Immunobiology of pregnancy.

This report presents new findings on two conditions that permit genetically disparate tissues to coexist during pregnancy: (a) regulation of major histocompatibility genes in placental trophoblast, and (b) synthesis of uterine and placental polypeptide growth factors with immunosuppressive properties. Recent experiments examining inter-relationships between these two protective mechanisms are cited, and potential explanations for trophoblast resistance to factors with MHC-inducing properties are proposed.