Induction of cytokine formation by human intestinal bacteria in gut epithelial cell lines

Aims: To investigate the effects of human gut micro-organisms on cytokine production by human intestinal cell lines. Methods and Results: Quantitative real-time PCR assays were developed to measure the production of pro-inflammatory (IL-1 alpha, IL-6, IL-18 and TNF alpha) and anti-inflammatory (TGF-beta 1, TGF-beta 2, TGF-beta 3, IL-4 and IL-10) cytokines in HT-29 and Caco-2 cell lines. They were co-cultured with a range of mucosal bacteria isolated from ulcerative colitis patients, together with lactobacilli and bifidobacteria obtained from healthy people. HT-29 cells were also co-cultured with Campylobacter jejuni, enterotoxigenic Escherichia coli (ETEC), enteropathogenic E. coli and Salmonella typhimurium. The majority of commensal bacteria tested suppressed the expression of anti-inflammatory cytokine mRNA, increased IL-18, reduced IL-1 alpha, and with the exception of nonpathogenic E. coli, reduced TNF-alpha. All overtly pathogenic species increased both pro-inflammatory and anti-inflammatory cytokine mRNA. Conclusion: Commensal and pathogenic species induced fundamentally different cytokine responses in human intestinal epithelial cell lines. Significance and Impact of the Study: Interactions between commensal bacteria tested in this study and the innate immune system were shown to be anti-inflammatory in nature, in contrast to the pathogenic organisms investigated. These data contribute towards our understanding of how potential probiotic species can be used to suppress the pro-inflammatory response in inflammatory bowel disease.