Monocyte infiltration into obese and fibrilized tissues is regulated by PILRα.

Paired immunoglobulin-like type 2 receptor α (PILRα) is an inhibitory receptor that is mainly expressed on myeloid cells, and negatively regulates neutrophil infiltration during inflammation. However, PILRα role on monocyte has not been described. Under both steady-state and inflammatory conditions, monocytes migrate into tissues and differentiate into macrophages. Macrophages in adipose and liver tissues play important roles in tissue homeostasis and pathogenesis of metabolic diseases. Here, we found that PILRα controls monocyte mobility through regulating integrin signaling and inhibiting CD99-CD99 binding. Moreover, we found that Pilra(-/-) mice developed obesity and hepatomegaly with fibrosis, and the numbers of macrophages in adipose and liver tissues are significantly increased in Pilra(-/-) mice. These data suggest that immune inhibitory receptor, PILRα, plays an important role in the prevention of obesity and liver fibrosis.