Immunosuppressive factors in pregnancy serum: a preliminary report

A serum component with suppressive activity on human lymphocyte responses to phytohemagglutinin was examined in pregnancy serum. No correlation could be found between the elevated level of alpha-2AP glycoprotein and the immunosuppressive activity. The active constituent was isolated by ultracentrifugation, salt fractionation, ion exchange chromatography and gel filtration. The immunosuppressive activity was found to be associated with alpha-globulin which consisted of neither lipoprotein nor alpha-2-AP glycoprotein. In terms of its antigenicity, the active fraction was found to be a mixture of 5 components.