Evaluation of potential immunity against the novel severe acute respiratory syndrome (SARS) coronavirus that emerged in 2019 (SARS-CoV-2) is essential for health, as well as social and economic recovery. Generation of antibody response to SARS-CoV-2 (seroconversion) may inform on acquired immunity from prior exposure, and antibodies against the SARS-CoV-2 spike protein receptor binding domain (S-RBD) are speculated to neutralize virus infection. Some serology assays rely solely on SARS-CoV-2 nucleocapsid protein (N-protein) as the antibody detection antigen; however, whether such immune responses correlate with S-RBD response and COVID-19 immunity remains unknown. Here, we generated a quantitative serological ELISA using recombinant S-RBD and N-protein for the detection of circulating antibodies in 138 serial serum samples from 30 reverse transcription PCR–confirmed, SARS-CoV-2–hospitalized patients, as well as 464 healthy and non–COVID-19 serum samples that were collected between June 2017 and June 2020. Quantitative detection of IgG antibodies against the 2 different viral proteins showed a moderate correlation. Antibodies against N-protein were detected at a rate of 3.6% in healthy and non–COVID-19 sera collected during the pandemic in 2020, whereas 1.9% of these sera were positive for S-RBD. Approximately 86% of individuals positive for S-RBD–binding antibodies exhibited neutralizing capacity, but only 74% of N-protein–positive individuals exhibited neutralizing capacity. Collectively, our studies show that detection of N-protein–binding antibodies does not always correlate with presence of S-RBD–neutralizing antibodies and caution against the extensive use of N-protein–based serology testing for determination of potential COVID-19 immunity.
Kathleen M. McAndrews, Dara P. Dowlatshahi, Jianli Dai, Lisa M. Becker, Janine Hensel, Laura M. Snowden, Jennifer M. Leveille, Michael R. Brunner, Kylie W. Holden, Nikolas S. Hopkins, Alexandria M. Harris, Jerusha Kumpati, Michael A. Whitt, J. Jack Lee, Luis L. Ostrosky-Zeichner, Ramesha Papanna, Valerie S. LeBleu, James P. Allison, Raghu Kalluri