antigensecretion of antibodiesclonal expansionHarvard-MIT Division of Health Sciences and TechnologyHST.176: Cellular and Molecular ImmunologyCourse Director: Dr. Shiv PillaiSerum Electrophoresis +_ A l b u m i n G l o b u l i n s α β γFab Fragment Fc fragment CDR1 CDR2 CDR3 Hinge VH VL CL CH1 CH2 CH3 N CC N N C Papain cleavage NY Y YYYYY YYY Neutralization Functions of Antibodies Agglutination Complement fixation YYYC YYY Opsonization YYY Antibody dependent cellular cytotoxicityIgG IgD IgE J chain Pentameric IgM J chain Dimeric IgADifferent Ig isotypes mediate distinct functions 1. Complement fixation- (IgM, IgG1, and IgG3) 2. Opsonization- (IgG1 and IgG3) 3. Placental transfer- (IgG2 and IgG4) 4. Mucosal immunity - (IgA1, IgA2, and IgM) 5. Immediate type hypersensitivity - (IgE) 6. Antibody Dependent Cellular CytotoxicityY YY YY YY Poly Ig receptor YYYY Y Y Y Y J chain Y Dimeric IgA IgA SECRETING PLASMA CELL secretory IgA Generation of secretory IgA Secretory component YYIMMEDIATE TYPE HYPERSENSITIVITY Crosslinking antigen IgE Y Y YYFcεRI MAST CELLN N Primary structure Secondary structures alpha - helix beta-strand C C N N C NC NCN C Tertiary structure Quaternary structure CComplementarity determining regions = CDRs = HVRs See Immunobiology, by Janeway,C., Travers, P.,Walport, M. and Capra, J., Garland Publishing, 5th edition, 2001 & Cellular and Molecular Immunology by Abbas, A., Pober, J., and Lichtman, A., W B Saunders; 4th edition.Isotypes Allotypes Anti -mannose Anti-glucose IgG IgG IgGIgD IgG IgG Idiotypessecreted membrane form form K V K V 13 aa 26 aa 3aa KKPoly A sites Cµ1 Cµ2 Cµ3 Cµ4 µM1 µM2 AAAA Choice of first polyadenylation site AAAA Choice of second polyadenylation site AAAA µs mRNA AAAA µm mRNA µVDJLHapten Polyvalent antigen polysaccharidemonosaccharide antigen receptor NO SIGNAL SIGNAL TRANSDUCTIONHaptens, Antigens, Immunogens • Haptens are small molecules or moieties. They are antigens but not immunogens • All immunogens are antigens • All antigens are not immunogensIgs and the secretory pathway Y Y Y Y Y Y Y Y Y Y ER GolgiEndocytosis, recycling, and lysosomes Early endosomes Late ER Golgi Lysosomes endosomes Vesiculo-Tubular CompartmentProteins are endocytosed after Monovalent small molecule Polyvalent biopolymer biopolymer/ Y NO SIGNAL they are seen by the BCR Hapten YYSIGNAL ENDOCYTOSED FOR Y T-independent antigen “Monovalent” Y ANTIGEN PRESENTATIONproteinViral envelope protein MHC class I-peptide complex T T cell receptor Antibodies -missing the forest for the trees?α1 α2 α3 β 2-microglobulin Transmembrane domain Cytoplasmic tail peptide Heavy chainpeptide α1 β1 β2α2activated T TCR CD4 gp 39/CD40L Y CD40BCR MHC class II (loaded) Y BHELPER T CELL Nucleus Endoplasmic reticulum T cell receptor CD4 MHC class II membrane immunoglobulin protein antigen CLIPPeptide -CLIP exchange mediated by HLA-DM Invariant chaini B cell epitope or hapten linear peptides presented to T cells ("carrier determ nant") H a p t e n-p r o t ein conjugate (T dependent immunogen) WILL NOT CROSSLINK RECEPTORYYYY NO SIGNAL SIGNAL Y ENDOCYTOSED FOR ANTIGEN PRESENTATION Hapten T-independent antigen T-dependent