Cytokines of the IL-17 family include IL-17A, IL-17B, IL-17C, IL-17D, IL-17E (also called IL-25), and IL-17F. All members of the IL-17 family have a similar protein structure, with four highly conserved cysteine residues critical to their 3-dimensional shape. Cytokines of IL-17 family are all well conserved in mammals, with as much as 62–88% of amino acids conserved between the human and mouse homologs.
IL-17 family of cytokines have been reported to function in numerous immune processes. Most notably, IL-17 is involved in inducing and mediating proinflammatory responses. This proinflammatory activity is exemplified by their involvement in pulmonary inflammatory responses. Both IL-17A and IL-17F are involved in the recruitment of neutrophils, and IL-17E is able to induce Th2 cytokine production and eosinophilia.
The IL-17 receptor family consists of five members, IL-17RA, IL-17RB, IL-17RC, IL-17RD and IL-17RE. Functional IL-17R is a heteromeric complex consisting of at least IL17RA and IL17RC. IL-17 receptors are broadly distributed, with individual ligand specificities. IL-17R binds both IL-17A and IL-17F and is expressed in multiple tissues. IL-17RB, binds both IL-17B and IL-17E.