Theileria orientalis is a tick-transmitted, intraerythrocytic protozoan belonging to the phylum Apicomplexa. It is a member of the non-transforming group of Theileria species ( Theileria sergenti / buffeli / orientalis ) that proliferates in the bovine host as an intraerythrocytic form (Sugimoto and Fujisaki 2002). This Theileria group is now collectively referred to as T . orientalis . It can occasionally cause symptoms that include fever, anaemia and anorexia in infected cattle (Shiono and others 2001). The livestock industry in Japan suffers enormous economic losses due to bovine piroplasmosis caused by this parasite (Ota and others 2009).
Major piroplasm surface protein (MPSP) is an immunodominant protein present on the parasite surface during the intraerythrocytic stage (piroplasm) (Kawazu and others 1992). Erythrocyte-stage 30–34 kDa proteins, such as MPSP, are conserved among other bovine Theileria species and Theileria equi (Formerly Babesia equi ), a tick-transmitted protozoan parasite of horses (Knowles and others 1997). The MPSP proteins have a putative signal peptide and a putative membrane anchor domain at the N-terminus and C-terminus, respectively (Kim and others 1998). The MPSP gene is a useful molecular marker for the epidemiological study of T . orientalis ; however, the molecular components that interact with the MPSP protein remain unknown. The interaction between MPSP and the surface molecules of host red blood cells (RBC) is difficult to investigate experimentally, because no T . orientalis parasites have been adapted to in vitro culture. Here, we examined the binding of MPSP recombinant proteins to RBCs.
An RBC binding assay was performed as previously described …