Polyclonal activation of murine B lymphocytes by Fe fragments. II. Replacement of T cells by a soluble helper T cell-replacing factor (TRF).

Fc fragments of human gamma-globulin stimulate T cell-dependent polyclonal antibody responses in murine splenic B cells. The T cell signal can be delivered by a soluble T cell-replacing factor, derived by concanavalin A stimulation of spleen cells. TRF interacts directly with responding B cells and appears to provide the second, differentiative, trigger that initiates the polyclonal response. TRF is maximally active even if added at 24 hr after Fc and does not alter the response kinetics. Although macrophages are requird for the polyclonal activation of B cells in intact spleen cell cultures, they are not necessary for the delivery of the TRF signal to B cells.