CONSERVATION OF THE SPOROZOITE P67 VACCINE ANTIGEN IN CATTLE-DERIVED THEILERIA-PARVA STOCKS WITH DIFFERENT CROSS-IMMUNITY PROFILES

Immunity to Theileria parva infection in cattle is often parasite stoc k specific. The antigenic diversity which is expressed at the schizont stage of the parasite together with a wild reservoir of the organism in buffalo has complicated the development of effective disease contro l by immunization. We have previously shown that about 70% of cattle i noculated with recombinant forms of p67, a sporozoite stage-specific s urface antigen from the cattle-derived Muguga stock of the parasite, a re immune to a homologous challenge. Thus, immune responses to p67 can play a role in immunity. The genes encoding this protein in five othe r parasite stocks have been sequenced. Here, we report that the p67 mo lecule encoded by four cattle-derived parasite stocks (Boleni, Uganda, Mariakani, and Marikebuni) that fall into different cross-immunity gr oups is identical in sequence to Muguga p67. The protein encoded by a buffalo-derived parasite exhibits 95% sequence identity with Muguga p6 7, the major difference being the presence of a 43 residue peptide ins ert. As predicted by these data, cattle inoculated with recombinant p6 7 can resist a heterologous cattle-derived parasite challenge. Seven o f 12 cattle receiving a homologous Muguga challenge and 6 of 11 cattle receiving a heterologous Marikebuni challenge were immune to East Coa st fever. These results extend earlier data suggesting that p67 is a c onserved molecule and confirm its potential as a broad-spectrum vaccin e antigen for the control of T. parva infection.