FIGURE 5.

Histological assessment of cardiac allografts. a, C57BL/6 donor allograft harvested from a BALB/c rag^−/− recipient left unreconstituted at >60 days demonstrating normal cardiomyocytes and vasculature without evidence of rejection. b, C57BL/6 control donor allograft rejected in BALB/c rag^−/− recipient reconstituted with enriched CD4⁺ T cells demonstrating a moderate to severe lymphocytic infiltration and cardiomyocyte necrosis. c, B6 → C2D chimeric donor allograft (MHC class II expression isolated to the bone marrow-derived compartment) harvested 60 days after CD4⁺ T cell transfer demonstrating mild lymphocytic infiltration, relatively intact cardiomyocytes, and no obvious evidence of necrosis. d, B6 → B6 control chimeric donor allograft demonstrating moderate to severe lymphocytic infiltration and cardiomyocyte necrosis similar to that of C57BL/6 control allografts. e, C2D → B6 (MHC class II expression isolated to the somatic compartment) harvested 60 days after CD4⁺ T cell transfer demonstrating mild lymphocytic infiltration and mild cardiomyocyte damage (some minimal early necrosis). f, C2D → B6 donor allograft rejected 18 days after CD4⁺ T cell transfer and 16 days after transfer of C57BL/6 rag^−/− splenocytes (source of MHC class II⁺ APCs) demonstrating moderate to severe lymphocytic infiltration and cardiomyocyte necrosis. Immunoperoxidase staining for CD4 and CD8 demonstrated CD4⁺ staining and a lack of CD8⁺ staining in all allografts (data not shown).