Localization of CD8 T cell epitope within cardiac myosin heavy chain-α_334-352 that induces autoimmune myocarditis in A/J mice

Background: Cardiac myosin heavy chain-α (Myhc), an intracellular protein expressed in the cardiomyocytes, has been identified as a major autoantigen in cardiac autoimmunity. In our studies with Myhc_334-352-induced experimental autoimmune myocarditis in A/J mice (H-2ª), we discovered that Myhc_334-352, supposedly a CD4 T cell epitope, also induced antigen-specific CD8 T cells that transfer disease to naive animals. Methods and results: In our efforts to identify the CD8 T cell determinants, we localized Myhc_338-348 within the full length-Myhc_334-352, leading to four key findings. (1) By acting as a dual epitope, Myhc_338-348 induces both CD4 and CD8 T cell responses. (2) In a major histocompatibility complex (MHC) class I-stabilization assay, Myhc_338-348 was found to bind H-2D^d - but not H-2K^k or H-2L^d - alleles. (3) The CD8 T cell response induced by Myhc_338-348 was antigen-specific, as evaluated by MHC class I/H-2D^d dextramer staining. The antigen-sensitized T cells predominantly produced interferon-γ, the critical cytokine of effector cytotoxic T lymphocytes. (4) Myhc_338-348 was found to induce myocarditis in immunized animals as determined by histology and magnetic resonance microscopy imaging. Conclusions: Our data provide new insights as to how different immune cells can recognize the same antigen and inflict damage through different mechanisms.