Th17, or T helper 17 cells, are a type of immune cell that play a crucial role in the body's defense against infections, particularly those caused by fungi and certain bacteria. They are characterized by their production of a specific set of signaling molecules called cytokines, including IL-17, which help recruit other immune cells to sites of infection and inflammation. These cells are important for maintaining the balance of the immune system, but an overactive Th17 response can contribute to autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis. Understanding Th17 cells is essential for developing targeted therapies for these conditions and improving overall immune health.