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

Abstract

Myocarditis/dilated cardiomyopathy (DCM) patients can develop autoantibodies to various cardiac antigens and one major antigen is β1-adrenergic receptor (β1AR). Previous reports indicate that animals immunized with a β1AR 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 β1AR 171–190, β1AR 181–200, and β1AR 211–230 as the major T cell epitopes that bind major histocompatibility complex class II/IAk or IEk alleles, and by creating IAk and IEk 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, β1AR 181–200 to induce severe myocarditis in naive mice. Finally, we demonstrate that all three β1AR epitopes to be unique for T cells as none of them induced antibody responses. Conversely, animals immunized with a non-T cell activator, β1AR 201–220, an equivalent of β1AR 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 β1AR may be helpful to determine β1AR-reactive autoimmune responses in various experimental settings in A/J mice.

Autoimmune Myocarditis, Old Dogs and New Tricks

“…Other heart autoantigens such as ANT 1 , β1AR, and SERCA2a (Ca 2+ adenosine triphosphatase 2a) could also be targeted by pathogenic T cells implicated in the development of autoimmune myocarditis. [71][72][73] Recent studies implemented pathogenic T cells as potential diagnostic or therapeutic targets for autoimmune myocarditis including ICI myocarditis, demonstrating promising outcomes at both clinical and preclinical levels. 51,64,238,254,260,311,312 However, the current evidence primarily relies on animal studies, lacking sufficient clinical data.…”

“…It has been reported that heart antigens including ANT 1 (adenine nucleotide translocator 1), β1AR (β1-adrenergic receptor), and SERCA2a (sarcoplasmic/endoplasmic reticulum Ca 2+ adenosine triphosphatase 2a) can serve as targets for autoreactive T cells, leading to autoimmune myocarditis development in mice. [71][72][73] Additionally, Kaya et al 74 demonstrated that autoreactive T cells specific for cTnI can induce myocarditis development in mice. 75 Further investigations should focus on elucidating the clinical relevance of these findings.…”

Identification of Immunogenic Epitopes That Permit the Detection of Antigen-Specific T Cell Responses in Multiple Serotypes of Group B Coxsackievirus Infections

“…To determine the MHC-binding affinity of VP1 epitopes, we used empty IA k monomers as described previously [22]. By using HEL 46-61 as a competitor reference [27,28,38], we analyzed the binding ability of VP1 681-700, VP1 721-740 and VP1 771-790 and determined their IC50 values (Figure 3a) [27,28,39]. We noted that the binding affinity of VP1 771-790 (IC50, 6.50 ± 0.27 µM) was relatively stronger than VP1 721-740 (IC50, 41.50 ± 1.0 µM), whereas the IC50 value for VP1 681-700 was low (>100 µM).…”

Transgenic Mice Expressing Functional TCRs Specific to Cardiac Myhc-α 334–352 on Both CD4 and CD8 T Cells Are Resistant to the Development of Myocarditis on C57BL/6 Genetic Background

“…To address autoimmune events, various autoimmune myocarditis models have been developed since their disease features resemble those of human disease [27,28]. The adjuvant models of myocarditis involve immunizations with complete Freund's adjuvant (CFA) supplemented with myocarditogenic epitopes, such as Myhc-α 334-352, SERCA2a 971-990, ANT 21-40, β1AR 181-200, BCKDk 111-130, and cTNI 105-122 in A/J mice [29][30][31][32][33][34]; Myhcα 614-643 in BALB/c mice [35]; and Myhc-α 1304-1320 in rats [30][31][32][33][34]36]. Although most of these disease models involve the mediation of CD4 T cells and/or antibodies, the role of CD8 T cells is unclear, and it has been a challenge to ascertain the antigen specificity of cardiac-reactive T cells in the causation of myocarditis for routine investigations.…”