T-cell reactivity against streptococcal antigens in the periphery mirrors reactivity of heart-infiltrating T lymphocytes in rheumatic heart disease patients

Abstract

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.

FIG. 1

Reactivity against N-terminal M5 peptides and heart tissue proteins. (A) Intralesional T-cell clones from patients with severe RHD; (B) peripheral T-cell clones from RHD patients. PBMC-derived T-cell clones were not tested with myocardium protein fractions. Abbreviations: LA, left atrium; Mi V, mitral valve; Ao V, aortic valve; PM, papillar muscle. Black squares, M5 peptide-heart tissue protein cross-reactive T-cell clones; gray squares, non-cross-reactive T-cell clones recognizing either M5 peptide or heart tissue proteins.

FIG. 2

Frequency of M5(81–96) peptide recognition by PBMC from HLA-DR7⁺ DR53⁺ patients with severe RHD. The proportion of responders to the M5(81–96) peptide was measured by proliferation assay. DR7⁺ individuals are HLA-DR53⁺; DR53⁺ individuals are DR7⁺, DR4⁺, or DR9⁺; DR7⁻ individuals can be DR53⁺ (if they are DR4⁺ or DR9⁺); HLA-DR53⁻ individuals are DR7⁻, DR4⁻, or DR9⁻. ∗, P = 0.008 for HLA-DR7⁺ patients with severe RHD versus HLA-DR7⁺ controls (N.C); ∗∗, P < 0.001 for HLA-DR53⁺ patients with severe RHD with HLA-DR53⁺ controls.