T-cell-dependent modulation of the polyclonal B-lymphocyte responses in normal spleen cell cultures stimulated by lipopolysaccharide.

The in vitro polyclonal B-cell proliferative and plaque-forming cell (PFC) responses to the T-independent (TI) mitogen lipopolysaccharide (LPS) are increased by the addition of normal syngeneic splenic T cells. Normal irradiated Lyt-2- T cells also alter the IgG subclass distribution from the typical predominance of IgG3 and IgG2b PFC to the appearance of IgG1, IgG2a and IgA PFC in T-cell-depleted spleen cell (SC) cultures. Furthermore, secondary LPS blast cultures yield increased PFC responses when co-cultured which syngeneic fresh normal T cells which, even in the absence of mitogen, induce PFC responses in such activated B cells. As LPS blasts induce normal syngeneic T cells to proliferate and significant numbers of L3T4+ blast cells are found in LPS-stimulated normal spleen cell cultures, we conclude that T cells actively participate in the regulation of these responses. The significance of these findings for the regulation of TI responses in vivo by "autoreactive" T cells is considered.