On the molecular basis of T helper cell function. III: B-lymphocyte promotor factors: production by T hybridoma and tumour cells; preliminary biochemical characterization

B-lymphocyte promotor factors (B-LPF) are defined as T-cell-derived, released molecules that trigger polyclonal induction of B-cell differentiation into antibody-forming cells. B-LPF activity is independent of antigen, and it apparently induces only IgM-producing B cells. B-LPF was discovered as products of an antigen-specific, I-Ab-restricted T-cell line. We here show that B-LPF is produced also by lymphoma cells derived from this T-cell line or by T-cell hybrids constructed by fusing the T-cell line with BW5147 thymoma cells. A chicken gamma globulin-specific T-cell hybridoma clone also produced B-LPF. Biological assays demonstrated that B-LPF-containing supernatants did not contain IL-1, IL-2, B-cell growth factor, or allogeneic effector factor. Biochemical studies showed that B-LPF was precipitated by 50% (NH4)2SO4 saturation and that at least three types of molecules were involved in B-LPF activity: molecules with molecular weights of greater than 90,000, 50,000-90,000 and 10,000-25,000. The relationship between B-LPF and antigen-specific helper/inducer factors is discussed.