Influence of immunoglobulin-dependent T cells on antibody class switching

Normal and B cell-deficient, carrier-primed mice were irradiated and were adoptively transferred with B cells to evaluate the role of putative Ig- and B cell-dependent T cells in anti-hapten antibody responses. The response was analyzed by using the splenic focus assay, which allowed us to examine the frequency of responding B cells and the production of multiple isotypes by single precursor B cells. This analysis revealed that both primary and secondary B cells were activated at higher frequency in the spleens of normal recipients, and production of isotypes other than IgM and IgG1 was enhanced in normal recipients as compared with anti-mu-treated recipients. Both changes could be restored to control levels by co-transfer of T cells from normal donors primed with an unrelated carrier, provided the free carrier was added to the assay culture. These results are consistent with a role for Ig or B cell-dependent helper T cells in the optimal activation and the resulting isotype expression of both primary and secondary B cells.