Effect of granulocyte-macrophage colony-stimulating factor on the number of leucocytes and course of Listeria monocytogenes infection in naive and leucocytopenic mice.

This study concerns the effect of recombinant murine granulocyte-macrophage colony-stimulating factor (GM-CSF) on the number of circulating leucocytes, activation of peritoneal macrophages and proliferation of Listeria monocytogenes in various organs of naive and leucocytopenic mice. Mice were rendered leucocytopenic by sublethal total body irradiation or cyclophosphamide treatment. GM-CSF treatment enhanced the number of granulocytes and monocytes in peripheral blood during L. monocytogenes infection in naive mice, but not in irradiated or cyclophosphamide-treated mice. In naive mice, irradiated and cyclophosphamide-treated mice, GM-CSF did not affect the course of L. monocytogenes infection in thigh muscle, spleen and liver. However, GM-CSF treatment significantly increased the number of macrophages in the peritoneal cavity of naive mice during infection; these macrophages were more enlarged and showed a higher frequency of binucleated and multinucleated cells relative to non-GM-CSF-treated mice. Together, these results demonstrated that GM-CSF increased the number of circulating granulocytes and monocytes, and the number of peritoneal macrophages during infection with L. monocytogenes in naive mice, but did not affect the course of the infection in thigh muscle, spleen or liver of these mice. In leucocytopenic mice, however, GM-CSF did not affect the number of circulating phagocytes, which explains that this factor had no effect on the proliferation of the bacteria in the various organs.