Th17 cells are a type of immune cell that play a crucial role in the body's defense against infections, particularly those caused by bacteria and fungi. They are a subset of T helper cells and are characterized by their production of a specific cytokine called IL-17. This cytokine helps recruit other immune cells to sites of infection, enhancing the inflammatory response. These cells are important for maintaining the balance of the immune system, but an overactive response can lead to autoimmune diseases, where the body mistakenly attacks its own tissues. Understanding Th17 cells is essential for developing therapies for conditions like multiple sclerosis and rheumatoid arthritis.