Autopsy data from 80 patients who died of the COVID-19 infection were analysed. Using macro- and microscopic studies, specific features of pathological processes in various organs were identified. The obtained experimental data, along with information from literature sources, allowed conclusions to be drawn about the mechanisms of damaging internal organs and body systems, as well as assumptions to be made about individual links in the pathogenesis of COVID-19. The thanatogenesis of the disease and the main causes of death are discussed, including acute cardiopulmonary failure, acute renal failure, pulmonary thromboembolism, shock involving multiple organ failure and sepsis. The critical importance of autopsy is emphasized, which provides valuable information on the morphological substrate for this infection closely associated with possible clinical manifestations.

Диагностика и лечение идиопатического легочного фиброза Федеральные клинические рекомендации

Aim Despite the regular heart damage in patients with coronavirus pneumonia caused by SARS-Cov-2, a possibility of developing lymphocytic myocarditis as a part of COVID-19 remains unsubstantiated. The aim of this study was to demonstrate a possibility of lymphocytic myocarditis and to study its morphological features in patients with the novel coronavirus infection (COVID-19) with a severe course. Material and methods  Postmortem data were studied for 5 elderly patients (74.8±4.4 years; 3 men and 2 women) with the novel coronavirus infection and bilateral, severe polysegmental pneumonia (stage 3–4 by computed tomography). COVID-19 was diagnosed based on the typical clinical presentation and positive polymerase chain reaction test in nasopharyngeal swabs. All patients were treated in different hospitals repurposed for the treatment of patients with COVID-19. A standard histological study was performed with hematoxylin and eosin, toluidine blue, and van Gieson staining. Serial paraffin slices were studied immunohistochemically with antibodies to CD3, СD68, CD20, perforin, and toll-like receptors (TLR) 4 and 9. Results In none of the cases, myocarditis was suspected clinically, added to the diagnosis or indicated as a possible cause of death. IHD and acute myocardial infarction were mentioned as error diagnoses not confirmed by the postmortem examination. The morphological examination of the heart identified signs of lymphocytic myocarditis consistent with Dallas criteria for this diagnosis. Myocardial infiltrate was characterized in detail, and a combined inflammatory damage of endocardium and pericardium was described. The immunohistochemical study with cell infiltrate typing confirmed the presence of CD3-positive Т lymphocytes and the increased expression of TLR-4. A picture of coronaritis, including that with microvascular thrombosis, was found in all cases. Conclusion A possibility for development of lymphocytic viral myocarditis in COVID-19 was confirmed morphologically and immunohistochemically. Specific features of myocarditis in COVID-19 include the presence of coronaritis and a possible combination of myocarditis with lymphocytic endo- and pericarditis.

Immune responses to tissue-engineered grafts made of xenogeneic materials remain poorly studied. The scope of current investigations is limited by the lack of information on orthotopically implanted grafts. A deeper understanding of these processes is of great importance since innovative surgical approaches include the implantation of xenogeneic decellularized scaffolds seeded by cells. The purpose of our work is to study the immunological features of tracheal repair during the implantation of tissue-engineered constructs based on human xenogeneic scaffolds modified via laser radiation in rabbits. The samples were stained with hematoxylin and Safranin O, and they were immunostained with antibodies against tryptase, collagen II, vimentin, and CD34. Immunological and inflammatory responses were studied by counting immune cells and evaluating blood vessels and collagen. Leukocyte-based inflammation prevailed during the implantation of decellularized unseeded scaffolds; meanwhile, plasma cells were significantly more abundant in tissue-engineered constructs. Mast cells were insignificantly more abundant in tissue-engineered construct samples. Conclusions: The seeding of decellularized xenogeneic cartilage with chondrocytes resulted in a change in immunological reactions upon implantation, and it was associated with plasma cell infiltration. Tissue-engineered grafts widely differed in design, including the type of used cells. The question of immunological response depending on the tissue-engineered graft composition requires further investigation.