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n this study, the researchers wanted to find out which role MAIT cells play in COVID-19 disease pathogenesis. They examined the presence and character of MAIT cells in blood samples from 24 patients admitted to Karolinska University Hospital with moderate to severe COVID-19 disease and compared these with blood samples from 14 healthy controls and 45 individuals who had recovered from COVID-19. Four of the patients died in the hospital.

The results show that the number of MAIT cells in the blood decline sharply in patients with moderate or severe COVID-19 and that the remaining cells in circulation are highly activated, which suggests they are engaged in the immune response against SARS-CoV-2. This pattern of reduced number and activation in the blood is stronger for MAIT cells than for other T cells. The researchers also noted that pro-inflammatory MAIT cells accumulated in the airways of COVID-19 patients to a larger degree than in healthy people.

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