Immunomodulation by α₂‐macroglobulin and α₂‐macroglobulin‐proteinase complexes: the effect on the human T lymphocyte response

Alpha 2-macroglobulin (alpha 2M), various alpha 2M-proteinase complexes and methylamine-treated alpha 2M were added to human lymphocyte cultures stimulated with the specific antigen purified protein derivative of tuberculin (PPD), pokeweed mitogen (PWM) and anti-CD3. alpha 2M-trypsin diminished all reactions in a dose-dependent way. In the PPD-induced stimulation of peripheral blood mononuclear cells, both change of configuration and remaining proteinase activity contributed to the suppressive activity. Separate exposure of adherent cells or the highly purified T lymphocytes to alpha 2M-trypsin complexes indicated that the effect was mediated through adherent cells. Addition of indomethacin did not modify the results. In the interleukin 2 (IL2)-dependent stimulation of purified T lymphocytes by anti-CD3 the effect of alpha 2M-proteinase complexes was probably due to the digestion of IL 2 through remaining proteinase activity. As alpha 2M-proteinase complexes are formed at sites of inflammation, the multiple immunomodulatory effects of alpha 2M-proteinase complexes might contribute to the dysregulation of the immune system in inflammatory diseases.