Valle et al.
Multiplex Serology for Sensitive and Specific Flavivirus IgG Detection: Addition of Envelope Protein Domain III to NS1 Increases Sensitivity for Tick-Borne Encephalitis Virus IgG Detection. Viruses. 2024;16(2):286. doi:10.3390/v16020286

The standard test for TBE virus antibody detection is the enzyme-linked immunosorbent assay (ELISA) based on whole virus preparations containing complete glycoprotein E (gE) as antigen. Due to cross-reactivities of TBE gE with envelope proteins of other flaviviruses, false-positive results may be generated.

However, discrimination among flaviviruses can be achieved by using the nonstructural protein 1 (NS1) as antigen, because this is virus specific. A multiplex assay has been developed based on the domain III of gE (EDIII) (with higher specificity for TBE virus) and NS1 to increase a powerful specific diagnostic tool.

The newly developed multiplex assay allowed a rapid, high-throughput simultaneous detection of antibodies against a number of orthoflavivirus proteins using a low specimen volume. The combined use of EDIII and NS1 antigens increased the microarray sensitivity for TBE virus IgG detection and allowed to set a microarray titer cut-off that is predictive for positivity in TBE virus plaque reduction neutralization test (PRNT). Sera that were negative for EDIII and NS1 in this micro assay could not neutralize TBE virus.

Serological discrimination between TBE virus infection and vaccination is important to diagnose and study vaccine breakthrough cases of infection (see e.g., Snapshot week 26/2021, Newsletter December 2023, April 2020, February 2020). NS1 specific antibodies can be a tool to distinguish an antibody response after infection from vaccination. In the vaccinee cohort tested here, no specific NS1 response was observed, however, an absence of NS1 reactivity was observed in most of the PRNT-confirmed sera (13/15). This lack of sensitivity could be overcome by the EDIII specific reactivity in the assay.

This novel micro assay potentially allows a low-volume based, simultaneous analysis of IgG responses to a range of orthoflaviviruses with overlapping geographic circulation and clinical manifestations (e.g., TBE- WNF- and Usutu virus).

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