Determination of the concentration of IgG against the Spike Receptor-Binding Domain that predicts the viral neutralizing activity of convalescent plasma and serum against SARS-CoV-2.

Llipsy Santiago, Iratxe Uranga-Murillo, Maykel Arias, Andrés Manuel González-Ramírez, Javier Macías-León, Eduardo Moreo, Sergio Redrado, Ana García-García, Víctor Taleb, Erandi Lira-Navarrete, Ramón Hurtado-Guerrero, Nacho Aguilo, Maria del Mar Encabo-Berzosa, Sandra Hidalgo, Eva M. Galvez, Ariel Ramirez-Labrada, Diego de Miguel, Rafael Benito, Patricia Miranda, Antonio Fernández, José María Domingo, Laura Serrano, Cristina Yuste, Sergio Villanueva, José Ramón Paño and Julián Pardo. Determination of the concentration of IgG against the Spike Receptor-Binding Domain that predicts the viral neutralizing activity of convalescent plasma and serum against SARS-CoV-2. Biology, 2021. DOI: 10.3390/biology10030208

Several hundred millions of people have been diagnosed of coronavirus disease 2019 (COVID-19), causing millions of deaths and a high socioeconomic burden. SARS-CoV-2, the causative agent of COVID-19, induces both specific T- and B-cell responses, being antibodies against the virus detected a few days after infection. Passive immunization with hyperimmune plasma from convalescent patients has been proposed as a potentially useful treatment for COVID-19. Using an in-house quantitative ELISA test, we found that plasma from 177 convalescent donors contained IgG antibodies specific to the spike receptor-binding domain (RBD) of SARS-CoV-2, although at very different concentrations which correlated with previous disease severity and gender. Anti-RBD IgG plasma concentrations significantly correlated with the plasma viral neutralizing activity (VN) against SARS-CoV-2 in vitro. Similar results were found using an independent cohort of serum from 168 convalescent health workers. These results validate an in-house RBD IgG ELISA test in a large cohort of COVID-19 convalescent patients and indicate that plasma from all convalescent donors does not contain a high enough amount of anti-SARS-CoV-2-RBD neutralizing IgG to prevent SARS-CoV-2 infection in vitro. The use of quantitative anti-RBD IgG detection systems might help to predict the efficacy of the passive immunization using plasma from patients recovered from SARS-CoV-2.

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