Immunosuppressive activity of isolated rat and human fetoproteins.

Alpha-fetoprotein (AFP) was purified from rat hepatoma sera and pooled human cord sera. Both AFP-rich fractions prepared by consecutive ion exchange and gel filtration chromatography and pure rat AFP prepared by liquid phase immunoabsorption lacked in vitro suppressive activity. Human AFP purified by affinity chromatography was suppressive, but so was similarly purified human cord albumin. Alteration of ionic conditions was shown to affect the activity of both human AFP and cord albumin. The primary mixed lymphocyte response, the generation of the secondary response, and the memory cell, per se, were all found to be sensitive to active human AFP under the appropriate culture conditions.