Interleukin-17 is a potent pro-inflammatory cytokine produced by activated memory T cells. There are at least six members of the IL-17 family in humans and in mice. Today, IL-17 represents a family of structurally related cytokines that share a highly conserved C-terminal region but differ from one another in their N-terminal regions and in their distinct biological roles. The six known members of this family, IL-17A through IL-17F, are secreted as homodimers. IL-17F also regulates cartilage matrix turnover and inhibits angiogenesis.