Protective effect of recombinant murine granulocyte-macrophage colony-stimulating factor against Pseudomonas aeruginosa infection in leukocytopenic mice

The effects of recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) against Pseudomonas aeruginosa infection in ICR mice were investigated. Mice were treated with cyclophosphamide (CPA) and were then injected intraperitoneally with rmGM-CSF three times daily, beginning on the day after CPA treatment, for 7 days. The number of peripheral blood leukocytes in both CPA- and rmGM-CSF-treated mice and control CPA-treated mice reached a nadir on day 4, when P. aeruginosa was injected intraperitoneally. The administration of rmGM-CSF significantly increased the proportion of survivors among mice infected with a lethal dose of P. aeruginosa. This effect was further analyzed by monitoring sequential changes in leukocyte count and bacterial growth in various organs. The number of bacteria in the peritoneal cavities, peripheral blood samples, and livers of GM-CSF-treated mice decreased to an undetectable level after a transient increase, and the number was significantly lower than that in control mice. In GM-CSF-treated mice, the neutrophil levels in peripheral blood started to increase 5 days after CPA administration and were consistently higher than those in controls. Furthermore, the neutrophils in GM-CSF-treated mice were more mature morphologically. Thus, the prophylactic effect of rmGM-CSF against P. aeruginosa infection may result from a rapid recovery of myelopoiesis and a partial enhancement of mature neutrophil function.