Serological characterisation of Lagovirus virus-like particles originating from native and mutated VP60 of rabbit haemorrhagic disease virus 2 and European brown hare syndrome virus.

Introduction: Since lagoviruses cannot be cultivated in vitro, using expression systems is an alternative and promising way of producing diagnostic viral antigens. It opens up their use as active immunogens for vaccine production.

Material and methods: Virus-like particles (VLPs) were produced in a baculovirus expression system in Spodoptera frugiperda 9 (Sf9) insect cells based on wild-type and mutated variants of the virus capsid VP60 protein from a Polish strain of European brown hare syndrome virus (EBHSV) and wild-type and mutated versions of this protein from a Polish strain of rabbit haemorrhagic disease virus 2 (RHDV2). The mutations were the substitution of an arginylglycylaspartic acid (Arg-Gly-Asp/RGD) motif in the P2 subdomain and, in the S or P2 domain, the substitution of three lysines. The VLPs were purified with sucrose gradient ultracentrifugation.

Results: Protein production was confirmed by Western blot analysis using rabbit or hare sera and ELISA tests with different types of monoclonal antibody. The haemagglutination properties of some VLPs were also evaluated. Electron microscopy of wild-type EBHSV, wild-type RHDV2 and the four VP60 variants produced in this experiment revealed the formation of characteristic VLP structures.

Conclusion: For the first time, mutated VLPs of RHDV2 with an RGD motif in the VP60 sequence were obtained, which could potentially be used to deliver cargo to eukaryotic cells. Virus-like particles based on the VP60 proteins of EBHSV and RHDV with a three-lysine substitution in the S or P2 domains were also obtained. Potential exists for VLPs of EBHSV and RHDV2 as vaccine candidates.