Lymphopenia is a frequent hematological manifestation, associated with a severe course of COVID-19, with an insufficiently understood pathogenesis. We present molecular genetic immunohistochemical, and electron microscopic data on SARS-CoV-2 dissemination and viral load (VL) in lungs, mediastinum lymph nodes, and the spleen of 36 patients who died from COVID-19. Lymphopenia <1 × 10⁹/L was observed in 23 of 36 (63.8%) patients. In 12 of 36 cases (33%) SARS-CoV-2 was found in lung tissues only with a median VL of 239 copies (range 18–1952) SARS-CoV-2 cDNA per 100 copies of ABL1. Histomorphological changes corresponding to bronchopneumonia and the proliferative phase of DAD were observed in these cases. SARS-CoV-2 dissemination into the lungs, lymph nodes, and spleen was detected in 23 of 36 patients (58.4%) and was associated with the exudative phase of DAD in most of these cases. The median VL in the lungs was 12,116 copies (range 810–250281), lymph nodes—832 copies (range 96–11586), and spleen—71.5 copies (range 0–2899). SARS-CoV-2 in all cases belonged to the 19A strain. A immunohistochemical study revealed SARS-CoV-2 proteins in pneumocytes, alveolar macrophages, and bronchiolar epithelial cells in lung tissue, sinus histiocytes of lymph nodes, as well as cells of the Billroth pulp cords and spleen capsule. SARS-CoV-2 particles were detected by transmission electron microscopy in the cytoplasm of the endothelial cell, macrophages, and lymphocytes. The infection of lymphocytes with SARS-CoV-2 that we discovered for the first time may indicate a possible link between lymphopenia and SARS-CoV-2-mediated cytotoxic effect.

Multi-organ failure is one of the common causes of fatal outcome in COVID-19 patients. However, the pathogenetic association of the SARS-CoV-2 viral load (VL) level with fatal dysfunctions of the lungs, liver, kidneys, heart, spleen and brain, as well as with the risk of death in COVID-19 patients remains poorly understood. SARS-CoV-2 VL in the lungs, heart, liver, kidneys, brain, spleen and lymph nodes have been measured by RT qPCR using the following formula: N^SARS-CoV−2/N^{ABL1 ×} 100. Dissemination of SARS-CoV-2 in 30.5% of cases was mono-organ, and in 63.9% of cases, it was multi-organ. The average SARS-CoV-2 VL in the exudative phase of diffuse alveolar damage (DAD) was 60 times higher than in the proliferative phase. The SARS-CoV-2 VL in the lungs ranged from 0 to 250,281 copies. The “pulmonary factors” of SARS-CoV-2 multi-organ dissemination are the high level of SARS-CoV-2 VL (≥4909) and the exudative phase of DAD. The frequency of SARS-CoV-2 dissemination to lymph nodes was 86.9%, heart–56.5%, spleen–52.2%, liver–47.8%, kidney–26%, and brain–13%. We found no link between the SARS-CoV-2 VL level in the liver, kidneys, and heart and the serum level of CPK, LDH, ALP, ALT, AST and Cr of COVID-19 patients. Isolated detection of SARS-CoV-2 RNA in the myocardium of COVID-19 patients who died from heart failure is possible. The pathogenesis of COVID-19-associated multi-organ failure requires further research in a larger cohort of patients.

Цель исследования: иммуногистохимическая и электронно-микроскопическая визуализация коронавируса SARS-CoV-2 в тканях легких, лимфатических узлов и почек пациентов, умерших от COVID-19. Материалы и методы. Для иммуногистохимических исследований в качестве материала использованы срезы фиксированных в формалине и заключенных в парафин тканей легких, лимфатических узлов и почек пациентов, умерших от COVID-19. Количественная оценка уровня вирусной нагрузки SARS-CoV-2 проведена с использованием оригинального способа кПЦР РВ и рассчитана по формуле: число копий SARS-CoV-2/число копий ABL1 х 100, выражена отношением истинного числа копий кДНК SARS-CoV-2 на 100 копий кДНК гена ABL1. Для морфологических исследований взяты нативные образцы тканей легких, лимфатических узлов и почек. Результаты. При иммуногистохимическом и электронно-микроскопическом исследовании частицы коронавируса SARS-CoV-2 были обнаружены в цитоплазме эндотелиальных клеток аэрогематического барьера легких, сосудистого клубочка почек, в цитоплазме макрофагов лимфатического узла, а также в цитоплазме лимфоцитов в просвете капилляров легких.