Interleukinâ17C is a 15â20 kDa disulfide-linked dimeric cytokine that plays an important role in mucosal immunity and chronic inflammation. ILâ17C binds to ILâ17 RE with high affinity and to ILâ17 RA with low affinity. These two receptor chains can associate into a heterodimeric receptor for ILâ17C. ILâ17C expression is induced by inflammatory stimulation in colon and airway epithelial cells, keratinocytes, CD4+ T cells, macrophages, and dendritic cells. It is upregulated in various chronic inflammatory diseases including psoriasis, cystic fibrosis, and chronic obstructive pulmonary disease (COPD). The interaction of ILâ17C with ILâ17 RE promotes mucosal immunity through the induction of antiâbacterial peptides and proâinflammatory cytokines and chemokines. ILâ17C action supports the integrity of the colon epithelium following infection induced damage but also contributes to psoriatic skin thickening and the progression of arthritis.