Characterization ofToxoplasma gondiiSAG2 Expressed in Insect Cells by Recombinant Baculovirus and Evaluation of Its Diagnostic Potential in an Enzyme-Linked Immunosorbent Assay

Publisher Website
Google Scholar
Abstract
A baculovirus carrying the SAG2 gene ofToxoplasma gondiiwas constructed, and recombinant SAG2 protein (S-rSAG2) was expressed in insect cells. S-rSAG2 was recognized by sera from cats and pigs infected withT. gondii. Mice immunized with S-rSAG2 produced high titers of specific immunoglobulin G2a (IgG2a) and IgG1 antibodies. In an indirect fluorescent antibody test, all mouse antisera against S-rSAG2 reacted strongly to the natural parasites, but those against rSAG2 expressed inEscherichia coli(E-rSAG2) only showed very weak reaction, although no markedly difference was found in the reaction to denatured antigen,T. gondiilysate, in Western blot analysis. The results suggest that S-rSAG2 is better than E-rSAG2 in both antigenicity and immunogenicity. Enzyme-linked immunosorbent assay (ELISA) with S-rSAG2 could differentiate clearly between sera from 30 specific-pathogen-free cats and 4 experimentally infected cats. Serum samples from domestic cats in Japan were tested by the ELISA and compared with a latex agglutination test (LAT) and ELISA with E-rSAG2. Of 187 samples, all 35 LAT-positive sera had strong reactions to S-rSAG2 and E-rSAG2. Of the 152 LAT-negative sera, 18 were positive in the ELISA with S-rSAG2, whereas only 2 were positive in the ELISA with E-rSAG2. Although there were significant correlations among the three methods, the ELISA with S-rSAG2 was more sensitive than the others, which could be attributed to the fact that S-rSAG2 shares some common conformational structure with the native antigen. The results suggest that S-rSAG2 would be a useful reagent for the detection ofT. gondiiinfection in cats.