Effect of Listeria monocytogenes infection on serum levels of colony-stimulating factor and number of progenitor cells in immune and nonimmune mice

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Abstract
Studies were performed to determine changes in serum macrophage colony-stimulating factor (M-CSF) levels and the number of macrophage progenitor cells in bone marrow and spleens of nonimmune and immune mice infected with L. monocytogenes. Immunity in mice was established by infecting mice 6 wk before use with a sublethal dose of L. monocytogenes. When challenged with 104 L. monocytogenes organisms, immune mice had an early (12 h) peak in M-CSF serum concentrations. Levels remained elevated for 24 h but fell towards normal by 48 h. M-CSF levels in nonimmune mice did not rise until 24 h after challenge, remained elevated for 7 days, and returned to normal by 14 days. The number of macrophage progenitor cells in the bone marrow of immune mice rose slightly during infection, whereas the number in nonimmune mice fell significantly by days 4 and 7. Progenitor cells in spleens of immune mice more than doubled during infection; in nonimmune mice a 6-fold increase was noted. Thus, important parameters of monocyte production differ in immune and nonimmune mice during listeria infection; a possible mechanism for differences in resistance to infection was offered.