Effect of pregnancy on augmentation of natural killer cell activity by Corynebacterium parvum and Toxoplasma gondii

Studies were performed to determine the effect of pregnancy on NK cell activity and the augmentation of NK cell activity which normally follows injection of killed C. parvum or live T. gondii. When compared to cells from virgin mice, peritoneal and splenic cells from unstimulated pregnant mice showed no significant difference in NK activity. In contrast, NK activity of peritoneal cells from pregnant mice that received C. parvum or T. gondii was significantly lower than that found in comparably treated virgin mice. This reduced augmentation of NK activity in the peritoneal cells of pregnant mice could not be altered by the removal of plastic-adherent cells or of T cells by treatment with anti-Thy-1.2 antibody and complement. The number of effector-target conjugates was quantitated with a single cell assay, and was found to be comparable between cells from treated pregnant mice and treated virgin controls. However, the magnitude of lysis of target cells by peritoneal and splenic effector cells from pregnant mice previously injected with C. parvum was markedly and significantly reduced when compared to cells from comparably treated virgin mice. Thus, pregnancy is associated with an impaired ability to augment NK activity. This decrease in NK activity was not due to the depletion or dilution of NK cells, but to a functional impairment of the individual NK cells.