In severe cases of COVID-19 disease, not only classic immune cells play a role.
In a new study, researchers found that the release of immature precursor cells from the bone marrow into the blood shows a particularly severe course of the disease and could contribute to COVID-19 complications.
The research was conducted by a team at Kiel University and elsewhere.
While many infections with the COVID-19 virus are mild or even asymptomatic, the disease can become life-threatening, especially in older people.
In these severe cases, other organs such as the heart or kidneys can be affected in addition to the lung.
Previous studies have found that damage to small blood vessels and over-activated blood clotting are decisive factors for a severe course.
One of the most common direct causes of death from COVID-19 is blood clots in the lungs.
Despite numerous studies, researchers actually know relatively little about the course of the disease over time.
In the study, the team examined blood samples from COVID-19 patients who were hospitalized at the university hospitals in Kiel, Bonn, Cologne, and Nijmegen.
In a group of 14 patients, circulating blood cells were analyzed in a time series. Blood samples from healthy people were used as a comparison.
They were able to analyze hundreds of thousands of cells in parallel with the help of so-called single-cell genomics and were thus able to identify rare cell types.
Together with other data, they were able to create a kind of fingerprint, a signature, of the altered functioning of these cells and track it over time.
The team found signatures of two immature cell types are particularly characteristic of severe COVID-19 disease: platelet precursor cells, so-called megakaryocytes, and immature red blood cells.
The scientists gained important insights from a group of 39 COVID-19 patients who had been treated in the intensive care unit in Nijmegen, i.e. had particularly severe courses of disease.
In this group of patients, a signature of the megakaryocytes and red blood cell progenitor cells was particularly strong in patients who died of the disease compared to patients who recovered.
The megakaryocytes reflect a well-known COVID-19 problem: blood platelets are responsible for blood coagulation. One of the most common direct causes of death from COVID-19 is coagulation problems.
The emergency-activated megakaryocytes in the blood may produce platelets that aggregate more easily and thus lead to coagulation problems, the team says.
The increase in red blood cell progenitor cells indicates a lack of oxygen and is known as an emergency reaction in severe lung diseases.
With the present work, the researchers have now created the basis for validating novel biomarkers at an early stage of COVID-19 disease to identify patients at risk for a severe course of the disease.
This would enable them to improve the care of particularly severely affected patients even more strongly.
One author of the study is Professor Philip Rosenstiel.
The study is published in the journal Immunity.
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