In Covid-19 and many other diseases caused by virus attacks, immune cells in the lungs can contribute to worsening the attack.
Researchers have described how different kinds of immune cells develop in the lungs, and which of them may be behind severe lung diseases.
The structure of the lungs exposes them to viruses and bacteria from both the air and the blood. The study looked at the role of certain immune cells, called macrophages, during a virus attack.
Macrophages are immune cells that protect the lungs from such attacks. But under certain conditions, lung macrophages can also contribute to severe lung diseases, such as COPD and Covid-19.
Researchers used a model to study the development of lung macrophages directly in a living lung. They combined this with another method to study RNA sequencing and discovered how blood monocytes become human lung macrophages.
Researchers identified a special kind of monocyte, HLA-DRhi, which is an intermediate immune cell between a blood monocyte and an airway macrophage. These HLA-DRhi monocytes can leave the blood circulation and migrate into the lung tissue.
In an infection with the novel coronavirus SARS-CoV-2, researchers believe that protective, anti-inflammatory macrophages are replaced with pro-inflammatory lung macrophages from blood monocytes.
Patients with severe Covid-19 also have fewer HLA-DRhi monocytes in their blood, probably because they move away from the blood into the lungs.
Given their important role in rapid inflammatory responses, the results indicate that future treatments should focus on inflammatory macrophages and monocytes to reduce lung damage and mortality from severe COVID-19.