Interleukin-17 in Health and Disease: A Double-Edged Sword in Immunity

Interleukin-17 (IL-17), a key pro-inflammatory cytokine primarily produced by T-helper 17 (Th17) cells, plays a crucial role in immune regulation and host defense, particularly against extracellular pathogens such as bacteria and fungi. As part of the IL-17 family of cytokines, IL-17A and IL-17F are the most well-characterized members, essential for recruiting neutrophils and promoting the production of antimicrobial peptides. However, IL-17’s potent inflammatory effects make it a double-edged sword in immunity, contributing not only to protective immune responses but also to chronic inflammation and autoimmunity when dysregulated. IL-17 is implicated in the pathogenesis of various autoimmune and inflammatory diseases, including rheumatoid arthritis (RA), psoriasis, multiple sclerosis (MS), inflammatory bowel disease (IBD), and systemic lupus erythematosus (SLE). In these conditions, IL-17 promotes the production of other pro-inflammatory cytokines and matrix metalloproteinases, driving sustained inflammation and tissue damage. This dual role of IL-17—protective in infection but harmful in chronic inflammation—highlights its complexity in immune regulation. The therapeutic targeting of IL-17 has led to the development of biologics such as secukinumab and ixekizumab, which have shown significant efficacy in treating autoimmune diseases like psoriasis and ankylosing spondylitis. However, the use of IL-17 inhibitors presents challenges, particularly in balancing infection control with immune modulation. This review examines the biology of IL-17, its role in health and disease, and the potential therapeutic implications of modulating its activity in clinical settings. Keywords: Interleukin-17 (IL-17), Th17 cells, Autoimmunity, Chronic inflammation, Biologic