With the current global pandemic, tests for detecting antibodies against SARS-CoV-2 have become widely available. These tests are used to determine if a person has been exposed to the virus and can suggest whether they have developed immunity. Traditional wash-based ELISA assays are the most prevalent assay format used for these tests. Detection of anti-virus antibodies in serum samples taken from patients have been used for diagnosis as well as for basic research into the efficacy of developed vaccines. However, for some viral antibody tests, several unconfirmed and false-positive results have been reported due to the insufficient sensitivity and stability of ELISA assays. In some instances, true-positive cases are being missed, and the same holds true when conducting research for the development of vaccines. As an alternative, assay formats such as AlphaLISA™ HTRF™, and DELFIA™ would be a better option for research purposes as they can provide higher sensitivity, higher assay stability, and higher throughput.
Antibody detection provides key information on efficacy of vaccines
Nucleic acid-based vaccines, which consist of in vitro transcribed mRNAs within lipid nanoparticles have been in the news recently as a type of vaccine being developed for COVID-19. mRNA vaccines can be consistently manufactured and have shown to elicit strong immune responses. In a recent publication, Espeseth et al. (2020) tested chemically modified mRNA vaccines toward the respiratory syncytial virus (RSV) in rodent models. They set-up competition AlphaLISA assays to detect the anti-viral antibodies developed in response to the vaccine in the mice and rats. Sera from vaccinated mice and rats were tested in the assay and a decrease in Alpha signal was proportional to the level of antibodies produced in response to the vaccine. They found that the mRNA vaccines produced neutralizing antibodies and did not elicit vaccine-enhanced respiratory disease (VERD) in rats. The AlphaLISA assays gave robust reliable results that correlated with their ELISA assays but with higher throughput and without the laborious wash steps. PubMed.
Measuring different antibody isotypes provides information about recent infections and long-term immunity
Different types of antibodies are expressed depending on if a patient has been recently exposed to a virus or has acquired long term immunity. For example, IgM antibodies are the first antibodies that the body makes against a new infection and detection of these antibodies suggests an acute infection. IgG antibodies take longer to develop, are the most abundant in the body, and provide longer term protection against the virus. Detection of IgGs in a symptomatic patient points toward a chronic viral infection.
TR-FRET has recently been used for high throughput serodiagnosis of antibodies toward a variety of viruses in patient samples. Most recently, Kareinen et al. (2019) developed three different high-throughput TR-FRET assays which were used to detect different isotypes of antibodies from Zika patients. These TR-FRET assays measured either all anti-Zika NS1 antibodies (LFRET), IgM and IgA (acute-LFRET), or just IgG antibodies (immunity-LFRET). They performed a side-by-side comparison with commercially available IgG and IgM Zika ELISA assays. The trends in the patient samples for each of the assays correlated strongly. However, the LFRET assay demonstrated higher sensitivity for IgM than the ELISA. The TR-FRET assay detected samples positive for IgM where the ELISA showed a negative result. They show diagnostic specificity and high sensitivity suggesting the wash-free LFRET assay has potential for assisting in clinical decision-making. PubMed.
Currently, clinical detection of Hepatitis C Virus (Hep C) viral IgG antibodies is performed by ELISA assays. However, the single detection of Hep C viral IgG does not distinguish between acute and chronic hepatitis. A simultaneous measurement of both IgM and IgG can save time and material and provide extra information about the timing of the patient’s infection. In a recent publication, Yang et. al developed a DELFIA assay for the dual measurement of IgG and IgM antibodies against Hep C. They tested 200 serum samples from patients with Hep C infection and serum from control heathy patients. They compared their assay to commercially available IgM and IgG ELISA kits and saw a >90% correlation in the data. Their assay showed high sensitivity, high specificity, high stability, a wide detection range, and good clinical value. PubMed.
AlphaLISA™, HTRF™, LANCE™ Ultra™, and DELFIA assays are for research use only. They are not for use in diagnostic procedures.
Sources:
- Espeseth AS, Cejas PJ, Citron MP, et al. Modified mRNA/lipid nanoparticle-based vaccines expressing respiratory syncytial virus F protein variants are immunogenic and protective in rodent models of RSV infection. NPJ Vaccines. 2020;5:16. Published 2020 Feb 14. doi:10.1038/s41541-020-0163-z
- Kareinen L, Hepojoki S, Huhtamo E, et al. Immunoassay for serodiagnosis of Zika virus infection based on time-resolved Förster resonance energy transfer. PLoS One. 2019;14(7):e0219474. Published 2019 Jul 23. doi:10.1371/journal.pone.0219474
- Yang X, Ye Y, Wang T, et al. Eu3+ /Sm3+ dual-label time-resolved fluoroimmunoassay for measurement of hepatitis C virus antibodies. J Clin Lab Anal. 2019;33(2):e22659. doi:10.1002/jcla.22659
