QUANTITATIVE-DETERMINATION OF CIRCULATING SOLUBLE EGG ANTIGEN IN URINE AND SERUM OF SCHISTOSOMA-MANSONI-INFECTED INDIVIDUALS USING A COMBINED 2-SITE ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Two enzyme-linked immunosorbent assays (ELISA-5B1 using monoclonal ant ibody [MAb] 114-5B1-A [IgG1] and ELISA-4D12 using MAb 114-4D12-A [IgG3 ]) that detect circulating soluble egg antigen (CSEA) of Schistosoma m ansoni were combined into one assay. This assay showed better performa nce than either of the two MAbs alone in detecting egg antigen, which was demonstrated with 80 urine samples from patients infected with Sch istosoma mansoni from Zaire. The lower detection limit of the combined ELISA was 90 pg of the trichloroacetic acid-soluble fraction of solub le egg antigen (SEA-TCA) per milliliter. Thirty-two serum samples and 107 urine samples from uninfected Dutch individuals were negative when tested with the combined ELISA. This assay showed the same sensitivit y (86.3%) with patients' urine samples as parallel testing with ELISA- 5B1 and ELISA-4D12 (85%), while ELISA-5B1 and ELISA-4D12 showed sensit ivities of 81.3% and 75%, respectively. The sensitivity of the combine d ELISA with 51 serum samples was 84.3%, and three of five serum sampl es available from the seven patients with negative urine were positive for CSEA. The concentration of CSEA calculated from a four-parameters logistic curve for samples tested showed a correlation with egg outpu t and serum circulating anodic antigen (P < 0.0001). Circulating solub le egg antigen in urine showed a significant decrease with an increase in age of the patients in relation to serum CSEA and egg output.