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 alpha 2-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.

The effect of the diffusion medium on quantification of human IgM by radial immunodiffusion.

The results of quantification of human IgM by radial immunodiffusion (RID) are influenced by the charge of the diffusion medium and by the radio of IgM to other serum proteins. Agarose has almost no influence, while some heavily charged agars are unsuitable for RID, even after reduction of the IgM. Reference and test sera should not differ too widely in IgM levels. The interaction between charged agar and human IgM explains the subgroup phenomenon described earlier by Klein et al. (1973).