Microscopy-based assay for semi-quantitative detection of SARS-CoV-2 specific antibodies in human sera

Emergence of the novel pathogenic coronavirus Sars-CoV-2 and its rapid pandemic spread presents numerous questions and challenges that demand immediate attention. Among these is the urgent need for a better understanding of humoral immune response against the virus and assessment of seroprevalence levels in the population, both of which form the basis for developing public health strategies to control viral spread. For this sensitive, specific and quantitative serological assays are required. Here, we describe the development of a semi-quantitative high-content microscopy-based assay for detection of three major classes (IgG, IgA and IgM) of Sars-CoV-2 specific antibodies in human samples. The possibility to detect antibodies against the entire viral proteome together with a robust semi-automated image analysis workflow resulted in improvement of sensitivity and specificity compared to an approved ELISA-based diagnostic test. Combining both resulted in maximum specificity in a negative control cohort, while maintaining high sensitivity. The procedure described here is compatible with high-throughput microscopy approaches and may be applied for serological analysis of other virus infections.