The Early Innate Intestinal Immune Response to Listeria monocytogenes in BALB/c Mice
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Listeria monocytogenes is a facultative intracellular bacterial pathogen capable of escape from vacuoles and intercellular spread. Escape from vacuoles is in part mediated by a broad-range phospholipase C (PC-PLC) whose activity is regulated by pH. Deletion of the sequence coding for the PC-PLC propeptide (plcB?pro) generates an enzyme that is constitutively active. Results from oral mouse infections indicated that L. monocytogenes plcB?pro is cleared more rapidly from the intestinal tissues than wild-type bacteria. We hypothesized that the loss of regulation of PC-PLC leads to an enhanced immune response to infection. To test this hypothesis, we infected mice by gavage with either wild-type or mutant bacteria, and we used uninfected mice as controls. The mice were sacrificed between 4 and 40 hours post-infection, and the intestines were collected and processed for evaluation of neutrophil infiltration by immunohistochemistry or for identification of immune cells populating the intestinal tissues by flow cytometry. We observed that the loss of regulation of PC-PLC activity does not change the kinetics, but slightly reduces the overall extent of neutrophil recruitment. However, by 40 hours post-infection there was an increase in the proportion of CD4+ CD8+ T cells in the epithelium; increases in the proportions of macrophages, dendritic cells, and T and B lymphocytes in the lamina propria; and increases in macrophages, natural killer cells and natural killer T cells in the lymph follicles. We concluded that the loss of regulation of PC-PLC results in an enhanced immune response to infection by L. monocytogenes.
dissertation or thesis