Effect of alpha 2-macroglobulin on the lymphocyte response.

We studied the effect of α-macroglobulin (αMG) on the proliferative response of lymphocytes to several different lectins. This response to concanavalin A (Con A) and phytohaemagglutinin (PHA) was markedly reduced by addition of αMG to the reaction mixture, while that to lipopolysaccharide (LPS) was reduced to a lesser extent. Preincubation of lymphocytes with αMG had little effect on the response of the lymphocytes to lectin, when the protein was washed out before addition of the lectin. The response of the lymphocytes to lectin was reduced when αMG was added within 12 hr after the addition of the lectin, while the reduction was not apparent when the protein was added 24 hr after the lectin. I-αMG prepared by the chloramine T method which maintained a 30% trypsin-protein esterase (TPE) activity did not bind to the cells, while the labelled protein prepared using the lactoperoxidase method which had full TPE activity, did bind to the cells. The binding of αMG with Con A was also demonstrated. Thus, the inhibitory effect of the protein on the proliferative response of lymphocytes to lectin may be due to binding of the protein to lymphocytes and consequently blocks the binding of the lectin to the cells or due to interaction of the protein with the lectin so as to diminish the number of the lectin molecules acting on the cells.