T helper 17 (Th17) 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 a subset of CD4+ T cells and are characterized by their production of the cytokine IL-17, which helps recruit other immune cells to sites of infection and inflammation. Th17 cells are important for maintaining the balance of the immune response. While they help protect against pathogens, 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.