Toxoplasma gondii antigens: Analysis by SDS-PAGE and immunoblotting; Relation with circulating antigens

Cytoplasmic antigenic extracts (CAE) and membranar antigenic extracts (MAE) from Toxoplasma gondii (T.g) purified trophozoites RH strain, were obtained after hypotonic lysis and sonication. Analysis in Polyacrylamide gel electrophoresis (SDS-PAGE) using Coomassie blue staining revealed 21 polypeptides (PP) in CAE and 8 in MAE, whereas the immunoblotting technique detected 28 PP in CAE and 23 in MAE. Immunoblotting is then more sensitive than Coomassie blue staining. This finding is particularly marked for MAE and could be explained by the high antigenicity of some PP that have a lower concentration than the threshold sensitivity of SDS-PAGE. In contrast, some PP in sufficient amount to be detected by SDS-PAGE did not show any antigenic activity since not found by immunoblotting. The molecular weight (MW) ranged from 8 to 130 kDa for cytoplasmic PP and from 4 to 110 kDa for membranar PP. Circulating antigens (CAG) from serum specimens of mice infected with the same strain of T.g were analysed by immunoblotting in comparison with CAE and MAE profiles. From the 7 bands obtained with CAG, 4 were shown to correspond to CAE PP, 2 to common CAE and MAE PP and only 1 to MAE PP (MW: 30 kDa).