As the response to the COVID-19 pandemic continues, officials and researchers have made a concentrated push to ramp up testing efforts. Testing not only helps inform us of the virus’ prevalence but can also give us insight into how the virus has spread and whether it has accumulated potentially relevant mutations.
Many testing methods are based on nucleic acid analysis. While these approaches are invaluable and allow the determination of an active infection, they do not provide the entire picture. How can we know if a seemingly healthy patient has been exposed to the virus? What if the person was an asymptomatic carrier and was tested after an infection has run its course?
To answer questions like these, we turn to antibody testing. In this post, we’d like to shine a spotlight on COVID-19 antibody testing, how it’s performed, and how some researchers are trying to make it better.
Lasting impressions: Antibody testing of COVID-19
As part of fighting off pathogens, your immune system produces antibodies against the pathogen. Even after the pathogen is eliminated, your body continues to produce these antibodies as a kind of immune "memory" that gives us a record of past infection.
One way to test for antibodies is with a technique called ELISA (Enzyme-Linked Immunosorbent Assay). Think of an ELISA as making a chain: the first link is your target antigen (SARS-COV-2), which is attached to a plate or membrane.
The patient sample is added and, if antibodies against SARS-COV-2 (termed primary antibodies) are present, they stick to the target antigen and form the second link in the chain.
A second antibody (termed the secondary antibody) is added, which is designed to only stick to the primary antibody. This forms the third link in the chain.
The secondary antibody is also attached to an enzyme (horseradish peroxidase, HRP) that allows it to generate a colored deposit that acts as the test result. If a person has antibodies to SARS-COV-2, the colored deposit is made. However, if someone has no antibodies to SARS-COV-2, the chain will be broken: no primary antibody means there is nothing for the secondary antibody to stick to, which means no HRP to make a colored deposit.
In this process, antibody specificity is extremely important: a poor antibody may fail to bind to the target, or it may bind indiscriminately. This is particularly important for the secondary antibody, as the conjugated HRP acts to amplify the signal, meaning minor off-target binding can lead to a false-positive result. So, with these concerns in mind, Agilent is excited to share that our secondary antibodies were provided to a research team at Stanford University School of Medicine for their SARS-COV-2 antibody test, which they built from scratch.
In late March 2020, Agilent was contacted by bioengineering researchers at Stanford School of Medicine, requesting HRP conjugated IgG, IgA, and IgM secondary antibodies. Agilent was able to provide a test vial about 48 hours later, and the full expedited order of material approximately two weeks later. Agilent also filled a second request for 50,000 ELISA plates in half the typical timeframe, delivering the urgently needed material in four weeks.
“We were grateful for Agilent’s timely and enthusiastic support during the development of our serological testing for SARS-CoV-2 antibodies in the clinical laboratory,” commented Scott Boyd, MD PhD, Associate Professor of Pathology, Stanford University.
Quality and quantity both matter in testing
As we approach what may be the peak of SARS-COV-2 cases, rapid and reliable testing will remain a priority for both researchers and clinicians. The speed with which the research community has mobilized and responded to this disease has been incredible to witness, and we are proud that we’ve been able to support these researchers in advancing understanding of this global pandemic.