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 potentially infectious pathogens, the young rabbit must diversify a limited initial repertoire by somatic mechanisms (the high copy number primary repertoire). The majority of rabbit B cells produce heavy chain variable regions by rearranging the VHa allotype-encoding VH1 gene. Thus in normal rabbits the majority of serum immunoglobulins bear VHa allotype (due to VH1 FR1 and FR3 sequences). The young rabbit appendix is a site of diversification of rearranged VH genes by gene-conversion-like and somatic hypermutation mechanisms. The newly generated B cells probably undergo selection processes that involve foreign and self-antigens and superantigens. We find preferential expansion and survival of B cells in normal and VH-mutant ali/ali rabbits based on their heavy chain FR1 and FR3 sequences (VHa allotype). This selection may involve "superantigen"-like interactions with endogenous as well as exogenous ligands.