Background and Aims: Interleukin (IL)-15 exerts functional effects on lymphocytes similar to those of IL-2. IL-15 is expressed by nonlymphoid cells and may integrate these cells into classical immune responses. The aim of this study was to characterize the expression of IL-15 by intestinal epithelial cells and determine the functional roles of IL-15 within the mucosal immune system. Methods: Rat IL-15 was cloned from a rat jejunal library. Expression of IL-15 in rat and human intestinal epithelial cells was assessed by Northern and Western blotting. Tyrosine kinase activation in response to IL-15 in intestinal epithelial cells was determined by immunoprecipitation. Results: Rat and human intestinal epithelial cells express IL-15 messenger RNA. IL-15 activates Stat3 and stimulates the proliferation of intestinal epithelial cells. The relevance of the observations for intestinal epithelial cell function in vivo was supported by the demonstration of transcripts for IL-15 in primary human intestinal epithelial cells. Conclusions: IL-15 is expressed by intestinal epithelial cells and may be able to regulate intestinal epithelial cell function. These experiments suggest that IL-15 is an important mediator that could integrate intestinal epithelial cell function with the intestinal immune system.
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