Expression of Babesia equi merozoite antigen 1 in insect cells by recombinant baculovirus and evaluation of its diagnostic potential in an enzyme-linked immunosorbent assay

The gene encoding the entire Babesia equi merozoite antigen I (EMA-1) was i nserted into a baculovirus transfer vector, and a recombinant virus express ing EMA-1 was isolated. The expressed EMA-1 was transported to the surface of infected insect cells, as judged by an indirect fluorescent-antibody tes t (IFAT). The expressed EMA-1 was also secreted into the supernatant of a c ell culture infected with recombinant baculovirus. Both intracellular and e xtracellular EMA-1 reacted with a specific antibody in Western blots. The e xpressed EMA-I had an apparent molecular mass of 34 kDa that,vas identical to that of native EMA-1. The secreted EMA-1 was used as an antigen in an en zyme-linked immunosorbent assay (ELISA). The ELISA differentiated B. equi-i nfected horse sera from Babesia caballi-infected horse sera or normal horse sera. The ELISA was more sensitive than the complement fixation test and I FAT. These results demonstrated that the recombinant EMA-1 expressed in ins ect cells might be a useful diagnostic reagent for detection of antibodies to B. equi.