In Covid-19 and many other disease caused by virus attacks, immune cells in the lungs can contribute to worsening the attack. In a new study, researchers at Karolinska Institutet describe 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 what happens to certain immune cells, called macrophages, during a virus attack. Macrophages are immune cells that, among other things, 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.
The Karolinska Institutet researchers have used a model to study the development of lung macrophages directly in a living lung. Combining this with a method to study RNA sequencing, they discovered how blood monocytes become human lung macrophages, the Karolinska Institutet said in a statement.
“In our study, we show that classical monocytes migrate into airways and lung tissue and are converted into macrophages that protect the health and function of the lungs. We have also 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,” the institute quoted lead researcher Tim Willinger as saying.
The non-classical monocytes, however, develop into macrophages in the many blood vessels of the lungs and do not 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.
“The existence of these blood monocyte-derived macrophages has been shown in other studies to correlate with how severely ill a person becomes in Covid-19 and how extensive the damage to the lungs is. 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, our results indicate that future treatments should focus on inflammatory macrophages and monocytes to reduce lung damage and mortality from severe COVID-19,” Willinger was quoted as saying.
The study was published in the journal Immunity on December 30.
Source: Karolinska Institutet
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