Immunosuppressive properties of pregnancy serum on the mixed lymphocyte reaction.

The human fetus may escape immunological attack because of serum factors which have immunomodulatory influence on maternal cellular effector responses. Paired peripheral and retroplacental sera were shown to inhibit the allogenic mixed lymphocyte reaction (MLR) used as an in-vitro model of cell-mediated immunity. There was no correlation between the suppressive effect of the peripheral and retroplacental sera and the serum concentrations of four pregnancy-related proteins (alpha-fetoprotein, pregnancy-associated alpha 2 glycoprotein, pregnancy-associated plasma protein A and Schwangerschaftsprotein 1) to which immunosuppressive properties have been ascribed, but there was a negative correlation between peripheral AFP and MLR inhibition (r = -0.62, P less than 0.001). Hence, the factor or factors responsible for suppressing the MLR are not those investigated in the present study.