When antigen is presented by APCs to Th0 lymphocytes, Th0 cells may differentiate into either Th1 or Th2 subtypes. In humans, Th1 cells express IFN-gamma and TGF-beta, whereas Th2 cells express IL-4, IL-5, and IL-9. Both sets of human lymphocytes express IL-2, IL-3, IL-10, IL-13, and GM-CSF. Th1 cells induce macrophage activation and granuloma formation. Th2 cells induce atopy and promote IgE, mast cell, and eosinophil production. This fundamental division in T cells appears to correlate with the phenotypic expression of various human diseases.
APC: antigen-presenting cell; Th0: undifferentiated T helper cell; Th1: T helper type 1 cell; Th2: T helper type 2 cell; IFN-gamma: interferon-gamma; TGF-beta: tumor growth factor-beta; NO: nitric oxide; IL: interleukin; GM-CSF: granulocyte macrophage colony-stimulating factor; DTH: delayed-type hypersensitivity.
