ABSTRACT. Twelve monoclonal antibodies (MAbs) against Neospora caninum tachyzoites were produced to specify the antigens related to the invasion of tachyzoites into host cells. In the assay to evaluate the inhibition activity, all these MAbs prevented the cultured Vero cells from the invading by the tachyzoites. These MAbs recognized approximately a 73 kDa antigen in Western blot analysis. Immunofluorescence assay and immune electron microscopy revealed that this 73 kDa antigen is a part of the surface antigens of N. caninum tachyzoite, and that the tachyzoite antigen identified plays an important role for invasion of host cells. KEY WORDS: invasion process, monoclonal antibody, Neospora caninum, surface antigen.J. Vet. Med. Sci. 66(11): 1355-1358, 2004 Neospora caninum is a coccidian protozoon first isolated from the brain of a puppy by Dubey in 1988, which developed paralysis in the hind limbs [5]. Dogs infected with this parasite mainly show neurological symptoms and infected cows are attached with abortion and stillborn, so serious economical damages are produced [4]. In 1998, McAllister et al. reported that definitive host of the protozoon is dogs [14]. However, the life cycle of N. caninum is not completely clarified yet, and the procedures for prevention and treatment of neosporosis also are not established. The pathogenesis of N. caninum is known to be caused by multiplication of parasites resulting destruction of many kinds of host cells by invasion [2,3,20]. To develop the prevention and treatment of neosporosis, analyses of antigens related with the invasion process into host cells are required. Antigens of some protozoan parasites belonging to phylum Apicomplexa, such as Toxoplasma gondii participate in invading the host cells and were thought to be surface antigens, secretory proteins and those in the structures of apical complex such as microneme, rhoptry and dense granule [6,11,15,18]. Also in N. caninum, some antigens, possibly affecting the invasion, were studied, and the antigens on the body surface [9,10] In this study, we prepared monoclonal antibodies (MAbs) against N. caninum tachyzoites which obstruct the invasion of tachyzoites into host cells, and further, we tried to specify the antigen of N. caninum concerning with attachment and invasion into the host cells.
MATERIALS AND METHODSParasites: Neospora caninum JPA-1 strain used was isolated and passaged by Yamane et al. in the National Institute of Animal Health, Japan [23]. The isolate was inoculated into monolayer Vero cells maintained in Eagle's minimum essential medium (MEM; NISSUI PHARMACEUTICAL Co., Japan) supplemented with 10% fetal calf serum (FCS; HARLAN SERA-LAB, England), 2 mM L-glutamine (Wako Pure Chemical Industries, Japan), 1% MEM Vitamin solution (GIBCO BRL, U.S.A.), 13 mM sodium hydrogen carbonate (NaHCO 3 ) (Wako Pure Chemical Industries), and 4 µl/ml Fungizone (GIBCO BRL). The tachyzoites cultured were used for examination.
Purification of tachyzoites:The tachyzoites cultured were purified according to an improved metho...