Researchers from Korea Advanced Institute of Science and Technology (KAIST) and Chungnam National University Hospital (CNUH) have found that the antiviral function of natural killer (NK) cells weakens in Covid-19 patients.
According to the team, led by Professors Shin Eui-chul of the College of Medicine at KAIST and Kim Yeon-sook and Cheon Shin-hye at CHUH, such functional changes of the NK cells disappear within a week in mild Covid-19 patients but persist for a long time in severe patients.
“When a patient tests positive with a virus, an innate immune response appears primarily against it,” KAIST said in a press release Tuesday. “At this time, the main cells responsible for the antiviral innate immune response are NK cells, and most of these NK cells are cytotoxic NK cells that directly kill virus-infected cells.”
While there have been reports that the number or function of these cytotoxic NK cells reduce in Covid-19 patients, there has been no clarification on the specific change or mechanism of function reduction of NK cells, the team added.
The researchers conducted a follow-up study of Korean Covid-19 patients from the initial diagnosis to recovery to identify the exact mechanism and function. In addition, they identified the changes in NK cells according to the course of the disease in the Covid-19 virus infection.
The team also revealed the differences in the characteristics and functions of NK cells in severe and mild patients. As a result, the team discovered atypical NK cells characteristic of only Covid-19 patients but not in normal people or flu patients and revealed that these atypical NK cells have a reduced cytotoxic function than normal NK cells.
“We found that these atypical NK cells rapidly increase in the early stages of disease in patients infected with the Corona 19 virus, regardless of the severity of the disease, and this weakens the innate immune response of the patients,” the research team said.
In addition, the team confirmed that the heightened state of these atypical NK cells persisted for a longer period in severe Covid-19 patients.
“The study has found that atypical NK cells are characteristically increased in Covid-19 virus infection,” said Doctor Im Ga-ram, a researcher at KAIST and the lead author of the study. “These NK cell changes, not seen in other respiratory viral infections, will serve as a clinical basis for understanding the clinical characteristics of Covid-19 virus infection and starting preemptive treatment at an early stage in critically ill patients.”