Ig Genetics 2001

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Ig Genetics 2001

  1. 1. Immunoglobulin Genetics
  2. 2. Immunoglobulin Genetics History <ul><li>Same C region could associate with many V regions </li></ul><ul><ul><li>IgG Ab with different specificities </li></ul></ul><ul><li>Same V region could associate with many C regions </li></ul><ul><ul><li>Same idiotype on IgG and IgM Ab </li></ul></ul><ul><li>V and C regions coded for by separate genes </li></ul>
  3. 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. 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. 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. 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. 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. 8. Mechanism of DNA Rearrangements <ul><li>Recombination signal sequences (RSS) </li></ul><ul><ul><li>Nonmer </li></ul></ul><ul><ul><li>Heptamer </li></ul></ul><ul><ul><li>1 or 2 turn signals </li></ul></ul><ul><li>Rag-1 and Rag-2 </li></ul>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. 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. 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. 11. Order of Ig Gene Expression Explains: <ul><li>Why an individual B cell only produces one kind of Ig with one kind of heavy and one kind of light chain </li></ul><ul><li>Why an individual B cell makes only makes antibodies of one specificity </li></ul><ul><li>Why there is allelic exclusion </li></ul>
  12. 12. Origin of Antibody Diversity History <ul><li>Definition – Diversity (repitoire) is the total of all the Ab specificities that an organism is capable of expressing </li></ul><ul><li>Theories </li></ul><ul><ul><li>Germ line theory </li></ul></ul><ul><ul><li>Somatic mutation theory </li></ul></ul>
  13. 13. Origin of Antibody Diversity Current concepts <ul><li>Multiple V genes </li></ul><ul><li>V-J and V-D-J joining </li></ul><ul><li>Junctional diversity </li></ul><ul><li>N region insertions </li></ul><ul><ul><li>Amino acid sequences not encoded in the germ line </li></ul></ul>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. 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. 15. Origin of Antibody Diversity Current concepts <ul><li>Multiple V genes </li></ul><ul><li>V-J and V-D-J joining </li></ul><ul><li>Junctional diversity </li></ul><ul><li>N region insertions </li></ul><ul><li>Somatic mutation </li></ul><ul><li>Combinatorial association </li></ul><ul><li>Multispecificity </li></ul>
  16. 16. Generation of Diversity <ul><li>Ag independent process </li></ul><ul><li>Clonal selection </li></ul>
  17. 17. T Cell Antigen Receptor <ul><li>Heterodimer of an  and a  chain </li></ul><ul><li>Gene structure and expression of the  chain is analogous to the immunoglobulin heavy chain </li></ul><ul><li>Gene structure and expression of the  chain is analogous to the immunoglobulin light chain </li></ul><ul><li>No somatic mutation in T cells </li></ul>

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