RESUMO
Usually mouse monoclonal antibodies are used in inhibition assays for antibody determination. Interference may occur in these inhibition assays due to presence of naturally occurring anti-mouse antibodies in some human serum samples. To avoid such interference, human IgG isolated from a pool of serum samples of S. mansoni patients and highly positive for IgG against S. mansoni soluble egg antigen [SEA] was used in inhibition ELISA for diagnosis of S. Mansoni infection. The assay was based on inhibition of binding of human IgG labeled with fluorescein to S. mansoni SEA coating microtitration plates by tested serum samples. Plates were washed and labeled human IgG reacted with SEA was linked to peroxidase enzyme by incubation with anti- fluorescein/peroxidase conjugate. The assay showed 90% sensitivity and 96.3% specificity. The level of inhibition in ELISA showed highly significant positive correlation with stool egg output. To make the assay quantitative, serial dilutions of the highly positive human serum pool used for preparation of human IgG were applied in each plate and concentration of anti-SEA antibodies in serum samples tested was calculated from a 4-parameters logistic curve equation