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Authors:Munitz et al 

Journal/ Pre-Print:MedRxiv 

Tags: Immunology/Immunity, Clinical/ Diagnostics 

Research Highlights 

1. Adapted an electrochemiluminescence-based ELISA assay for detecting IgM, IgG and IgA against SARS-CoV-2 RBD and NP antigens which was observed to have higher sensitivities and a broader dynamic range than the standard ELISA assay. 

2. Antibody responses were observed to develop more rapidly against the RBD antigen compared to the NP antigen in patients. 

3. Moderate/severe patients were observed to have a more rapid antibody response (anti-RBD IgM, IgG and IgA, and anti-NP IgG and IgA) compared to mild patients, but final antibody levels were similar in both groups. 

Summary

The authors adapted an electrochemiluminescence-based ELISA assay to detect IgM, IgG and IgA against SARS-CoV-2 RBD and NP antigens. Higher sensitivities were seen in side-by-side comparison with standard ELISA assay. Their assays were validated using sera from COVID-19 patients and recovered individuals (n=96) and 195 pre-pandemic controls. All antibody classes against RBD were developed rapidly. IgG and IgA anti-NP developed much slower and IgM did not develop significantly. Moderate/severe patients had a more rapid antibody response for IgG and IgA against RBD and NP, and IgM against RBD compared to mild patients. Final antibody levels were similar in both groups. 

Impact for SARS-CoV2/COVID19 research efforts  

Understand the immune response to SARS-CoV2/COVID19  

Develop diagnostic tools for SARS-CoV2/COVID19 

Others: Multiplexed assay design could be used for serological studies in vaccine development and further patient and/or diagnostic studies 

Study Type  

  • In vitro study 

Strengths and limitations of the paper 

Novelty: Multiplexed electrochemiluminescence serological assay with broader dynamic range and sensitivity than the standard ELISA 

Standing in the field:Building on well-established knowledge and technology 

Appropriate statistics:Statistics are appropriate and accurate 

Viral model used:RBD and NP SARS-CoV-2 antigens 

Translatability:Possible use in diagnostics and further serological studies 

Main limitations: 

  • Did a side-by-side comparison between standard ELISA assay and the electrochemiluminescence-based ELISA assay for IgG and IgM, but did not include IgA. Comparison was also only made using SARS-CoV-2 RBD antigen and did not include NP. 

  • Not clear when homemade RBD or company-bought RBD was used in ELISA assay comparison and in further serological assays. Integrity of homemade RBD compared to the company-bought was not analysed. 

  • Only 29 mild patients and 28 moderate/severe patients used in antibody response analysis, and no breakdown of the number of moderate and severe patients in the latter group. 

  • Would have been useful to have included viral load measurements 

  • Data includes both recovered and moderate/severe individuals in the same group for > 28DPS to analyse long term antibody response, when these could differ greatly between the groups and skew data. 

  • Figures using violin plots are difficult to interpret as are the conclusions made from them.  

  • No description of replicates, and samples are not distinguished into unique samples and those with multiple time points.