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

Abstract

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 Vb4-Jb1 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 Vb-Jb combinations, including Vb4-Jb1. In Vb4-Jb1, 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 Vb4-Jb1 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 Vb4-Jb1 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 Vb4-Jb1 response and designated the 6 aa Vb4-Jb1 response as potentially directed to a T-cell epitope common to VHSV and IHNV.

A Single Amino Acid Mutation (I1012F) of the RNA Polymerase of Marine Viral Hemorrhagic Septicemia Virus Changes In Vitro Virulence to Rainbow Trout Gill Epithelial Cells

“…The importance of the G protein in VHSV virulence has been subjected to a lot of research, motivated partly by the fact that the G protein is involved in virus attachment and entry (25). However, it has not been possible to link particular residues or motifs of the G protein to virulence.…”

“…For the NV ORF, we also introduced a three-amino-acid en-block mutation, VSE to ILD (positions 55 to 57). The candidate proteins (G, NV, and L) were chosen because the G protein is a membrane protein involved in virus attachment and entry (25) and the NV protein has been shown to have an impact on antiapoptosis functions and virulence (23). There are very few, if any, studies addressing to what extent the polymerase plays a role in the virulence of novirhabdoviruses, but it is well known that a single amino acid mutation in PB2 (polymerase B2 protein) of human influenza virus renders the virus able to replicate in chicken cells (26).…”

The antiviral defense mechanisms in mandarin fish induced by DNA vaccination against a rhabdovirus

“…Viral G protein can interact with cell-surface receptors to mediate not only virus entry, but also the host immune system activation (Verjan et al, 2008), and N protein plays a critical role in the encapsidation and replication of viral genomic RNA (Green et al, 2006). Previous reports of DNA vaccination with VHSV G gene have shown that injected plasmids could be taken up by muscle cells at the site of injection and the viral G protein is expressed on the surface of myocytes, hereby interacting with the surface cell receptors to activate the immune system of the fish (Boudinot et al, 2004;Lorenzen et al, 2005Lorenzen et al, , 2009. It is likely that plasmid DNA containing SCRV G gene functions in a similar way to activate the immune system of the mandarin fish, thus protecting the fish from virus infection.…”

Identifying potential virulence determinants in viral haemorrhagic septicaemia virus (VHSV) for rainbow trout

“…Sequencing data previously available for the G protein of both isolates of VHSV used here identified 2 nt substitutions leading to a single aa substitution (Ser113Gly position; 0.2%); this finding was further verified in the present study, both from infected cells and harvested tissue. The G protein is responsible for host cellular entry of the virus by means of receptormediated endocytosis, is the target molecule for neutralizing antibodies (Boudinot et al 2004), and has already been demonstrated to play a decisive role in determining the virulence of VHSV (Béarzotti et al 1995. The position of this mutation proved interesting.…”