Purification and properties of a lymphocyte inhibition factor from human serum.

Recognition of antigen by sensitized human lymphocytes can be demonstrated by cell electrophoresis. A serum factor able to block this recognition was found to be associated with the alpha-2 macroglobulin (αM) protein. The factor was heat labile, susceptible to certain proteases and produced an active low molecular weight component when treated with sulphydryl reagents. It appeared to act directly on the lymphocyte, preventing response to subsequently encountered antigen.