Heart-specific CD4+ T cells have been implicated in development and progression of myocarditis in mice and in humans. Here, using mouse models of experimental autoimmune myocarditis (EAM) we investigated the role of heart non-specific CD4+ T cells in the progression of the disease. Heart non-specific CD4+ T cells were obtained from DO11.10 mice expressing transgenic T cell receptor recognizing chicken ovalbumin. We found that heart infiltrating CD4+ T cells expressed exclusively effector (Teff) phenotype in the EAM model and in hearts of patients with lymphocytic myocarditis. Adoptive transfer experiments showed that while heart-specific Teff infiltrated the heart shortly after injection, heart non-specific Teff effectively accumulated during myocarditis and became the major heart-infiltrating CD4+ T cell subset at later stage. Restimulation of co-cultured heart-specific and heart non-specific CD4+ T cells with alpha-myosin heavy chain antigen showed mainly Th1/Th17 response for heart-specific Teff and up-regulation of a distinct set of extracellular signalling molecules in heart non-specific Teff. Adoptive transfer of heart non-specific Teff in mice with myocarditis did not affect inflammation severity at the peak of disease, but protected the heart from adverse post-inflammatory fibrotic remodelling and cardiac dysfunction at later stages of disease. Furthermore, mouse and human Teff stimulated in vitro with common gamma cytokines suppressed expression of profibrotic genes, reduced amount of α-smooth muscle actin filaments and decreased contraction of cardiac fibroblasts. In this study, we provided a proof-of-concept that heart non-specific Teff cells could effectively contribute to myocarditis and protect the heart from the dilated cardiomyopathy outcome.Electronic supplementary materialThe online version of this article (10.1007/s00395-019-0766-6) contains supplementary material, which is available to authorized users.

Background Microvesicles are vesicles shed by plasma membranes following cell activation and apoptosis. The role of lymphocyte‐derived microvesicles in endothelial function remains poorly understood. Methods CD4+ T cells isolated from peripheral blood of healthy human donors were stimulated using anti‐CD3/anti‐CD28‐coated beads. Proteomic profiling of microvesicles was performed using linear discriminant analysis (LDA) from activated T cells (MV.Act) and nonactivated T cells (MV.NAct). In addition, data processing analysis was performed using MaxQUANT workflow. Differentially expressed proteins found in MV.Act or MV.NAct samples with identification frequency = 100%, which were selected by both LDA (p < .01) and MaxQUANT (p < .01) workflows, were defined as “high‐confidence” differentially expressed proteins. Functional effects of MV.Act on human primary microvascular endothelial cells were analysed. Results T cells released large amounts of microvesicles upon stimulation. Proteomic profiling of microvesicles using LDA identified 2279 proteins (n = 2110 and n = 851 proteins in MV.Act and MV.NAct, respectively). Protein–protein interaction network models reconstructed from both differentially expressed proteins (n = 594; LDA p ≤ .01) and “high‐confidence” differentially expressed proteins (n = 98; p ≤ .01) revealed that MV.Act were enriched with proteins related to immune responses, protein translation, cytoskeleton organisation and TNFα‐induced apoptosis. For instance, MV.Act were highly enriched with IFN‐γ, a key proinflammatory pathway related to effector CD4+ T cells. Endothelial cell incubation with MV.Act induced superoxide generation, apoptosis, endothelial wound healing impairment and endothelial monolayer barrier disruption. Conclusions T cell receptor‐mediated activation of CD4+ T cells stimulates the release of microvesicles enriched with proteins involved in immune responses, inflammation and apoptosis. T cell‐derived microvesicles alter microvascular endothelial function and barrier permeability, potentially promoting tissue inflammation.