Abstract
Maintenance of the immunological tolerance and homeostasis in the gut is associated with the composition of the intestinal microbiota. We here report that cultivation of Lactobacillus casei ATCC 334 in the presence of human intestinal epithelial cells promotes functional changes in bacteria. In particular, the interaction enhanced the immunosuppressive phenotype of L. casei as demonstrated by the ability of L. casei to generate functional regulatory T cells (CD4+CD25+FoxP3+) and production of the anti-inflammatory cytokine interleukin-10 by human peripheral blood mononuclear cells. The results indicate microbe-host cross-talk that changes features of microbes, and suggest that in vitro simulation of epithelial cell interaction can reveal functional properties of gut microbes more accurately than conventional cultivation.
Highlights
The commensal microbiota in the intestine helps us to maintain the barrier function of intestinal mucosa and educates the gut immune system to function properly [1,2]
Intestinal Epithelial Cells Support Growth of L. casei While developing cultivation conditions that would simulate the life of commensal organisms in host intestine, we observed that L. casei ATCC 334 could be cultivated on human intestinal epithelial cells
Plain serum-free cell culture medium without the human cells did not promote proliferation of L. casei (p.0.05; plain medium vs inoculum; one-way ANOVA and Tukey; Figure 1A), indicating that the effect was due to epithelial cells (p,0.001; HT-29 cells vs plain medium and HT-29 cells vs inoculum; one-way ANOVA and Tukey)
Summary
The commensal microbiota in the intestine helps us to maintain the barrier function of intestinal mucosa and educates the gut immune system to function properly [1,2]. Signaling between commensal bacteria and TLR appears necessary for maintaining intestinal homeostasis and keeping up tolerance towards harmless non-self molecules [3,4]. Disturbance in tolerance towards gut microbiota can lead to severe inflammation in the intestinal mucosa, which is characteristic for immunological disorders affecting the gut such as inflammatory bowel disease (IBD) [5]. Regulatory T cells (Treg) are CD4-positive, FOXP3-positive lymphocytes with immunosuppressive properties and ability to induce immunological tolerance [6,7]. Induction of immunosuppressive Treg from naive CD4-positive T cells is especially important in creating immunological tolerance in the gut, and it was recently suggested that both natural Treg and induced Treg are essential for the establishment of full tolerance in vivo [8]. IL-10, which counteracts effects of proinflammatory cytokines such as tumor necrosis factor alpha (TNFa), prevents colitis in mouse models of human IBD [5]
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