The Interleukin-17 (IL-17) family proteins, comprising six members (IL-17 and IL-17B through IL-17F), are secreted, structurally related proteins that share a conserved cysteine-knot fold near the C-terminus, but have considerable sequence divergence at the N-terminus (1, 2). With the exception of IL-17B, which exists as a
non-covalently linked dimer, all IL-17 family members are disulfide-linked dimers (3). IL-17 family proteins are pro-inflammatory cytokines that induce local cytokine production and are involved in the regulation of immune functions (1, 2). Two receptors (IL-17 R, and IL-17B R), which are activated by IL-17 family members, have been identified. In addition, at least three additional orphan type I transmembrane receptors with homology to IL-17 R, including IL-17 RL (IL-17 RC), IL-17 RD, and
IL‑17 RE, have also been reported (1-4). The functions of IL-17 RC, D, and E are not known.
Human IL-17C cDNA encodes a 197 amino acid (aa) residues protein with a putative 18 aa signal peptide (5). IL-17C shares from 15-30% aa sequence identity with other IL-17 family members. Human and mouse IL-17C also share 83% aa sequence identity. IL-17C has a very restricted expression pattern and was detected as a rare expressed sequence tag (EST) sequence in an adult prostate and fetal kidney libraries (2). IL-17C has been shown to stimulate the release of TNF-alpha and IL-1 beta from the monocytic cell line THP-1, a property it shares with IL-17B (5, 6). The receptor of IL-17C has not yet been identified. The IL-17C preparations from R&D Systems have been found to bind immobilized recombinant IL-17B R/Fc in a functional ELISA.
