β1-Adrenergic Receptor Contains Multiple IA and IE Binding Epitopes That Induce T Cell Responses with Varying Degrees of Autoimmune Myocarditis in A/J Mice.

Myocarditis/dilated cardiomyopathy (DCM) patients can develop autoantibodies to various cardiac antigens and one major antigen is β1-adrenergic receptor (βAR). Previous reports indicate that animals immunized with a βAR fragment encompassing， 197-222 amino acids for a prolonged period can develop DCM by producing autoantibodies， but existence of T cell epitopes， if any， were unknown. Using A/J mice that are highly susceptible to lymphocytic myocarditis， we have identified βAR 171-190， βAR 181-200， and βAR 211-230 as the major T cell epitopes that bind major histocompatibility complex class II/IA or IE alleles， and by creating IA and IE dextramers， we demonstrate that the CD4 T cell responses to be antigen-specific. Of note， all the three epitopes were found also to stimulate CD8 T cells suggesting that they can act as common epitopes for both CD4 and CD8 T cells. While， all epitopes induced only mild myocarditis， the disease-incidence was enhanced in animals immunized with all the three peptides together as a cocktail. Although， antigen-sensitized T cells produced mainly interleukin-17A， their transfer into naive animals yielded no disease. But， steering for T helper 1 response led the T cells reacting to one epitope， βAR 181-200 to induce severe myocarditis in naive mice. Finally， we demonstrate that all three βAR epitopes to be unique for T cells as none of them induced antibody responses. Conversely， animals immunized with a non-T cell activator， βAR 201-220， an equivalent of βAR 197-222， had antibodies comprising of all IgG isotypes and IgM except， IgA and IgE. Thus， identification of T cell and B cell epitopes of βAR may be helpful to determine βAR-reactive autoimmune responses in various experimental settings in A/J mice.