The adverse effect of pregnancy on macrophage activation

Recently a remarkable decrease in the resistance to infection with Listeria monocytogenes and Toxoplasma gondii in pregnant mice was demonstrated. Since activated macrophages are important in the resistance against these organisms, studies were performed to determine whether pregnancy has an adverse effect on the activation of macrophages and effector functions of these macrophages. Peritoneal macrophages from normal pregnant and virgin mice or from pregnant and virgin mice previously injected with Corynebacterium parvum to activate peritoneal macrophages were challenged with EL-4 tumor cells to test for macrophage cytotoxicity or with T. gondii to test for the capacity to kill an intracellular pathogen. There was no consistent difference between the enhanced cytotoxic capacity of activated macrophages from pregnant and virgin mice. Macrophages from C. parvum-treated pregnant mice were deficient in their ability to kill or inhibit multiplication of T. gondii when compared to macrophages from C. parvum-treated control mice (P < 0.001). Activated macrophages from pregnant mice were only able to mildly inhibit multiplication of T. gondii when compared to macrophages from control mice. Thus, there was a dissociation of effector function of activated macrophages from pregnant mice; they were defective in their ability to kill an intracellular pathogen but killed tumor target cells as well as did activated macrophages from virgin mice.