The production of migration inhibitory factor and reproductive capacity in allogeneic pregnancies.

Migration inhibitory factor (MIF) is produced during allogeneic pregnancies but not during syngeneic pregnancies. Removal of the paraaortic or paraaortic and renal lymph nodes significantly decreased MIF production whereas splenectomy did not. Removal of these regional lymph nodes decreased the mean litter size and increased the variance in the weights of the offspring, with the greatest changes occurring when both the paraaortic and renal lymph nodes were removed; splenectomy did not alter either parameter. None of the surgical procedures affected the gestation period significantly, but removal of the paraaortic and renal lymph nodes greatly reduced the rate of conception and increased the incidence of stillbirths. These findings support the proposition that a vigorous immune response occurs during allogeneic pregnancies and that this response provides reproductive advantages to the offspring.