A longitudinal analysis of lymphocyte proliferative responses to mitogens and antigens during human pregnancy.

T-cell number and mitogen- and antigen-induced lymphocyte proliferative were assessed longitudinally in 18 normal human pregnancies to examine the effects of pregnancy on cellular immunity. The T-cell percentage and mitogen-induced responses did not change significantly in pregnant women as compared to nonpregnant, non-postpartum control adults. However, cell-mediated immune responses to three antigens were dramatically depressed during the third trimester and then returned to early pregnancy levels by 90 days post partum. This reduction in antigen-specific cellular immunity may be necessary to prevent rejection of the histoincompatible fetus by the mother and at the same time may render women in late gestation more susceptible to infection.