T helper (Th) cells are crucial components of the adaptive immune system, coordinating defense against pathogens and mediating tissue inflammation through unique cytokines and effector functions. The recently identified Th17 cells, a third subset of effector T helper cells, have been extensively studied for their roles in immunity and disease. Th17 cells produce IL-17A, IL-17F, and IL-22, which are critical for host defense against extracellular pathogens and are potent inducers of autoimmunity and tissue inflammation. Their differentiation is driven by IL-6 and TGF-β, with IL-21 and IL-23 playing key roles in amplifying and stabilizing their function. Th17 cells are involved in both host defense and autoimmune diseases, where they contribute to tissue inflammation and autoimmunity. They also interact reciprocally with regulatory T (Treg) cells, which help prevent tissue inflammation and maintain self-tolerance. Th17 cells are essential for immune responses against certain pathogens, such as Mycobacterium tuberculosis, and their dysfunction is linked to various autoimmune diseases. The differentiation of Th17 cells involves a three-step process: induction by IL-6 and TGF-β, amplification by IL-21, and stabilization by IL-23. Understanding the regulation of Th17 cell differentiation and function is crucial for developing therapies for inflammatory and autoimmune diseases.T helper (Th) cells are crucial components of the adaptive immune system, coordinating defense against pathogens and mediating tissue inflammation through unique cytokines and effector functions. The recently identified Th17 cells, a third subset of effector T helper cells, have been extensively studied for their roles in immunity and disease. Th17 cells produce IL-17A, IL-17F, and IL-22, which are critical for host defense against extracellular pathogens and are potent inducers of autoimmunity and tissue inflammation. Their differentiation is driven by IL-6 and TGF-β, with IL-21 and IL-23 playing key roles in amplifying and stabilizing their function. Th17 cells are involved in both host defense and autoimmune diseases, where they contribute to tissue inflammation and autoimmunity. They also interact reciprocally with regulatory T (Treg) cells, which help prevent tissue inflammation and maintain self-tolerance. Th17 cells are essential for immune responses against certain pathogens, such as Mycobacterium tuberculosis, and their dysfunction is linked to various autoimmune diseases. The differentiation of Th17 cells involves a three-step process: induction by IL-6 and TGF-β, amplification by IL-21, and stabilization by IL-23. Understanding the regulation of Th17 cell differentiation and function is crucial for developing therapies for inflammatory and autoimmune diseases.