The IL-17 family include IL-17A, IL-17B, IL-17C, IL-17D, IL-17E (also called IL-25), and IL-17F. The family is comprised of at least six proinflammatory cytokines that share a conserved cysteine-knot structure but diverge at the N-terminus. All members of the IL-17 family have a similar protein structure, with four highly conserved cysteine residues critical to their 3-dimensional shape, yet they have no sequence similarity to any other known cytokines. IL-17 family members are glycoproteins secreted as dimers that induce local cytokine production and recruit granulocytes to sites of inflammation. IL-17 is induced by IL-15 and IL-23, mainly in activated CD4+ T cells distinct from Th1 or Th2 cells. IL-17F is the most homologous to IL-17, but is induced only by IL-23 in activated monocytes.