Antigens derived from the midgut of Boophilus microplus have previously been associated with vaccine-induced protection against tick infestation. Polyclonal sera from cattle hyperinfested with B. microplus, and from cattle vaccinated and protected against B. microplus challenge were used in conjunction with the monoclonal antibody QU13, which recognises protective glycan epitopes of B. microplus, to identify cross-reacting and protective antigens in various tick extracts. Western blot and dot-ELISA assays using the above antibody probes revealed that known protective antigens were conserved across 10 isolates of B. microplus in Queensland, Australia. Known protective antigens were also found to be conserved across several species of ixodid ticks of veterinary significance in South Africa and Zimbabwe including B. microplus, B. decoloratus, Amblyomma variegatum,
Amblyomma hebraeum, Hyalomma truncatum and Rhipicephalus appendiculatus. Cross-reacting antigens were identified by QU13 in the midgut and salivary glands of all species and strains investigated.
Immunohistological techniques were employed to investigate whether protective antigens recognised by QU13 were concealed from, or exposed to, the host during infestation. Biopsies of cattle skin at B. microplus attachment sites were probed with QU13, which bound specifically to areas surrounding the feeding lesion indicating that the protective carbohydrate epitopes recognised by QU13 are exposed to the host during infestation.
These results suggest that potential exists for a multi-specific tick vaccine and for enhancing naturally acquired immune responses to protect against tick infestation.