Possible mechanism identified for resistance to COVID-19 virus

TOKYO (Jiji Press) — A group of researchers at government-affiliated research institute Riken has identified a possible mechanism behind resistance to the COVID-19 virus seen in people who have been infected with seasonal coronaviruses causing the common cold.

Experiments showed that killer T cells with a memory of having removed cells infected with seasonal coronaviruses may also be responsible for resistance to the virus causing COVID-19, in a phenomenon called cross-reaction, the group said. The findings were published in the international scientific journal Communications Biology.

While it is not known what percentage of COVID-19 cases experience such cross-reaction, Shinichiro Fujii, leader of the group, said this cross-reaction might be one factor behind the fewer number of COVID-19 cases and smaller share of severe cases among Japanese people than among populations in Europe and the United States.

The findings may contribute to the development of therapies for people in whom vaccines do not increase antibodies, Fujii said.

When a virus enters the body, antibodies work to prevent the virus from invading cells first. If the virus breaks through the antibody defense and infects cells, killer T cells then come to destroy and remove those infected cells.

Infected cells have a protein called HLA on the surface. When HLA presents a part that serves as a mark of the virus as an antigenic determinant, or an epitope, to killer T cells, those cells react to the epitope and destroy the infected cells.

The Riken group, including senior researcher Kanako Shimizu, investigated whether the spike protein on the COVID-19 virus has a part or parts that can easily be presented as a mark by a type of HLA that many Japanese people have, and identified the one that can be most easily presented as a mark.