Regulatory Eosinophils in Inflammation and Metabolic Disorders

Abstract

Eosinophils are potent effector cells implicated in allergic responses and helminth infections. Responding to stimuli, they release their granule-derived cytotoxic proteins and are involved in inflammatory processes. However, under homeostatic conditions, eosinophils are abundantly present in the intestine and are constantly in contact with the gut microbiota and maintain the balance of immune responses without inflammation. This situation indicates that intestinal eosinophils have an anti-inflammatory function unlike allergic eosinophils. In support of this notion, some papers have shown that eosinophils have different phenotypes depending on the site of residence and are a heterogeneous cell population. Recently, it was reported that eosinophils in the small intestine and adipose tissue, respectively, contribute to homeostasis of intestinal immune responses and metabolism. Accordingly, in this review, we summarize new functions of eosinophils demonstrated in recent studies and discuss their homeostatic functions.

Keywords: Anti-inflammation; Eosinophils; IL-1R antagonist; IL-4; IgA; Th17 cells.

Figure 1. Anti-inflammatory functions of eosinophils. Small-intestinal eosinophils suppress differentiation and/or proliferation of Th17 cells via production of a large amount of IL-1Ra and are involved in homeostasis of intestinal immunity. Meanwhile, eosinophils in adipose tissue activate M2 macrophages through IL-4 expression and inhibit inflammation, thereby contributing to metabolic homeostasis.