# A Novel Application of Virus Like Particles in the Hemagglutination Inhibition Assay

## TL;DR

Researchers explored using virus-like particles as a safe and scalable alternative antigen in hemagglutination inhibition assays for detecting antibodies against H5N1 viruses.

## Contribution

The study introduces virus-like particles as a novel antigen source for hemagglutination inhibition assays, offering a safer and scalable alternative to inactivated whole virus.

## Key findings

- VLPs behaved similarly to standard HI assay antigens in detecting serum antibodies.
- VLPs prepared in tissue culture or insect cells are safer and more scalable than traditional inactivated whole virus antigens.
- HI titers correlated with the similarity between VLP antigens and vaccinal seeds.

## Abstract

The hemagglutination inhibition (HI) assay is a traditional laboratory procedure for detection and quantitation of serum antibodies of hemagglutinating viruses containing the hemagglutinin (HA) gene. The current study aimed to investigate the novel use of virus like particles (VLP) as an antigen for the HI assay. VLPs were prepared from a strain of H5N1 using a baculovirus expression system. The VLPs were characterized using the hemagglutination test, Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, and transmission electron microscopy. The comparative HI assay was performed using three different seed antigens: A/chicken/Mexico/232/94 (H5N2), A/chicken/Egypt/18-H/09(H5N1) and A/goose/Guangdong/1/1996(H5N1). The HI assay of serum antibody titrations using homologous antigens to these vaccinal seeds were compared to the VLP’s antigens for the same serum. The HI titers were logically relevant to the similarity between VLP antigens and vaccinal seeds, indicating the VLPs behave similarly to the standard HI assay which uses inactivated whole virus as an antigen. VLPs could be considered as an alternative to the HI assay antigen as they show a relatedness between the similarity with vaccinal seed and serum antibodies. Compared to typical entire H5N1 viral antigen prepared in SPF eggs that require proper inactivation to avoid any public health risk, VLPs prepared in tissue culture, plants or insect cells are a safe, inexpensive and scalable alternative to inactivated whole virus antigen.