Role of neutrophil-epithelial interactions in SARS-CoV-2 inf
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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is the virus that causes coronavirus disease 2019 (COVID-19), is associated with high mortality and hospitalization rates. However, many patients who are infected with SARS-CoV-2 remain asymptomatic or develop mild symptoms. In a recent study researchers focus on the relationship between the pre-existing airway neutrophils and SARS-CoV-2 infection to determine the impact that neutrophils have on COVID-19.

An overview of neutrophils
Neutrophils are the first and predominant immune cells that are recruited to the respiratory tract in response to viral infection. Upon their arrival, neutrophils release various inflammatory mediators in an effort to rapidly eliminate the pathogen from the infected area. Neutrophils are capable of recognizing infectious sites as well as act as sites of infections which, together, leads to an acute inflammatory response. An uncontrolled massive inflammatory response, which is also known as the cytokine storm, has been documented in patients with severe COVID-19.

The researchers developed a novel in vitro model to assess neutrophilic airway inflammation in SARS-CoV-2 infection. To this end, primary human airway basal epithelial cells were isolated from the lung tissue. The current study involved the isolation of neutrophils from peripheral blood. Following their isolation, the purity of the neutrophils was confirmed by flow-activated cell sorting (FACS).

Freshly isolated neutrophils were then added to the differentiated airway epithelial cells, followed by infection with SARS-CoV-2 for a total of 4 hours. Along with these experiments, the researchers also performed immunohistochemistry of the primary human lung tissues obtained from severe COVID-19 patients.

Study findings
The analysis of the lung pathologies of COVID-19 patients confirmed the extensive infiltration of inflammatory cells, including neutrophils. More specifically, these post-mortem samples were found to have increased neutrophil elastase (NE) activity as compared to the neutrophils that were identified in healthy lung tissues. High neutrophil invasion and epithelial shedding were also observed, which suggested that neutrophils play an important role in SARS-CoV-2 infection.

The peripheral blood samples of COVID-19 patients also showed higher concentrations of pro-inflammatory cytokines that disrupt epithelial permeability in patients with severe disease.