Abstract. In a previous study, we reported that a wbpP gene mutation in Vibrio vulnificus was significantly impaired in its ability to synthesize surface capsular polysaccharide (CPS). In this study, we evaluated the functions of the V. vulnificus capsular polysaccharide on interleukin (IL)-8 production, as well as its underlying mechanisms in human intestinal epithelial cells. The CPS-defective wbpP mutant induced significantly lower levels of IL-8 production, IL-8 gene promoter activation and NF-κB activity in INT-407 cells than was noted with the wild-type or wbpP-complemented V. vulnificus. The expression levels of Toll-like receptor (TLR)2 mRNA and protein were also found to be lower in INT-407 cells infected with the CPS-defective wbpP mutant than in those cells infected with the wild-type or the wbpPcomplemented strains. Additionally, the treatment of INT-407 cells with anti-TLR2 antibody proved to significantly block IL-8 production and NF-κB minimal promoter activity induced by the wild-type or the wbpP-complemented strains. Furthermore, purified V. vulnificus CPS was found to significantly induce IL-8 production and NF-κB activation, both of which were inhibited upon the addition of the anti-TLR2 antibody. Taken together, these results demonstrate that V. vulnificus capsular polysaccharide is involved in the induction of IL-8 production of human intestinal epithelial cells via a TLR2/NF-κB-dependent pathway.
Abstract. In a previous study, we reported that a gene mutation of repeat in toxin E (RtxE), a transporter of cytotoxic factors, resulted in a significant impairment of epithelial cell cytotoxicity in Vibrio vulnificus, and that the expression of the rtxE gene was induced by the exposure to the host cells. In this study, we evaluated and compared the effects of coculture supernatants from V. vulnificus-infected INT-407 cells and either the V. vulnificus wild-type or rtxE mutant on the production of interleukin (IL)-8, a pro-inflammatory cytokine, as well as its underlying mechanisms in human intestinal epithelial cells. INT-407 cells were co-cultured with the wild-type V. vulnificus or the rtxE mutant strain to obtain the conditioned supernatants. IL-8 production and nuclear factor (NF)-κB activation from the INT-407 cells treated with each supernatant, were investigated. The co-culture supernatants from the rtxE mutant V. vulnificus-infected INT-407 cells significantly induced lower levels of IL-8 production and promoter activation, NF-κB DNA binding activity, and NF-κB minimal promoter activation in human intestinal epithelial cells, than those from the wild-type V. vulnificus-infected INT-407 cells. Importantly, the reduced IL-8 production and NF-κB activity of the V. vulnificus rtxE mutant, were restored by co-culture supernatants from the rtxE-complemented V. vulnificus. On the whole, these results show that the rtxE gene of V. vulnificus performs a critical role in the secretion of factors from bacteria and host cells, which are involved in IL-8 production via the NF-κB activation pathway in host cells.
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