Theileria annulata sporozoite surface antigen expressed in Escherichia coli elicits neutralizing antibody.

Theileria annulata is an economically important protozoan parasite that threatens an estimated 250 million cattle with the disease tropical theileriosis. Development of a defined subunit vaccine is one means of trying to develop control measures against the disease. To this end we have characterized a surface antigen complex of the infective stage (sporozoite), by using a monoclonal antibody that neutralizes sporozoite infectivity in vitro. We have cloned the gene coding for this complex and have demonstrated that a fusion protein expressed from a fragment of this gene elicits strong neutralizing antibodies. Furthermore we provide data on the structure and expression of this gene. In particular we show that the region of the gene, expressed in one clone, codes for a protein segment relatively rich in proline residues. Also we demonstrate that expression of this gene appears to be stage specific, transcripts being present only in the sporoblast and sporozoite stages. The relevance of these findings to the production of a defined subunit vaccine is discussed.