Identification of a Theileria annulata antigen expressed in multiple stages of the parasite life cycle.

In order to identify sporozoite surface molecules which may be involved in invasion and could act as potential vaccine candidates, a number of Mabs were raised in mice against T. annulata sporozoites. These were assayed for their ability to block sporozoite invasion of bovine peripheral blood mononuclear (PBM) cells in vitro. One of these, Mab 4B11, was found to neutralize sporozoite invasion to a high degree and to recognize a group of sporozoite antigens on Western blots. A T. annulata lambdagt11 genomic expression library was screened with Mab 4B11 and a positive clone containing a 900-bp insert (KP8) analysed further. Data from Southern and Northern blotting indicated that the gene containing the KP8 sequence, termed sporozoite and macroschizont gene 2 (spm2), was expressed both in T. annulata sporozoites and in later parasite life-cycle stages, macroschizont-infected leucocytes and piroplasms. The KP8 sequence was expressed in E. coli as a fusion protein with glutathione-S-transferase (GST) using the vector pGEX1lambdaT. Bovine antiserum raised against GST-KP8 recognised a single high molecular weight molecule on Western blots corresponding to one of the antigens recognised by Mab 4B11, expressed in sporozoites, macroschizont-infected leucocytes, and piroplasms. While our evidence suggests that the spm2 molecule alone is not responsible for sporozoite neutralization, it is a multistage antigen likely to function both in T. annulata sporozoites and in subsequent parasite life-cycle stages.