Onset of human maternal cell-mediated immune reaction to placental antigens during the first pregnancy.

The macrophage migration inhibition technique was employed to study the development of human maternal cell-mediated immune reactions to placental antigens during the first pregnancy. Cell-mediated immune reaction to pooled antigens from five placentas could not be demonstrated during the first trimester. In the 4th month, peripheral blood leucocytes from seven out of eight primigravidous women tested were reactive to placental antigens. The one nonreactor became reactive by the 5th month. All of the primigravidous women tested during subsequent months were reactive. Serial studies suggested a gradual increase in the degree of cell-mediated immune reactivity in the course of the first pregnancy.