Early pregnancy factor (EPF): a link between fertilization and immunomodulation.

Early pregnancy factor (EPF) is a pregnancy-dependent, suppressor-releasing hormone, which can be differentiated from other known pregnancy-associated substances by its physiological, biochemical and immunological characteristics. To date studies have shown that the presence of EPF in serum at anytime except during pregnancy is pathological and is associated with tumors of germ cell origin. EPF can be detected in serum within hours of fertilization, thus providing for the first time a means of monitoring in vitro the continuing viability of a fertilized egg in vivo. EPF has been shown to be a link between fertilization and immunomodulation. Fertilization of the ovum initiates a chain of events which includes production of EPF. EPF then binds to lymphocytes, releasing soluble suppressor substances, which in turn modulate the mother's immune system. Thus it is proposed that the conceptus ensures its own defence against immunological rejection.