# Development of a High-Hydrostatic-Pressure-Treated Recombinant Vaccine Targeting the Major Capsid Protein of Red Sea Bream Iridovirus

## TL;DR

A new recombinant vaccine for red sea bream iridovirus was developed using high-pressure technology to preserve protein structure and induce strong immune responses.

## Contribution

The novel use of high-hydrostatic-pressure refolding to solubilize and preserve the structural integrity of a viral capsid protein for vaccine development.

## Key findings

- HHP treatment under alkaline conditions solubilized the recombinant MCP while preserving its structure.
- HHP–RSIV-rMCP induced strong IgM responses and improved disease resistance in red sea bream.
- Structural preservation is crucial for antigenicity, as commercial vaccines showed minimal reactivity to HHP–RSIV-rMCP.

## Abstract

Red sea bream (Pagrus major) aquaculture represents one of the most economically important marine aquaculture industries in Japan and East Asia. However, viral diseases, particularly those caused by red sea bream iridovirus (RSIV), pose a serious threat to aquaculture production in this region. In this study, we applied high-hydrostatic-pressure (HHP) refolding technology to develop a recombinant vaccine targeting the RSIV major capsid protein (MCP). The recombinant MCP (RSIV-rMCP) expressed in Escherichia coli was insoluble; however, HHP treatment under alkaline (pH 10) conditions in the presence of arginine successfully solubilised the protein while preserving its structural integrity. The solubilised protein (HHP–RSIV-rMCP) induced strong RSIV-specific IgM responses and enhanced disease resistance in red sea bream. In contrast, sera from fish immunised with a commercial formalin-inactivated vaccine exhibited minimal reactivity to HHP–RSIV-rMCP but reacted significantly to formalin-treated HHP–RSIV-rMCP. These results indicate that the HHP–RSIV-rMCP vaccine induces conformation-specific IgM antibodies and that structural preservation is crucial for maintaining antigenicity. Collectively, our findings demonstrate that HHP refolding technology is an effective strategy for preparing structurally preserved antigens.