Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in late 2019 and has since become a global pandemic. Pathogen-specific Abs are typically a major predictor of protective immunity, yet human B cell and Ab responses during COVID-19 are not fully understood. In this study, we analyzed Ab-secreting cell and Ab responses in 20 hospitalized COVID-19 patients. The patients exhibited typical symptoms of COVID-19 and presented with reduced lymphocyte numbers and increased T cell and B cell activation. Importantly, we detected an expansion of SARS-CoV-2 nucleocapsid protein-specific Ab-secreting cells in all 20 COVID-19 patients using a multicolor FluoroSpot Assay. Out of the 20 patients, 16 had developed SARS-CoV-2-neutralizing Abs by the time of inclusion in the study. SARS-CoV-2-specific IgA, IgG, and IgM Ab levels positively correlated with SARS-CoV-2-neutralizing Ab titers, suggesting that SARS-CoV-2-specific Ab levels may reflect the titers of neutralizing Abs in COVID-19 patients during the acute phase of infection. Last, we showed that IL-6 and C-reactive protein serum concentrations were higher in patients who were hospitalized for longer, supporting the recent observations that IL-6 and C-reactive protein could be used as markers for COVID-19 severity. Altogether, this study constitutes a detailed description of clinical and immunological parameters in 20 COVID-19 patients, with a focus on B cell and Ab responses, and describes tools to study immune responses to SARS-CoV-2 infection and vaccination.
26Coronavirus disease 2019 , caused by severe acute respiratory syndrome 27 coronavirus 2 (SARS-CoV-2), emerged in late 2019 and has since become a global 28 pandemic. Pathogen-specific antibodies are typically a major predictor of protective 29immunity, yet B cell and antibody responses during COVID-19 are not fully understood. 30 Here, we analyzed antibody-secreting cell (ASC) and antibody responses in twenty 31 hospitalized COVID-19 patients. The patients exhibited typical symptoms of COVID-19, and 32 presented with reduced lymphocyte numbers and increased T cell and B cell activation. 33 Importantly, we detected an expansion of SARS-CoV-2 nucleocapsid protein-specific ASCs 34 in all twenty COVID-19 patients using a multicolor FluoroSpot assay. Out of the 20 patients, 35 16 had developed SARS-CoV-2-neutralizing antibodies by the time of inclusion in the study. 36 SARS-CoV-2-specific IgA, IgG and IgM antibody levels positively correlated with SARS-37CoV-2-neutralizing antibody titers, suggesting that SARS-CoV-2-specific antibody levels 38 may reflect the titers of neutralizing antibodies in COVID-19 patients during the acute phase 39 of infection. Lastly, we showed that interleukin 6 (IL-6) and C-reactive protein (CRP) 40 concentrations were higher in serum of patients who were hospitalized for longer, supporting 41 the recent observations that IL-6 and CRP could be used to predict COVID-19 severity. 42Altogether, this study constitutes a detailed description of clinical and immunological 43 parameters in twenty COVID-19 patients, with a focus on B cell and antibody responses, and 44 provides tools to study immune responses to SARS-CoV-2 infection and vaccination. 45 46
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