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Some of the severe respiratory symptoms of COVID-19 seem to result from the activity of specific immune cells, which can cause long-term inflammation of the lungs. Alexander Misharin at Northwestern University in Evanston, Illinois, and his colleagues examined fluid from the lungs of 88 people with severe pneumonia caused by SARS-CoV-2 infection (R. A. Grant et al. Nature https://doi.org/fqds; 2021). Most of these individuals had high numbers of a certain type of T cell, a class of immune cells, in their lungs. The researchers also found that nearly 70% of alveolar macrophages, a type of immune cell that is located in the tiny air sacs of the lungs, contained SARS-CoV-2. The cells harbouring the virus showed relatively high expression of genes involved in inflammation. The findings suggest that, once the virus reaches the lungs, it can infect macrophages, which respond by producing inflammatory molecules that attract T cells. T cells, in turn, produce a protein that stimulates macrophages to make more inflammatory molecules. This persistent lung inflammation could lead to some of the life-threatening consequences of SARS-CoV-2 infection.
Findings Published in Nature (Jan. 11, 2021):
