[A colloidal gold immunochromatographic assay for detecting p38 antigen of Schistosome japonicum].

Objective: To establish a colloidal gold immunochromatographic assay (GICA) for detecting Schistosome japonicum (Sj).

Methods: Eight monoclonal antibodies (mAbs) against Sj p38 antigen (1A6, 3C4, 3D12, 6F10, 6G12, 9H6, 9G7 and A5H) prepared previously were purified by protein-G affinity chromatography. The affinity constant (K(aff)) was determined by indirect enzyme-linked immunosorbent assay. All the mAbs were labeled with horseradish peroxidase by sodium oxidation method and the mAb pairs with high affinity and stability were identified according to their optical density at 450 nm (OD450). Four mAbs (1A6, 6G12, 9H6 and 9G7) were chosen for colloidal gold labeling. GICA was then performed by further optimization of the labeling and the conditions were determined. The sera of mice at different infection stages were examined with GICA dipstick, with the sera collected before infection and those of Toxoplasma gondii-infected mice as negative controls.

Results: The purity of the 8 mAbs was higher than 95% with K(aff) ranging from 2.8x10(-10) to 1x10(-8) mol/L. 9G7 coating (2.5 mg/ml) as the capture antibody and detection with 1A6 (diluted at 1:4) as the labeling antibody was determined as the best reaction model. With this combination, the positivity rates of the detection were 40%, 50%, 60% and 80% for mouse sera collected at 3, 4, 5 and 6 weeks after Schistosome japonicum infection, respectively, without positive results for the negative control samples.

Conclusion: GICA established in this study is characterized by simplicity, rapidity and good sensitivity, and the prepared rSjP38 dipstick can test the circulating antigen SjP38 in early stage of infection.