Immunoglobulin Genetics Immunoglobulin Genetics History Same C region

Immunoglobulin Genetics

Immunoglobulin Genetics History • Same C region could associate with many V regions – Ig. G Ab with different specificities • Same V region could associate with many C regions – Same idiotype on Ig. G and Ig. M Ab • V and C regions coded for by separate genes

Light Chain Gene Families Germ line gene organization Lambda light chain genes; n=30 Vλ 1 L P L Vλ 2 P L Vλ n Jλ 1 P Cλ 1 Jλ 2 E Cλ 2 Jλ 3 E Cλ 3 Jλ 4 E Cλ 4 E Kappa light chain genes; n=300 L P Vκ 1 L P Vκ 2 L P Vκn Jκ 1 Jκ 2 Jκ 3 Jκ 4 Jκ 5 Cκ E

Light Chain Gene Families Gene rearrangement and expression L Vκ 1 P L Vκ 2 P Jκ 1 Jκ 2 Jκ 3 J 4 Jκ 5 P DNA Rearrangement L Vκ 1 L Vκ 2 Jκ 4 Jκ 5 P L V J DNA C Primary transcript RNA L V J C m. RNA Translation DNA Cκ E E RNA Processing Cκ E P Transcription Vκ n L RNA L V J C Protein Transport to ER V J C Protein V C

Heavy Chain Gene Family Germ line gene organization Heavy chain genes; Vn=1000, Dn=15 L P V 1 L V 2 P L D 1 D 2 D 3 Vn Dn J 1 J 2 J 3 J 4 J 5 P Cµ Cδ E Cγ 3 C γ 1 C γ 2 C γ 4 Cε Cα 1 Cα 2 CH 1 H CH 2 CH 3 CH 4 Introns separate exons coding for H chain domains

Heavy Chain Gene Family Gene rearrangement and expression L P V 1 L V 2 P D 1 D 2 D 3 Vn L Dn Cµ J 1 J 2 J 3 J 4 J 5 Cδ E P DJ rearrangement L V 1 L P V 2 L P D 1 D 2 J 4 J 5 Vn P Cµ Cδ E DNA VDJ rearrangement L V 1 L P V 2 D 2 J 4 P Cµ J 5 Cδ DNA E Transcription L V 2 D 2 J 4 Cµ J 5 E Cδ Primary transcript RNA

Heavy Chain Gene Family Gene rearrangement and expression L V 2 D 2 J 4 J 5 Cµ L V 2 D 2 J 4 J 5 Cδ Primary transcript E Cµ Cδ E RNA Processing L V DJ Cδ L V DJ Cµ An An m. RNA for Cδ m. RNA for Cµ Translation L V DJ Cµ L V DJ Cδ Cµ heavy chain Cδ heavy chain Transport to ER V DJ Cµ V DJ Cδ V C Cµ heavy chain V C Cδ heavy chain

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

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

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

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 V gene D region CCCCCC T GG C C GG Pro Trp V gene D region CCCCCC T GG CCCCCG Pro Arg

Generation of N region insertions D J Break DNA J D - OH Td. T adds nucleotides D -GTCAATG J Ligate D -GTCAATG- J N region insertion + Intron

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