Molecular cloning and characterization of the polypeptide backbone of Schistosoma mansoni circulating cathodic antigen.

One of the candidate schistosome antigens for the development of a circulating antigen detection diagnostic assay is the circulating cathodic antigen (CCA). Detection of CCA in urine provides a non-invasive assay with high sensitivity. Previously we reported that CCA is secreted in patients' urine as a small molecular weight material which is probably of a proteinaceous nature. In an attempt to further characterize the secreted component of CCA, we used a monoclonal antibody (MAb) reactive with urine-CCA to isolate an adult worm cDNA clone (SmN3-1) that encodes the polypeptide backbone of CCA. The sequence, gene organization and expression of SmN3-1 were analyzed. The 1.6 kb nucleotide and 347 amino acid sequences of SmN3-1 showed no significant homology to any published sequence. The size and antigenic properties of the expression product of SmN3-1 in Escherichia coli greatly resembled the CCA molecule excreted in urine, suggesting that the latter is primarily composed of the protein element of CCA.