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By IANS 
3h ago
In a new study by researchers at the Karolinska Institutet in Sweden, it has been described how different types of immune cells, called macrophages, develop in the lungs and which of them may be behind severe lung disease.
The study, which was published in Immunity, may contribute to future treatments for Covid-19, among other diseases.
The structure of the lungs exposes them to viruses and bacteria from both the air and the blood. Macrophages are immune cells that, among other things, protect the lungs from such attacks.
But under certain conditions, lung macrophages can also contribute to serious lung diseases, such as chronic obstructive pulmonary disease (COPD) and Covid-19.
To date, research on the development of human lung macrophages has been limited.
Macrophages can have different origins and develop, among other things, from white blood cells, monocytes, which are divided into different main genetically determined types. In humans, two of these are “classical” CD14 + monocytes and “non-classical” CD16 + monocytes.
In a new study at the Karolinska Institutet, researchers have used a model to study the development of pulmonary macrophages directly in a living lung.
This has been combined with a method to study gene activity in individual cells, RNA sequencing, and thus it has been discovered how blood monocytes turn into human lung macrophages.
“In our study, we showed that classical monocytes migrate into the airways and lung tissue and become macrophages that protect the health and function of the lungs.
“We have also identified a special type of monocyte, HLA-DRhi, which is an intermediate immune cell between a blood monocyte and a macrophage in the airways.
“These HLA-DRhi monocytes can leave the bloodstream and migrate into the lung tissue,” says Tim Willinger, associate professor at the Department of Medicine, Huddinge, Karolinska Institutet, who led the study.
Nonclassic monocytes, however, become macrophages in the many blood vessels of the lungs and do not migrate into lung tissue.
“Certain macrophages in the lungs probably have a connection to a number of serious lung diseases.
“In respiratory infections, for example, monocytes in the lungs turn into macrophages, which fight viruses and bacteria. But certain types of macrophages can also contribute to inflammation and serious infections, “says study first author Elza Evren, a doctoral student on Tim Willinger’s research team.
In an infection with the new coronavirus, SARS-COV-2, which causes Covid-19, researchers believe that protective anti-inflammatory macrophages are replaced by pro-inflammatory lung macrophages from blood monocytes.
“It has been shown in other studies that the existence of these macrophages derived from blood monocytes correlates with the severity of a person’s illness with Covid-19 and the extent of damage to the lungs.
“Patients with severe COVID-19 also have fewer HLA-DRhi monocytes in their blood, probably because they move from the blood to the lungs.
Given their important role in rapid inflammatory responses, our results indicate that future treatments should target inflammatory macrophages and monocytes to reduce lung damage and severe Cövid-19 mortality, “says Tim Willinger.
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