Interleukin 17 (IL-17) are a small family of similarly structured cytokines that plays a role in pro-inflammatory responses of the immune system, particularly allergic reactions. Each variant of IL-17 appears to have slightly nuanced function in different organs, but on the whole the cytokines behave similarly. IL-17 induces inflammation by stimulating the secretion of pro-inflammatory molecules such as IL-6, IL-8, GM-CSF, IL-1, TNF-α, and MCP-1 from their respective cell types. For this reason, IL-17 is linked to inflammatory and autoimmune diseases such as rheumatoid arthritis, asthma, lupus, psoriasis, and multiple scelrosis. Overactivity of IL-17 is commonly found in severe cases of asthma and psoriasis, where it contributes to inflammation that damages the airway and skin, respectively. IL-17 suppression is under investigation as a clinical target for reducing symptoms of inflammatory diseases, improving recovery following stroke, and treatment of some types of cancer.