Researchers from Skoltech, U.S. companies VirIntel and Argentys Informatics, and two Russian Academy of Sciences institutes have studied the immune response to in patients with different levels of disease severity. The team found that half of the patients without symptoms did not actually produce significant amounts of IgG antibodies of a kind targeted by many popular test kits. That said, nearly all patients produced another kind of antibodies, whose count was sometimes even higher in asymptomatic cases, leading the researchers to suggest the ratio between the two counts as an indicator of disease severity. The study was published in the journal Viruses.
Blood tests for detecting prior infection with the coronavirus rely on antibodies called immunoglobulins G. IgGs usually develop a few weeks after infection and come in multiple varieties, depending on which part of the virus they attach to. Two common kinds are the antibodies targeting the nucleocapsid protein and the receptor-binding domain, or RBD, of the spike protein of the coronavirus. The recent Russian-U.S. study reports the levels of these two antibodies in patients at various times following recovery from COVID-19. It accounts for mild and asymptomatic cases, as well as serious ones.
“Our main finding is that asymptomatic COVID-19 patients often have no IgG antibodies to an internal component of the virus known as the nucleocapsid protein. Yet tests detecting that very kind of antibodies are often recommended to check whether someone has had COVID-19,” commented the study’s first author Maria Tutukina of Skoltech, the Institute of Cell Biophysics and the Institute for Information Transmission Problems of RAS.
“But regardless of disease severity, every patient we tested but one exhibited IgG antibodies to the RBD of the spike protein, which is located on the surface of the viral particle,” said study co-author Anna Kaznadzey of IITP RAS and VirIntel.
The researchers say it might therefore be more reasonable to check the level of antibodies to RBD to determine if a person has had the infection.
But why would it ever be the case that someone has IgGs to RBD but not to the nucleocapsid protein? This might have to do with whether the antibody in question targets the inside or the outside of the virus particle.
The team hypothesizes… Brinkwire News Summary.