Peripheral tolerance in transgenic mice expressing class I MHC L ^d only on cardiac cells

Background: The fate of autoreactive T cells exposed to extrathymic self-antigen is examined in a double transgenic (DTG) mouse [(L^d+ cardiac X 2C)F1], where cardiac myocytes alone express L^d and T cells express an antigen receptor (2C TCR) against L^d. Methods: Naïve cardiac L^d+ single transgenic (STG) mice (before breeding with 2C) and DTG mice were examined for evidence of autoimmunity. The L ^d+ STG hearts were then transplanted to syngeneic L^d- wild type C57BL/6 to evaluate the heart's immunogenicity. L^d+ skin grafts were transplanted to non-transgenic B6, transgenic 2C, STG, and DTG mice. Phenotype analysis of peripheral 1B2 + (identifies 2C T cells), CD4+, and CD8+ T cells was performed by FACS. In vitro MLC and CTL, with and without the addition of IL-2 and suppressor cell assays, were evaluated. Results: Neither STG nor DTG hearts developed any evidence of autoimmunity by histology. In contrast, B6 mice rejected the L^d+ STG heart in 17 ± 9.7 days (P < 0.01), while a syngeneic B6 heart transplant was accepted indefinitely. Survival of L^d+ skin grafts was prolonged in both STG and DTG mice. FACS quantitation revealed that while there was no deletion of peripheral 2C cells in the DTG, these 2C T cells did have a significantly reduced proliferative and cytotoxic response to H-2L^d. Restoration of the proliferative and cytotoxic response of the DTG cells by the addition of IL-2 was consistent with a state of anergy. Conclusions: These findings suggest that the expression of extrathymic class I MHC expression alone did not trigger autoimmune reactions but that the T cells can be rendered anergic to the specific 'self' antigen.