Study sheds light on new research that may explain severe virus attacks on lungs
How different kinds of immune cells, called macrophages, develop in the lungs and which of them may be behind severe lung diseases, has been described in a new study by researchers at Karolinska Institutet in Sweden.
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
severe 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, that are divided into different
genetically determined main types. In humans, two of these are
“classical” CD14+ monocytes and “non-classical” CD16+ monocytes.
In a new study at Karolinska Institutet, researchers have used a model
to study the development of lung macrophages directly in a living lung.
This has been combined with a method to study gene activity in
individual cells, RNA sequencing, and thereby discovered how blood
monocytes become human lung macrophages.
“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,” says Tim Willinger, Associate Professor
at the Department of Medicine, Huddinge, Karolinska Institutet, who led
the study.
The non-classical monocytes, however, develop into macrophages in the
many blood vessels of the lungs and do not migrate into the lung tissue.
“Certain macrophages in the lungs probably have a connection to a number
of severe lung diseases. 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,” says the study’s first author Elza Evren, a
doctoral student in Tim Willinger’s research team.