A B Cell Superantigen–Induced Persistent “Hole” in the B-1 Repertoire

The bacterial toxin protein A from Staphylococcus aureus (SpA) interacts with B cell antigen receptors encoded by variable region heavy chain (V_H) clan III genes via a V region framework surface that has been highly conserved during the evolution of the adaptive immune system. We have investigated the consequences of exposure to this prototypic B cell superantigen, and found that treatment of neonates or adults induces a T cell–independent deletion of a large supraclonal set of susceptible B cells that includes clan III/V_H S107 family–expressing lymphocytes. In studies of different SpA forms, the magnitude of the induced deletion directly correlated with the V_H-specific binding affinity/avidity. Upon cessation of SpA exposure, the representation of conventional splenic (B-2 subset) lymphocytes normalized; however, we found that the V_H family–restricted deficit of peritoneal B-1 cells persisted. SpA treatment also induced a persistent loss of splenic S107-μ transcripts, with a loss of certain natural antibodies and specific tolerance to phosphorylcholine immunogens that normally recruit protective antimicrobial responses dominated by the S107-expressing B-1 clone, T15. These studies illustrate how a B cell superantigen can exploit a primordial Achilles heel in the immune system, for which B-1 cells, an important source of natural antibodies and host immune responses, have special susceptibility.