Bacteroidales recruit IL-6-producing intraepithelial lymphocytes in the colon to promote barrier integrity.
Kuhn KA, Schulz HM, Regner EH, Severs EL, Hendrickson JD, Mehta G, Whitney AK, Ir D, Ohri N, Robertson CE, Frank DN, Campbell EL, Colgan SP
Mucosal Immunol. Aug 2017. doi: 10.1038/mi.2017.55
COMMENT: It is known that, in the small intestine, intraepithelial lymphocytes (IELs) are positioned within the epithelial barrier maintaining epithelial homeostasis. The authors of this work hypothesizes that also in colon IELs promote epithelial barrier function and that this function is mediated by the expression of cytokines in response to interactions with commensal bacteria.
Our results demonstrate that bacterial members in the order Bacteroidales aid in establishing IL-6-producing IELs in the colon, and MyD88-dependent signals are required for IEL production of IL-6. Importantly, the loss of IL-6-producing IELs impairs the integrity of the epithelial barrier through reductions in both tight junction expression and mucus thickness
This was demonstrated in this study using as model of infection the colitis produced by Citrobacter rodentium. To reinforce the importance of IL-6 the authors analize the response to Citrobacter rodentium infection in mice deficient in IL6. These mice had increased paracellular permeability, decreased claudin-1 expression, and a thinner mucus gel layer that were reversed by transfer of normal IELs able to produce IL6.
These studies suggest a novel pathway of microbiota stimulation of cytokine production in intestinal epithelial barrier homeostasis