Characterisation of the gene encoding a candidate vaccine antigen of Theileria parva sporozoites.

We have cloned and characterised the gene encoding the 67-kilodalton stage-specific surface antigen, p67, of Theileria parva (Muguga) sporozoites. The gene which is present in a single copy, is divided into 2 exons by an intron 29 bp long and is transcribed into mRNA of about 2500 nucleotides. The gene is present in all stocks of T. parva and there is a related gene in Theileria annulata. The deduced amino acid sequence of 709 residues predicts that p67 is a membrane protein and that it lacks tandemly repeated sequences. Recombinant p67 has been expressed in Escherichia coli as a fusion protein with Sj-26, a glutathione-S-transferase of Schistosoma japonicum. Antibodies to purified recombinant proteins containing residues 9-316 or 397-709 of p67 bind to p67 in immunoblots and neutralise sporozoite infectivity in vitro. Recombinant p67 is, therefore, a candidate antigen for development of an anti-sporozoite vaccine for East Coast fever in cattle.