Antibodies against Covid-19 preferentially target a different part of the virus in mild cases and a different part in severe cases, according to a new study by researchers at Stanford Medicine. The study is published in the journal Science Immunology.
SARS-CoV-2 binds to human cells via a structure on its surface called the spike protein. Once inside, the virus sheds its outer coat to reveal an inner shell encasing its genetic material. Soon, the virus created multiple copies of itself, which are then released to infect other cells.
Antibodies that recognise and bind to the spike protein block its ability to bind to the human cell, preventing infection. On the other hand, antibodies that target other viral components are unlikely to prevent viral spread.
The researchers studied 254 people with asymptomatic, mild or severe Covid-19. Twenty-five people in the study died of the disease. They found that people with severe Covid-19 have a lower proportion of antibodies targeting the spike protein used by the virus to enter human cells than of antibodies targeting proteins of the virus’s inner shell.
The research analysed the levels of three types of antibodies — IgG, IgM and IgA — and the proportions that targeted the viral spike protein or the virus’s inner shell as the disease progressed and patients either recovered or grew sicker. They also measured the levels of viral genetic material in nasal samples and blood from the patients. Finally, they assessed the effectiveness of the antibodies in preventing the spike protein from binding to the human protein ACE2 in a laboratory dish.
“We found that the severity of the illness correlates with the ratio of antibodies recognising domains of the spike protein compared with other non-protective viral targets. Those people with mild illness tended to have a higher proportion of anti-spike antibodies, and those who died from their disease had more antibodies that recognized other parts of the virus,” Stanford Medicine quoted pathologist Boyd as saying.
The findings raise concerns about whether people can be re-infected, whether antibody tests to detect prior infection may underestimate the breadth of the pandemic and whether vaccinations may need to be repeated at regular intervals to maintain a protective immune response, Stanford Medicine said in a media release.
“This is one of the most comprehensive studies to date of the antibody immune response to SARS-CoV-2 in people across the entire spectrum of disease severity, from asymptomatic to fatal. We assessed multiple time points and sample types, and also analysed levels of viral RNA in patient nasopharyngeal swabs and blood samples. It’s one of the first big-picture looks at this illness,” Boyd was quoted as saying.
Source: Stanford Medicine
📣 The Indian Express is now on Telegram. Click here to join our channel (@indianexpress) and stay updated with the latest headlines