modulating B cell coactivation 2 :Later on : Shaping the Immune response & setting long term memory TCR CD154 CD4O CD70 CD27 CD28 The CD27-CD70 pathway Required for development of: Memory cells plasma cells Terminal diff of B memory cells in plasma cells Late expression during T cell activ.

The BAFF / APRIL pathway TNF like TNF-R

The molecular events : surface receptors & ligands First signals : Ag recognition and initiation of the synapse Coactivation signals : a) crucial signals b) modulating signals c) negative signals CTLA-4 – CD80, CD86 CD30 – CD153 BTLA – B7H-RP CD95 – CD95L

Controling and terminating B cell proliferation/activation 1 : short term control within a synapse TCR CD28 CTLA4 within the CD28 pathway CD154 CD4O CD86 CD80 CTLA4 initial Few hours 1 – 2 days Time

PD1 – PD-L1, 2 pathway : an autoregulatory and Tolerogenic pathway CTLA-4 CD80 TCR CD28 PD1 PD-L1, PD-L2 BCR PD1

- + BTLA – BTx : an attenuator pathway for T & B cells BTLA & ICOS favour TH2 development in opposite way BTLA+++ ICOS- TH1 BTLA++ Naive T cell - BTLA++ BTLA- TH2 BTLA+- ICOS- + ICOS+++ T cell dependant in B cell help augmented in BTLA-/- mice (increasd B cell proliferation to BCR crosslink) BCR primed B cell Naive B cell B7x (ubiquitous) BTLA++ BTLA-

A model for a fine tuning of GC formation by the CD28-B7 pathways Coyle & Gutierez-Ramos Nat Immunol 4, 647, 2003 T cell Zone Ag Activating signals Inhibitory signals Naive B cell STOP B CD80/86 CD28+ CTLA-4+ B B7RP-1 ICOS B Primed Th PDL1/2 PD-1 Naive T cell B7x B BTLA CD28+ Primed Th Primed Th STOP

Controling and terminating B cell proliferation/activation 2 :Later control : inhibiting isotype switch : the CD30/CD153 pathway 3 : Ultimate B cell extinction : Apoptosis via CD95 TCR CD154 CD4O CD153 CD30 CD28 Controling and terminating B cell proliferation/activation CD95 CD95L death inhibition

Long lived plasmocytes CD40 ICOSL CD134L CD27 CD80 Germinal center Long lived plasmocytes follicle Long term memory B 3 B2 cells 4.. Somatic Hypermutation & selection. 1 Ag contact Ag contact 2 Class Switch Recombin. DC Shorted lived plasmocytes Th cells 1 Memory Th Memory Th

Molecular pathways in T – B cell cooperation functions B cell receptor T cell ligand adhesion activation Ag presentation , Enhance activation no Class II TCR, CD4 CD18/11a CD54, 18/11a ++++ Enhance activation Development of B1 cells Enhance activation IgG production CD72 CD100 CD40 CD154 CD134L CD134 CD137L CD137 CD30/153 CD27 CD170 CD30/153 CD95 CD95L