The document discusses immunoglobulin and T cell receptor genetics. It describes: 1) The organization of light and heavy chain gene loci, including multiple V, D, and J genes. 2) The mechanisms of V(D)J recombination and junctional diversity that generate antibody diversity prior to antigen exposure. 3) The processes of heavy and light chain gene rearrangement and expression that produce a single antibody specificity per B cell.

1. Immunoglobulin Genetics

2. 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

3. Light Chain Gene Families Germ line gene organization J  1 C  1 E J  2 C  2 E J  3 C  3 E J  4 C  4 E P L V  1 P L V  n P L V  2 Lambda light chain genes; n=30 P L V  1 P L V  n P L V  2 J  2 J  3 J  5 C  E J  1 J  4 Kappa light chain genes; n=300

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

5. Heavy Chain Gene Family Germ line gene organization Introns separate exons coding for H chain domains Heavy chain genes; Vn=1000, Dn=15 P L V1 P L Vn P L V2 D2 D3 D1 Dn C  C  C  3 C  C  2 C  1 C  4 C  1 C  2 J2 J3 J5 J1 J4 E C H 1 H C H 2 C H 3 C H 4

6. Heavy Chain Gene Family Gene rearrangement and expression P L V1 P L Vn P L V2 D2 D3 D1 Dn C  C  J2 J3 J5 J1 J4 E DJ rearrangement P L Vn P L V1 P L V2 D2 D1 C  C  J5 J4 E DNA VDJ rearrangement D2 C  C  J5 J4 E P L V1 P L V2 DNA Transcription D2 C  C  J5 J4 E L V2 RNA Primary transcript

7. Heavy Chain Gene Family Gene rearrangement and expression E Primary transcript E J4 D2 V2 C  C  J5 L C  C  J5 L D2 J4 V2 RNA Processing A n mRNA for C  C  L D J V C  L D J V A n mRNA for C  Translation C  heavy chain C  L D J V C  L D J V C  heavy chain Transport to ER C  heavy chain V C C  D J V C  D J V C  heavy chain V C

8. 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 2 1 1 D Heptamer CACAGTG GTGTCAC Nonamer ACAAAAACC TGTTTTTGG 23 bp 23 bp Two turn RSS 2 Nonamer GGTTTTTGT CCAAAAACA Heptamer CACTGTG GTGACAC 12 bp 12 bp One turn RSS 1

9. 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    (  ) Heavy chain Paternal Maternal

10. Order of Ig Gene Expression + - Light chain gene VJ recombination Productive rearrangement ? Yes No Transcribe/translate Light chain 4 th Apoptosis 1st -  2nd -  3rd -  4th -  or Pre B cell Mature B cell     + 

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

12. 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

13. 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 T G G C C C Pro Trp C C C C C C V gene T G G D region C C C C C C V gene T G G C G G C C C Pro Arg C C C C C C V gene T G G D region C G C C C C Pro Pro

14. - GTCAATG - GTCAATG - + Break DNA TdT adds nucleotides Ligate N region insertion Intron J D J J J D D D Generation of N region insertions

15. 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

16. Generation of Diversity Ag independent process Clonal selection

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