Classically two subclasses of CD4+ T-helper cells, Th1 and Th2, have been recognized. Th1 cells are responsible for clearing intracellular pathogens and are involved in cell-mediated immunity. They produce IL-2, interferon-γ, and TNFα but not IL-4, IL-5, and IL-10. Selective activation of Th1 cells is promoted by interferon-γ and IL-12 and inhibited by IL-4 and IL-10, the products of Th2 cells. Th2 cells are involved with the humoral immune response, produce IL-4, IL-5, and IL-10, and promote antibody production; IL-4 is essential for growth and differentiation of Th2 cells. There is cross-inhibition between the two classes; if one subclass is activated it will inhibit the activity of the other so that the response is polarized. More recently a third class of Th cells that produce IL-17 in response to autoimmune tissue damage has been identified (see Th17 cells).
Subjects: Medicine and Health.