membrane form secreted form 13 aa 26 aa K K V V K K 3aa

Transcription

1 Harvard-MIT Division of Health Sciences and Technology HST.176: Cellular and Molecular Immunology Course Director: Dr. Shiv Pillai secreted form membrane form 13 aa 26 aa K K V V K K 3aa

2 Hapten monosaccharide Polyvalent antigen polysaccharide antigen receptor NO SIGNAL SIGNAL TRANSDUCTION

3 Y Y Igβ Igα Src-family kinase Y Y ITAM

4 ITAM YxxL/IxxxxxxYxxL/I Immune-receptor Tyrosine based Activation Motif

5 Y Y Y Y Igβ Igα Activated Syk Y Y Y Y ITAM Inactive Syk

6 The T cell receptor α β γ ε ε δ ζζ ITAM

7 CO-RECEPTORS CELL SURFACE PROTEINS THAT BIND TO THE SAME ANTIGEN AS THE ANTIGEN RECEPTOR DISTINGUISHABLE FROM COSTIMULATORS

8 CD4 TCR α β γ ε ε δ ζζ Lck Fyn Zap-70

9 CO-RECEPTORS CD4 ON HELPER T CELLS CD8 ON CYTOTOXIC T CELLS CD21/CR2 ON B CELLS

10 CD21/CR2 is a co-receptor and a positive regulator of BCR signaling CR2/CD21 YYYY Immune complex BCR CD19 CD81 β α Lyn Fyn Syk Vav PI3K

11 Generation of Diversity 1. V(D)J Recombination Combinatorial Diversity Junctional Diversity N Regions P nucleotides 2. Somatic Mutation

12 V D J - C V D J DNA junctional diversity, bases added and removed mrna

13 Rearrangement is temporally ordered B LINEAGE T LINEAGE IgH D to J Then Vto DJ Then Ig Kappa V to J TCR D beta to J beta Then V beta to DJ Then TCR V alpha to J alpha

14 L VDJ µ Poly 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

15 V(D)J Recombination Lymphoid specific Locus-specific, cell-type specific, stage specific Accessibility model

16 Heptamer 12-bp spacer 23-bp spacer Heptamer Coding segment Nonamer Nonamer Coding segment RAG-2 RAG-1 NICK PRECEDES CUT OH P CLEAVE AND MAKE HAIRPINS

17 SIGNAL JOINT TRIM ADD N REGIONS JOIN RAG-1/RAG-2 still required TdT DNA-PK/Ku70/Ku80 XRCC4/DNA ligase CODING JOINT + N-region

18 RAG time RAG-1 dimers associate with RAG-2 dimers RAG-1 dimers bind to nonamers, cleave DNA RAG-2 has a beta-propeller like structure - probably brings in other proteins such as accessibility factors Rag genes evolved from a transposable element?

19 coding segment RSS RSS coding segment Looping out and Deletion Inversion

20 The 12/23 Rule Heptamer 12 bp spacer 23 bp spacer Heptamer Coding segment Nonamer Nonamer Coding segment

21 Cleave at heptamer junction ATTCTTTGAGATAGCTCGA TAAGAAACTCTATCGAGCT heptamer ATTCTTTGAGATAGCTCGA TAAGAAACTCTATCGAGCT Open up hairpin ATTCTTTGAGATAGCTCGATCG TAAGAAACTCTATCGAGCTAGC Add P nucleotides

22 HAIRPINS Resolved by Artemis, an enzyme which works in conjunction with DNA-PKcs

23 Severe Combined Immunodeficiency Rag-1 and Rag-2 deficiencies: SCID No VDJ recombination Artemis deficiency: SCID Defective coding joints Many other causes of SCID

24 V(D)J recombination and human lymphomas Many human lymphomas involve chromosomal translocations In some lymphomas (e.g. follicular lymphomas, lymphomas associated with Ataxia Telangiectasia, etc) the machinery involved in V(D)J recombination drives the translocation process

25 Regulation of V(D)J recombination 1. Allelic exclusion - role of pre-antigen receptors 2. Receptor editing

26 pre-bcr MEDIATED POSITIVE SELECTION (defective in X-linked agammaglobulinemia) V H to DJ H rearrangement Ψ Large pre-b C' pre-bcr Ψ Large pre-b C' pre-bcr Early pro-b Intermediate pro-b Late pro-b Ψ Large pre-b pre-bcr Small pre-b Y Immature B YY A B C C' D E F IgM IgD Mature B D H to J H rearrangement BONE MARROW Ψ Large pre-b C' pre-bcr V L to J L rearrangement Ψ Large pre-b C' pre-bcr

27 Pre-B receptor µ vpreb λ5 Igβ Igα S y k ITAM Blk/Lyn/Fyn

28 Pre-TCR No known ligand β ptα γ ε ε δ ζζ ITAM

29 Pre-antigen receptors Select cells that have made in-frame rearrangements Signals for survival, proliferation and allelic exclusion (rearrangement at second allele is shut off)

30 Central lymphoid organs Periphery antigen receptor "The death/ editing window" Proliferation and activation Rearrangement of Ig heavy chain or TCR β chain genes Selection by pre-antigen receptor of cells with in- frame Ig heavy chain or TCR β chain rearrangements Elimination or editing of self reactive cells F i n a l repertoire in responders

31 For more information and examples, 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.