免疫学：体はどのようにしてSARS-CoV-2を「記憶」しているのか

Immunity to SARS-CoV-2 infection may last at least six months, according to a study published online in Nature. An analysis of 87 individuals who had been infected with SARS-CoV-2 reveals that levels of specific memory B cells — immune cells that remain in the body after infection and can rapidly proliferate and generate antibodies against SARS-CoV-2 upon reinfection — remained constant over the study period. The findings suggest that individuals who have previously been infected with SARS-CoV-2 can potentially mount a fast and effective response to the virus upon re-exposure.

The human immune system responds to infection by producing antibodies that can specifically neutralize the infectious agent. Human antibodies against SARS-CoV-2 have been shown to protect against infection in animal models. Levels of these antibodies may decrease over time, but memory B cells, as their name suggests, ‘remember’ the infectious agent and can prompt the immune system to produce the same antibodies upon reinfection.

Michel Nussenzweig and colleagues assessed 87 people with a confirmed diagnosis of COVID-19 at 1.3 and 6.2 months after infection with SARS-CoV-2. They found that although neutralizing antibody activity decreases with time, the number of memory B cells remains unchanged. Moreover, the authors show that the antibodies produced by these cells are more potent than the original antibodies, and may be more resistant to mutations in the spike protein of the virus that mediates cell entry.

These observations demonstrate that memory B cells have the capacity to evolve in the presence of small amounts of persistent viral antigen (small proteins from the virus that can be detected by the immune system). The continued presence and evolution of memory B cells suggests that people may be able to rapidly produce potent virus-neutralizing antibodies upon reinfection with SARS-CoV-2, the authors conclude.