Role of Th1 and Th2 cells in anterior chamber-associated immune deviation

The immunological privilege of the anterior chamber (AC) of the eye is due, at least in part, to a selective antigen-specific down-regulation of delayed-type hypersensitivity (DTH) and a normal induction of antibody responses: a phenomenon that has been termed anterior chamber-associated immune deviation (ACAID). This dichotomy in the systemic immune responses is suggestive of a T-helper type-2 (Th2)-dominated immune phenotype in which a Th2 cell population is preferentially activated and T-helper type-1 (Th1) effector elements. This cross-re gulates a hypothesis was tested by comparing the cytokine pattern of antigen-pulsed spleen cells from mice primed in the anterior chamber with antigens that induce ACAID with responses in hosts primed with antigens that do not induce ACAID. The results indicated that CD4⁺ spleen cells from hosts primed in the AC with antigens that induce ACAID produced significant quantities of interleukin-10 (IL-10) but insignificant levels of IL-2, IL-4 and interferon-γ (IFN-γ). In contrast, hosts primed in the AC with antigens that do not induce ACAID, but instead elicit normal DTH, displayed cytokine patterns indicative of a Th1 response: significant quantities of IL-2 and IFN-γ were produced while IL-4 and IL-10 secretion was insignificantly different from normal controls. The immunological phenotype of the AC-primed hosts could be altered by systemic treatment with antibodies against either a Th1 cytokine (IFN-γ) or a Th2 cytokine (IL-10). Hosts treated with anti-IL-10 antibody and subsequently primed in the AC with ACAID-inducing antigens developed normal DTH responses, while hosts treated with anti-IFN-γ antibody and primed in the AC with antigens that normally produce positive DTH responses failed to develop positive DTH. Collectively the results support the proposition that immune privilege in the AC of the eye is due to the selective activation of a Th2 population that cross-regulates Th1 responses.