Role of IFN-γ in the establishment of anterior chamber-associated immune deviation (ACAID)-induced CD8 ⁺ T regulatory cells

ntroduction of alloantigens into the AC induces a form of immune tolerance known as ACAID, which induces antigen-specific CD8 ⁺ Tregs, contributing to ocular immune privilege by down-regulating immune responses. Recent evidence suggests IFN-γ is needed for the suppressive function of CD8 ⁺ ACAID Tregs. This study tested the hypothesis that IFN-γ is needed for alloantigen-specific ACAID CD8 ⁺ Tregs to execute their suppressive function but is not required for the establishment of ACAID CD8 ⁺ Tregs. To address this hypothesis, ACAID was induced by injecting BALB/c spleen cells into the AC of WT C57BL/6 mice, IFN-γ ^-/- C57BL/6 mice, or anti-IFN-γ-treated WT C57BL/6 mice. LAT assays using C57BL/6 APCs as stimulators, CD4 ⁺ T cells from C57BL/6 mice previously immunized toward BALB/c alloantigens as effector cells, and IFN-γ-competent, IFN-γ ^-/-, or IFN-γR ^-/- CD8 ⁺ Tregs were used to evaluate the suppressive function of CD8 ⁺ ACAID Tregs in response to IFN-γ. IFN-γ ^-/- mice or mice treated with anti-IFN-γ antibody prior to AC injection of alloantigen failed to develop ACAID. The suppressive function of IFN-γ ^-/- ACAID CD8 ⁺ Tregs was restored through the administration of exogenous IFN-γ. This suppressive responsiveness toward IFN-γ was CD8 ⁺ Treg-intrinsic, as CD8 ⁺ Tregs from IFN-γR ^-/- mice, which were primed in the AC with alloantigens, were not able to suppress alloantigen-specific DTH responses. These results indicate that IFN-γ is not needed for the induction of CD8 ⁺ ACAID Tregs but is required for ACAID Tregs to exert the suppression of allospecific DTH responses.