Interleukin 17 promotes scar formation by inducing macrophage infiltration.

Trauma or burns injuries which affect the deep dermis often produce a hypertrophic scar, which limits patients' joint movement and generates an aesthetic problem. Inflammation is believed to be one of the main pathogenic mechanisms. We found that interleukin (IL)-17 was increased in scar tissues from patients with hypertrophic scar compared with normal skin. Recombinant mouse IL-17 was subcutaneously injected into mice that received full-thickness excision surgery to investigate the role of IL-17 in scar formation. Mice stimulated with IL-17 showed aggravated fibrogenesis, delayed wound healing, and increased inflammation. Additionally, macrophage infiltration was also increased. According to the results of the Transwell assay, IL-17 promoted macrophage infiltration through an indirect mechanism. After depleting macrophages with clodronate-liposomes, the effect of IL-17 disappeared. Levels of monocyte chemotactic protein (MCP) 1, MCP2, and MPC3 (together referred to as MCPs) were increased by IL-17 stimulation. Bindarit (an inhibitor of MCPs) was used to verify the role of MCPs. In addition, the Ly6C-low macrophages were responsible for wound fibrogenesis in mice. In this study, we detected the increased levels of IL-17 for the first time, revealed that IL-17 induced the infiltration of a specific subtype of macrophages to aggravate fibrosis through an MCP-dependent mechanism. Thus, our results provide a better understanding of scar formation and new strategies for scar prevention.