Abstract
Protective immunity first becomes evident at 3 to 4 days after inoculation of mice with a sublethal dose of Listeria monocytogenes. Recent evidence suggests that production of gamma interferon (IFN-gamma) occurs earlier (within the first 24 h of infection). The purpose of this study was to define better the sequence of cytokine mRNA expression during the early stages of L. monocytogenes infection. Cytokine mRNA expression was detected by polymerase chain reaction-assisted amplification of RNA extracted from the spleen cells of individual mice euthanized at 0.5 to 120 h after L. monocytogenes challenge. By using this method, mRNAs for tumor necrosis factor alpha, interleukin-1 alpha (IL-1 alpha), IL-2, IL-4, IL-5, and IFN-gamma were detected in RNA from the spleen cells of uninfected mice. The intensity of the bands for IFN-gamma, however, was increased greatly at 16 h after intravenous injection of 5 x 10(4) CFU (nearly 1 50% lethal dose) of L. monocytogenes. IL-6 and granulocyte-macrophage colony-stimulating factor mRNAs were not detected in spleen cell RNA from uninfected mice but were induced within 30 and 60 min, respectively, after inoculation with L. monocytogenes. Increased amounts of mRNAs for IFN-gamma, IL-6, and granulocyte-macrophage colony-stimulating factor were detected after injection of viable, but not killed, L. monocytogenes. IL-3 mRNA was not detected at any time in RNA extracted from the spleen cells of uninfected or L. monocytogenes infected mice. These results suggest that infection with L. monocytogenes elicits a detectable cytokine mRNA response within the first few hours of infection.