Identification of immunodominant regions and linear B cell epitopes of the gE envelope protein of varicella-zoster virus

The envelope proteins of varicella-zoster virus (VZV) are highly immunogenic and one of the most abundant is glycoprotein E (gE). However, its immunodominant regions and epitopes have not been identified. In this study, using human sera from individuals with recent varicella or zoster infections, we have localized antigenic sequences of gE using recombinant hybrid Ty-virus-like particles (VLPs) carrying overlapping fragments of the gE protein. gE(1-134)-VLPs (particles carrying amino acids 1-134 of gE) and, to a lesser extent, gE(101-161)-VLPs were found to be the most antigenic when tested by Western blotting and ELISA. Other fragments of gE (spanning residues 161-623) showed weak or no antigenicity. Pepscan analysis of human sera on overlapping synthetic peptides representing residues 1-135 of gE revealed that the most antigenic region was between residues 50 and 135. Three immunodominant sequences (residues 86-105, 116-135, and, to a lesser extent, 56-75) were detected using sera from both varicella and zoster patients. All sera from varicella, but not zoster, patients reacted strongly with an epitope in peptide 66-85. Other epitopes were recognized weakly by some varicella or zoster sera. More sera need to be tested to assess the potential disease specificity of these epitopes. The neutralizing monoclonal antibody (MAb) IF-B9 reacted with residues 71-90; however, another neutralizing MAb, SG1A, which bound to both gE(1-134)-VLPs and gE(101-161)-VLPs did not bind to any peptide. The identification of immunodominant sequences of gE will help toward the development of a subunit VZV vaccine.

A baculovirus expression vector derived from the basic protein promoter of Autographa californica nuclear polyhedrosis virus

The basic protein of Autographa californica nuclear polyhedrosis virus (AcMNPV) is associated with virus DNA in virion nucleocapsids and is produced in infected cells during the late phase of gene expression. A transfer vector was constructed containing the beta-galactosidase gene, under the control of a copy of the putative basic protein promoter, in place of the polyhedrin gene within the AcMNPV EcoRI fragment I. After cotransfection of Spodoptera frugiperda cells with the transfer vector and infectious AcMNPV DNA, polyhedrin-negative recombinant viruses were selected which expressed high levels of beta-galactosidase. Radiolabelling of infected cell proteins showed that beta-galactosidase was expressed at the same time as the viral basic protein, between 8 to 24 h post-infection, with a peak synthesis at 12 to 15 h. These results demonstrated that the temporal regulation of the basic protein promoter was not affected by its position within the virus genome. Furthermore, a new baculovirus vector system is now available for high level expression of foreign genes at earlier times in infected cells.