Differential effect of pregnancy or gestagens on humoral and cell-mediated immunity.

The reactivity of spleen lymphocytes in a mixed lymphocyte culture and the in vivo PFC response to sheep erythrocytes have been evaluated in pregnant female mice and data compared with those observed in virgin sexually mature female mice daily treated either with progesterone or human chorionic gonadotropin (HCG) or human prolactin. The mixed lymphocyte reactivity is depressed at mid-pregnancy, whereas PFC response is increased. Comparable immunological modifications have been found in mice treated with HCG, but not in animals treated with progesterone or prolactin. The similarity between HCG treatment and pregnancy suggests that the rate of gonadotropin release may be one of the earliest events responsible for the immunological disturbances present during pregnancy, although its action on the lymphoid system seems to require the presence of the ovary. From these data and from the observation that HCG increases the PFC response also in thymusless nude female mice, it can be deduced that it acts on both T and B cells.