Immunoglobulin Genetics

Immunoglobulin Genetics History Same C region could associate with many V regions –IgG Ab with different specificities Same V region could associate with many C regions –Same idiotype on IgG and IgM Ab V and C regions coded for by separate genes

Light Chain Gene Families Germ line gene organization Jλ1Jλ1 Cλ1Cλ1 E Jλ2Jλ2 Cλ2Cλ2 E Jλ3Jλ3 Cλ3Cλ3 E Jλ4Jλ4 Cλ4Cλ4 E P L Vλ1Vλ1 P L VλnVλn P L Vλ2Vλ2 Lambda light chain genes; n=30 P L V κ 1 P L V κ n P L V κ 2 Jκ2Jκ2Jκ3Jκ3Jκ5Jκ5 CκCκ E Jκ1Jκ1Jκ4Jκ4 Kappa light chain genes; n=300

Light Chain Gene Families Gene rearrangement and expression L Vκ 1Vκ 1 L Vκ nVκ n L Vκ 2Vκ 2 Jκ2Jκ2Jκ3Jκ3Jκ5Jκ5 CκCκ Jκ1Jκ1J4J4 DNA PPP E P P E L Vκ 1Vκ 1 L Jκ5Jκ5 CκCκ Vκ 2Vκ 2Jκ4Jκ4 DNA Rearrangement VC J V C Protein Transport to ER Protein Translation C L V J E L V CJ RNA Transcription Primary transcript C L V J RNA Processing RNA mRNA

Heavy Chain Gene Family Germ line gene organization

Heavy Chain Gene Family Gene rearrangement and expression P L V1 P L Vn P L V2 D2D2 D3D3 D1D1DnDn CµCµ CδCδ J2J2J3J3J5J5J1J1J4J4 E DJ rearrangement P L Vn P L V1 P L V2 D2D2 D1D1 CµCµ CδCδ J5J5 J4J4 E DNA VDJ rearrangement D2D2 CµCµ CδCδ J5J5 J4J4 E P L V1V1 P L V2V2 DNA Transcription D2D2 CµCµ CδCδ J5J5 J4J4 E L V2V2 RNA Primary transcript

Heavy Chain Gene Family Gene rearrangement and expression E Primary transcript E J4J4D2D2 V2V2 CµCµ CδCδ J5J5 L CµCµ CδCδ J5J5 L D2D2J4J4 V2V2 RNA Processing AnAn mRNA for C µ CµCµ L DJV CδCδ L DJV AnAn mRNA for C δ Translation C µ heavy chain CµCµ L DJVCδCδ L DJV C δ heavy chain Transport to ER C µ heavy chain V C CµCµ DJVCδCδ DJV C δ heavy chain V C

Mechanism of DNA Rearrangements Recombination signal sequences (RSS) –Nonmer –Heptamer –1 or 2 turn signals Rag-1 and Rag-2 L V 2 J C 1 Lambda light chains L V 1 J C 2 Kappa light chains Heavy chains L V 2 J C D Heptamer CACAGTG GTGTCAC Nonamer ACAAAAACC TGTTTTTGG 23 bp Two turn RSS 2 Nonamer GGTTTTTGT CCAAAAACA Heptamer CACTGTG GTGACAC 12 bp One turn RSS 1

Order of Ig Gene Expression + - Heavy chain gene VDJ recombination Productive rearrangement ? Yes No Transcribe/translate 1st 2nd or Apoptosis Progenitor B cell Pre B cell µ µ µ (δ) Heavy chain Paternal Maternal

Order of Ig Gene Expression + - Light chain gene VJ recombination Productive rearrangement ? Yes No Transcribe/translate Light chain 4 th Apoptosis 1st - κ 2nd -κ 3rd λ 4th - λ or Pre B cell Mature B cell µ µ µ µ+ δ

Order of Ig Gene Expression Explains: Why an individual B cell only produces one kind of Ig with one kind of light chain Why an individual B cell makes only makes antibodies of one specificity Why there is allelic exclusion Importance of allelic exclusion??

Origin of Antibody Diversity History Definition – Diversity (repitoire) is the total of all the Ab specificities that an organism is capable of expressing Theories –Germ line theory –Somatic mutation theory

Origin of Antibody Diversity Current concepts Multiple V genes V-J and V-D-J joining Junctional diversity N region insertions – Amino acid sequences not encoded in the germ line D region TGGCCC Pro Trp CCCCCC V gene TGG D region CCCCCC V gene TGG CGGCCC Pro Arg CCCCCC V gene TGG D region CGCCCC Pro

TdT adds nucleotides JD - GTCAATG JD - GTCAATG -+ Ligate N region insertionIntron JD Generation of N region insertions D J Break DNA J D - OH

Origin of Antibody Diversity Current concepts Multiple V genes V-J and V-D-J joining Junctional diversity N region insertions Somatic mutation Combinatorial association Multispecificity

Generation of Diversity Ag independent process Clonal selection

T Cell Antigen Receptor Heterodimer of an α and a β chain Gene structure and expression of the α chain is analogous to the immunoglobulin light chain Gene structure and expression of the β chain is analogous to the immunoglobulin heavy chain No somatic mutation in T cells