Induction of B cell differentiation by T cell factors. I. Stimulation of IgM secretion by products of a T cell hybridoma and a T cell line

We have attempted to determine the requirements for slg and T cell factors in the polyclonal activation of murine B lymphocytes. Highly enriched normal (neonatal or adult) or neoplastic B cells were cultured with T cell supernatants in the absence or presence of Sepharose-coupled anti-μ or anti-δ and assayed for polyclonal IgM secretion. The T cell supernatants were derived from Con A pulsed normal spleen cells, the C.C3.11.75 T cell line stimulated with antigen, or the B151K12 hybridoma (not pulsed with Con A). Unlike the spleen cell supernatants, the C.C3.11.75 and B151K12 supernatants lack Interleukin-1 (IL-1) and Interleukin-2 (IL-2); all 3 supernatants contain T cell-replacing factor (TRF). We have confirmed previous data which demonstrated that a) anti-Ig induces proliferation of mature B cells, and b) terminal differentiation to IgM secretion requires the presence of both anti-Ig and supernatant from Con A-pulsed spleen cells (CAS). In addition, we have shown that immature B cells, which do not proliferate in response to anti-Ig, can be induced to secrete IgM by anti-Ig plus CAS. In contrast to supernatants from Con A-pulsed spleen cells, supernatants from the C.C3.11.75 and B151K12 cell lines alone induced polyclonal IgM secretion by all populations of B cells tested; this was not accompanied by detectable proliferation. Furthermore, the polyclonal responses induced by the supernatants from the line and the hybridoma were not enhanced by anti-Ig. These results suggest that there are at least 2 pathways for T cell-induced B cell differentiation in vitro and that these pathways may involve different subpopulations of B cells. The 1st pathway requires 2 signals: 1 is provided by soluble macrophage or T cell factor(s) and the other is provided by cross-linking of slg. The 2nd pathway involves differentiation of some B cells in response to T cell help alone. These pathways can be distinguished by the source of the T cell supernatants.