Researchers grow new serological assay for discovery of SARS-CoV-2 antibodies

Overview

• Post By : Kumar Jeetendra


• Source: University of California - Santa Cruz


• Date: 13 Dec,2020

Researchers at UC Santa Cruz have developed a novel serological assay for the detection of antibodies to SARS-CoV-2, the coronavirus which causes COVID-19. Rebecca DuBois, associate professor of biomolecular engineering at UC Santa Cruz, said the new method her staff developed is as accurate as the most dependable antibody tests now available, but is less complex and can be carried out much faster.

The golden standard for serological testing is a complex laboratory method known as ELISA that requires four to six hours to operate and provides quantitative results indicating the strength of the immune reaction. Easier assays using test strips deliver rapid results, but are less reliable and don’t quantify antibody levels.

The new method, called biolayer interferometry immunosorbent assay (BLI-ISA), provides complete quantifiable results in under 20 minutes. DuBois and her colleagues described the assay in a newspaper published December 10 in Scientific Reports.

A positive antibody test indicates prior infection with the virus. These tests aren’t used to diagnose active infections, however, which requires a different test that detects the virus’s genetic material or the virus antigens.

Serological testing is important for understanding the spread of the coronavirus by determining how a lot of people in a population have been infected. The tests are also utilized to assess the responses to experimental vaccines in both people and laboratory animals. Quantitative information about antibody levels may be especially significant in the future if scientists are able to determine that a certain degree of particular antibodies is required to provide protection against infection with the coronavirus.

“That’s still to be determined, but we do know that those who have been infected with SARS-CoV-2 have very diverse levels of carcinogens, and it would not be surprising to find that under some baseline level they may not be protective,” DuBois said. “So it is really helpful to have that qualitative ability to understand what someone’s antibody status is, whether it’s from a past infection or a vaccination.”

The instruments required to perform biolayer interferometry are increasingly common in research labs. The BLI tool at UCSC is used by several research teams, and DuBois has been using it in her research to study antibody-antigen interactions.

The new serological assay involves several steps performed by the tool in an automatic”dip-and-read” format. In the first step, the biosensor tip is dipped into a solution containing the antigen (a viral protein) which is recognized by the antibody to be tested for. As the antigen binds to the biosensor tip, it generates a signal that may be used for quality control to guarantee consistency in the antigen loading step. Next, after dipping into a clean solution, the biosensor is dipped into the blood plasma sample, generating a signal as antibodies bind to the antigen.

The immune system makes different types of antibodies, known as isotypes, including IgM, which can be produced early in the infection and declines later, and IgG, which can be generated afterwards and lasts longer. In the antibody binding measure, the BLI tool finds any type of antibody that binds to the antigen.

“Depending on when the blood sample was taken after infection, there could be different types of antibodies, and this measure gives us the entire antibody level,” DuBois said.

The next step detects and quantifies IgG antibodies specifically by measuring the binding of anti-IgG antibodies. The assay thereby provides quantitative measurements of both total antibodies and IgG antibodies, and it can be designed to measure various isotypes also.

In response to infection with the coronavirus, the immune system makes antibodies against a range of different coronavirus antigens. Many serological testing methods for SARS-CoV-2 are designed to detect antibodies to structural proteins of the virus such as the spike protein, which studs the surface of the virus and enables it to bind to and enter human cells. Antibodies to one part of the spike protein–the receptor binding domain, or RBD–are of special interest since they’re capable of neutralizing the virus in laboratory assays.

Our assay is as sensitive if not better than other assays in detecting low levels of antibodies, and the specificity [false-positive rate] is as good as the best antibody tests out there. It combines the advantages of the test strips that take 20 minutes with the quantitative results and higher performance of ELISA.”

Rebecca DuBois, Associate Professor, Biomolecular engineering, UC Santa Cruz

DuBois’s team developed and tested the new assay using RBD antigens, but she noticed that it can be used to detect a wide range of antigens. The BLI instrument allows simple”multiplexing,” meaning that multiple tests can be conducted in parallel to the same blood sample to detect antibodies to different viral antigens as well as different antibody isotypes.

Because it requires lab equipment, BLI-ISA couldn’t be utilised as a point-of-care test at doctor’s offices or pharmacies. But it allows high-throughput processing of samples and is quicker and less labor intensive than other quantitative lab tests such as ELISA, Immunofluorescent Assay, and Chemiluminescent Immunoassay. The amount of blood necessary for the test is available with a finger prick.

Another advantage of BLI-ISA over other methods is the ease of standardizing the assay in order that a sample gives the same quantitative results in repeated tests at different times or in different labs. ELISA requires an enzyme-based signal amplification step, which may change depending on temperature and other factors, resulting in a lot more test-to-test variability in the quantitative measurements.

First writer John Dzimianski, a postdoctoral researcher in DuBois’s lab, said the new assay might be especially useful for researchers in vaccine development. “This method provides a standardized means to quantify antibody levels, which might be used to compare antibody responses to various vaccine candidates. In addition, running the assay itself is simple, requiring little more than the push of a button,” he said. “It’s a very simple but effective tool.”

DuBois’s team is also interested in using the assay to perform a surveillance study to assess the prevalence of coronavirus infections in certain groups in the Santa Cruz community. The team is exploring funding opportunities for this research project.