Edgar Meinl and his team show that SARS-CoV-2-recognizing memory B cells circulate in the blood even after the loss of specific antibodies.
In the third year of the COVID-19 pandemic, one of the central questions remains whether and how permanent immune protection can be achieved after an infection or vaccination.
In principle, the adaptive immune system can protect against re-infection or disease caused by the same pathogen. The effect of vaccinations is also based on this ability. The defense reaction requires the interaction of T cells, B cells and antibodies produced by B cells. The maturation of the B cells in so-called germinal centers in lymphatic organs such as the lymph nodes and the spleen is decisive for the development of “high-affinity” (highly effective) antibodies. Two types of B cells leave the germinal centers, antibody-producing plasma cells and memory B cells.
While some COVID-19 patients still have antibodies in their blood 6-9 months after infection, others lose their specific antibodies. Edgar Meinl’s research group at the Biomedical Center has now been able to show that after infection with SARS-CoV-2 memory B cells remain in the blood, even if no antibodies can be detected. To study these memory B cells, group B cells from the blood were differentiated into antibody-producing cells in cell culture and the antibodies produced were analyzed further. Blood cells from a total of 17 COVID-19 patients who had already recovered were examined, in five of them no specific antibodies were detectable in the blood 5-8 months after infection.
Edgar Meinl and his team found SARS-CoV-2-specific memory B cells that produced antibodies of the immunoglobulin G (IgG) type in all patients, and those that produced antibodies of the immunoglobulin A type in 11 of the 17 patients (IgA) produced. These antibodies blocked the binding of the viral receptor-binding domain to the cellular receptor ACE-2 and had neutralizing effects against infectious viruses in cell culture, as shown in cooperation with Prof. Oliver Keppler from the Max von Pettenkofer Institute, LMU Virology.
The work thus shows that functional SARS-CoV-2-specific memory B cells can be detected in the blood for a long time after a COVID-19 infection. This is of crucial importance for the question of long-term immunity, since memory B cells can differentiate very quickly into antibody-producing cells when reinfected (or infected after a vaccination) and can also evolve to better detect virus variants tie. The results of Edgar Meinl’s team also show that the analysis of memory B cells in cell cultures can be more suitable for detecting a past infection than the analysis of antibodies in the blood, since these cells, in contrast to the antibodies, are preserved over a longer period of time .
Publikation: Winklmeier et al.: Persistence of functional memory B cells recognizing SARS-CoV-2 variants despite loss of specific IgG, iScience 2022