Interleukin-17A (IL-17A): Molecular Mechanisms and Its Roles in Immune and Neuroimmune Systems

Interleukin-17A (IL-17A) is a proinflammatory cytokine that plays a pivotal role in immune responses and tissue homeostasis. Its expression is strictly regulated by transcription factors including RORγt, and it is mainly produced by Th17 cells, γδ T cells, and innate lymphoid cells. IL-17A signals through a heterodimeric receptor complex consisting of IL-17RA and IL-17RC, activating NF-κB, MAPK, and C/EBP pathways via the adaptor protein Act1. IL-17 signaling is counterbalanced by negative regulators including A20 and Regnase-1. Beyond its classical roles in antimicrobial defense and autoimmune inflammation, recent studies have highlighted its functions in the central nervous system, with associations to multiple sclerosis, autism spectrum disorder, and Alzheimer’s disease. The development of IL-17A inhibitors, including the dual IL-17A/F antagonist bimekizumab, has advanced markedly, with demonstrated efficacy in immune-mediated diseases such as psoriasis and psoriatic arthritis. This review provides a comprehensive overview of current knowledge of IL-17A, from its molecular characteristics to clinical applications.