Characterization of a suppressive factor produced by a human T hybridoma

The mode of action and the target cell of a suppressive factor continuously and spontaneously produced by a human hybrid T cell line constructed recently are reported. This factor was shown to suppress pokeweed mitogen-induced B cell differentiation when added within the first 48 hr of culture. It does not suppress B cell differentiation induced by Nocardia extracts, a relatively T-independent mitogen. The target cell for this factor seems to be a T lymphocyte in that it can be absorbed by E-rosetting cells but not by B lymphocytes or monocytes. This factor does not impair mitogen or allogeneic-induced lymphocyte proliferation and has an apparent m.w. of approximately 45,000 as estimated by Sephacryl S200 gel chromatography.