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 involve d 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 peri pheral blood mononuclear (PBM) cells in vitro. One of these, Mab 4B 11 , was found to neutralize sporozoite invasion to a high degree and to recognize a group of sporozoite antigens on Western blots. A T. annula ta lambda gt11 genomic expression library was screened with Mab 4B11 a nd a positive clone containing a 900-bp insert (KP8) analysed further. Data from Southern and Northern blotting indicated that the gene cont aining the KP8 sequence, termed sporozoite and macroschizont gene 2 (s pm2), was expressed both in T annulata sporozoites and in later parasi te life-cycle stages, macroschizont-infected leucocytes and piroplasms . The KP8 sequence was expressed in E. coil as a fusion protein with g lutathione-S-transferase (GST) using the vector pGEX 1 lambda T. Bovin e 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-infect ed leucocytes, and piroplasms. While our evidence suggests that the sp m2 molecule alone is not responsible for sporozoite neutralization, it is a multistage antigen likely to function both in T. annulata sporoz oites and in subsequent parasite life-cycle stages. (C) 1998 Academic Press.