Background β-Hemolytic streptococcal infection in developing countries still causes thousands of cases of rheumatic heart disease, demanding surgical valve correction. Antigenic mimicry between self and streptococcal components has been proposed as the triggering factor leading to autoimmunity in individuals with genetic susceptibility. Although heart streptococcal–M protein cross-reactive antibodies have been demonstrated, heart tissue damage seems to be T lymphocyte–dependent. We studied the infiltrating T lymphocytes in rheumatic heart lesions with the aim of understanding the role of cellular immune response at the site of the lesions. Methods and Results We obtained 107 T-cell clones from surgical fragments of cardiac tissue from four rheumatic heart disease patients. We tested their capacity to recognize streptococcal M protein–derived synthetic peptides and heart proteins. We found eight infiltrating T-cell clones from all four patients that simultaneously recognize streptococcal M and heart proteins. Among the M-protein sequences tested, only synthetic peptides corresponding to regions 1 through 25, 81 through 103, and 163 through 177 were simultaneously recognized with heart protein fractions. Interestingly, regions 81 through 103 and 163 through 177 have been known to bear heart cross-reactive epitopes at the antibody level. Five of these clones are CD4 ⁺ , and one is CD8 ⁺ . Conclusions The presence of heart–M protein cross-reactive T-cell clones in rheumatic heart lesions suggests their direct involvement in the pathogenesis of this disease. The dissection of protective and pathogenic epitopes of streptococcal M protein is an important step in allowing the development of a safe anti-streptococcal synthetic vaccine.

1. Introduction There are currently a wide modalities of interventional strategies – both transcatheter and surgical – which can be indicated for patients with valvular heart diseases (VHD), with the objective of reducing the morbidity and mortality. The correct timing for indication and the type of interventional treatment are linked to the precise anatomical and functional diagnosis of the VHD, and comprehensive global evaluation of the patient. The 2020 Update of the Brazilian Guidelines for VHD, in addition to compiling [...] 1. Introduction There are currently a wide modalities of interventional strategies – both transcatheter and surgical – which can be indicated for patients with valvular heart diseases (VHD), with the objective of reducing the morbidity and mortality. The correct timing for indication and the type of interventional treatment are linked to the precise anatomical and functional diagnosis of the VHD, and comprehensive global evaluation of the patient. The 2020 Update of the Brazilian Guidelines for VHD, in addition to compiling

T-cell molecular mimicry between streptococcal and heart proteins has been proposed as the triggering factor leading to autoimmunity in rheumatic heart disease (RHD). We searched for immunodominant T-cell M5 epitopes among RHD patients with defined clinical outcomes and compared the T-cell reactivities of peripheral blood and intralesional T cells from patients with severe RHD. The role of HLA class II molecules in the presentation of M5 peptides was also evaluated. We studied the T-cell reactivity against M5 peptides and heart proteins on peripheral blood mononuclear cells (PBMC) from 74 RHD patients grouped according to the severity of disease, along with intralesional and peripheral T-cell clones from RHD patients. Peptides encompassing residues 1 to 25, 81 to 103, 125 to 139, and 163 to 177 were more frequently recognized by PBMC from RHD patients than by those from controls. The M5 peptide encompassing residues 81 to 96 [M5(81–96) peptide] was most frequently recognized by PBMC from HLA-DR7⁺DR53⁺patients with severe RHD, and 46.9% (15 of 32) and 43% (3 of 7) of heart-infiltrating and PBMC-derived peptide-reactive T-cell clones, respectively, recognized the M5(81–103) region. Heart proteins were recognized more frequently by PBMC from patients with severe RHD than by those from patients with mild RHD. The similar pattern of T-cell reactivity found with both peripheral blood and heart-infiltrating T cells is consistent with the migration of M-protein-sensitized T cells to the heart tissue. Conversely, the presence of heart-reactive T cells in the PBMC of patients with severe RHD also suggests a spillover of sensitized T cells from the heart lesion.

Rheumatic heart disease (RHD) is a sequel of post-streptococcal throat infection. Molecular mimicry between streptococcal and heart components has been proposed as the triggering factor of the disease, and CD4⁺ T cells have been found predominantly at pathological sites in the heart of RHD patients. These infiltrating T cells are able to recognize streptococcal M protein peptides, involving mainly 1–25, 81–103 and 163–177 N-terminal amino acids residues. In the present work we focused on the TCR β chain family (TCR BV) usage and the degree of clonality assessed by β chain complementarity-determining region (CDR)-3 length analysis. We have shown that in chronic RHD patients, TCR BV usage in peripheral blood mononuclear cells (PBMC) paired with heart-infiltrating T cell lines (HIL) is not suggestive of a superantigen effect. Oligoclonal T cell expansions were more frequently observed in HIL than in PBMC. Some major BV expansions were shared between the mitral valve (Miv) and left atrium (LA) T cell lines, but an in-depth analysis of BJ segments usage in these shared expansions as well as nucleotide sequencing of the CDR3 regions suggested that different antigenic peptides could be predominantly recognized in the Miv and the myocardium. Since different antigenic proteins probably are constitutively represented in myocardium and valvular tissue, these findings could suggest a differential epitope recognition at the two lesional heart sites after a common initial bacterial challenge.