Analysis of swinepox virus antigens using monoclonal antibodies

Development of a dot blot neutralizing assay for HHV-6 and HHV-7 using specific monoclonal antibodies

To elucidate further immune responses to human herpesviruses 6 and 7 (HHV-6 and -7), a neutralizing antibody assay was established for these viruses using a dot blot method. Three monoclonal antibodies against HHV-6 and 12 monoclonal antibodies against HHV-7 were developed and characterized by radio-immunoprecipitation. One monoclonal antibody which recognizes the 135 kDa late polypeptide of HHV-6 and several which recognize the 125 kDa late polypeptide of HHV-7 were selected to monitor virus growth by a dot blot antigen-detection method. The dot blot method was then used for the assay of HHV-6 and -7 neutralizing antibodies in human serum samples. The neutralization endpoints determined by the dot blot were comparable to those determined by immunofluorescence (IF). The neutralizing antibody titers appeared to correlate with the antibody titers determined by the indirect IF antibody test. The dot blot neutralization assay is easy to perform, is highly reproducible and objective when compared with the conventional methods based on cytopathology or IF for determining neutralization endpoints.

Recombinant swinepox virus expressing beta-galactosidase: investigation of viral host range and gene expression levels in cell culture

Swinepox virus (SPV) has been proposed as a potential vector for generating recombinant vaccines for swine. However, little is known about important aspects of SPV biology, such as the functionality of SPV promoters or the host range of SPV. Using a transient expression assay, well-characterized vaccinia virus promoters were shown to be active in cells infected with SPV. A recombinant SPV expressing beta-galactosidase (beta-gal) was constructed and characterized. The E. coli LacZ gene was placed under the control of a strong vaccinia synthetic early/late promoter and was inserted by homologous recombination in a noncoding region of the SPV genome. The recombinant SPV expressing beta-gal was used to characterize the host range of the virus by measuring protein expression and virus production in different cell lines. In general, SPV expressed more protein and grew more efficiently than vaccinia virus in porcine cell lines. Surprisingly, the recombinant SPV was able to infect and replicate in several cell lines of nonswine origin. The virus directed regulated early and late gene expression of beta-gal in those cells and formed blue plaques in cell monolayers in the presence of X-gal. Upon infection with the recombinant SPV, there was a significant level of viral replication, and the virus can be serially passaged in some nonswine cell lines. The data presented suggest that despite the strict host tropism of SPV, the virus exhibits a relatively broad host range in cell culture.

In vitro selection of variants of herpes simplex virus type 1 which differ in cytopathic changes

To analyze the mechanisms for in vitro emergence of the syncytial variants of herpes simplex virus type 1 (HSV-1), several cell lines were infected with a mixture of equal amounts of two HSV-1 variants, one syncytial and the other non-syncytial, and changes in their relative abundance were monitored during passage. With a combination of two variants of the Miyama strain of HSV-1, the syncytial variant became dominant during passage in Vero, RK-13 and FL cells. On the other hand, the ratios of the two variants remained around 1:1 during the passage in HEp-2, MGC and HEL cells. In another set of variants of the SKO strain of HSV-1, the outcomes were different from those of the Miyama strain in the FL, MGC and HEp-2 cells. The ratios of the two variants remained around 1:1 during passage in FL cells, while the non-syncytial variant became dominant during passage in MGC and HEp-2 cells. In addition, we examined the effects of a complement and interferon-beta (IFN-beta) on the outcome of the selection. As a result, the complement slowed the selection of a syncytial variant, whereas IFN-beta facilitated it.