The healing myocardium mobilizes a distinct B-cell subset through a CXCL13-CXCR5-dependent mechanism.

AIMS: Recent studies have revealed that B cells and antibodies can influence inflammation and remodelling following a myocardial infarction (MI) and culminating in heart failure-but the mechanisms underlying these observations remain elusive. We therefore conducted in mice a deep phenotyping of the post-MI B-cell responses in infarcted hearts and mediastinal lymph nodes, which drain the myocardium. Thereby, we sought to dissect the mechanisms controlling B-cell mobilization and activity in situ. METHODS AND RESULTS: Histological, flow cytometry, and single-cell RNA-sequencing (scRNA-seq) analyses revealed a rapid accumulation of diverse B-cell subsets in infarcted murine hearts, paralleled by mild clonal expansion of germinal centre B cells in the mediastinal lymph nodes. The repertoire of cardiac B cells was largely polyclonal and showed no sign of antigen-driven clonal expansion. Instead, it included a distinct subset exclusively found in the heart, herein termed 'heart-associated B cells' (hB) that expressed high levels of Cd69 as an activation marker, C-C-chemokine receptor type 7 (Ccr7), CXC-chemokine receptor type 5 (Cxcr5), and transforming growth factor beta 1 (Tgfb1). This distinct signature was not shared with any other cell population in the healing myocardium. Moreover, we detected a myocardial gradient of CXC-motif chemokine ligand 13 (CXCL13, the ligand of CXCR5) on Days 1 and 5 post-MI. When compared with wild-type controls, mice treated with a neutralizing CXCL13-specific antibody as well as CXCR5-deficient mice showed reduced post-MI infiltration of B cells and reduced local Tgfb1 expression but no differences in contractile function nor myocardial morphology were observed between groups. CONCLUSION: Our study reveals that polyclonal B cells showing no sign of antigen-specificity readily infiltrate the heart after MI via the CXCL13-CXCR5 axis and contribute to local TGF-ß1 production. The local B-cell responses are paralleled by mild antigen-driven germinal centre reactions in the mediastinal lymph nodes that might ultimately lead to the production of specific antibodies.

Evaluating physiology of a human heart during ventricular tachycardia: new insights of mechanical alterations via beat to beat strain analysis-case report.

BACKGROUND: Ventricular tachycardia can be triggered by myocardial ischaemia. These often fatal events are nearly always accompanied by a significant circulatory depression. However, the exact mechanical alterations and mechanisms of adaption during such arrhythmia episodes are still unknown. CASE SUMMARY: We report on a 71-year-old male patient with a distinct cardiovascular risk profile, recurrent incidences of dizziness and palpitations. A Holter electrocardiogram was performed showing multiple episodes of ventricular tachycardia. He was immediately transferred to our hospital for further monitoring and diagnostics. During echocardiography, one of these episodes could be recorded with a four-dimensional (4D) probe in triplane acquisition mode and strain analysis was done. Afterwards, a heart catheter examination was performed. A one-vessel coronary heart disease was diagnosed and treated with three drug-eluting stents. The burden of non-sustained ventricular tachycardia (nsVT) significantly reduced post-procedure. During the follow-up, new episodes of nsVT occurred after 6 weeks, which were treated by electrophysiological examinations. DISCUSSION: Modern 4D echocardiography machines offer the possibility to visualize the entire heart simultaneously. Thus ventricular arrhythmias can be evaluated using off-line strain analysis. This technology allows new real-time insights into the human heart showing compensatory mechanisms to overcome stressful episodes, such as ventricular tachycardia.

CpG blocks immunosuppression by myeloid-derived suppressor cells in tumor-bearing mice.

PURPOSE: The Toll-like receptor (TLR) 9 ligand CpG has been used successfully for the immunotherapy of cancer. Chronic CpG application in tumor-free hosts leads, however, to the expansion of myeloid-derived suppressor cells (MDSC), which can cause T-cell suppression and may thus hamper the development of an effective immune response. Here, we investigated the effect of TLR9 activation on the function of MDSC in tumor-bearing mice. EXPERIMENTAL DESIGN: We investigated the effect of CpG treatment on the number, phenotype, and function of MDSC in mice bearing subcutaneous C26 tumors and in CEA424-TAg mice bearing autochthonous gastric tumors. RESULTS: CpG treatment blocks the suppressive activity of MDSC on T-cell proliferation in both tumor models. Inhibition of MDSC function by CpG was particularly pronounced for a highly suppressive Ly6G(hi) polymorphonuclear subset of MDSC. We further show that TLR9 activation by CpG promotes maturation and differentiation of MDSC and strongly decreases the proportion of Ly6G(hi) MDSC in both tumor-bearing and tumor-free mice. We demonstrate that IFN-α produced by plasmacytoid dendritic cells upon CpG stimulation is a key effector for the induction of MDSC maturation in vitro and show that treatment of mice with recombinant IFN-α is sufficient to block MDSC suppressivity. CONCLUSIONS: We show here for the first time that TLR9 activation inhibits the regulatory function of MDSC in tumor-bearing mice and define a role for the antitumoral cytokine IFN-α in this process.