Development of an immunochromatographic test based on monoclonal antibodies against surface antigen 3 (TgSAG3) for rapid detection of Toxoplasma gondii

The immunochromatographic test (ICT) is a convenient and low-cost method that can rapidly obtain results (10 min) under normal conditions. In this study, we established an ICT assay with two monoclonal antibodies: TgSAG3-3A7 and TgSAG3-4D5 based on the conserved protein of TgSAG3 that can be expressed in all the infective stages of T. gondii. 20 nm gold particles were prepared and conjugated with TgSAG3-3A7 MAb at the concentration of 12.5 μg/mL. TgSAG3-4D5 MAb were used as the capture antibody because of its higher affinity tested by ELISA. The detection limit of the ICT assay was 100 ng with visual detection under optimal conditions of analysis. Positive porcine serum of Cryptosporidium suis, Mycoplasma suis, Streptococcus suis, Salmonella choleraesuis, Cysticercus cellulosae, Isospora suis, and Trichinella spiralis were used to evaluate the specificity of this ICT and no cross-reactivity was observed. 310 porcine serum samples obtained from pig farms in Zhejiang Province, China were detected by this ICT and ELISA kit, 23 positive samples were found by the developed strip with the rate of 7.42% comparing with 22 positive samples detected by the commercially ELISA kit which the positive rate was 7.1%, the relative sensitivity and specificity of this ICT are 100% and 99.65%. Therefore, the ICT established in this study is proved effective, simple, specific and sensitive of T. gondii detection.