Interleukin-17A (IL-17A) is a cytokine, a type of signaling molecule in the immune system. It is primarily produced by a subset of T cells known as Th17 cells. IL-17A plays a crucial role in the body's defense against infections, particularly by promoting inflammation and recruiting other immune cells to sites of infection. In addition to its protective functions, IL-17A is also involved in various autoimmune diseases, such as psoriasis and rheumatoid arthritis. Elevated levels of IL-17A can lead to chronic inflammation and tissue damage, making it a target for therapeutic interventions in these conditions.