A high through-put Luminex antibody assay for the diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may provide accurate results in less time while using less material, according to a study recently published in The Journal of Infectious Diseases.
Currently, polymerase chain reaction (PCR)-based assays are used for diagnosis through the detection of nucleic acids in specimens from the respiratory tract. However, testing of serum and other bodily fluids for antibodies to infectious diseases, including typhoid and syphilis, has been used for over a century. In the context of the SARS-CoV-2 pandemic, high through-put, rapid serologic methods are needed. A high through-put Luminex antibody assay was developed, and this study investigated its accuracy in a SARS-CoV-2 setting.
Researchers evaluated 25 specimens from 18 people with confirmed coronavirus disease 2019 (COVID-19). Additionally, 13 specimens from people without COVID-19 infection: sera from 3 people without infection and plasma from 10 blood bank donors.
SARS-CoV-2 antigens for the Luminex antibody assay were a soluble recombinant trimerized form of the S protein and a recombinant receptor-binding domain (RBD) protein. Each antigen was covalently coupled to a uniquely labeled fluorochrome carboxylated xMAP bead set. Serum and plasma were added to the beads per the manufacturer’s instructions, and were read with a Luminex Flexmap 3D instrument. Samples were tested in duplicate, and results were recorded as mean fluorescent intensity. Specimens from people without infection were used as negative controls.
Results demonstrated that the high through-put Luminex antibody assay may be more efficient at diagnosing SARS-CoV-2 than PCR-based assays. There was clear differentiation between specimens from people with and without infection, and a statistically significant difference between the antibody levels in specimens with and without COVID-19 (P <.0001).
Of the 25 specimens from people with confirmed COVID-19, all specimens were positive for the trimeric spike and the RBD proteins. None of the 13 specimens from people without infection showed antibodies to either antigen. The Luminex antibody assay showed to be accurate, required only 2.5 hours, and used 5 nanograms of antigen per test.
An Emergency Use Authorization by Luminex Corporation had been submitted for this assay 10 weeks after this study was published online. The Luminex antibody assay offers advantages like being able to prepare antigen-coated beads for thousands of tests in a single day and using 20-fold less antigen than ELISA. Additionally, assessments of antibodies to RBD and S proteins can be performed simultaneously, which provides a screen and titrated confirmatory test in a single step. As a result, this assay could produce results on thousands of specimens per day.
“A high through-put assay such as this can be used for a multitude of purposes including as a diagnostic assay in hospitals and reference labs, serosurveillance of communities, screening of health care workers who may have developed immunity to SARS-CoV-2, identification of donors for COVID-19 convalescent plasma therapy, and selection of individuals who are potentially immune to reinfection,” the researchers concluded.
Weiss S, Klingler J, Hioe C, et al. A high through-put assay for circulating antibodies directed against the S protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [published online August 29, 2020]. J Infect Dis. doi: 10.1093/infdis/jiaa531/5898999