The serological relationship of BIV, other lentiviruses and retroviruses, can be assessed by various methods. In Western blots, BIV antiserum and CA antigen cross-react with corresponding CA antigen and antisera, respectively, from equine infectious anemia virus (EIAV), SIV and HIV-1. Cross-reactivity has also been found between the NC proteins of BIV and HIV-1. Heterologous competitive radioimmunoassays using radiolabeled HIVp24 (CA antigen) as competing antigen and a polyvalent BIV serum that contains reactivity to BIV CA antigen also have proved most informative in determining the serologic relationship of BIV to other lentiviruses (Fig. 5). In this assay, the lentiviruses, BIV, HIV-1, EIAV and SIV, all appear to compete completely; no other lentivirus or oncovirus gives appreciable competition. Thus, this assay indicates that the CA proteins of the competing lentiviruses share some common antigenic determinants that can be detected with precipitating anti-BIV serum.
Several functional proviral molecular clones of BIV have been sequenced, permitting an assessment of the amount of genetic variability which exists within a single isolate. Numerous point mutations are present within the genome; those which cause coding substitutions are most prevalent in the env coding region. The present data suggest that BIV displays significant genomic variability. It is not yet known whether coding substitutions in Env translate into antigenic variants, as has been shown for visna virus and EIAV.
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