Characterization of envelope proteins of alcelaphine herpesvirus 1

Alcelaphine herpesvirus 1 glycoprotein B: recombinant expression and antibody recognition

The gammaherpesvirus alcelaphine herpesvirus 1 (AlHV-1) causes fatal malignant catarrhal fever (MCF) in susceptible species including cattle, but infects its reservoir host, wildebeest, without causing disease. Pathology in cattle may be influenced by virus-host cell interactions mediated by the virus glycoproteins. Cloning and expression of a haemagglutinin-tagged version of the AlHV-1 glycoprotein B (gB) was used to demonstrate that the AlHV-1-specific monoclonal antibody 12B5 recognised gB and that gB was the main component of the gp115 complex of AlHV-1, a glycoprotein complex of five components identified on the surface of AlHV-1 by immunoprecipitation and radiolabelling. Analysis of AlHV-1 virus particles showed that the native form of gB was detected by mAb 12B5 as a band of about 70 kDa, whilst recombinant gB expressed by transfected HEK293T cells appeared to be subject to additional cleavage and incomplete post-translational processing. Antibody 12B5 recognised an epitope on the N-terminal furin-cleaved fragment of gB on AlHV-1 virus particles. It could be used to detect recombinant and virus-expressed gB on western blots and on the surface of infected cells by flow cytometry, whilst recombinant gB was detected on the surface of transfected cells by immunofluorescence. Recombinant gB has potential as an antigen for ELISA detection of MCF virus infection and as a candidate vaccine antigen.

Identification of immuno-reactive capsid proteins of malignant catarrhal fever viruses

Malignant catarrhal fever (MCF) is a fatal disease of cattle and other ungulates caused by certain gamma-herpesviruses including alcelaphine herpesvirus-1 (AlHV-1) and ovine herpesvirus-2 (OvHV-2). An attenuated virus vaccine based on AlHV-1 has been shown to induce virus-neutralising antibodies in plasma and nasal secretions of protected cattle but the targets of virus-specific antibodies are unknown. Proteomic analysis and western blotting of virus extracts allowed the identification of eight candidate AlHV-1 virion antigens. Recombinant expression of selected candidates and their OvHV-2 orthologues confirmed that two polypeptides, the products of the ORF17.5 and ORF65 genes, were antigens recognised by antibodies from natural MCF cases or from AlHV-1 vaccinated cattle. These proteins have potential as diagnostic and/or vaccine antigens.

Malignant catarrhal fever: a review

Malignant catarrhal fever (MCF) is a fatal lymphoproliferative disease of cattle and other ungulates caused by the ruminant gamma-herpesviruses alcelaphine herpesvirus 1 (AlHV-1) and ovine herpesvirus 2 (OvHV-2). These viruses cause inapparent infection in their reservoir hosts (wildebeest for AlHV-1 and sheep for OvHV-2), but fatal lymphoproliferative disease when they infect MCF-susceptible hosts, including cattle, deer, bison, water buffalo and pigs. MCF is an important disease wherever reservoir and MCF-susceptible species mix and currently is a particular problem in Bali cattle in Indonesia, bison in the USA and in pastoralist cattle herds in Eastern and Southern Africa. MCF is characterised by the accumulation of lymphocytes (predominantly CD8(+) T lymphocytes) in a variety of organs, often associated with tissue necrosis. Only a small proportion of these lymphocytes appear to contain virus, although recent results with virus gene-specific probes indicate that more infected cells may be present than previously thought. The tissue damage in MCF is hypothesised to be caused by the indiscriminate activity of MHC-unrestricted cytotoxic T/natural killer cells. The pathogenesis of MCF and the virus life cycle are poorly understood and, currently, there is no effective disease control. Recent sequencing of the OvHV-2 genome and construction of an AlHV-1 bacterial artificial chromosome (BAC) are facilitating studies to understand the pathogenesis of this extraordinary disease. Furthermore, new and improved methods of disease diagnosis have been developed and promising vaccine strategies are being tested. The next few years are likely to be exciting and productive for MCF research.

Proteomic analysis of pathogenic and attenuated alcelaphine herpesvirus 1

The gammaherpesvirus alcelaphine herpesvirus 1 (AlHV-1) causes malignant catarrhal fever in susceptible ungulates but infects its natural host, wildebeest, without obvious clinical signs. In tissue culture, AlHV-1 is initially predominantly cell associated and virulent but on extended culture becomes cell-free and attenuated. We wanted to determine what changes in protein composition had taken place during the transition from virulent to attenuated virus in culture. Purified virus preparations were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and proteins were analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry. Peptides were identified in serial gel slices by using MASCOT software to interrogate virus-specific and nonredundant sequence databases. Twenty-three AlHV-1-encoded proteins and six cellular proteins were identified in the attenuated and virulent viruses. Two polypeptides were detected in only the virulent virus preparations, while one other protein was found in only the attenuated virus. Two of these virus-specific proteins were identified by a single peptide, suggesting that these may be low-abundance virion proteins rather than markers of attenuation or pathogenesis. The results suggest that attenuation of AlHV-1 is not the result of gross changes in the composition of the virus particle but probably due to altered viral gene expression in the infected cell.

Malignant catarrhal fever virus. Characterization of a United States isolate and development of diagnostic assays

Malignant catarrhal fever (MCF) is a severe lymphoproliferative disease of certain domestic and wild ruminants. Two distinct but closely related viruses cause clinically indistinguishable syndromes in susceptible ruminant species: wildebeest-associated MCF virus (WA-MCFV) and sheep-associated MCF virus (SA-MCFV). Neither the pathogenesis nor the epidemiology of SA-MCF is understood, primarily because of a lack of adequate detection methods for the etiologic agent or antibody against that agent. Work designed to develop these tests has been under way in our laboratory. To obtain basic information about the virus, the in vitro growth properties of a US isolate of MCF virus were studied and its major viral proteins identified and characterized by a panel of monoclonal antibodies generated against the isolate. A monoclonal antibody to a broadly conserved epitope of MCF virus was identified, and a competitive-inhibition ELISA (CI-ELISA) was developed for detection of anti-MCF antibody in sheep and other ruminants. The monoclonal antibody (15-A) reacted with an epitope located on a glycoprotein complex, which was present in all isolates of MCF virus examined. Antibody from a wide variety of ruminants infected with MCF virus of both sheep and wildebeest origin competed with the monoclonal antibody 15-A for the epitope, which was not present on 14 other common ruminant viruses. The assay detected antibody in inapparently infected sheep, and in cattle, deer, and bison with clinical MCF. A PCR assay for DNA of the sheep-associated virus was developed, based on previously reported primers. Comparative studies demonstrated that the CI-ELISA was specific for MCFV antibody and that the PCR was more reliable for diagnosis of clinical MCF.

Identification and analysis of an alcelaphine herpesvirus 1 (AHV-1) cDNA clone expressing a fusion protein recognized by AHV-1-neutralizing antisera

Rabbit antiserum to psoralen-inactivated alcelaphine herpesvirus 1 (AHV-1) virions was shown to react specifically with AHV-1-infected cells by indirect immunofluorescence. Western blot analysis using this antiserum identified a 15-kD virion protein that was also detected in infected-cell proteins between 12 and 144 h p.i., and a 37-kD protein present in infected cells between 24 and 120 h p.i. A cDNA library was constructed using mRNA obtained from AHV-1-infected fetal mouflon sheep kidney (FMSK) cells at 48 h p.i., when infected-cell proteins detected by antiserum were in abundance. Screening of the library with the rabbit anti-AHV-1 serum identified several positive clones. Southern blot analysis showed that one clone, designated 8'a, hybridized to a 4.4 kb HindIII fragment of AHV-1 DNA. This AHV-1 cDNA clone expressed a fusion protein that was recognized by serum from a naturally and asymptomatically infected white-bearded wildebeest (Connochaetes taurinus albojubatus). The insert was sequenced and found to contain 833 bp. A search of the GenBank database for related sequences revealed greater than 40% homology to several other gammaherpesviruses: herpesvirus saimiri, cottontail herpesvirus, and Epstein-Barr virus.

Analysis of bovine herpesvirus 4 (DN 599) major antigens with monoclonal antibodies and polyclonal immune serum

Monoclonal antibodies (MAbs) and polyclonal immune sera were produced and used to identify the major antigens of bovine herpesvirus type 4 (BHV-4). SDS-polyacrylamide gel electrophoresis of immunoprecipitates of radiolabeled lysates from infected cells resolved 24 peptide bands varying from 12 kDa to over 300 kDa. Six peptides were identified as major viral antigens by immunoprecipitation. Based on the pattern of radioimmunoprecipitation, MAbs were assigned into four groups. Group 1 precipitated a tunicamycin-sensitive glycoprotein complex which contained six components (245, 190, 152, 123, and 48/46 kDa). Deglycosylation with endoglycosidase F revealed two peptides with Mr of 93 and 38 kDa as the basic peptides of the glycoprotein complex. In addition, a 115 kDa glycopeptide containing glycan-peptide bonds of mixed type was identified. Group 2 precipitated a non-glycosylated protein complex consisting of three monomers (33/31/30 kDa). Groups 3 and 4 reacted with single monomeric non-glycosylated peptides with Mr of 48 and 14 kDa, respectively. Although none of the MAbs exhibited significant neutralizing activity, some reacted strongly in immunosorbent and/or immunohistochemical assays, suggesting they may be good candidates for use in diagnostic assays.