Natural infection with SARS-CoV-2 generates durable Spike S1 Receptor-Binding-Domain-specific memory B cell and neutralizing antibody responses

Abstract Since human infection with coronavirus SARS-CoV-2 was first detected in December 2019, we are still developing an understanding of the nature and duration of protection against this infection. Most neutralizing antibodies, which are a key component of the protective response against SARS-CoV-2 infection, target the Receptor Binding Domain (RBD) of the Spike glycoprotein and critically prevent binding of the virus to the host cell receptor, and viral entry. Thus, it is of vital importance to monitor the presence of neutralizing antibodies and RBD-specific B cells that are key for rapid production of protective antibodies upon reinfection with SARS-COV2 infection. In this study, we developed a multicolor flow cytometric assay to enumerate the RBD-specific memory B cell and memory B cell subsets. We collected peripheral blood cells and plasma from 22 subjects 1–2 months since COVID-19 diagnosis (early time point - ET) and then again after 5–7 months (late time point – LT). Comparing the data collected from these two time points, we observed a significant decrease in plasma blasts and double-negative memory B cell and an increase in the IgG+ switched-memory B cells and decrease in the IgM+ switched-memory B cells at LT relative to ET. We concurrently observed a trend toward decreased anti-RBD IgG titers over time. When we tested plasma neutralizing activity employing ACE2-expressing HeLa cell lines infected with mNeonGreen(mNG)SARS-CoV-2, we also observed reduced neutralizing antibody titers over time. Thus, a correlation exists between titers of RBD-specific IgG antibody and neutralizing titers. In addition, the presence of RBD-specific B-cell memory in circulating blood is a strong indication of a durable protective response.