SARS-CoV-2 Neutralizing Antibodies Immunoassay Detection Episode 1: S- RBD IgG

Currently there are no known safe and effective treatments for the most severe symptoms of COVID-19. The lack of effective treatments means that vaccines are the only way to end the devastating impact of the pandemic. Fortunately, several different types of vaccines have already been developed against SARS-CoV-2.

SARS-CoV-2 S-RBD binds to ACE2 to infect host cells. Studies have shown that neutralizing antibodies which act mainly against S-RBD can prevent SARS-CoV-2 RBD from binding with ACE2. Vaccines can stimulate the immune system to generate neutralizing antibodies. The degree of protection given by these vaccines, or by prior infection, could be proven by detecting neutralizing antibodies.

Identifying neutralizing antibodies may help indicate

The immune response induced by natural infection and vaccines (post vaccination).
The significance for vaccine receivers to know the real immune response before being vaccinated. It makes sense for the government to reasonably distribute the vaccines to the populations at higher risks, like healthcare workers.

Why use immunoassay

The conventional approach is to carry out a Virus Neutralization Test (VNT).

Standard method
High biosafety requirements
Time consuming
Very limited lab resources and high cost

The drawbacks of VNT mean that immunoassays are critical for evaluating vaccines, both in clinical trials and as part of national immunization programs.

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We can effectively deduce the result of a VNT by carrying out a Plaque Reduction Neutralization Test (PRNT).

Chemiluminescent immunoassay is a reliable choice for monitoring vaccine efficacy

Immunoassay can detect antibodies
Protective antibodies only constitute 1%-3% of the total antibodies in circulation (IgGs)
The table below illustrates the differences in immunoassay technologies

Mindray S-RBD IgG Antibodies Design

The spike protein consists of two domains, S1 and S2, which are responsible for binding.

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The S1 domain contains the Receptor Binding Domain (RBD) protein which is involved in host cell receptor recognition and binding, while the S2 domain contains the putative fusion peptide as well as the heptad repeat HR1 and HR2.