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Severe COVID-19 Linked to Myeloid Immune Cells in Blood

T cells are part of the immune system and play an important part in the body's protection against viral infections.

Investigators from the Karolinska Institutet in Sweden have discovered that patients with a severe case of the coronavirus disease 2019 (COVID-19) have significantly elevated levels of myeloid-derived suppressor immune cells (M-MDSCs) in their blood. The finding may lead to a more comprehensive understanding of how early responses from the immune system impacts disease severity. The study was published in the Journal of Clinical Investigation.

Investigators behind the study worked in collaboration with Karolinska University Hospital, Stemirna Therapeutics in Shanghai, and Stanford University to study the type M-MDSC immune cells and how they play a role in a COVID-19 infection.

The study had 147 participants who had a case of COVID-19 that ranged from mild to fatal. Repeat blood and respiratory tract samples were taken from them and compared to other patients with influenza, as well as healthy individuals.

Findings from the study showed that the patients who had a more severe infection with COVID-19 had significantly elevated levels of M-MDSCs in their blood when compared to those with milder cases and the healthy samples. Additionally, investigators found that the levels of the immune cell in the early course of the disease reflected the severity of the disease later on.

"Our results help increase the understanding of what causes severe COVID-19 and is an important piece of the puzzle in understanding the connection between the early, innate immune system, which includes M-MDSC, and the later, adaptive immune system, which includes T cells,” Anna Smed Sorensen, first author on the study and an associate professor at the Department of Medicine, Solna, Karolinska Institutet said. “There is also a strong clinical connection, as you could potentially use the results to find new biomarkers for severe illness.”

While the study showed promising results, there were limitations that the authors noted, like the number of patients in the study and the amount of sample material that could be collected.

"The next step in our research is to further study the connection between different parts of the immune system, such as M-MDSC, T cells, and antibodies,” Sorensen said.