A new study carried out by researchers at Karolinska Institutet in Sweden has revealed that immune cells in the lungs can contribute to exacerbating a virus attack.
The study, published in the journal Immunity, described how different kinds of immune cells, called macrophages, develop in the lungs and which of them may be behind severe lung diseases.
According to the study, the structure of the lungs exposes them to viruses and bacteria from both air and blood. Macrophages are immune cells that, among other things, protect the lungs from such attacks.
However, under certain conditions, lung macrophages can also contribute to severe lung diseases. This includes chronic obstructive pulmonary disease (COPD) and Covid-19.
Lead author Tim Willinger, Associate Professor at the Department of Medicine, Huddinge, Karolinska Institutet, said: “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.”
He added: “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 non-classical monocytes, however, develop into macrophages in the many blood vessels of the lungs and do not migrate into the lung tissue.
The study’s first author Elza Evren, a doctoral student in Tim Willinger’s research team, said in a statement: “Certain macrophages in the lungs probably have a connection to a number of severe lung diseases.”
She added: “In respiratory infections, for example, monocytes in the lungs develop into macrophages, which combat viruses and bacteria. But a certain type of macrophage may also contribute to severe inflammation and infections.”
The researchers speculated that protective, anti-inflammatory macrophages are replaced by pro-inflammatory lung macrophages from blood monocytes during the Covid-19 infection.
“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,” concluded Tim Willinger.