The blood of recovered COVID-19 patients contains antibodies that act against the coronavirus. While plasma has not yet shown any benefit in randomized trials, some small retrospective studies suggest that it may reduce the severity of the disease and shorten hospital stay.
This week in mBioResearchers, an open access journal from the American Society for Microbiology, report that antibody levels in the blood of COVID-19 patients drop rapidly in the weeks after their bodies clears the virus and symptoms have subsided. Ultimately, if convalescent plasma is found to have a clear benefit, the authors say, it must be collected during a specific time window after recovery. However, convalescent patients cannot donate blood for at least 14 days after symptoms have subsided to give the body time to remove virus particles.
“We don’t want to transfuse the virus, just the antibodies,” said Dr. Andrés Finzi from the University of Montreal in Canada. “At the same time, our work shows that the ability of the plasma to neutralize virus particles decreases in these first few weeks.”
The SARS-CoV-2 spike protein plays a critical role in the detection and invasion of the virus by host cells. Antibodies produced by the body’s immune system bind to part of this protein and block the ability of this “key” to contact the host’s cellular “barrier,” said Finzi, and prevent the virus particle from infecting a cell host.
Previous studies suggest that antibodies to the SARS-CoV-2 spike protein peak 2 or 3 weeks after symptoms appear. Results from a previous cross-sectional study by the Finzi group of more than 100 patients indicated that the ability of the plasma to neutralize the virus decreased significantly between 3 and 6 weeks after symptoms appeared.
In the new longitudinal study, Finzi and his colleagues analyzed blood samples from 31 people who had recovered from COVID-19 at one-month intervals. They measured the immunoglobulin levels that act against the coronavirus S protein and tested the antibodies’ ability to neutralize the virus.
The researchers observed differences in the concentration of individual patients, but identified a consistent overall signal: levels of immunoglobulins G, A, and M, which target the binding site, decreased between 6 and 10 weeks after symptoms began. During the same period, the ability of the antibodies to neutralize the virus similarly decreased.
Finzi’s group continued to examine blood samples from the patients. Understanding how antibody levels change over time is important not only to optimize the use of convalescent plasma, but also to understand the effectiveness of the vaccine and to determine whether previously infected people are at risk of re-infection exists or not.
“How long do antibodies protect you?” He asked.
Finzi’s other research focuses on the immune response to human immunodeficiency virus (HIV), which is dramatically different from SARS-CoV-2.
Decrease in humoral reactions to SARS-CoV-2 spike in convalescent subjects. mBio, October 16, 2020.
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