CD25⁺, interleukin-10-producing CD4⁺ T cells are required for suppressor cell production and immune privilege in the anterior chamber of the eye

An important factor in the establishment of ocular immune privilege is the dynamic down regulation of T helper 1 (Th1) immune responses that occurs in response to antigens delivered intraocularly; a phenomenon that has been termed anterior chamber-associated immune deviation (ACAID). ACAID is characterized by the generation of splenic regulatory cells that inhibit the expression of delayed-type hypersensitivity. Previous studies have shown that antigens introduced into the anterior chamber of the eye induce the generation of a CD4⁺ T-cell population that suppress the induction of Th1 immune responses and the appearance of a second population of CD8⁺ T regulatory cells that suppresses the expression of Th1 inflammatory responses (= efferent suppressor cells). Experiments described here characterized the function of the CD4⁺ ACAID suppressor cell population and its effect on the generation of CD8⁺ efferent suppressor cells that inhibit the expression of DTH in situ. Both in vivo and in vitro experiments demonstrated that CD4⁺ T cells are required for the generation of CD8⁺ efferent suppressor cells. CD4⁺ T cells do not require cell contact with CD8⁺ T cells; instead they produce soluble IL-10 that is sufficient for the generation of ACAID suppressor cells. Finally, the CD4 ⁺ afferent T suppressor cells are not natural killer T cells, but do express the CD25 cell surface marker.