Induction of protective immunity to Theileria annulata using two major merozoite surface antigens presented by different delivery systems.

Allelic forms (Tams1-1 and Tams1-2) of the major merozoite surface antigen gene of Theileria annulata have recently been expressed in Escherichia coli and in Salmonella typhimurium aroA vaccine strain SL3261. To test the potential of subunit vaccines against T. annulata infection, we immunized four groups of three calves with either recombinant (re-) (Tams1-1 and Tams1-2) proteins or naked DNA encoding these antigens. Group I was immunized intramuscularly with both re-proteins incorporated into immunostimulating complexes (ISCOMs). Group II was inoculated intramuscularly with naked plasmid DNA encoding Tams1-1 and Tams1-2. Groups III and IV received S. typhimurium SL3261 [pSTams1-1][pIP5] and SL3261 [pSTams1-2] [pIP5] subcutaneously and orally, respectively. A final group of three animals (Group V) served as an unimmunized control group. Four weeks after the last immunization all calves were challenged with a T. annulata stabilate generated from blood of an infected animal with 30% piroplasm parasitaemia. All calves vaccinated with ISCOMs proved to be protected from T. annulata infection and had generated antibodies against both re-(Tams1-1 and Tams1-2) at the time of challenge. In two of these animals the antibody had a surface binding profile by IFAT. Two of three calves immunized with naked DNA also proved to be protected, but none of the animals had generated any detectable antibodies against the recombinants. Salmonella-based delivery of the recombinants did not induce any protection; two of six animals died of theileriosis and there was no difference between subcutaneous or oral administration. These preliminary results show that re-(Tams1-1 and/or Tams1-2) may elicit protective immune responses in cattle, depending on the antigen delivery system.