Soluble factors for B cell activation: a T cell hybridoma that secretes a specific B cell growth factor.

A murine T cell hybridoma, T91, has been established by fusion of BALB/c Con A-activated spleen cells with BW 5147 HAT-sensitive thymoma cells. T91 constitutively produced a factor that markedly enhanced the proliferative response to LPS of B cells cultured at low cell density. This factor is nonmitogenic by itself. It maintains in the absence of LPS, the proliferation of B cell blasts previously activated with LPS for 3 days. T91 supernatant contains neither IL 1 nor IL 2 nor TRF activity, and mixing experiments indicate the absence of factors suppressing these activities. The data suggest the existence of a specific B cell growth factor compatible with a two-signal model for B lymphocyte activation.