The sinoatrial node (SAN) is composed mostly of pacemaker, transitional and Purkinje‐like cells. Pacemaker cells, especially in the centre of the SAN, are surrounded by dense fibrous tissue and do not have any contact with transitional cells. We hypothesize that the SAN contains telocytes that have contacts with pacemaker cells and contractile myocardium. Immunohistochemistry using antibodies against HCN4 and antibody combinations against CD34 and HCN4 was carried out on 12 specimens. Confocal laser scanning microscopy (CLSM) with two mixtures of primary antibodies, namely CD34/S100 and vimentin/S100, was performed in three cases. In two cases, CLSM was carried out with CD117 antibody. Specimens for electron microscopy and immunocytochemistry with HCN4 immunogold labelling were taken from another three patients. In our study, we found cells with the immunophenotype of telocytes in the SAN. There were twice as many of these cells in the centre of the SAN as in the periphery (20.3 ± 4.8 versus 10.8 ± 4.4 per high‐power field). They had close contact with pacemaker cells and contractile cardiomyocytes and expressed HCN4. The ultrastructural characteristics of these cells are identical to those of telocytes observed earlier in other organs. Our study provides evidence that telocytes are present in the SAN.

Background: Few studies have compared COVID-19 patients from different waves. This study aims to conduct a clinical and morphological analysis of patients who died from COVID-19 during four waves. Methods: The study involved 276 patients who died from COVID-19 during four waves, including 77 patients in the first wave, 119 patients in the second wave, and 78 patients in the third wave. We performed a histological examination of myocardium samples from autopsies and additionally analyzed the samples by PCR. We conducted immunohistochemistry of the myocardium for 21 samples using antibodies against CD3, CD45, CD8, CD68, CD34, Ang1, VWF, VEGF, HLA-DR, MHC1, C1q, enteroviral VP1, and SARS-CoV-2 spike protein. We also did immunofluorescent staining of three myocardial specimens using VP1/SARS-CoV-2 antibody cocktails. Further, we ran RT-ddPCR analysis for 14 RNA samples extracted from paraffin-embedded myocardium. Electron microscopic studies of the myocardium were also performed for two samples from the fourth wave. Results: Among the 276 cases, active myocarditis was diagnosed in 5% (15/276). Of these cases, 86% of samples expressed VP1, and individual cells contained SARS-CoV-2 spike protein in 22%. Immunofluorescence confirmed the co-localization of VP1 and SARS-CoV-2 spike proteins. ddPCR did not confidently detect SARS-CoV-2 RNA in the myocardium in any myocarditis cases. However, the myocardium sample from wave IV detected a sub-threshold signal of SARS-CoV-2 by qPCR, but myocarditis in this patient was not confirmed. Electron microscopy showed several single particles similar to SARS-CoV-2 virions on the surface of the endothelium of myocardial vessels. A comparison of the cardiovascular complication incidence between three waves revealed that the incidence of hemorrhage (48 vs. 24 vs. 17%), myocardial necrosis (18 vs. 11 vs. 4%), blood clots in the intramural arteries (12 vs. 7 vs. 0%), and myocarditis (19 vs. 1 vs. 6%) decreased over time, and CD8-T-killers appeared. Immunohistochemistry confirmed the presence of endotheliitis in all 21 studied cases. Conclusions: This study compared myocardial damage in patients who died during three COVID-19 waves and showed a decrease in the incidence of endotheliitis complications (thrombosis, hemorrhage, necrosis) and myocarditis over time. However, the connection between myocarditis and SARS-CoV-2 infection remains unproven.

The presence of coronavirus-associated myocarditis remains controversial despite elevations in cardiac troponin and natriuretic peptide in many patients.Aim. To assess the morphological changes in the myocardium of patients who died due to coronavirus disease 2019 (COVID-19) and compare them with the intravital level of cardiac biomarkers.Material and methods. A total of 420 hospital charts and 77 autopsies of those who died from COVID-19 were analyzed. In 15 of 77 cases (19%) with histologically suspected myocarditis, an immunohistochemical examination of the myocardium with antibodies to CD3, CD45, CD8, CD68, CD34, Ang1, VWF, VEGF, HLA-DR, MHC1, C1q, VP1 of enteroviruses was performed, and in 8 patients with immunohistochemically confirmed myocarditis (10%) — polymerase chain reaction for SARS-CoV-2.Results. Hemorrhage, intramural thrombosis, necrosis of non-coronary origin, myocardial infarction and lymphocytic myocarditis were detected in 43%, 10%, 17%, 19% and 10% of cases, respectively, without coronavirus N and E gene sequences in the myocardium. Dysplasia, hyperplasia and hypertrophy of the vascular endothelium, expression of Ang1, VWF, VEGF, MHC1, C1q, VP1 of enteroviruses were determined in 100, 100, 87, 100, 75 and 62% of cases of myocarditis, respectively. There were no significant correlations between inflammatory biomarkers and myocarditis.Conclusion. The main morphological manifestation of COVID-19 in the myocardium is the so-called endotheliitis with dysplasia and endothelial activation, leading to hemorrhages, intramural thrombosis and necrosis. There is no convincing evidence of a direct involvement of coronavirus in myocarditis induction.

// <![CDATA[ $('.header-date').hide();$('#titleAuthors').hide();$('#abstractHeader').hide(); // ]]> Lubov Mitrofanova1, Anton Hazratov1, Boris Galkovsky1, Andrey Gorshkov1^,2, Danila Bobkov2^,3, Dmitry Gulyaev4 and Evgeny Shlyakhto5 1 Almazov National Medical Research Centre, Pathomorphology Research Laboratory, St. Petersburg, Russia 2 Smorodintsev Research Institute of Influenza, Laboratory of Intracellular Signaling and Transport, St. Petersburg, Russia 3 Institute of Cytology of the Russian Academy of Science, Laboratory of Cell Biology in Culture, St. Petersburg, Russia 4 Almazov National Medical Research Centre, Research Department of Neurosurgery, St. Petersburg, Russia 5 Almazov National Medical Research Centre, General Director, St. Petersburg, Russia Correspondence to: Lubov Mitrofanova, email: lubamitr@yandex.ru Keywords: telocytes; pericytes; confocal microscopy; primary culture of glioma telocytes; glioblastoma Received: June 05, 2019 Accepted: October 26, 2019 Published: Invalid Date NaN, NaN ABSTRACT Telocytes (Tcs) and pericytes (Pcs) are two types of perivascular interstitial cell known to be widespread in various organs and tissues, including the brain. We postulated that Tcs and Pcs may be involved in glioblastoma (GBM) neovascularization. Objective Morphological study of Tc and Pc roles in GBM. Materials and Methods Samples from 15 GBM, 10 diffuse astrocytoma, as well as 5 control samples were studied. We used immunohistochemistry (IHC) with antibodies (Abs) to GFAP, Ki-67, CD117, NeuroD1, NG2, CD34, and SMA. Confocal laser scanning microscopy (CLSM) of 4 glioma tissue cultures and 4 GBM sections was performed with GFAP, CD117, CD34/connexin43, NeuroD1/connexin43, CD34/NG2 and CD13/CD117 Abs. Electron microscopy (EM) of GBM was performed in 4 cases. Results The presence of Tcs and Pcs was shown in GBM (IHC, EM, CLSM) and glioma cultures (CLSM). The Tc immunophenotype was CD117⁺/CD34⁺/connexin43⁺/NeuroD1⁺. The Pc immunophenotype was SMA⁺/NG2⁺/CD13⁺. The number of Tcs in GBM specimens was 10 times higher than in astrocytoma. We also identified CD13/CD117 and CD34/NG2 co-expressing cells in GBM blood vessels. Conclusion Four immunophenotypes were found in GBM vessels, corresponding to endotheliocytes, Pcs, Tcs, and a mixed Pc/Tc immunophenotype. These and forthcoming improvements in our understanding of the origin and function of Tcs, including their relationship with Pcs, are necessary steps in oncology. Study of these cell types (Tcs, Pcs) and their roles in brain tumor oncogenesis will likely enable improved targeted therapies and support development of new forms of anti-neoplastic drugs. <!--x2o[7816ca9c]-->

The clinical manifestation study of post-acute sequelae of SARS-CoV-2 infection (PASC) has shown a lack of knowledge regarding its morphology and pathogenesis. The aim of this research was to investigate morphological manifestations of PASC in the myocardium. Materials and Methods: The study included 38 patients requiring endomyocardial biopsy (EMB) during the post-acute phase of coronavirus infection and a control group including patients requiring EMB prior to the SARS-CoV-2 pandemic. The patients’ clinical and laboratory data were analyzed. Histological examination and immunohistochemistry (IHC) of the myocardial tissue was conducted with antibodies to CD3, CD68, HLA-DR, MHC1, C1q, VP1 enteroviruses, spike protein SARS-CoV-2, Ang1, von Willebrand factor (VWF), and VEGF. The morphometric analysis included counting the mean number of inflammatory infiltrate cells per mm² and evaluating the expression of SARS-CoV-2 spike protein, HLA-DR, MHC1, C1q, Ang1, VWF, and VEGF using a scoring system. If the expression of SARS-CoV-2 spike protein was >3 points, an additional IHC test with antibodies to ACE2, CD16 as well as RT-PCR testing of the myocardial tissue were performed. For two patients, immunofluorescence tests of the myocardial tissue were performed using antibody cocktails to SARS-CoV-2 spike protein/CD16, SARS-CoV-2 spike protein/CD68, CD80/CD163. The statistical data analysis was carried out using the Python programming language and libraries such as NumPy, SciPy, Pandas, and Matplotlib. Results: The study demonstrated a significant increase in the number of CD68+ macrophages in the myocardium of PASC patients compared to patients who did not have a history of COVID-19 (p = 0.014 and p = 0.007 for patients with and without myocarditis, respectively), predominantly due to M2 macrophages. An increase in the number of CD68+ macrophages was more frequently observed in patients with shorter intervals between the most recent positive SARS-CoV-2 PCR test and the time of performing the EMB (r = −0.33 and r = −0.61 for patients with and without myocarditis, respectively). The expression scores of Ang1, VEGF, VWF, and C1q in PASC patients did not significantly differ from those in EMB samples taken before 2019. Conclusion: The myocardium of PASC patients demonstrated a significant increase in the number of CD68+ macrophages and a decrease in the expression of markers associated with angiopathy. No evidence of coronavirus-associated myocarditis was observed in any PASC patient.

RBM20 (RNA-binding motif protein 20) is a splicing factor targeting multiple cardiac genes, and its mutations cause cardiomyopathies. Originally, RBM20 mutations were discovered to cause the development of dilated cardiomyopathy by erroneous splicing of the gene TTN (titin). Titin is a giant protein found in a structure of the sarcomere that functions as a molecular spring and provides a passive stiffness to the cardiomyocyte. Later, RBM20 mutations were also described in association with arrhythmogenic right ventricular cardiomyopathy and left ventricular noncompaction cardiomyopathy. Here, we present a clinical case of a rare arrhythmogenic phenotype and no structural cardiac abnormalities associated with a RBM20 genetic variant of uncertain significance.