The glycoprotein of a fish rhabdovirus profiles the virus-specific T-cell repertoire in rainbow trout

T-cell responses to viruses are still poorly investigated in lower vertebrates. In rainbow trout, a specific clonal expansion of T cells in response to infection with viral haemorrhagic septicaemia virus (VHSV) was recently identified. Expanded T-cell clones expressed a unique 8 aa Vbeta4-Jbeta1 junction (SSGDSYSE) in different individuals, reminiscent of a typical public response. To get further insight into the nature of this response the modifications of the T-cell repertoire following immunization with plasmid expressing the VHSV external glycoprotein (G), which is the only protein involved in protective immunity, was analysed. After G-based DNA immunization, CDR3-length spectratypes were skewed for several Vbeta-Jbeta combinations, including Vbeta4-Jbeta1. In Vbeta4-Jbeta1, biases consisted of 6 and 8 aa junctions that were detected from day 52, and were still present 3 months after DNA immunization. Sequence analysis of the Vbeta4-Jbeta1 junctions showed that the 8 aa junction (SSGDSYSE) was clearly expanded, indicating that viral G protein was probably the target of the anti-VHSV public response. Additional 6 and 8 aa Vbeta4-Jbeta1 junctions were also expanded in G-DNA-vaccinated fish, showing that significant clonotypic; diversity was selected in response to the plasmid-delivered G protein. This higher clonotypic diversity may be related to the demonstrated higher efficiency of G-based DNA vaccines over whole virus immunization. The use of infectious hematopietic necrosis virus (IHNV) recombinant viruses, expressing the VHSV G protein, further substantiated the VHSV G-protein specificity of the 8 aa Vbeta4-Jbeta1 response and designated the 6 aa Vbeta4-Jbeta1 response as potentially directed to a T-cell epitope common to VHSV and HNV.