Cytokines are communication signals between leukocytes and organ resident cells. Interleukin 1 (IL-1), a pleiotropic cytokine produced by many cell types~most notably macrophages, can stimulate a general inflammatory reaction by causing the activation of a variety of cells which then, among their other functions, release a cascade of other cytokines. One of these cytokines is interleukin 8 (IL-8), which takes the more direct action of activating neutrophils and T lymphocytes. CD4 cells can be subtyped to T helper 1 and 2 (Th-1 and Th-2) cells on the basis of the cytokines they release. Th-1 cells produce IL-2, interferon-gamma (IFN-gamma), and tumor necrosis factor (TNF), while Th-2 cells produce IL-4, IL-5, IL-6, and IL-10. Th-1 cells are involved in the cell-mediated immune response, while Th-2 cells are involved in allergy and extracellular parasitic infection. Cytokines, lymphokines, and adhesion molecules also are located in ocular inflammatory sites of patients with uveitis and animals with experimental uveitis. Ocular antigens play an important role in autoimmune diseases. S-antigen (S-Ag), a retinal soluble antigen, can induce experimental autoimmune uveoretinitis (EAU). The expression of S-Ag mRNA of nonretinal tissues in fetuses may suggest its involvement in certain ocular diseases. The expression of S-Ag mRNA was found in the iris of some patients with uveitis after prolongation of corticosteroid therapy. This finding was confirmed by treating EAU rats with long- term steroids.
