Immunosuppressive properties of alpha 1-microglobulin

alpha 1-Microglobulin (alpha 1m), a serum glycoprotein (26,000 d), was found to impede the proliferative response of human lymphocytes to purified protein derivative (PPD) and tetanus toxoid. The data suggest that alpha 1m operates through an unstable suppressor mechanism, which no longer can function after 24 h of preculturing. This effect of alpha 1m on antigen stimulation did not seem to be due to binding of alpha 1m to PPD or cells, to altered kinetics of the PPD response, or to non-specific cytotoxicity. In contrast, PPD-induced leucocyte migration was not reversed by alpha 1m. alpha 1m did not cause significant inhibition in experiments in which lymphocytes were stimulated by the mitogens phytohaemagglutinin or concanavalin A. Finally, alpha 1m had its own leucocyte migration inhibitory effect.