The current pandemic showcases the need for proper testing of infectious diseases such as SARS-CoV-2. With regard to vaccinations, the investigation of neutralizing antibodies is essential for the evaluation of vaccine candidates. To conduct large-scale studies and similar SARS-CoV-2-related research, a reliable, scalable, and specific method for the detection of neutralizing antibodies is needed. The first choice would be virus neutralization tests (NTs), but these require biosafety level 3 (BSL3) facilities. Therefore, surrogate Enzyme-Linked Immunosorbent Assays (sELISA kits) are a viable alternative.
SARS-CoV-2 sELISA kits are based on the principle of competitive inhibition of the interaction between the SARS-CoV-2 receptor-binding domain (RBD) and recombinant human ACE2 receptor (hACE2). Chemiluminescence Detection is performed using horseradish peroxidase (HRP) coupled to one of the interacting partners. Since no active virus is used (only a viral protein), these sELISA kits are safe to handle in standard laboratories.
sELISA kits are fast, scalable, and safe to use, but are they able to detect neutralizing antibodies effectively? A recent study by Müller et al. tried to answer this question by comparing two commercially available kits (AdipoGen Life Sciences and GenScript) with results acquired by micro neutralization tests.
Figure 1. Distribution of inhibition values determined by AdipoGen Life Sciences (A) and GenScript (B) within neutralization test titers <1:5 (negative) and >1:40 (Source: Müller et al.).
Comparing both sELISA kits (figure 1) the AdipoGen Life Sciences kit shows high specificity and yields almost no false positive results, while the distribution of positive results is more dispersed. These results are reinforced when looking at the calculated sensitivities and specificities (table 1).
| Neutralization test |
AdipoGen postive |
AdipoGen negative | GenScript positive | GenScript negative | |
| Total | 276 | 133 | 143 | 158 | 84 |
| Neutralization test positive | 158 | 131 | 27 | 156 | 2 |
| Neutralization test negative | 118 | 2 | 116 | 36 | 82 |
| Sensitivity [%] | 82.9 | 98.7 | |||
| Specificity [%] | 98.3 | 69.5 | |||
But what do these results mean for future application of both kits? The authors (Müller et al.) came to the following conclusion:
“Both sELISAs were able to qualitatively detect neutralizing antibodies in plasma samples. […] However, in a two-step diagnostic algorithm, AdipoGen could potentially replace NT as a subsequent confirmatory test due to its high specificity.”
