β1-Adrenergic Receptor Contains Multiple IA(k) and IE(k) 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 (β(1)AR). Previous reports indicate that animals immunized with a β(1)AR 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 β(1)AR 171–190, β(1)AR 181–200, and β(1)AR 211–230 as the major T cell epitopes that bind major histocompatibility complex class II/IA(k) or IE(k) alleles, and by creating IA(k) and IE(k) 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, β(1)AR 181–200 to induce severe myocarditis in naive mice. Finally, we demonstrate that all three β(1)AR epitopes to be unique for T cells as none of them induced antibody responses. Conversely, animals immunized with a non-T cell activator, β(1)AR 201–220, an equivalent of β(1)AR 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 β(1)AR may be helpful to determine β(1)AR-reactive autoimmune responses in various experimental settings in A/J mice.