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AIM: To investigate the effect of interaction between enteric epithelial cells and lymphocytes of Peyers patch on the release of nitric oxide (NO) and IL-6 in response to Shigella lipopolysaccharide (LPS).METHODS: Human colonic epithelial cells (Caco-2)were mixed cocultured with lymphocytes of Peyers patch from wild-type (C57 mice) and inducible NO synthase knockout mice, and challenged with Shigella F2a-12LPS. Release of NO and mIL-6 was measured by Griess colorimetric assay and enzyme-linked immunosorbent assay (ELISA), respectively.RESULTS: In the absence of LPS challenge, NO was detected in the culture medium of Caco-2 epithelial cells but not in lymphocytes of Peyers patch, and the NO release was further up-regulated in both cocultures with lymphocytes from either the wild-type or iNOS knockout mice, with a significantly higher level observed in the coculture with iNOS knockout lymphocytes. After Shigella F2a-12 LPS challenge for 24-h, NO production was significantly increased in both Caco-2 alone and the coculture with lymphocytes of Peyers patch from the wild-type mice but not from iNOS knockout mice.LPS was found to stimulate the release of mIL-6 from lymphocytes, which was suppressed by coculture with Caco-2 epithelial cells. The LPS-induced mIL-6production in lymphocytes from iNOS knockout mice was significantly greater than that from the wild-type mice.CONCLUSION: Lymphocytes of Peyers patch maintain a constitutive basal level of NO production from the enteric epithelial cell Caco-2. LPS-induced mIL-6 release from lymphocytes of Peyers patch is suppressed by the cocultured epithelial cells. While no changes are detectable in NO production in lymphocytes from both wild-type and iNOS knockout mice before and after LPS challenge, NO from lymphocytes appears to play an inhibitory role in epithelial NO release and their own mIL-6 release in response to LPS.