Impaired negative selection of CCR7-deficient thymocytes in response to endogenous SAgs. (A) Negative selection of Vβ5⁺, Vβ11⁺, and Vβ12⁺, but not of Vβ3⁺, thymocytes is impaired in CCR7-deficient mice. (B) Increased proportions of Vβ5, Vβ11, and Vβ12 lymphocytes in the spleen of CCR7-deficient mice, indicating that autoreactive cells escaping negative selection in the thymus are not deleted in the periphery and, therefore, could induce the development of autoimmunity in these mice. Data has been subjected to unpaired T test. P values less than or equal to .05 were considered significant. (C) Clusters of G8.8⁺/UEA-1⁺ epithelial cells are present in the medulla of CCR7-deficient animals, demonstrating that impaired negative selection of thymocytes reactive to endogenous SAg is not due to the absence of cells able to induce their deletion. Cryosections of the thymus from wild-type and mutant mice were stained with antibodies to EpCAM1 (G8.8, red) as well as with UEA-1 (blue). Images were acquired using a Zeiss Axiovert M200 microscope. Objective magnification, 10×/0.45 NA.