In a new study, researchers may have come one step closer toward understanding how the immune system contributes to severe COVID-19.
They found that so-called natural killer (NK) cells were strongly activated early after SARS-CoV-2 infection but that the type of activation differed in patients with moderate and severe COVID-19.
The discovery contributes to our understanding of the development of hyper-inflammation in some patients.
The research was conducted by a team at Karolinska Institutet in Sweden and elsewhere.
SARS-CoV-2 infection can in some cases cause severe COVID-19 disease.
Although this is thought to be partially driven by a misdirected innate immune response, many aspects of the early immune response to the infection remain elusive.
In the study, the team examined the early response to SARS-CoV-2 infection of NK cells, a cell type in the immune system known to be important in the control of viral infections.
They analyzed blood samples from 27 patients with moderate (10) and severe (17) COVID-19 infection.
The researchers also included blood samples from 17 healthy individuals as a control group. The result showed that NK cells were strongly activated in the blood shortly after infection.
They found the type of NK cell activation detected differed considerably in patients with moderate compared to severe disease.
It is likely that the type of NK cell response observed in SARS-CoV-2 infected patients with the moderate disease is a canonical NK cell response shared between many types of viral infections, according to the researchers.
However, patients who developed severe COVID-19 had a different composition of responding to NK cells.
The researchers are now testing to what extent the NK cell-mediated immune response observed in the critically ill patients might contribute to COVID-19 severity and the extent to which other parts of the response may be beneficial.
The study is part of the larger Karolinska COVID-19 Immune Atlas project, which aims to increase knowledge about the characteristics of immune cells in patients with COVID-19.
One author of the study is Niklas Björkström, a physician and immunology researcher.
The study is published in Science Immunology.
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