Immunosuppressive properties of mouse amniotic fluid.

Previous reports have suggested that the alpha-fetoprotein present in mouse amniotic fluid is a potent nontoxic immunosuppressant. In the present studies mouse amniotic fluid (1:50) from 9- to 20-day gestations markedly inhibited the in vitro responses of mouse spleen cells to SRBC, and spleen cells from nonpregnant females were more affected than were cells from pregnant mice. On the other hand, MAF was less effective in depressing antigen- and mitogen-induced proliferation of human blood cells than were NMS or human serum. Human AF and cord sera did not significantly depress the immune responses of cells from mouse or man when added to cultures at concentrations sufficient to achieve levels of alpha-fetoprotein reported to be immunosuppressive if mouse AFP is used. While these studies do not identify the inhibitory agent(s) present in MAF, they do suggest that mouse AFP either is pharmacologically different from human AFP and/or that the immunosuppressive activity attributed to mouse AFP is actually produced by another agent physically associated with it.