When a person contracts a viral infection, the immune system releases proteins called antibodies to disable the virus. Once attached to viral particles, immune cells can finish the job. But during a new infection, plasmablasts take early actions to produce antibodies against this unknown virus. After the infection, plasmablasts retreat to let other cells do long-term duties. The memory B cells patrol the whole body for reinfection while bone marrow plasma cells (BMPCs) hide within bones and spill out antibodies for years.
“A plasma cell is our life history, in terms of the pathogens we’ve been exposed to,” said study’s lead author Ali Ellebey, Washington University in St. Louis, Missouri. The team believed that SARS-CoV-2 could trigger the creation of BMPCs since almost all viral infections do. Yet certain studies indicated that severe COVID-19 may disrupt the formation of these cells. That was one reason why scientists got warried about long-term immunity. Disrupted BMPC formation might point at short-term immunity from natural infection or even vaccination.
To better understand, researchers tracked 77 people who recovered from mild COVID-19. They analyzed antibodies from these individuals for reactivity against the coronavirus. Results showed that SARS-CoV-2 neutralizing antibodies dropped four months after infection. However, the decline was slow and even 11 months after infection, tests could still detect these antibodies capable of recognizing the coronavirus’ spike protein. To find out the source of these antibodies, researchers collected memory B cells and bone marrow from a subset of participants. Samples showed that even seven months following the onset of symptoms, their memory B cells remained adept at recognizing SARS-CoV-2. Of 18 bone marrow samples, 15 had ultra-low, detectable BMPCs formed by COVID-19 7 to 8 months prior. In 5 people who gave additional bone marrow samples, the BMPC levels were stable several months later. The findings demonstrated that mild COVID-19 could induce neutralizing antibodies. These antibodies could last for months or even a lifetime with the help of BMPCs.
A study, posted online at BioRxiv, a site for biology research, found that these so-called memory B cells continue to mature and strengthen for at least 12 months after the initial infection (2). Of course, this study is propagandistic, trying to convince us that those infected with COVID-19 need to be vaccinated.
“The papers are consistent with the growing body of literature that suggests that immunity elicited by infection and vaccination for SARS-CoV-2 appears to be long-lived,” said Scott Hensley, an immunologist at the University of Pennsylvania who was not involved in the research. The studies may soothe fears that immunity to the virus is transient, as is the case with coronaviruses that cause common colds. But those viruses change significantly every few years, Dr. Hensley said. “The reason we get infected with common coronaviruses repetitively throughout life might have much more to do with variation of these viruses rather than immunity,” he said (3).
Upon first encountering a virus, B cells rapidly proliferate and produce antibodies in large amounts. Once the acute infection is resolved, a small number of the cells take up residence in the bone marrow, steadily pumping out modest levels of antibodies.
To look at memory B cells specific to the new coronavirus, researchers led by Ali Ellebedy of Washington University in St. Louis analyzed blood from 77 people at three-month intervals, starting about a month after their infection with the coronavirus. Only six of the 77 had been hospitalized for Covid-19; the rest had mild symptoms.
Antibody levels in these individuals dropped rapidly four months after infection and continued to decline slowly for months afterward — results that are in line with those from other studies.
Some scientists have interpreted this decrease as a sign of waning immunity, but it is exactly what’s expected, other experts said. If blood contained high quantities of antibodies to every pathogen the body had ever encountered, it would quickly transform into a thick sludge.
Instead, blood levels of antibodies fall sharply following acute infection, while memory B cells remain quiescent in the bone marrow, ready to take action when needed.
Our immune systems include B cells, which are a type of white blood cell (WBC) responsible for humoral immunity. They originate and mature in the bone marrow, then migrate to the spleen and lymph nodes. B cells become activated in response to an antigen, a virus, or bacterium. B cells have receptors on their surface that can bind to these pathogens. With help from the T cells, another component of the immune system, the B cells will differentiate into plasma cells to produce antibodies that will trap the virus or bacterium invader and allow other cells (macrophages) to destroy the invader. After infection, the “memory” B cells stay around, so if that same virus or bacterium invades again, the immune system “remembers” and reactivates to fight it off.
- Turner, J.S., Kim, W., Kalaidina, E. et al. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Nature, 2021. https://www.nature.com/articles/s41586-021-03647-4
- Wang Z, Muecksch F, Schaefer-Babajew D, et al. Vaccination boosts naturally enhanced neutralizing breadth to SARS-CoV-2 one year after infection. bioRxiv. May 09, 2021. https://www.biorxiv.org/content/10.1101/2021.05.07.443175v1.abstract
- Mandavilli A. Immunity to the Coronavirus May Persist for Years, Scientists Find. The New York Times. May 26, 2021. https://www.nytimes.com/2021/05/26/health/coronavirus-immunity-vaccines.html
Doctor of Naturopathy-Nutritionist-Author
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