IL17C is a pro-inflammatory cytokine that functions primarily in epithelial innate immunity and barrier defense. It stimulates production of antibacterial peptides and pro-inflammatory molecules through NF-κB and MAPK signaling pathways 1. IL17C acts synergistically with IL22, TNF, and IL1B to induce antimicrobial peptides including S100A8, S100A9, REG3A, REG3G, and DEFB2 from keratinocytes 1. The cytokine plays context-dependent roles: maintaining epithelial homeostasis after inflammatory challenge or promoting pathogenic inflammation 1. IL17C is differentially expressed across inflammatory skin conditions. In hidradenitis suppurativa, dermal tunnel keratinocytes express elevated IL17C alongside IL1A, IL1B, and IL6, contributing to the IL-1β-driven T17 cell axis 2. In psoriasis, IL17C represents part of the broader IL-17 family involvement in disease pathogenesis 3. IL17C is also induced in intestinal inflammation associated with dysbiosis and DUOX2 deficiency, serving as a marker for epithelial activation by gram-negative bacteria in inflammatory bowel disease 4. Enhanced IL17C/IL17RE signaling may increase susceptibility to autoimmune diseases 1. Therapeutically, IL-17 pathway inhibitors show efficacy in treating IL-17-driven inflammatory skin diseases 5. IL17C reduction has been observed following dupilumab therapy in atopic dermatitis 6 and probiotic intervention in colorectal cancer patients 7.