[Prolonged survival of skin allografts in rats by injection of serum or a serum fraction extracted from pregnant rats].

This work report the partial purification of an alpha 2-macroglobulin present in the serum of allopregnant rats. Ultrogel filtration followed by immune absorption on different antisera were used giving a single band on polyacrylamide gel electrophoresis. This fraction was able to inhibit in vitro T cell cytotoxic response to allogenic cells. When administered repeatedly to rats it significantly increased the survival of skin allograft. This alpha 2-macroglobulin fraction isolated from allopregnant rats was denominated IRG to its graft rejection inhibitory activity.