According to researchers from the Karolinska Institutet in Sweden, immune cells in the lungs can contribute to aggravating serious lung diseases such as Covid-19.
- Researchers demonstrate that immune cells derived from blood monocytes can migrate into the lungs and aggravate certain viral diseases such as Covid-19.
How to explain that in the event of a viral attack, the lungs are the organs most often affected? In a study published in the journal Immunityresearchers from the Karolinska Institutet (Sweden) offer an answer: it is macrophages that contribute to aggravating viral diseases.
Key elements of the immune system, macrophages are cells belonging to white blood cells, monocytes, which infiltrate tissues, and whose role is to phagocytose cellular debris and pathogens. In humans, two of them are “classical” CD14+ monocytes and “non-classical” CD16+ monocytes.
Supposed to protect the lungs against viral attacks, these monocytes can however, under certain conditions, contribute to the aggravation of lung diseases, such as chronic obstructive pulmonary disease (COPD) and Covid-19.
Pro-inflammatory macrophages in the lungs
To understand how macrophages can worsen a viral pathology, the researchers used a model to study the development of lung macrophages directly in a living lung. This model was combined with a method for studying gene activity in individual cells, RNA sequencing. Thanks to him, researchers have discovered how blood monocytes become human lung macrophages.
“In our study, we show that classical monocytes migrate through the airways and lung tissue and are converted into macrophages that protect lung health and function. 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 respiratory tract. These HLA-DRhi monocytes can leave the bloodstream and migrate into the lung tissue.”details Tim Willinger, professor at the Karolinska Institutet and director of the study.
However, nonclassical monocytes develop into macrophages in the many blood vessels of the lungs and do not migrate into lung tissue. They are the ones according to the researchers who can contribute to the aggravation of lung diseases.
In the case of infection with SARS-COV-2, which causes Covid-19, researchers believe, for example, that protective and anti-inflammatory macrophages are replaced by pro-inflammatory lung macrophages from blood monocytes.
“The existence of these blood monocyte-derived macrophages has been shown in other studies to correlate with the severity of a person’s illness with Covid-19 and the extent of damage to the lungs. Patients people with a severe form of Covid-19 also have fewer HLA-DRhi monocytes in their blood, probably because they move away from the blood to go to the lungs”, advance Tim Willinger, co-author of the work.
“Given their important role in rapid inflammatory responses, our results indicate that future treatments should focus on inflammatory macrophages and monocytes to reduce lung injury and mortality from severe forms of Covid-19,” concludes the researcher.
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