2. ANTIGEN PROCESSING The conversion of native proteins to peptides which can combine with MHC molecules
3. ANTIGEN PRESENTATION The course of formation and display of peptide-MHC complexes on the surface of APCs and the course of peptide MHC complexes recognition by T cells
4. ANTIGEN PRESENTING CELLS A group of cells that play important role in immune response which can uptake ,process antigens and present peptide-MHC complexes to T cells
5. GENERAL PROPERTIES OF APC Capacity to uptake proteins Ability to process proteins to peptides Capacity to present peptides depends on type of MHC molecules expressed Must express co-stimulatory signals for T cell stimulation
14. MACROPHAGE ( MΦ) First identified APC Differentiated from monocyte in blood Cannot stimulate naïve T cell Capture antigens by phagocytosis ,pinocytosis and receptor mediated phagocytosis
15. B CELLS Originates in bone marrow Mature B cell co-express IgM and IgD on their cell surface
21. P Mhc class i α2 α1 α3 * α1, α2, α3 are the domains of α chain,45kDa * β2 microglobulin ,12kDa,small soluble domain * P->Peptide-binding site * T->Hydrophobic Transmembrane segment * ER.M->Endoplasmic reticulum membrane * C->Hydrophilic Cytoplasmic tail β2 ER.M T C
22. α-chain Encoded by HLA-A,B,C genes Consist of carboxyl-terminal short domain, transmembrane hydrophobic region,extracellular domain,aminoterminal signal peptide α-chain consists of α1,α2,α3 domain α1 and α2 forms a groove for the peptide-binding site
23. β2-microglobulin Interacts non-covalently with α3 domain Encoded by highly conserved gene located on a different chromosome Required for the expression of Class I molecules on cell membrane
24. ANTIGEN PRESENTATION BY MHC I 4.Presenting to CD8+T cells 1.Processing of endogenous Ag 2.Transporting of antigen peptide into ER 3.Peptide loading of class I MHC molecules
25. 1.PROcessing of endogenous Antigen 20S Endogenous antigens are degraded by Proteasome(26S) Consist of 20S proteasome(a catalytic core) and 19S particle(a regulatory component) Degradation of protein requires ubiquitin molecule Cytokine(IFNγ) enhance the production of LMP2, LMP7 and MECL-1(LMP10) and replace β1,β5,β2 respectively to form IMMUNOPROTEASOME β α α β 19S
26. Ubiquitination of protein Ub E1 ATP Ub ADP + Pi E1 Ub-Ubiquitin E1-Ubiquitin-activating enzyme E2-Ubiquitin-conjugating enzyme E3-Ubiquitin ligase E2 Ub Ub E1 Ub E3 Ub Ub Proteasome Ub Peptides Polyubiquitinated protein
27. 2.Transporting of antigen peptide into er TAP( Transporter associated with antigen processing) TAP2 TAP1 Consisting of TAP1 and TAP2 ATP dependent transporter Selective transporting (8-11aa)
28. Hydrophobic transmembrane domain Lumen of ER Peptide ER membrane TAP-1 TAP-2 Cytosol ATP-binding cassette (ABC) domain Peptide antigens from proteasome Transporters associated with antigen processing (tap1 & tap2)
29. Peptide TAP-1 TAP-2 Endoplasmic reticulum 3.Peptide loading of class I mhc molecules Nascent class I chain Class I MHC ERP57 β2-M Calnexin Tapasin Calreticulin 2-M binds and stabilises floppy MHC Tapasin, calreticulin,ERP57, TAP 1 & 2 form a complex with the floppy MHC Calnexin binds to nascent class I chain Until 2-M binds Cytoplasmic peptides are loaded onto the MHC molecule and the structure becomes compact β
30. 4.Presenting to cd8+t cells Tc Cell TCR Antigen peptide-class I MHC molecules presented on cell membrane by exocytosis P α2 CD8 α1 α3 β2 C.M T C
32. 1. Capture of exogenous antigen 2. Processing of antigen 3. Synthesis and transportation of class II molecule 4. Association of processed peptide with MHC II 5. Presenting to CD4+ T cells EXOGENOUS OR ENDOCYTIC PATHWAY
33. Endocytosis Phagocytosis Pinocytosis Receptor mediated endocytosis Form Endosome CAPTURE OF EXOGENOUS ANTIGEN
34. Processing of antigen Takes place in endosome(MIIC/CIIV) and lysosome Protease – Cathepsin cleaves peptides from Protein Cell surface Endosome Peptides in endosome
35. Mhc ii molecule α1 β1 MHC II is synthesized in ER Folding and assembly is aided by ER resident chaperon- calnexin INVARIANT CHAIN ( Ii ) Ii is a trimer ,each binding to newly formed MHC II Transport to GA through ER vesicle Fusion with MIIC containing HLA-DM ,cathepsin S α2 β2
36. Association of processed peptide with MHC II Invariant chain degradation leaving CLIP by proteolytic enzyme Cathepsin S Replacement of peptide in place of CLIP by HLA -DM
37. Presenting to CD4 T cells Formed peptide-MHC molecule is presented on surface of APC TCR binds with α1,β1 of MHC II and peptide
