A comparison of four serological assays for detecting anti–SARS-CoV-2 antibodies in human serum samples from different populations

Grzelak, Ludivine; Temmam, Sarah; Planchais, Cyril; Demeret, Caroline; Tondeur, Laura; Huon, Christèle; Guivel-Benhassine, Florence; Staropoli, Isabelle; Chazal, Maxime; Dufloo, Jeremy; Planas, Delphine; Buchrieser, Julian; Rajah, Maaran Michael; Robinot, Remy; Porrot, Françoise; Albert, Mélanie; Chen, Kuang-Yu; Crescenzo-Chaigne, Bernadette; Donati, Flora; Anna, François; Souque, Philippe; Gransagne, Marion; Bellalou, Jacques; Nowakowski, Mireille; Backovic, Marija; Bouadma, Lila; Le Fevre, Lucie; Le Hingrat, Quentin; Descamps, Diane; Pourbaix, Annabelle; Laouénan, Cédric; Ghosn, Jade; Yazdanpanah, Yazdan; Besombes, Camille; Jolly, Nathalie; Pellerin-Fernandes, Sandrine; Cheny, Olivia; Ungeheuer, Marie-Noëlle; Mellon, Guillaume; Morel, Pascal; Rolland, Simon; Rey, Felix A.; Behillil, Sylvie; Enouf, Vincent; Lemaitre, Audrey; Créach, Marie-Aude; Petres, Stephane; Escriou, Nicolas; Charneau, Pierre; Fontanet, Arnaud; Hoen, Bruno; Bruel, Timothée; Eloit, Marc; Mouquet, Hugo; Schwartz, Olivier; van der Werf, Sylvie

It is of paramount importance to evaluate the prevalence of both asymptomatic and symptomatic cases of SARS-CoV-2 infection and their differing antibody response profiles. Here, we performed a pilot study of four serological assays to assess the amounts of anti–SARS-CoV-2 antibodies in serum samples obtained from 491 healthy individuals before the SARS-CoV-2 pandemic, 51 individuals hospitalized with COVID-19, 209 suspected cases of COVID-19 with mild symptoms, and 200 healthy blood donors. We used two ELISA assays that recognized the full-length nucleoprotein (N) or trimeric spike (S) protein ectodomain of SARS-CoV-2. In addition, we developed the S-Flow assay that recognized the S protein expressed at the cell surface using flow cytometry, and the luciferase immunoprecipitation system (LIPS) assay that recognized diverse SARS-CoV-2 antigens including the S1 domain and the carboxyl-terminal domain of N by immunoprecipitation. We obtained similar results with the four serological assays. Differences in sensitivity were attributed to the technique and the antigen used. High anti–SARS-CoV-2 antibody titers were associated with neutralization activity, which was assessed using infectious SARS-CoV-2 or lentiviral-S pseudotype virus. In hospitalized patients with COVID-19, seroconversion and virus neutralization occurred between 5 and 14 days after symptom onset, confirming previous studies. Seropositivity was detected in 32% of mildly symptomatic individuals within 15 days of symptom onset and in 3% of healthy blood donors. The four antibody assays that we used enabled a broad evaluation of SARS-CoV-2 seroprevalence and antibody profiling in different subpopulations within one region.