Interleukin-22 Induces the Infiltration of Visceral Fat Tissue by a Discrete Subset of Duffy Antigen Receptor for Chemokine-Positive M2-Like Macrophages in Response to a High Fat Diet

Interleukin-22 (IL-22) is a cytokine with important functions in host defense and inflammatory responses and has recently been suggested to play a role in immune-inflammatory system in the context of obesity and its metabolic consequences. The specific cellular targets and mechanisms of IL-22-mediated obesity are largely unknown however. We here identified a previously unknown subset of monocyte-derived Duffy antigen receptors for chemokines (DARC)(+) macrophages in epididymal fat adipose tissue and found that they are preferentially recruited into the crown-like structures of adipose tissue in the mouse upon high fat diet-induced obesity. Importantly, DARC(+) macrophages highly express the IL-22 receptor (IL-22Ra1). Exposure to recombinant IL-22 shifts macrophages to an alternative M2 polarization pathway and augments DARC expression via a STAT5b signaling axis. STAT5b directly binds to the DARC promoter and a STAT5 inhibitor abrogates the IL-22-mediated induction of DARC. These M2-like DARC(+) subpopulations of monocytes/macrophages were elevated in obese db/db mice compared to WT lean mice. Furthermore, subsets of CD14(+) and/or CD16(+) monocytes/macrophages within human peripheral blood mononuclear cell populations express DARC and the prevalence of these subsets is enhanced by IL-22 stimuli. This suggested that IL-22 is a critical cytokine that promotes the infiltration of adipose tissue macrophages, that regulate inflammatory processes. Taken together, our present findings provide important insights into the molecular mechanism by which IL-22 signal modulates DARC expression in M2-like macrophages.