Internal image rabbit anti-idiotypic antibody detects sheep antibodies to the bluetongue virus core protein VP7.

BACKGROUND Rabbit polyclonal anti-idiotypic antibodies (anti-Id) were generated against three murine monoclonal antibodies (MAbs) specific for the group-specific antigen VP7 of bluetongue virus (BTV) by the sequential immunization method. It was demonstrated by serological tests that part of the anti-Id possesses the characteristics of internal image anti-Id. By affinity purification against the individual MAbs, the internal image anti-Id, designated RAb2-A, was isolated and identified as specific for the MAb, M1875. OBJECTIVES To examine the ability of RAb2-A to detect sheep anti-VP7 antibodies by recognition of the common idiotype (Idx). STUDY DESIGN Affinity-purified RAb2-A IgG, along with VP7, was applied on the solid-phase of ELISA plate and the membrane for Western blot analysis to detect anti-VP7 antibodies from sheep that were immunized with VP7 or were experimentally infected with BTV. An inhibition ELISA was employed to determine whether sheep anti-VP7 and M1875 recognize the same or similar epitope(s). RESULTS RAb2-A recognised the Idx on anti-VP7 antibodies from sheep that were either immunized with VP7 or experimentally infected with BTV. Specificity of the reaction was confirmed by the observation that RAb2-A did not react with normal sheep serum or sheep antibodies against epizootic haemorrhagic disease of deer virus, a bluetongue-related disease virus in the Orbivirus genus. CONCLUSION The ability of RAb2-A to detect anti-VP7 antibodies through recognition of the Idx suggests that RAb2-A can be used as a probe to detect anti-BTV antibodies.