Abstract
Enteropathogenic Escherichia coli (EPEC) produces attaching and effacing (A/E) lesions and watery diarrhea, both of which are intimin and EspA dependent. In this work, we explored the mucosal immune response by detecting cytokine induction in rabbits with diarrhea caused by rabbit EPEC (REPEC). Orally inoculated rabbits exhibited weight loss and mucosal inflammation, developed watery diarrhea, and died (day 7). At day 6 postinoculation, animals were analyzed for the induction of proinflammatory cytokines in enterocytes. The role of lymphocyte-dependent immunity was determined through the expression of proinflammatory cytokines by lymphocytes from Peyer's patches (PP) and the spleen. EspA and intimin mutants were used to explore the role of A/E lesions in the expression of these cytokines. REPEC-infected rabbit enterocytes showed increased interleukin 1beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) mRNA expression, but that of anti-inflammatory IL-10 was increased only slightly. In contrast, intimin mutant-infected rabbits were unable to produce this proinflammatory cytokine profile but did produce a remarkable increase in IL-10 expression. Bacteria lacking EspA increased the expression of IL-8 and TNF-alpha, but that of IL-10 was increased only slightly. PP lymphocytes also produced proinflammatory cytokines, which were dependent on EspA (except for TNF-alpha) and intimin, while IL-10 was induced by EspA and intimin mutants. In contrast, spleen lymphocytes (systemic compartment) were unable to produce IL-1beta and TNF-alpha. These data show the importance of the proinflammatory cytokines secreted by enterocytes and those expressed locally by PP lymphocytes, which can activate effector mechanisms at the epithelium. Furthermore, this cytokine profile, including IL-6 and IL-1beta, which may be involved in the diarrhea produced by EPEC, depends on intimin.