Induction of antibodies to the bluetongue virus core polypeptide VP7 in sheep by internal image rabbit antiidiotypic antibodies.

We previously generated rabbit polyclonal antiidiotypic antibody (anti-Id) to a murine monoclonal antibody (M1875) specific for the bluetongue virus core protein VP7, and demonstrated that this anti-Id (designated RAb2-A) had the characteristics of an internal image anti-Id (Ab2 beta). In this communication, RAb2-A was used to induce immune responses in sheep and the responses were compared to immunization with VP7. The immune sera were tested for the presence of anti-VP7 antibodies and the expression of the Id of M1875. Animals immunized with RAb2-A were able to produce M1875-like antibody responses, i.e., they recognized the same or a similar epitope as M1875 and possessed the M1875 Id, without subsequent exposure to the original antigen. This was demonstrated by showing that antibodies induced by RAb2-A (i) reacted specifically with the immunizing anti-Id, (ii) were capable of binding VP7, (iii) inhibited M1875 from binding to VP7, and (iv) inhibited M1875 from binding to RAb2-A. Animals immunized with purified VP7 produced antibodies that possessed the epitope and idiotope specificity of M1875. No antibody responses to VP7 were detected in control animals immunized with either rabbit anti-Id to the pseudorabies virus glycoprotein gII or BHK-21 cell proteins. We conclude that rabbit anti-Id RAb2-A serologically mimics an M1875-defined VP7 epitope sufficiently to function as a surrogate antigen for inducing anti-bluetongue virus VP7 responses.