Salmonella infections continue to cause major illness and economic loss. Various mouse models with Salmonella enterica serovar Typhimurium (ST) infection have been established to study Salmonella pathogenesis and host defense. Though invasion of the gram-negative bacterium Salmonella into the sub-epithelial region of the small intestine has been well described, it is not yet clear how Salmonella can overcome the natural antimicrobial agents, which cover the intestinal epithelium. Recent studies have shown that wild-type but not mutant ST can decrease production of these intestinal antimicrobials including lysozyme. Lysozyme is well known for its peptidoglycan hydrolyzing activity. In addition, it has recently been shown that it also has a direct bactericidal activity against gram-negative bacteria. In mice, there are two types of lysozyme, P-lysozyme from Paneth cells and M-lysozyme produced by macrophages and other myeloid cells. These two forms can be distinguished by their mobility pattern in acid urea polyacrylamide (AU-PAGE) electrophoresis. Employing immunoblot with lysozyme specific antisera we aimed to determine whether the described decreased production of antimicrobial peptides in the small intestine induced by wild type ST is a local Paneth cell specific effect or whether it reflects a broader down regulation of immune responses involving macrophages and other immune cells. Mice were orally infected with wild type and mutant ST, or PBS as control. Small intestinal luminal washes, whole gut and crypt extracts were collected. Cationic proteins were subjected to AU-PAGE followed by immunoblot analysis. Resulting band intensities were compared to protein standards and quantified using an imaging system. Our findings suggest that Salmonella mediated decrease of lysozyme involves host defenses beyond the intestinal epithelium. Our future research will explore changes of cytokine levels in infected mice to elucidate the chain of events occurring during the infection.
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