Effects of IL-17 on Epidermal Development

Abstract

Immunotherapies targeting interleukin 17 (IL-17) have a strong effect on plaque psoriasis. However, many previous studies on IL-17 focused only on the T-helper 17 (Th17) immune response, and a few studies have reported that IL-17A may affect psoriatic epidermal structure. IL-17 includes six family members, namely IL-17A–F, which are involved in a wide variety of biological responses. IL-17A is produced mainly by Th17 cells or group 3 innate lymphoid cells (ILC3), while IL-17C is locally produced by epithelial cells, such as keratinocytes. In contrast to IL-17C, which is locally produced in various cells such as keratinocytes, it is predicted that IL-17A, which is produced by limited cells and has systemic effects, has different roles in epidermal development. For example, several research studies have shown that IL-17A affects terminal differentiation of epidermis by suppressing the expression of filaggrin or loricrin in keratinocytes. On the other hand, IL-17C, which is produced by keratinocytes themselves, does not have as strong as an effect on epidermal development as IL-17A. In this chapter, we summarized the effects of IL-17A and other IL-17 members on epidermal development and their comprehensive roles based on previously reported papers.