Induction of antibody responses in vivo by antigen specific helper factor

T helper cell factors (HF) have been preparated against protein and synthetic antigens by restimulating in vitro induced helper cells with small amounts of antigen. HF when tested in vitro are antigen specific and capable of replacing T cells, initiating a thymus dependent IgM response. In the in vivo adoptive transfer assay HF is capable of replacing T helper cells and is active at very high dilution, inducing both IgM and IgG responses. When tested on unirradiated DNP primed animals the HF was able to initiate a thymus dependent anti-hapten response, comparable to that seen with helper T cells, of both IgM and IgG class. It was also shown that HF acts on anti-Thy 1 treated spleen cells. The results indicate that antigen specific helper factors may be one of the physiologic mediators of T-B interactions in intact animals.