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

Introduction: 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. Methods: ). 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. Resutls: 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. Discussion: 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.