# Contrasted modifications of IgM and IgT repertoires induced by high- and low-virulent infectious pancreatic necrosis virus strains in rainbow trout (Oncorhynchus mykiss)

## TL;DR

This study shows how different strains of a fish virus affect immune responses in rainbow trout, with one strain causing a strong but short-lived immune reaction.

## Contribution

The study reveals strain-specific differences in B cell repertoire modifications induced by IPNV, emphasizing the impact of VP2 variations on immune responses.

## Key findings

- IPNV-PT caused significant and diverse IgM repertoire changes in trout spleens, with clonotypic expansions in specific VH subgroups.
- The IgM response to IPNV-PT was largely non-convergent, with limited clonotype sharing across individuals.
- IPNV-TA induced only modest changes in the IgM repertoire, and IgT repertoire changes remained limited.

## Abstract

Infectious pancreatic necrosis virus (IPNV) is a significant pathogen in salmonid aquaculture, with virulence determined mainly by amino acid residues in the VP2 capsid protein.

This study investigates the modifications of rainbow trout (Oncorhynchus mykiss) IgM and IgT repertoire induced by two IPNV strains that differ at VP2 positions 217 and 221, specifically IPNV-TA (T217A221) and IPNV-PT (P217T221). For these studies, doubled-haploid isogenic trout were immunised with IPNV-TA or IPNV-PT, and IgHμ and IgHτ repertoires were analysed by high-throughput sequencing.

We demonstrated that IPNV-PT elicited a strong and diverse modification if the IgM repertoire in the spleen, with significant clonotypic expansions including public components, particularly within VH1, VH4, and VH8 subgroups, observed two months post-immunization. Despite this robust response, clonotype usage largely reflected a non-convergent immune profile, consisting essentially of private responses, with limited sharing across individuals. In contrast, IPNV-TA triggered only modest changes in the repertoire. Notably, the IgM response to IPNV-PT diminished by four months, with limited persistence of public clonotypes. Changes of spleen IgT repertoire remained limited.

These findings demonstrate that even minor VP2 variations can profoundly affect not only the magnitude but also the clonal architecture and composition of antiviral B cell responses, highlighting the importance of detailed, strain-specific immune profiling in guiding vaccine development for aquaculture.