Study shows MAIT cells highly engaged in the immunological response to COVID-19

A type of anti-bacterial T cell, called mucosa-associated invariant T cells (MAIT cells), are strongly activated in people with moderate to severe COVID-19 disease, according to a new study. The research was conducted at Karolinska Institutet, Sweden.

According to the researchers, these findings contribute to increased understanding about how the immune system responds against COVID-19 infection.

“To find potential treatments against COVID-19, it is important to understand in detail how our immune system reacts and, in some cases, perhaps contribute to worsening the disease,” said Professor Johan Sandberg, the study’s corresponding author.

The team 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 the researchers say 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.

“Taken together, these analyses indicate that the reduced number of MAIT cells in the blood of COVID-19 patients is at least partly due increased accumulation in the airways,” said Sandberg.

In convalescent patients, the number of MAIT cells in the blood recovered at least partially in the weeks after disease, which can be important for managing bacterial infections in individuals who have had COVID-19, according to the researchers. In the patients who died, the researchers noted that the MAIT cells tended to be extremely activated with lower expression of the receptor CXCR3 than in those who survived.

“The findings of our study show that the MAIT cells are highly engaged in the immunological response against COVID-19,” said Sandberg. “A likely interpretation is that the characteristics of MAIT cells make them engaged early on in both the systemic immune response and in the local immune response in the airways to which they are recruited from the blood by inflammatory signals. There, they are likely to contribute to the fast, innate immune response against the virus. In some people with COVID-19, the activation of MAIT cells becomes excessive and this correlates with severe disease.”

The findings were published in Science Immunology.