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Natural killer cell abnormality in patients with COVID-19

Published online: August 02, 2021

Many patients with COVID-19, which is caused by infection with SARS-CoV-2, recover spontaneously, complaining of only mild symptoms. However, other patients with this disease develop severe or critical disease. Natural killer (NK) cells are innate lymphocytes that exert antiviral functions by killing virus-infected cells and producing antiviral cytokines. Changes in the NK cell population have not yet been longitudinally elucidated in patients with COVID-19.

In a recent article in The Journal of Allergy and Clinical Immunology (JACI), Leem et al. describe how the NK cell population changes during the course of mild or severe COVID-19 by analyzing cryopreserved peripheral blood immune cells obtained from patients with COVID-19. They performed transcriptome and flow cytometric analyses to examine the molecular and functional characteristics of NK cells. In particular, they focused on changes in the proportions of NK cell subpopulations. They also directly assessed the cytotoxic activity of NK cells.

The authors reported that an unconventional NK cell population (CD56dimCD16neg) which is scarcely present in healthy controls or influenza patients, expanded in patients with COVID-19 regardless of the disease severity. In addition, they found that the expansion of unconventional NK cells is accompanied by decreased cytotoxic activity of NK cells, indicating decreased anti-viral functions of NK cells in patients with COVID-19. Though this abnormality in the NK cell population disappeared rapidly in patients with mild COVID-19, it persisted for 2 weeks in patients with severe COVID-19.

These findings show that NK cells undergo abnormal changes at the molecular and functional levels during COVID-19. These changes are more persistent in severe COVID-19 infections as opposed to mild infections. The implication of these changes in the course of the disease remain to be fully elucidated.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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