Role of membrane receptors in the induction of an in vitro secondary anti-hapten response. II. Antigen-immunoglobulin receptor interaction is not required for B memory cell proliferation.

In this study it has been investigated whether the interaction of antigen and B cell surface immunoglobulin (sIg) is required for full clonal expansion of memory B cells specific for the hapten, p-azophenyl-lactoside (lac). Cultures of lac-primed B cells and keyhole limpet hemocyanin (KLH)-specific T cells were activated in three ways: (a) by the antigen lac-KLH, (b) in the absence of lac epitopes by attaching KLH to the H-2 antigens of the B cells, and (c) in similar conditions where lac epitopes were supplied on carriers unrecognized by helper T cells. Dilution analyses showed that the yield of IgG anti-lac plaques per activated precursor was identical in all situations, and that the increased responses observed in the presence of lac epitopes were due to an increase in the frequency of activated precursors. Our results thus indicate that specific interacting T cells convey both the differentiative and proliferative signals to B memory cells, and are at variance with proposals advocating that an antigen-induced proliferative phase is succeeded by a T-cell-dependent differentiative event. We suggest that the effect of sIg-antigen interaction may be to cycle some precursors into a more easily activated state.