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New insight into NK cells’ reaction to COVID-19

Quirin Hammer

An international team of scientist led by researchers from Karolinska Institutet shows that natural killer (NK) cells respond to a certain peptide on the surface of infected cells.

The study, published in Cell Reports, is an important piece of the puzzle in our understanding of how the immune system reacts to COVID-19, state the researchers.

An important piece of the puzzle

The study shows why certain NK cells are activated when encountering a cell infected with SARS-CoV-2. The infected cells contain a peptide from the virus that triggers a reaction in NK cells that carry a particular receptor, NKG2A, able to detect the peptide.

“Our study shows that SARS-CoV-2 contains a peptide that is displayed by molecules on the cell surface,” says Quirin Hammer, researcher at the Center for Infectious Medicine (CIM), Karolinska Institutet. “The activation of NK cells is a complex reaction, and here the peptide blocks the inhibition of the NK cells, which allows them to be activated. This new knowledge is an important piece of the puzzle in our understanding of how our immune system reacts in the presence of this viral infection.”

“These findings are important to our understanding of how immune cells recognize cells infected with SARS-CoV-2,” adds Hammer. “This may become significant when monitoring new virus variants with the aim to determine how well the immune system responds to them.”

Researchers from Sweden, Italy, Norway, Germany and the US

The study was a major collaboration between Karolinska Institutet, Karolinska University Hospital and research laboratories and universities in Italy, Germany, Norway and the USA. The first phase was to test their hypothesis using computer simulations that were then confirmed in the laboratory. The decisive phase was the infection of human lung cells with SARS-CoV-2 in a controlled environment, whereupon the researchers could show that NK cells with the receptor in question are activated to a greater degree than the NK cells without it.

The study is now being followed up with the help of a biobank at Karolinska University Hospital and Karolinska Institutet containing blood samples from over 300 people treated for COVID-19 during the first wave of the pandemic.

“We’ll be examining if the composition of NK cells a person has contributes to how severe their symptoms are when infected with SARS-CoV-2,” continues Hammer.

Photo of Quirin Hammer, researcher at the Center for Infectious Medicine (CIM), Karolinska Institutet: Private