The Interleukin-17 family proteins, comprising six members (IL-17, 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. IL-17 family proteins are proinflammatory cytokines that induce local cytokine production and are involved in the regulation of immune functions. Among IL-17 family members, IL-17D is most closely related to IL-17B, sharing 27% aa sequence homology. IL-17D is expressed preferentially in skeletal muscle, heart, adipose tissue, lung, pancreas, and nervous system. Like other IL-17 family members, IL-17D modulates immune responses indirectly by stimulating the production of myeloid growth factors and chemokines including IL-6, IL-8, and GM-CSF. IL-17D has also been shown to suppress the proliferation of myeloid progenitors in colony formation assays.