IMMUNOSUPPRESSIVE PROPERTIES OF ALPHA-1-MICROGLOBULIN

.alpha.1-Microglobulin (.alpha.1m), a serum glycoprotein (26,000 daltons), impeded the proliferative response of human lymphocytes to purified protein derivative (PPD) and tetanus toxoid. Apparently, .alpha.1m operates through an unstable suppressor mechanism which no longer can function after 24 h of preculturing. This .alpha.1m effect 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 nonspecific cytotoxicity. PPD-induced leukocyte migration inhibition was not reversed by .alpha.1m. .alpha.1m did not cause significant inhibition in experiments in which lymphocytes were stimulated by the mitogens phytohemagglutinin or concanavalin A. .alpha.1m had its own leukocyte migration inhibitory effect.