Non-redundant role of the chemokine receptor CX3CR1 in the anti-inflammatory function of gut macrophages

Mucosal immunity at the intestinal level is constantly challenged by the presence of external food and microbial antigens and must be kept under strict control to avoid the rise of aberrant inflammation. Among cells of the innate immunity, macrophages expressing the chemokine receptor CX3CR1 are strategically located near the gut epithelial barrier. These cells contribute to the maintenance of homeostasis by producing the anti-inflammatory cytokine IL-10; however, their role in the control of full blown inflammation and tissue injury is controversial. In this study we investigated mice proficient or deficient for the expression of the CX3CR1 receptor in a model of dextran sulphate sodium (DSS) induced acute colitis. We found that KO mice (CX3CR1GFP/GFP) had a more severe disease compared to WT mice (CX3CR1GFP/+), both in terms of histological examination of colonic tissues and leukocyte infiltration, with an expansion of macrophages and CD4-Th17 lymphocytes. The expression of several inflammatory mediators (IL-1β, IL-6, IFNγ, iNOS) was also significantly upregulated in KO mice, despite higher IL-10 production. Overall, our study demonstrates that macrophages expressing a functional CX3CR1 receptor have an important and non-redundant role in controlling the abnormal intestinal inflammation that may lead to tissue damage.