Endotoxin-induced serum factor controlling differentiation of bone-marrow-derived lymphocytes.

Serum from bacillus Calmette-Guerin-infected mice injected with endotoxin induces the appearance of surface immunoglobulin, Ia antigen, and complement receptor on the surface of precursor bone-marrow-derived (B) cells. While endotoxin itself causes phenotypic conversion of both thymus-derived (T) cells and B cells in vitro, the endotoxin-induced serum factor was found to be a selective inducer of B cell differentiation. Spleen cells rendered immunodeficient by removal of B cells bearing the complement receptor regained the capacity to cooperate with helper T cells and to produce antibody against red cell antigens in vitro upon upon addition of the serum factor to the culture medium. Thus, a factor that controls selective phenotypic and functional differentiation of B cells has been identified and can now be characterized,