Protection of cattle from bovine herpesvirus type I (BHV-1) infection by immunization with individual viral glycoproteins

Expression of bovine herpesvirus 1 glycoproteins gI and gIII in transfected murine cells

Genes encoding two of the major glycoproteins of bovine herpesvirus 1 (BHV-1), gI and gIII, were cloned into the eucaryotic expression vectors pRSVcat and pSV2neo and transfected into murine LMTK- cells, and cloned cell lines were established. The relative amounts of gI or gIII expressed from the two vectors were similar. Expression of gI was cell associated and localized predominantly in the perinuclear region, but nuclear and plasma membrane staining was also observed. Expression of gI was additionally associated with cell fusion and the formation of polykaryons and giant cells. Expression of gIII was localized predominantly in the nuclear and plasma membranes. Radioimmunoprecipitation in the presence or absence of tunicamycin revealed that the recombinant glycoproteins were proteolytically processed and glycosylated and had molecular weights similar to those of the forms of gI and gIII expressed in BHV-1-infected bovine cells. However, both recombinant glycoproteins were glycosylated to a lesser extent than were the forms found in BHV-1-infected bovine cells. For gI, a deficiency in N-linked glycosylation of the amino-terminal half of the protein was identified; for gIII, a deficiency in O-linked glycosylation was implicated. The reactivity pattern of a panel of gI- and gIII-specific monoclonal antibodies, including six which recognize conformation-dependent epitopes, was found to be unaffected by the glycosylation differences and was identical for transfected or BHV-1-infected murine cells. Use of the transfected cells as targets in immune-mediated cytotoxicity assays demonstrated the functional recognition of recombinant gI and gIII by murine antibody and cytotoxic T lymphocytes. Immunization of mice with the transfected cells elicited BHV-1-specific virus-neutralizing antibody, thus verifying the antigenic authenticity of the recombinant glycoproteins and the important role of gI and gIII as targets of the immune response to BHV-1 in this murine model system.

Passively administered neutralizing monoclonal antibodies do not protect calves against bovine herpesvirus 1 infection

Monoclonal antibodies specific for defined epitopes on the gI, gIII and gIV envelope glycoproteins of BHV-1 were used individually or in glycoprotein-monospecific pools for passive immunization of young calves. Although serum antibody titres comparable to those found in naturally infected and recovered calves were achieved, passive immunization failed to prevent the growth of BHV-1 in nasal and ocular mucosa and did not decrease the duration of viral shedding.

Epitope specificity and protective efficacy of the bovine immune response to bovine herpesvirus-1 glycoprotein vaccines

Bovine herpesvirus-1 (BHV-1) envelope glycoproteins gI, gIII and gIV were individually purified on monoclonal antibody affinity columns and injected intradermally into BHV-1 seronegative calves. The calves developed serum neutralizing antibodies that monospecifically precipitated the immunizing glycoprotein from a preparation of 125I-labelled BHV-1 envelope proteins. A competitive radioimmunoassay using the bovine antisera demonstrated that known functional epitopes had been retained in the glycoprotein vaccines. Calves immunized with the gI, gIII or gIV glycoproteins were not protected from intranasal challenge with BHV-1 and had levels and duration of viral shedding in their nasal secretions similar to those of non-immunized control calves.

Monoclonal antibody analysis of bovine herpesvirus-1 glycoprotein antigenic areas relevant to natural infection

Neutralizing antigenic areas on the glycoproteins of bovine herpesvirus-1 (BHV-1) were identified by reciprocal competition radioimmunoassays using monoclonal antibodies. Three interrelated and two independent antigenic areas were identified on the 77-kDa (K) gIV envelope glycoprotein. Antigenic analysis of this protein has not been previously described. Four interrelated and one independent antigenic areas were found on the 97K gIII envelope glycoprotein. A third group of monoclonal antibodies reacting in Western blot with the 74K subunit of gI, a 130K disulfide-linked 74K/55K heterodimer, revealed four interrelated antigenic areas. All of the antigenic areas on all three glycoproteins were reactive with neutralizing monoclonal antibodies and all were targets for antibody-complement lysis. However, antibodies against gIV were the most efficient at neutralizing the virus and rendering infected cells susceptible to antibody-complement lysis. Convalescent sera from experimentally infected calves were used in a competitive radioimmunoassay to confirm that each antigenic area on the gI, gIII, or gIV glycoproteins was a target for bovine antibodies during primary infection with BHV-1.

Functional and topographical analyses of epitopes on bovine herpesvirus type 1 glycoprotein IV

Bovine herpesvirus type 1 (BHV-1) glycoprotein gIV was purified by affinity chromatography. Purified preparations showed two distinct components of 71 K and 140 K following electrophoresis in sodium dodecyl sulphate polyacrylamide gels. The polypeptides were separated, excised from the gel and used to immunize rabbits; the resulting antisera showed a high degree of cross reactivity indicating that these polypeptides represent monomeric and dimeric forms of the same glycoprotein. Purified gIV was also used to develop a gIV-specific panel of monoclonal antibodies. Neutralizing monoclonal antibodies directed against gIV were conjugated to horseradish peroxidase and subjected to competition binding assays by ELISA. Three distinct neutralizing antigenic domains on gIV were identified. Domain 1 comprised two overlapping epitopes, whereas domain 2 was represented by a single monoclonal antibody. The third antigenic domain was made up of a complex of four identical or overlapping epitopes designated 3a, b, c, and d. Evidence is presented suggesting that domain 1 of gIV may be involved in penetration of the virus into the cell.