Role of polymorphonuclear neutrophils in a murine model of Chlamydia psittaci-induced abortion

To assess the role of polymorphonuclear neutrophils (PMNs) in Chlamydia psi ttaci infection in a pregnant mouse model, pregnant and nonpregnant Swiss O F1 mice were depleted of PMNs by treatment with the RB6-8C5 monoclonal anti body before intraperitoneal infection with C. psittaci serotype 1, Nondeple ted mice served as infection controls. Depleted mice aborted earlier and ha d a much higher mortality rate than nondepleted mice. Bacteriological analy sis showed that the number of chlamydiae isolated from the spleens of deple ted mice at 5 and 7 days postinfection was 100 times greater than that isol ated from nondepleted mice. Histopathological analysis of the placentas of depleted mice showed widespread necrosis of the uteroplacental units, with weak immunoreaction to chlamydial antigen, while the placentas of nondeplet ed mice showed substantial neutrophil infiltration but no large areas of ne crosis,,vith moderate to strong immunoreaction to chlamydial antigen, The l ivers of depleted mice showed numerous chlamydial inclusions in the hepatoc ytes, delayed microgranuloma formation, and in the pregnant animals extensi ve coagulative periportal necrosis, The livers of nondepleted mice displaye d multiple small foci of PMNs and mononuclear cells with microgranuloma for mation. Among this group of mice, the pregnant animals always had more hepa tic damage than nonpregnant animals. Our results suggest that PMNs play an essential role in the response to C psittaci primary infection, preventing the uncontrolled multiplication of chlamydiae in the liver and spleen.