Expression of the outer capsid protein, VP2, from a full length cDNA clone of genome segment 2 of bluetongue serotype 1 from South Africa, using both Sp6 and vaccinia expression systems and a comparison of the nucleic acid sequence of this segment with those of other serotypes

Phylogenetic comparison of the serotype-specific VP2 protein of bluetongue and related orbiviruses

Regions of the VP2 gene from various bluetongue virus serotypes were sequenced and phylogenetic comparisons were performed. The sequences were characteristic for each BTV serotype and isolates of the same serotype could be grouped geographically, mimicking the topotyping characteristics of BTV VP3 gene sequences. PCR amplification and sequence analysis were used to show the close relationship between Caribbean BTV isolates and South African BTV isolates of the same serotype. Similarly, Australian BTV isolates showed a close genetic relationship with Asian BTV isolates of the same serotype. A multiple amino acid sequence alignment of fifteen BTV serotypes and other orbiviruses over a proposed major neutralization site showed this region (317 335 aa.) was highly variable and nucleotide sequences showed that BTV serotypes could be grouped into nucleotypes, or related serotypes, in broad agreement with the inter-relationships postulated by Erasmus (1990), using plaque-reduction tests.

Genetic variation and evolutionary relationships amongst bluetongue viruses endemic in the United States

The genetic variation and evolutionary relationships amongst the five serotypes of bluetongue virus (BTV) endemic to the United States were investigated by oligonucleotide fingerprint analysis. The viruses analyzed include prototype viruses of the five U.S. serotypes, and 32 viruses isolated from domestic and wild ruminants from the U.S. in the years 1979-1981. With the exception of serotype 2, most genes encoding the viral core and non-structural proteins were demonstrated to be highly conserved both within and between serotypes and some also appear to have reassorted in nature. Gene segments 2 and 6, which encode the outer capsid proteins VP2 and VP5 respectively, were more variable and were not consistently linked as serotype determination was dependent solely on gene segment 2. Gene segment 2 was the most variable gene between serotypes, but it was highly conserved within serotypes and stable over time. This suggests that the emergence of new BTV serotypes, which would require the stable incorporation of numerous mutations, must be a very slow process. Fingerprint comparisons further suggested that BTV serotypes 10, 11, 13 and 17 have evolved together in the U.S. over a considerable period of time, whereas serotype 2, which is genetically distinct, has evolved elsewhere and is most likely a recent introduction to North America.

High level expression of the major core protein VP7 and the non-structural protein NS3 of bluetongue virus in yeast: use of expressed VP7 as a diagnostic, group-reactive antigen in a blocking ELISA

The major core protein VP7 and a non-structural protein NS3 of bluetongue virus serotype 1 have been synthesized from recombinant plasmids using both an in vitro transcription/translation system and a yeast expression system. Bluetongue virus genes were transcribed under the control of the bacteriophage SP6 promoter and the regulatable yeast metallothionein promoter. An indirect ELISA showed that expression of NS3 in yeast was inducible with 1 mM CuSO4 and VP7 synthesis was constitutive but could be further induced. The preferred procedure for antigen extraction from yeast was sonication for VP7 and SDS/NaOH treatment for NS3. Yeast-expressed VP7 antigen and a monoclonal antibody were used in a blocking ELISA to distinguish sera raised against bluetongue virus serotypes from those generated to viruses of the epizootic haemorrhagic disease serogroup.

Relationships amongst bluetongue viruses revealed by comparisons of capsid and outer coat protein nucleotide sequences

Sequence data from the gene segments coding for the capsid protein. VP3, of all eight Australian bluetongue virus serotypes were compared. The high degree of nucleotide sequence homology for VP3 genes amongst BTV isolates from the same geographic region supported previous studies (Gould, 1987; 1988b, c; Gould et al., 1988b) and was proposed as a basis for "topotyping" a bluetongue virus isolate (Gould et al., 1989). The complete nucleotide sequences which coded for the VP2 outer coat proteins of South African BTV serotypes 1 and 3 (vaccine strains) were determined and compared to cognate gene sequences from North American and Australian BTVs. These VP2 comparisons demonstrated that BTVs of the same serotype, but from different geographical regions, were closely related at the nucleotide and amino acid levels. However, close inter-relationships were also demonstrated amongst other BTVs irrespective of serotype or geographic origin. These data enabled phylogenic relationships of the BTV serotypes to be analysed using VP2 nucleotide sequences as a determinant.

Identification of a bluetongue virus serotype 1-specific ovine helper T-cell determinant in outer capsid protein VP2

Ovine T-cell lines (including one clone [101A]), which are specific for Bluetongue virus serotype 1 (BTV1), have been established and characterized. Although these T-cell lines react with different isolates of BTV1 (including those from South Africa, Australia, Nigeria, and Cameroon), they do not react with heterologous BTV serotypes. Antigen specificity of these T-cells was studied using purified virus particles, infectious subviral particles (ISVP) and cores, or using individual BTV structural proteins that were either isolated by SDS-PAGE or expressed by recombinant strains of vaccinia virus. The results showed that each of the T-cell lines reacted with outer capsid protein VP2 (the BTV protein exhibiting most serotype-specific variation and the major neutralization antigen). However, all of the uncloned T-cell lines also reacted with either the core structural proteins or the outer capsid protein VP5. In contrast, the T-cell clone 101A only reacted with outer capsid protein VP2. Cell surface marker analysis showed that 101A has a helper T-cell phenotype (CD5+, CD4+, CD8-, T-19-). The T-cell lines and clone 101A all produced large amounts of interleukin 2 (IL-2) when stimulated with purified BTV1 virus particles, or with VP2 (up to 120 IU/ml from 2 x 10(5) T-cells). BTV serotype-specific antigenic sites, for B cells and at least one site for ovine helper T-cells, are therefore located within VP2.