ANTIGEN PRESENTATION T – CELL RECOGNITION T – CELL ACTIVATION T – CELL EFFECTOR FUNCTIONS

1. ANTIGEN PRESENTATION T – CELL RECOGNITION T – CELL ACTIVATION T – CELL EFFECTOR FUNCTIONS

2. CLP T CELLS B CELLS Common lymphoid precursor T B Th CTL PC Activate B cells and macrophages T HELPER CELLS Kill virus- infected cells CYTOTOXIC T LYMPHOCYTES Produce antibodies PLASMA CELLS Lymphocyte subsets

3. Plasma cell B-lymphocyte cytokines BCR + antigen Antibody production Cytotoxic T-limfocyte (Tc) Cell killing TCR + peptide + MHC-I Effector cell retains specific receptor Effector cells secrete cytokines cytokines Helper T-lymphocyte (Th) Macrophage activation Lymphocyte activation Inflammation TCR + peptide + MHC-II RECOGNITION EFFECTOR CELL

4. Tc Th Exogenous Ag Endogenous Ag Peptides of exogenous proteins (toxin, bacteria, allergen) bind to class II MHC molecules Peptides of endogenous proteins (virus, tumor) bind to class I MHC molecules RECOGNITION OF EXOGENOUS AND ENDOGENOUS ANTIGENES BY T-LYMPHOCYTES

5. The number of different T cell antigen receptors is estimated to be 1,000,000,000,000,000 (1015 - 17) How can 6 invariant molecules have the capacity to bind to 1,000,000,000,000,000 different peptides?

6. A flexible binding site? A binding site that is flexible enough to bind any peptide? At the cell surface, such a binding site would be unable to • allow a high enough binding affinity to form a trimolecular complex with the T cell antigen receptor • prevent exchange of the peptide with others in the extracellular milieu

7. Venus fly trap Floppy Compact A flexible binding site? A binding site that is flexible at an early, intracellular stage of maturation formed by folding the MHC molecules around the peptide. Allows a single type of MHC molecule to • bind many different peptides • bind peptides with high affinity • form stable complexes at the cell surface • Export only molecules that have captured a peptide to the cell surface

8. MHC molecules • Adopt a flexible “floppy” conformation until a peptide binds • Fold around the peptide to increase stability of the complex • The captured peptides contribute to the stabilization of the complex • Use a small number of anchor residues to tether the peptide • - this allows different sequences between anchors • and different lengths of peptides WHERE PEPTIDE BINDING OCCURS?

9. INTRACELLULAR COMPARTMENTS ISOLATED BY MEMBRANSE 1) cytosol 2) vesicular system

10. CYTOSOL-DERIVED PEPTIDES ARE PRESENTED BY MHC-I FOR T-CELLS

11. Generation of endogenous peptides: Degradation of endogenous proteins in (immune) proteasomes TAP: Transporter associated with antigen processing

12. PEPTIDE-MHC INTERACTION IS SUPPORTED BY MULTIPLE PROTEINS IN THE ENDOPLASMIC RETICULUM

13. TRIMMING OF PEPTIDES FOR OPTIMAL SIZE BY BY ERAP Tomo Saric Alfred Goldberg

14. Hydrophobic transmembrane domain Lumen of ER Lumen of ER Peptide Peptide Peptide Peptide Peptide Peptide Peptide Peptide Peptide Peptide Peptide ER membrane ER membrane TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-1 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 TAP-2 Cytosol Cytosol ATP-binding cassette (ABC) domain Peptide antigens from proteasome Transporters associated with antigen processing (TAP1 & 2) Transporter has preference for longer than 8 amino acid peptides with hydrophobic C termini.

16. THE INVARIANT CHAIN PROTECTS THE MHC CLASS II BINDING SITE UNTIL REACHING THE APPROPRIATE COMPARTMENT DMA/DMB 1. Stabilization of peptide accessable conformation 2. Exchange of CLIP to peptides derived from exogenous proteins • INVARIANT CHAIN LÁNC (Ii) • Chaperon – Conformation • Inhibition of the peptide binding site • Transport and retention

17. GENERATION OF MHC – I EPITOPES GENERATION OF MHC – II EPITOPES HLA-DR1/HLA-DR4 Viral protein B35 A2 C42 B27 HLA-DQ2/HLA-DQ7 HLA-A,B,C binding Overlapping peptides The Tc response is focused to few epitopes ENSURE RECOGNITION OF ANY PATHOGENIC PROTEIN The Th response is directed to overlapping epitopes ENSURE RECOGNITION OF ALL PROTEINS

18. ++ ++ ++ + ± (?) + ± W W W W W W W W W W W W N N h e h e h h e t e t t t C H F Q U P O M S L E Z R K B G D T X V I A N C H F Q U P O M S L E Z R K B G D T X V I A N W W W W W Y W W W W W Y ++ ++ ++ ++ TARGETS OF EPSTEIN-BARR VIRUS-SPECIFIC Tc (CTL) RESPONSES LATENT ANTIGENS - EBNA3 EBNA4 EBNA6 LMP2 EBNA5 EBNA2 EBNA1 LMP1 LYTIC ANTIGENS BHRF1 BMLF1 BMRF1 BZLF1 BARF0 • A poliklonális CTL válasz elsősorban a litikus antigének és az • EBNA3,4,6 nukleáris fehérjék ellen irányul • Erősen fókuszált egy adott MHC - peptid kombinációra • Az endogén EBNA1 nem processzálódik és így nem ismerhető fel

19. OTHER GENES IN THE MHC – not polymorphic MHC Class 1b genes EncodingMHC class I-like proteins that associate with -2 microglobulin Restricted tissue expression HLA-Gtrophoblast, interacts CD94 (NK-cell receptor). Inhibits NK cell attack of foetus/ tumours HLA-E, binds conserved leader peptides from HLA-A, B, C. Interacts with CD94 HLA-F fetal liver, eosinophil surface, function unknown MHC Class II genes Encoding several antigen processing genes HLA-DMand in professional APC, proteasome components (LMP-2 & 7), peptide transporters(TAP-1 & 2), HLA-DO and DO Many pseudogenes MHC Class III genes Encoding complement proteins C4A and C4B, C2 and FACTOR B TUMOUR NECROSIS FACTORS-/ Immunologically irrelevant genes Genes encoding 21-hydroxylase, RNA Helicase, Caesin kinase Heat shock protein 70, Sialidase

20. The SXY module that is present in all classical MHC class II genes — as well as in the genes encoding invariant chain (Ii), HLA-DM, HLA-DO and MHC class I molecules — is bound cooperatively by four factors: the heterotrimeric X-box-binding factor regulatory factor X (RFX), which is composed of RFX5, RFX-associated protein (RFXAP) and RFX-associated ankyrin-containing protein (RFXANK); the X2-box-binding factor cyclic-AMP-responsive-element-binding protein (CREB); the Y-box-binding factor nuclear transcription factor Y (NFY); and an as-yet-unidentified S-box-binding factor. This multiprotein complex — which is known as the MHC class II enhanceosome — is a 'landing pad' for the class II transactivator (CIITA), which is a non-DNA-binding co-activator that is recruited by multiple protein–protein interactions with several components of the enhanceosome. CIITA coordinates the recruitment of additional factors that are involved in CHROMATIN MODIFICATION and remodelling: these are CREB-binding protein (CBP), p300, p300/CBP-associated factor (PCAF), brahma-related gene 1 (BRG1) and co-activator-associated arginine methyltransferase 1 (CARM1). CIITA also coordinates the recruitment of factors that are involved in transcription initiation (that is, transcription factor IID (TFIID) and TFIIB) and in transcription elongation (that is, positive transcription elongation factor b, P-TEFb).