Neutralizing Antibody Detection

Neutralizing Antibody Detection

Virus neutralization remains the gold standard for determining antibody efficacy. Therefore, a high-throughput assay to measure SARS-CoV-2 neutralizing antibodies is urgently needed for COVID-19 serodiagnosis, convalescent plasma therapy, and vaccine development.

Pseudoviral Neutralizing Antibody Detection Platform

Principle of Pseudovirus Neutralizing Antibody Assay

 In the Pseudovirus Neutralizing Antibody Assay, the inhibition of viral entry into cells by Neutralize Antibody is correlated to the decreased levels of reporter gene (usually use luciferase) signals in the cells. This method is superior to the conventional assay because of its simplicity, higher sensitivity and accuracy, suitability for high-throughput experiments. In addition, pseudovirus is used during the test. Therefore, this method could be used as an alternative for safely conducting serologic studies in a rapid response in assessing the threat posed by SARS-CoV-2.

Strategy of Pseudovirus Neutralizing Antibody Assay

To Set up a Pseudovirus Neutralizing Antibody Assay, the necessary requirements are 1) Pseudovirus, 2) Target Cell Line, 3) Standard Neutralizing Antibody, and 4) Enhancers.

(1)

Pseudovirus 

ACE Biolabs  to use the lentiviral packaging system, the SARS-CoV-2 (2019-nCoV, COVID-19 virus) S protein as a surface capsid glycoprotein and containing GFP and/or Luciferase reporter genes as a pseudovirus model. Therefore, this  pseudovirus can infect cell lines overexpressing the ACE2 gene. Researchers can determine the infection efficiency by observing GFP through a microscope and detecting the value of Luciferase. Strategy of Pseudovirus package for Neutralizing Antibody Assay please refer to our techinical support article. 

(2)

Cell line: express ACE2 receptor

An important aspect of Pseudovirus Neutralizing Antibody Assay lies in the basic mechanism of viruses invading cells. Cell line for Pseudovirus Neutralizing Antibody Assay can be natural cells expressing viral S protein receptors, or use artificially modified special cell types that can stably express S protein receptor genes.  The advantage of using artificially modified cell lines is that certain cell surface receptors can be expressed at a high level according to the research needs, especially those receptor types that mediate virus invasion into cells.

Natural cells expressing viral S protein receptors

Ma D. et al. determined the expressions of SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) and type II transmembrane serine protease (TMPRSS2) genes in human cells. https://doi.org/10.1038/s41433-020-0939-4

Stable cell line express ACE2 receptor genes

ACE2-3xFLAG-HEK293T stable cell line : The ACE2-3xFLAG-HEK293T stable cell line was obtained from lentivirus infected and multiple rounds of Puromycin screening. The lentivirus was packaged with pLV-ACE2-3FLAG plasmid, concentrated and purified, and then infected with HEK293T cells. 

Common cell line used for express ACE2 including HEK293T, Hela, BHK-21 and etc.  ACE Biolabs packaged lentivirus with pLV-ACE2-3FLAG plasmid. This ACE2-lentivirus is available to infect various cell lines. Stable cell lines that express ACE2 receptor are further generated  with selection by puromycin. 

(3)

Standard Neutralizing Antibody

Non-viral Neutralizing Antibody Detection Platform

PRINCIPLE OF THE ASSAY

This assay employs the competitive inhibition enzyme immunoassay technique. The microtiter plate provided in this kit has been pre-coated with RBD. Standards or samples are added to the appropriate microtiter plate wells with Horseradish Peroxidase (HRP) conjugated ACE2. The competitive inhibition reaction is launched between with HRP-ACE2 and SARS-CoV-2 neutralizing antibody in samples. A substrate solution is added to the wells and the color develops in opposite to the amount of SARS-CoV-2 neutralizing antibody in the sample. The color development is stopped and the intensity of the color is measured.

DETECTION RANGE

9.75 ng/ml-10000 ng/ml.

SENSITIVITY

The minimum detectable dose of human SARS-CoV-2 neutralizing antibody is typically less than 9.75 ng/ml. The sensitivity of this assay, or Lower Limit of Detection (LLD) was defined as the lowest human SARS-CoV-2 neutralizing antibody concentration that could be differentiated from zero.