Diagnostic evaluation of dot-binding assays for circulating cathodic antigen (CCA) and anti-CCA determinations in schistosomiasis japonica using defined biotinylated conjugates.

Using an affinity purified circulating cathodic antigen (CCA) preparation and an anti-CCA monoclonal IgM antibody, we modified dot-binding assays for anti-CCA and CCA detections with biotinylated conjugates. A study on 3 groups of 138 schistosomiasis japonica patients and 105 healthy individuals demonstrated a high predictive rate of over 95% in both assays, highly comparable to those of circumoral precipitin test (COPT). A blind test in 342 samples of various groups revealed higher detection rates in Ab-binding assay with both acute and chronic case groups (over 90%), but comparatively lower rates in Ag-binding assay with chronic groups (50%-76%). Distinct reductions of either GMRT and dot-indexes were found in 48 praziquantel treated patients whose sera were collected 9 months after chemotherapy. The major target molecules detected by the two binding assays were proved to be the protein incorporated moieties readily precipitated by trichloroacetic acid (TCA), ammonium sulphate and higher concentration of polyethylene glycol (PEG) suggestive of pathological, specific immunoglobulins in the free or complex forms. Non-specific dot reactions were found in some acute and chronic patients with non-relevant bovine serum albumin (BSA) conjugated peroxidase and streptavidin-PO controls, and also in normal sera with the McAb peroxidase conjugate or when working concentration of the biotinylated McAb was not properly titrated. The reliability and proper management of the dot binding assay as an immunodiagnostic tool were discussed.