Non-specific factor replaces T cells in an IgG response to soluble antigens.

The antigen and T-cell requirements for the final stages of proliferation and maturation of DNP-KLH primed and boosted mouse spleen cells into IgG antibody secreting cells have been studied in vitro. The requirement for free antigen ceases after 24-48 h in vitro. The carrier-specific T-cell requirement for triggering of activated B cells by a soluble antigen (DNP-KLH) can be replaced in T cell-depleted cultures by non-antigen specific T cell-replacing factors (TRF). However, if the carrier protein is changed, TRF restores the IgG response of T cell-depleted cultures only if antigen is presented to B cells in particulate form, e.g. on the surface of macrophages, or in the presence of small amounts of antibody against the carrier protein. Thus, direct interaction between soluble protein and B cells is not sufficient to allow TRF to effectively replace specific T cells. Since TRF must be added at the start of culture, the initiation of B-cell maturation into IgG secretion by TRF occurs during B-cell proliferation, and is followed by further proliferation before IgG antibody can be detected.