The injection of antigen into the anterior chamber (AC, intracameral injection) of a murine eye induces the generation of splenic CD8(+) regulatory T cells (AC-SPL cells) that effect the antigen-specific suppression of a delayed-type hypersensitivity (DTH) reaction. Here we show (i) for the first time that the local antigen-specific suppression of DTH-induced swelling in immunized mice either by an intracameral injection of antigen or by the direct injection of CD8(+) AC-SPL cells into an antigen-challenged site is associated with an absence of infiltrated mononuclear cells, (ii) that the local antigen-specific suppression of the DTH reaction by CD8(+) AC-SPL cells requires compatibility between the Qa-1 but not H2 antigen haplotype of the immunized recipient and the injected AC-SPL regulatory T cells, (iii) that the suppression of the DTH reaction by CD8(+) AC-SPL cells requires the expression of Qa-1 but not H2 antigens and is not due to bystander suppression.