The IL-17 family is comprised of at least six proinflammatory cytokines that share a conserved cysteine-knot structure but diverge at the N-terminus. 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. IL-17B binds the IL-17B receptor, but not the IL-17 receptor; it is most homologous with IL-17D, which is expressed by resting CD4+ T cells and CD19+ B cells. IL-17E is mainly produced by Th2 cells and recruits eosinophils to lung tissue. IL-17C has a very restricted expression pattern but has been detected in adult prostate and fetal kidney libraries.