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The SARS-CoV-2 virus shares an important feature with some viruses that cause the common cold, and the structural similarity suggests that people with a history of the common cold may carry some immunity against SARS-CoV-2 infection, new evidence reveals.
Infection with SARS-CoV-2 also boosts production of memory B cells, long-lasting components of immune protection. Even though antibodies to SARS-CoV-2 tend to wane over time, these memory B cells lie in wait and could mount a quick defense should re-infection occur, researchers report in a study published online September 25 in the journal mBio, a publication of the American Society for Microbiology.
“Much of the discussion about our study has focused on our evidence that memory B cells generated by human infection with common cold coronaviruses are cross-reactive with SARS-CoV-2 and produce antibodies in response to SARS-CoV-2 infection,” senior coauthor Mark Sangster, PhD, told Medscape Medical News.
“Perhaps most importantly, these memory B cells recognize the conserved S2 region of the SARS-CoV-2 spike protein and produce anti-S2 antibodies,” said Sangster, research professor at the David H. Smith Center for Vaccine Biology and Immunology, University of Rochester Medical Center, Rochester, New York.
Just how much immune protection these anti-S2 antibodies confer against COVID-19, however, remains unknown.
Of the four endemic virus strains linked to the common cold, two are betacoronaviruses. Because SARS-CoV-2 is in the same family of viruses, researchers initially searched for shared key structural proteins. However, early studies did not yield evidence of substantial cross-reactivity.
More recently, however, multiple investigators report finding relevant B- and T-cell immunity in people without COVID-19 that could offer some degree of future protection against SARS-CoV-2.
Building on these findings, Sangster, senior coauthor David J. Topham, PhD, and colleagues compared 26 nonhospitalized, convalescent COVID-19 patients with a group of 20 healthcare workers without a COVID-19 diagnosis at Strong Memorial Hospital in Rochester and another cohort of 21 healthy adults assessed before the pandemic.
One link to the common cold viruses was the finding that immunoglobulin G or “IgG reactive to the S2 was widespread in unexposed subjects and likely resulted from exposure to human coronaviruses,” the researchers write.
This discovery could help explain the wide spectrum of COVID-19 severity, Sangster said. “The clearest and most important takeaway message from our work is that SARS-CoV-2 infection generates and/or expands memory B cell populations that recognize SARS-CoV-2 proteins.”
Memory B cells mediate the secondary antibody response that is characterized by rapid production of large amounts of high-affinity antiviral antibodies, Sangster said. “It is also well established that memory B-cell populations are maintained for many years, perhaps decades.”
“Our findings indicate that, even if SARS-CoV-2-reactive antibody levels wane after infection, people will still retain memory B-cell populations that will rapidly produce highly effective anti-SARS-CoV-2 antibodies if re-infection occurs,” he said.
Although memory B cells will not prevent re-infection, Sangster added, they could “greatly reduce the severity of a second infection, assuming that SARS-CoV-2 does not change antigenically like influenza virus.”
The findings also were noteworthy for what the researchers did not find among those without SARS-CoV-2 infection. For example, none of the uninfected people had immunoglobulin G specific to SARS-CoV-2.
“Ongoing research in our lab is aimed at characterizing cross-reactive memory B cells generated by common cold coronaviruses in greater detail,” coauthor Topham told Medscape Medical News.
The investigators want to evaluate the extent of protection afforded by the memory B cells, including if early levels correspond to later COVID-19 severity, for example, said Topham, also with the Smith Center for Vaccine Biology and Immunology at Rochester Medical Center.
“We also plan to measure memory B-cell generation by COVID-19 vaccines that are currently being developed and tested,” he said. “The generation of neutralizing antibodies is not the only way that vaccines provide protection.”
The current study is limited by its retrospective design, Andreas Thiel, MD, told Medscape Medical News when asked to comment on the research.
“To get clear answers, large prospective studies are needed. We discussed this in our paper,” said Thiel, senior author of a July 29 Nature study comparing SARS-CoV-2 reactive T cells between people with COVID-19 and healthy donors.
“The real picture will be seen in some time,” added Thiel, from Charité Medical University of Berlin and the Berlin-Brandenburg Center for Regenerative Therapies in Germany. “It could well be that it will take longer to conduct these studies and get solid results than to have a safe and efficient vaccine.”
Funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, and the Department of Health and Human Services partially supported the study. Sangster, Topham, and Thiel have disclosed no relevant financial relationships.
mBio. Published online September 25, 2020. Full text
Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and neurology. Follow Damian on Twitter: @MedReporter. For more news, follow Medscape on Facebook, Twitter, Instagram, and YouTube.