Characteristics of the mitogenic activity found in the supernatant of pokeweed mitogen stimulated human mononuclear cells.

Human peripheral blood mononuclear cells were stimulated with pokeweed mitogen (PWM), washed, and cultured in fresh mitogen-free culture medium; a second set of peripheral blood mononuclear cells was used to assess the mitogenic activity of supernatants of these cultures. The effects of this stimulation resembled those of a normal PWM stimulation, including the formation of blast cells, proliferation of lymphoid cells, and immunoglobulin synthesis. Our findings led us to perform experiments to investigate the nature of this mitogenic factor. The molecular weight of the mitogenic activity was found in the region of 700 kD. Additional experiments indicated that human α2-macroglobulin was not responsible for the high molecular weight of the mitogenic factor. Protein digestion or precipitation with trichloroacetic acid only partially abolished the mitogenicity of the mitogenic supernatant. Comparison of the molecular weight of the mitogenic factor with that of the PWM in culture medium showed that the mitogenic activity in the supernatants could be caused by PWM associated with a high molecular weight component.