Pre-implantation immunosuppression in the pregnant rat: a possible role of seminal fluid

Successful reproduction involves exposure of the female to significant antigenic challenge. These experiments were done to test the possibility/hypothesis that seminal fluid has an immunosuppressive role in the early stages of pregnancy, which could protect the conceptus from immunological attack. A highly inbred strain of rat AO [RT1[u]] was used in this study. Eleven groups of animals were examined, one during the estrous phase of the ovarian cycle to provide base-line data, five during pseudopregnancy, designated as controls, and five groups during syngeneic pregnancy. Each group contained a minimum of six animals. For each animal, body weight and organ/tissue weights of the uterus, thymus, uterine and popliteal lymph nodes, were recorded together with total cell counts of the lymphoid tissues and their proliferating cell counts. The material was collected during each of the first five days of pregnancy and pseudopregnancy. The present study supports an immunological suppression by seminal fluid during early pregnancy as shown by a significant sustained depression of the proliferative lymphocyte response in the uterine regional lymph nodes