In a study published in Science Immunology, researchers at Karolinska Institutet in Sweden show that so-called natural killer (NK) cells were strongly activated early after SARS-CoV-2 infection but that the type of activation differed in patients with moderate and severe COVID-19. The discovery contributes to our understanding of development of hyperinflammation in some patients, MedicaXpress reported.

SARS-CoV-2 infection can in some cases cause severe COVID-19 disease. Although this is thought to be partially driven by a misdirected innate immune response, many aspects of the early immune response to the infection remain elusive.

Researchers at Karolinska Institutet have now, in collaboration with colleagues at the Karolinska University Hospital, investigated the early response to SARS-CoV-2 infection of NK cells, a cell type in the immune system known to be important in the control of viral infections.

The study analyzed blood samples from 27 patients with moderate (10) and severe (17) COVID-19 infection. The researchers also included blood samples from 17 healthy individuals as a control group. The result showed that NK cells were strongly activated in the blood shortly after infection.

“The type of NK cell activation detected differed considerably in patients with moderate compared to severe disease,” says Niklas Björkström, physician and immunology researcher at the Center for Infectious Medicine, Department of Medicine Huddinge, at Karolinska Institutet, who led the study.

It is likely that the type of NK cell response observed in SARS-CoV-2 infected patients with moderate disease is a canonical NK cell response shared between many types of viral infections, according to the researchers.

However, patients who developed severe COVID-19 had a different composition of responding NK cells. These patients’ NK cells generally had higher expression of the proteins perforin, NKG2C and Ksp37, which according to the researchers reflect a high presence of so-called adaptive NK cells. Adaptive NK cells have an even greater ability to kill target cells compared to other NK cells.

The researchers are now investigating to what extent the NK cell-mediated immune response observed in the critically ill patients might contribute to COVID-19 severity, and the extent to which other parts of the response may be beneficial.

“Taken together, our findings provide additional insights into immune reactions in early SARS-CoV-2 infection and ensuing COVID-19 disease,” Niklas Björkström says. “We hope that these insights will contribute to the improved care and treatment of patients with severe COVID-19 disease.”

The study is part of the larger Karolinska COVID-19 Immune Atlas project, which aims to increase knowledge about the characteristics of immune cells in patients with COVID-19.

The studies, which have yet to be peer-reviewed, uncovered that antibodies and immune cells capable of recognizing the coronavirus were apparently present months after mild infection concluded. The findings could help to eliminate the previous concerns over whether the virus could trick the immune system into having a poor memory of prior infections, Fox reported.

While scientists have yet to forecast how long the immune responses will last, researchers who have been monitoring immune responses to the virus for months now, believe the recent findings are encouraging signs.

Having those defense mechanisms present means the body has a good chance of fending off the coronavirus if reinfected.

“This is very promising,” said Smita Iyer, an immunologist at the University of California. “This calls for some optimism about herd immunity, and potentially a vaccine.”

“This is exactly what you would hope for,” said Marion Pepper, an immunologist at the University of Washington and an author on another of the new studies, which is currently under review at the journal Nature. “All the pieces are there to have a totally protective immune response.”

Protection against reinfection cannot be fully confirmed until there is proof that most people who encounter the virus a second time are actually able to keep it at bay, Dr. Pepper said. But the findings could help quell recent concerns over the virus’s ability to dupe the immune system into amnesia, leaving people vulnerable to repeat bouts of disease.

“Recent national surveillance data show that Canadians aged 20-39 years of age account for the highest incidence rates of COVID-19 across all ages,” Canada’s chief public health officer Theresa Tam said in a statement, AFP reported.

For the week ending July 22, the incidence rate was highest among young men and women aged 20-29 (14.4 and 13.8 cases per 100,000 people respectively), followed by those aged 30-39.

“Younger Canadians are not invincible” to the disease, Tam warned, noting that it is not only the elderly who are at risk of serious health problems if infected.

She pointed out that, of the cases of COVID-19 reported to public health last week, 63 percent involved people under 39 years of age, of whom roughly one-third were hospitalized.

There was an average of 485 new cases reported daily across the country last week.

As Canada continues to lift lockdown restrictions, Tam called on fellow citizens to be cautious and to respect social distancing and hygiene measures.

“In the absence of a vaccine, living with COVID-19 is not without risk,” she added.

According to the latest available figures, Canada has so far recorded some 113,800 cases of the new coronavirus and 8,900 deaths.