Interleukin-17 (IL-17) is a pro-inflammatory cytokine secreted by activated T-cells.
Recently discovered related molecules are forming a family of cytokines, the IL-17
family. The prototype member of the family has been designated IL-17A. Due to recent
advances in the human genome sequencing and proteomics five additional members have
been identified and cloned: IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. The cognate
receptors for the IL-17 family identified thus far are: IL-17R, IL-17RH1, IL-17RL
(receptor like), IL-17RD and IL-17RE. However, the ligand specificities of many of
these receptors have not been established. The IL-17 signaling system is operative
in disparate tissues such as articular cartilage, bone, meniscus, brain, hematopoietic
tissue, kidney, lung, skin and intestine. Thus, the evolving IL-17 family of ligands
and receptors may play an important role in the homeostasis of tissues in health and
disease beyond the immune system. This survey reviews the biological actions of IL-17
signaling in cancers, musculoskeletal tissues, the immune system and other tissues.