A recombinant viral haemorrhagic septicaemia virus glycoprotein expressed in insect cells induces protective immunity in rainbow trout

Abstract

Viral haemorrhagic septicaemia (VHS) is a fish rhabdovirus infection of world-wide importance. Control policies have been established but the disease still causes heavy losses in fish farming. The development of a recombinant subunit vaccine was initiated to produce a safe and effective vaccine to protect fish against VHS. The VHS virus (VHSV) glycoprotein, which induces neutralizing antibodies in rainbow trout, was chosen for expression in insect cells using a baculovirus vector. The Mr of the recombinant protein estimated by SDS-PAGE I was slightly lower than that of the native viral protein.The recombinant protein displayed different degrees of glycosylation and was recognized in ELISA by neutralizing antibodies. It was transported to the plasma membrane of insect cells where its ability to induce membrane fusion was preserved. The efficacy of the recombinant protein as a vaccine was compared with those of an inactivated and an attenuated vaccine. When injected intraperitoneally into rainbow trout, the baculovirus-encoded protein was shown (i) to induce the synthesis of VHSV-neutralizing antibodies and (ii) to confer protection against virus challenge. Immunization performed by immersion failed. This is the first report of a recombinant vaccine that protects fish against VHSV.

Temperature and pH requirements for viral haemorrhagic septicemia virus induced cell fusion

“…The optimal pH of fusion was approximately 6 (Fig 2). Similarly, infection of insect cells with VHSV gave rise to syncytia when the pH of the cell culture medium was 6.2 (Lorenzen & Olesen 1995), and insect cells transfected with plasmids expressing the G protein also gave rise to a pH 6 dependent fusion (Lecocq-Xhonneux et al 1994). Most probably, a pH of -6 is needed to induce conformational changes in the G protein of VHSV, thus exposing some regions for fusion, as suggested by the results obtained from binding experiments of anti-p2 to G (Estepa & Coll 1996).…”

Mutations in the glycoprotein of viral haemorrhagic septicaemia virus that affect virulence for fish and the pH threshold for membrane fusion.

“…Like mammalian rhabdoviruses, VHSV was shown to have a low-pH-induced fusogenic activity mediated by the viral G protein (Lecocq-Xhonneux et al, 1994 ;Estepa & Coll, 1996). As some of our attenuated mutants had mutations near domains involved in fusion (mutations at positions 139 and 140) or in control of low-pH-induced conformational change (mutations at positions 431 and 433), we decided to investigate this critical step in virus entry.…”

“…Like other rhabdoviruses , VHSV has a transmembrane G protein that is responsible for attachment to the cell membrane and entry into the cell by a process of receptor-mediated endocytosis (Lecocq-Xhonneux et al, 1994). Fusion of the viral membrane with the endosomal membrane, triggered by the low pH of the endosomal compartment, allows delivery of the viral nucleocapsid into the cytoplasm.…”

Vaccination Against Red Sea Bream Iridoviral Disease in Red Sea Bream.

“…Most vaccine experiments against viral diseases have also been conducted using inactivated viruses such as IPNV (Dorson 1988, Tatner 1993, IHN , Tatner 1993, VHS (de Kinkelin 1988, Tatner 1993, CCV (Plumb 1988, Tatner 1993 and SVC (Fijan 1988), though some trials have recently been made using component vaccines (Gilmore et al, 1988, Lecocq-Xhonneux et al, 1994. Difficulty of mass production of viral antigens sometimes become an obstacle for practical application of vaccines.…”