The T cell dependence of B cell differentiation induced by pokeweed mitogen.

The in vitro plasma cell response of human peripheral blood B lymphocytes to PWM was found to be dependent on the presence of T lymphocytes. B lymphocytes cultured alone with PWM did not respond with proliferation or differentiation into plasma cells. When T lymphocytes were added back to B lymphocytes before culture, the number of plasma cells of the IgM, IgG and IgA classes formed increased in proportion to the number of T lymphocytes returned. Allogeneic T lymphocytes from either peripheral blood or adult thymus could effectively substitute for autologous T lymphocytes. By comparing responses of B lymphocytes cultured with equal numbers of autologous or allogeneic T cells, it was found that the considerable variation in the magnitude of the plasma cell response from different normal donors was related to a quality of their T cells; T cells from high responders substantially enhanced plasma cell differentiation of B cells from low responders and vice versa. This T cell "helper function" was irradiation-resistant and was a property of thymocytes as well as peripheral T cells.