Antibody Tests To Detect SARS-CoV-2 Immune Status
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As many countries begin to ease lockdown measures, there is increasing interest in developing and implementing methods which can detect individuals who have already been infected with SARS-CoV-2. Research has demonstrated that humans generate SARS-CoV-2 specific antibodies within two to three weeks of infection, highlighting the potential that widescale antibody testing could have on efforts to tackle the pandemic.1
Beckman Coulter is currently developing assays to identify IgM and IgG antibodies to SARS-CoV-2. We recently spoke with Shamiram Feinglass, Global Chief Medical Officer at Beckman Coulter, to learn more about these antibody tests, what they can tell us, and the value of this information.
Anna MacDonald (AM): What can antibody tests tell us? Why will it be useful to know the immune status of individuals?
Shamiram Feinglass (SF): Antibody tests, also known as serology tests, tell us if a person had mounted an immune response following an infection. Antibody tests play a critical role in understanding the level of immune response an individual has developed against the SARS-CoV-2 virus. This type of understanding could help identify those more at risk of infection or when a previously infected individual could safely return to work. Wider scale testing will provide an overview of the immunity status of the population and potentially help guide the future management of this virus.
AM: What is the difference between IgM and IgG? What are the advantages of detecting each type of antibody?
SF: In the first few days following infection, only the virus can be detected. This is when it multiplies and may be transmitted to others. At this point, molecular diagnostic PCR based tests can be used to detect the virus. The individual’s immune system then starts to respond to the viral load as part of the acute phase of infection. This is when IgM antibodies are produced and increase to fight the virus. Following this, the convalescent phase of the infection is reached, and IgG is produced, while IgM starts to decline. IgG is thought to provide the necessary immune response to reduce the impact of future infection.
AM: Beckman Coulter is developing assays to identify IgM and IgG antibodies to SARS-CoV-2. Can you give us an overview of how the tests work?
SF: We are developing two separate assays, one for IgG and one for IgM. The IgG assay is launching in mid-May, followed by an IgM assay soon after. Both tests will be available on a variety of Beckman Coulter analyzers, including the high-throughput DxI 800 (up to 200 tests/hour) designed for large labs, the DxI 600 (up to 100 tests/hour) for mid-sized labs and the DxCi and Access 2 analyzers (up to 50 tests/hour) for smaller labs. Our Access SARS-CoV-2 IgG assay detects antibodies to the Receptor Binding Domain (RBD) of the spike protein, which may be important for immunity. Laboratory studies have shown that antibodies against the RBD are neutralizing in vitro, indicating that they may be an effective measure of immunity when compared to antibodies against other viral proteins. Though the coronavirus uses many different proteins to replicate and invade cells, the spike protein is the major surface protein that it uses to bind to a human cell receptor. After the spike protein binds to the receptor, the viral membrane fuses with the human cell membrane, allowing the genome of the virus to enter human cells and begin infection.2
AM: How soon after infection can the tests identify the antibodies?
SF: IgM is the first type of antibody developed in an infection and can be detectable approximately 4 to 7 days after the onset of symptoms.
AM: What is known so far about human immunity to SARS-CoV-2?
SF: Once a person contracts a virus, their body will begin to build an immune response to it. However, the immune response they build up depends not only on the virus but also on the individual. It is unknown at this time how long the SARS-CoV-2 antibodies remain in the body.
Shamiram Feinglass was speaking to Anna MacDonald, Science Writer, Technology Networks.
1. Long, Q., Liu, B., Deng, H., Wu, G., Deng, K., Chen, Y., . . . Huang, A. (2020). Antibody responses to SARS-CoV-2 in patients with COVID-19. Nature Medicine. doi:10.1038/s41591-020-0897
2. Saplakoglu, Y. (2020, February 19). Coronavirus 'spike' protein just mapped, leading way to vaccine. Retrieved May 1, 2020, from https://www.livescience.com/coronavirus-spike-protein-structure.html