Corona: the role of plasma cells

• ofPamela Dörhöfer

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A US study on immunity after a corona infection shows: Not only the antibodies are decisive.

A research team from the USA has found long-lived plasma cells in the bone marrow of people who were infected with Covid-19. Together with B memory cells in the blood, these could prevent a disease in the event of renewed infection with Sars-CoV-2, suspect the scientists working with immunologist Ali Ellebedy from the Washington School of Medicine in St. Louis. The study was published in the journal “Nature”.

Antibody producers

The duration of immunity after infection is as central as it is a complicated issue with Corona. The fact is that in most people the antibody titers decrease after a certain period of time. The researchers working with Ellebedy also examined the B memory cells in the blood and the plasma cells in the bone marrow as additional “players”. According to the study, long-lived plasma cells are a “permanent and essential source” of protective antibodies. As a result, people who were previously ill have a “significantly lower risk of reinfection”.

Plasma cells are white blood cells made by B cells. This always happens when B cells are activated by invading pathogens. The initially formed plasmablasts then migrate to the bone marrow, where they can survive for many years. The task of the plasma cells is the massive production of antibodies when needed. A plasma cell can produce up to 10,000 antibody molecules per second and release them into the blood.

The researchers had accompanied 77 women and men who were infected with Covid-19 during the first wave, most of them mild. Their antibodies were measured every three months. The result: the titer decreased rapidly during the first four months and more gradually in the following seven months, but remained at a detectable level for eleven months after infection. However, these antibodies no longer came from the plasma cells that were formed during the acute infection, Ellebedy suspects that they were produced by long-lived plasma cells in the bone marrow. To test this, the researchers took two tissue samples from the bone marrow of those participants who had agreed to this unpleasant procedure. In most of them, the number of antibody-producing plasma cells had not decreased seven to eight months after the disease. In addition, B memory cells could be detected in the blood, which can quickly form new plasma cells again in the event of an infection. pam

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