Innate immune system overreacts in severe COVID-19 patients

In patients with severe cases of the novel coronavirus (COVID-19), the innate immune system overreacts, which may underlie the formation of blood clots and deterioration in oxygen saturation that affect the patients, according to a new study in the journal Frontiers in Immunology.

For the study, researchers from Uppsala University studied 66 hospital inpatients with severe COVID-19 who were receiving care in the intensive care unit, and found pronounced activation of the innate immune system (IIIS).

Blood contains numerous proteins that constitute the body's primary barrier, by both recognizing and destroying microorganisms, including SARS-CoV-2, the virus that causes COVID-19. These proteins are part of the IIIS, which consists of certain white blood cells, platelets and what are known as the cascade systems of the blood, the researchers said.

Only 5 percent of present-day animal species have an immune system that includes T cells and B cells, while the rest rely solely on the natural immune system, which consists largely of the IIIS, according to the study. With its innate ability to recognize and eliminate foreign substances and particles, such as microorganisms and damaged cells, the IIIS serves as a kind of waste disposal system.

The degree of activation is, the researchers said, connected with survival and lung function. The new findings support the notion that the IIIS is among the drivers of severe COVID-19. One explanation why the IIIS acts in this way in some patients with COVID-19 may be that the cell damage is so extensive that the IIIS overreacts and, rather than helping to clean out the tissue, makes matters worse, the researchers said.

If the IIIS plays the part that the scientists suspect, the researchers said it might be possible to use therapies for hereditary angioedema to treat severe COVID-19.

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