Single-reaction multi-antigen serological test for comprehensive evaluation of SARS-CoV-2 patients by flow cytometry

Abstract

Here, we describe a new, simple, highly multiplexed serological test that generates a more complete picture of sero-conversion than single antigen-based assays. Flow cytometry is used to detect multiple Ig isotypes binding to fourSARS-CoV-2 antigens: the Spike glycoprotein, its RBD fragment (the main target for neutralizing antibodies), the nucle-ocapsid protein, and the main cysteine-like protease in a single reaction. Until now, most diagnostic serological testsmeasured antibodies to only one antigen and in some laboratory-confirmed patients no SARS-CoV-2-specific antibodiescould be detected. Our data reveal that while most patients respond against all the viral antigens tested, others showa marked bias to make antibodies against either proteins exposed on the viral particle or those released after cellularinfection. With this assay, it was possible to discriminate between patients and healthy controls with 100% confidence.Analysing the response of multiple Ig isotypes to the four antigens in combination may also help to establish a corre-lation with the severity degree of disease. A more detailed description of the immune responses of different patients toSARS-CoV-2 virus might provide insight into the wide array of clinical presentations of COVID-19.