The C-terminal regions of the envelope glycoprotein gp2 of equine herpesviruses 1 and 4 are antigenically distinct

Characterization of glycoproteins in equine herpesvirus-1

In this study, we attempted to express twelve glycoproteins of equine herpesvirus-1 (EHV-1) in 293T cells and to characterize these using monoclonal antibodies (MAbs) and horse sera against EHV-1. Expression of glycoprotein B (gB), gC, gD, gG, gI and gp2 was recognized by immunoblot analysis using horse sera, but that of gE, gH, gK, gL, gM and gN was not. Four MAbs recognized gB, four recognized gC and one recognized gp2. Two MAbs against gB cross-reacted with EHV-4. Interestingly, coexpression of gE and gI and gM and gN enhanced their antigenicity. Furthermore, immunoblot analysis of gp2 showed that different molecular masses of gp2 were recognized by the MAb against gp2 and horse sera against EHV-1. In this study, it was demonstrated that at least six glycoproteins were immunogenic to horses, and coexpression of gE and gI and gM and gN was important for enhancement of antigenicity.

MUC16/CA125 in the context of modular proteins with an annotated role in adhesion-related processes: in silico analysis

Mucin 16 (MUC16) is a type I transmembrane protein, the extracellular portion of which is shed after proteolytic degradation and is denoted as CA125 antigen, a well known tumor marker for ovarian cancer. Regarding its polypeptide and glycan structures, as yet there is no detailed insight into their heterogeneity and ligand properties, which may greatly influence its function and biomarker potential. This study was aimed at obtaining further insight into the biological capacity of MUC16/CA125, using in silico analysis of corresponding mucin sequences, including similarity searches as well as GO (gene ontology)-based function prediction. The results obtained pointed to the similarities within extracellular serine/threonine rich regions of MUC16 to sequences of proteins expressed in evolutionary distant taxa, all having in common an annotated role in adhesion-related processes. Specifically, a homology to conserved domains from the family of herpesvirus major outer envelope protein (BLLF1) was found. In addition, the possible involvement of MUC16/CA125 in carbohydrate-binding interactions or cellular transport of protein/ion was suggested.

Expression of the full-length form of gp2 of equine herpesvirus 1 (EHV-1) completely restores respiratory virulence to the attenuated EHV-1 strain KyA in CBA mice

Wild-type equine herpesvirus 1 (EHV-1) strains express a large (250-kDa) glycoprotein, gp2, that is encoded by EUs4 (gene 71) located within the unique short region of the genome. DNA sequence analysis revealed that EUs4 of the pathogenic EHV-1 strain RacL11 is an open reading frame of 2,376 bp that encodes a protein of 791 amino acids. The attenuated EHV-1 vaccine strain KyA harbors an in-frame deletion of 1,242 bp from bp 222 to 1461 and expresses a truncated gp2 of 383 amino acids. To determine the relative contribution of gp2 to EHV-1 pathogenesis, we compared the course of respiratory infection of CBA mice infected with either wild-type RacL11, attenuated KyA, or a recombinant KyA that expresses the full-length gp2 protein (KyARgp2F). Mice infected with KyA lost a negligible amount of body weight (0.18% total weight loss) on day 1 postinfection and regained weight thereafter, whereas mice infected with KyARgp2F or RacL11 steadily lost weight beginning on day 1 and experienced a 20 and 18% loss in body weight, respectively, by day 3. Immunohistochemical and flow cytometric analyses revealed higher numbers of T and B lymphocytes and an extensive consolidation consisting of large numbers of Mac-1-positive cells in the lungs of animals infected with KyARgp2F compared to animals infected with KyA. RNase protection analyses revealed increased expression of numerous cytokines and chemokines, including interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, MIP-2, interferon gamma-inducible protein, monocyte chemotactic protein 1, and T-cell activation gene 3 at 12 h postinfection with KyARgp2F. Three independent DNA array experiments confirmed these results and showed a 2- to 13-fold increase in the expression of 31 inflammatory genes at 8 and 12 h postinfection with KyARgp2F compared to infection with KyA. Taken together, the results indicate that expression of full-length gp2 is sufficient to restore full respiratory virulence to the attenuated KyA strain and raise caution concerning the inclusion of full-length gp2 in the development of EHV-1 vaccines.

In vitro and in vivo relevance of infectious laryngotracheitis virus gJ proteins that are expressed from spliced and nonspliced mRNAs

The positional homologue in the infectious laryngotracheitis virus (ILTV) genome of the glycoprotein gJ gene of herpes simplex virus and the gp2 gene of equine herpesvirus 1 is expressed into four proteins of 85, 115, 160, and 200 kDa (J. Veits, B. Kollner, J. P. Teifke, H. Granzow, T. C. Mettenleiter, and W. Fuchs, Avian Dis. 47:330-342, 2003). RNA analyses revealed that these proteins are expressed from two different late (gamma2) transcripts, an unspliced 5.5-kb and a spliced 4.3-kb mRNA that are translated into proteins of 985 and 611 amino acids, respectively. ILTV gJ is incorporated into virions and is modified by N- and O-linked glycosylation. After cotransfection of chicken cells with genomic DNA of a pathogenic ILTV strain and transfer plasmids, gJ-negative ILTV mutants could be isolated. In vitro growth studies demonstrated that deletion of the gJ gene has only minor effects on direct cell-to-cell spread as measured by plaque size. However, progeny virus titers of ILTV-DeltagJ were significantly reduced in comparison to those of the parental virus and a gJ rescue mutant. After experimental infection of chickens the gJ rescue mutant, like wild-type ILTV, caused severe disease and considerable mortality, whereas ILTV-DeltagJ was significantly attenuated. All immunized animals were protected against subsequent challenge infection with virulent ILTV. In sera collected after immunization with the gJ-rescue mutant or with wild-type ILTV, gJ-specific antibodies were detectable by immunofluorescence on cells that had been transfected with a gJ expression plasmid. As expected, no gJ-specific antibodies were found in sera obtained from chickens immunized with ILTV-DeltagJ. Thus, gJ deletion mutants of ILTV might be usable as attenuated live-virus vaccines. Furthermore, the gJ gene might constitute a reliable marker for serological discrimination between vaccinated and field virus-infected chickens.

The truncated form of glycoprotein gp2 of equine herpesvirus 1 (EHV-1) vaccine strain KyA is not functionally equivalent to full-length gp2 encoded by EHV-1 wild-type strain RacL11

Most equine herpesvirus 1 (EHV-1) strains, including the naturally occurring virulent RacL11 isolate, encode a large glycoprotein, gp2 (250 kDa), which is expressed from gene 71. Besides other alterations in the viral genome, the avirulent strain KyA harbors an in-frame deletion of 1,242 nucleotides in gene 71. To examine the contributions of gp2 variation to virus growth and virulence, mutant RacL11 and KyA viruses expressing full-length or truncated gp2 were generated. Western blot analyses demonstrated expression of a 250-kDa gp2 in cells infected with RacL11 virus or a mutant KyA virus harboring full-length gene 71, whereas a 75- to 80-kDa gp2 was detected in cells infected with KyA or mutant RacL11 virus expressing KyA gp2. The RacL11 gp2 precursor of 250 kDa in size and its truncated KyA counterpart of 80 kDa, as well as the 42-kDa carboxy-terminal gp2 subunit, were incorporated into virus particles. Absence of gp2 in RacL11 resulted in a 6-fold reduction of extracellular virus titers and a 13% reduction of plaque diameters, whereas gp2-negative KyA exhibited a 55% reduction in plaque diameter and a 51-fold decrease in extracellular virus titers. The massive growth defects of gp2-negative KyA could be restored by reinsertion of the truncated but not the full-length gp2 gene. The virulence of the generated gp2 mutant viruses was compared to the virulence of KyA and RacL11 in a murine infection model. RacL11 lacking gp2 was apathogenic for BALB/c mice, and insertion of the truncated KyA gp2 gene into RacL11 was unable to restore virulence. Similarly, replacement in the KyA genome of the truncated with the full-length RacL11 gene 71 did not result in the generation of virulent virus. From the results we conclude that full-length and truncated EHV-1 gp2 are not functionally equivalent and cannot compensate for the action of their homologues in allogeneic virus backgrounds.

Generation and characterization of an EICP0 null mutant of equine herpesvirus 1

The EICP0 gene (gene 63) of equine herpesvirus 1 (EHV-1) encodes an early regulatory protein that is a promiscuous trans-activator of all classes of viral genes. Bacterial artificial chromosome (BAC) technology and RecE/T cloning were employed to delete the EICP0 gene from EHV-1 strain KyA. Polymerase chain reaction, Southern blot analysis, and DNA sequencing confirmed the deletion of the EICP0 gene and its replacement with a kanamycin resistance gene in mutant KyA. Transfection of rabbit kidney cells with the EICP0 mutant genome produced infectious virus, indicating that the EICP0 gene is not essential for KyA replication in cell culture. Experiments to assess the effect of the EICP0 deletion on EHV-1 gene programming revealed that mRNA expression of the immediate-early gene and representative early and late genes as well as the synthesis of these viral proteins were reduced as compared to the kinetics of viral mRNA and protein synthesis observed for the wild type virus. However, the transition from early to late viral gene expression was not prevented or delayed, suggesting that the absence of the EICP0 gene did not disrupt the temporal aspects of EHV-1 gene regulation. The extracellular virus titer and plaque areas of the EICP0 mutant virus KyADeltaEICP0, in which the gp2-encoding gene 71 gene that is absent in the KyA BAC was restored, were reduced by 10-fold and 19%, respectively, when compared to parental KyA virus; while the titer and plaque areas of mutant KyADeltaEICP0Deltagp2 that lacks both the EICP0 gene and gene 71 were reduced more than 50-fold and 67%, respectively. The above results show that the EICP0 gene is dispensable for EHV-1 replication in cell culture, and that the switch from early to late viral gene expression for the representative genes examined does not require the EICP0 protein, but that the EICP0 protein may be structurally required for virus egress and cell-to-cell spread.