B-CELL SUPERANTIGENS MAY PLAY A ROLE IN B-CELL DEVELOPMENT AND SELECTION IN THE YOUNG-RABBIT APPENDIX

In order to develop protective antibodies against a wide range of pote ntially infectious pathogens, the young rabbit must diversify a limite d initial repertoire by somatic mechanisms (the high copy number prima ry repertoire). The majority of rabbit B cells produce heavy chain var iable regions by rearranging the V(H)a allotype-encoding V(H)1 gene. T hus in normal rabbits the majority of serum immunoglobulins bear V(H)a allotype (due to V(H)1 FR1 and FR3 sequences). The young rabbit appen dix is a site of diversification of rearranged V-H genes by gene-conve rsion-like and somatic hypermutation mechanisms. The newly generated B cells probably undergo selection processes that involve foreign and s elf-antigens and superantigens. We find preferential expansion and sur vival of B cells in normal and V-H-mutant ali/ali rabbits based on the ir heavy chain FR1 and FR3 sequences (V(H)a allotype). This selection may involve ''superantigen''-like interactions with endogenous as well as exogenous ligands. (C) 1998 Academic Press.