Researchers may have come one step closer toward understanding how the immune system contributes to severe COVID-19. In a study published in Science Immunology, researchers at Karolinska Institutet in Sweden show 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 development of hyperinflammation in some patients.

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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.

Researchers at Karolinska Institutet have now, in collaboration with colleagues at the Karolinska University Hospital, investigated 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.