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SARS-CoV-2 infection of lung endothelial cells and pulmonary capillary microthrombosis


In a recent study published in Pathology-Research and PracticeResearchers evaluated the presence of RNA in the lung tissue of deceased patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Study: Cell tropism and viral clearance during SARS-CoV-2 lung infection. Image Credit: CROCOTHERY / Shutterstock
study: Cell orientation and viral clearance during SARS-CoV-2 lung infection.. Image Credit: CROCOTHERY / Shutterstock

SARS-CoV-2 infection mainly causes mild or asymptomatic coronavirus infection 2019 (COVID-19), but develops severe illness, requires hospitalization, and is concentrated in severe cases You will need treatment and a ventilator. Elderly people and people with comorbidity are at increased risk of acute respiratory distress syndrome (ARDS).

Pulmonary capillary microthrombosis has been proposed to be a major proponent of severe COVID-19. Dermatitis was reported at several autopsies. However, it is unclear whether this is due to SARS-CoV-2 infection of endothelial cells or other mechanisms. Cytokine storm In COVID-19.

About research

In the current study, researchers used RNA in situ hybridization (RNA-ISH) to examine the presence of SARS-CoV-2 RNA in deceased COVID-19 patients. Forty COVID-19 patients were identified based on the COVID-19 test and mortality interval. Twelve patients are infected with the SARS-CoV-2 variant (VOC) of concern, including alpha (5), beta (5), and omicron (2) variants, and the rest are infected with their ancestral SARS-CoV-2. did.

The necropsy was performed according to a standardized protocol. Tissue specimens were fixed using 4% neutral buffered formalin immediately after dissection. Sections of 3 μm were taken from a formalin-fixed paraffin-embedded sample (FFPE) and stained for histological evaluation according to standard protocols. RNA-ISH was performed on a 5 μm lung tissue section using an RNAscope. A SARS-CoV-2 specific probe was used for single detection of the spike (S) gene.

The duplex kit was used for dual RNA-ISH, which combines a SARS-CoV-2 specific probe with keratin 18 (KRT18) for epithelial cells. melanoma Cell adhesion molecule (MCAM) for endothelial cells and differentiation cluster 68 (CD68) for macrophages.

Survey results

The average time from onset of symptoms to death was 10 days, with a median age of 79 years at death. On average, patients were hospitalized for 7 days. Histological examination revealed diffuse alveolar injury and edema during the exudative phase. The proliferative phase was characterized by the development of lung cell hyperplasia, squamous metaplasia, and desquamation, and then organized pneumonia leading to interstitial fibrosis. These changes were thought to be the underlying cause of death in 26 patients.

Elsewhere, septic shock, myocardial infarction, severe iron deficiency anemia, pulmonary artery embolism, bronchial pneumonia associated with overinfection, or compensatory cardiac dysfunction was presumed to cause death. Positive signals for S gene RNA were obtained from within the cytoplasm of cells in the alveoli and alveolar septum. Six were classified as high viral load, 10 as moderate viral load, and 16 as low viral load. There was no detectable viral RNA in the lung tissue of 8 patients.

Patients are based on the duration of COVID-19, a)<1週間、b)1〜2週間、およびc)>It was stratified in 2 weeks. They observed a significant inversely proportional relationship between the duration of the illness and the amount of signal. Viral load was significantly lower in patients with a disease duration of 2 weeks or longer than in the other two subgroups. In particular, six patients in this subgroup completed primary COVID-19 vaccination, and viral load was not significantly different between unvaccinated and vaccinated.

COVID-19 pneumonia was found in 18 patients with exudative phase, 6 patients with proliferative phase, and 14 patients with interstitial fibrosis. The remaining two patients can be classified because of overlapping bronchopneumonia. Researchers have observed an inverse correlation between the stage of COVID-19 pneumonia and the amount of signal. Therefore, lower viral load was detected during the fibrotic phase of COVID-19 pneumonia than during the exudative or proliferative phase.

The team did not find a statistically significant association between the abundance of viral RNA in lung tissue and gender, age, arterial hypertension, ventilator, or common obstructive pulmonary disease (COPD). did. but, Patients with type 2 diabetes Diabetes (T2DM) has been shown to have a low frequency of viral RNA signaling. At high viral loads, S gene RNA signals were detected primarily in KRT18 expressing lung cells and CD68-positive alveolar macrophages. The frequency of signaling was significantly lower in MCAM-positive endothelial cells.


SARS-CoV-2S gene RNA was detected in KRT18-expressing lung epithelial cells, consistent with the abundant expression of SARS-CoV-2 cell receptors such as angiotensin converting enzyme 2 (ACE2) in lung epithelial cells. .. Researchers used dual RNA-ISH to find a single SARS-CoV-2 positive endothelial cell, but in most cases the S gene in lung endothelial cells was negative.

Since COVID-19-related damage to lung tissue was histologically apparent in 38 cases, it is unlikely that infection with lung endothelial cells induced capillary microthrombosis. These findings indicate that pulmonary microthrombosis may not be a direct result of endothelial cell infection.




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