Effect of Bridge Heterologous Combination on Sensitivity in Enzyme Immunoassay for 11-Deoxycortisol

The effect of the bridge heterologous combination between antiserum and enzymelabeled steroid on sensitivity in heterogeneous enzyme immunoassay for 11-deoxycortisol has been investigated. Four 11-deoxycortisol derivatives possessing different bridges at C-4 were employed for the preparation of both antisera and enzyme-labeld antigens. They were 4-(carboxymethylthio)-11-deoxycortisol, 4-(2-carboxyethylthio)-11-deoxycortisol, 4-(2-hemisuccinoyloxyethylthio)-11-deoxycortisol, and 4-hemisuccinoyloxy-11-deoxycortisol. The N-succinimidyl esters of the carboxylated derivatives were reacted with β-galactosidase to give enzyme-labeled antigens. The antisera to 11-deoxycortisol used were those raised against the conjugates of these haptenic derivatives with bovine serum albumin. The sensitivities obtainable with four homologous and twelve heterologous systems were tested. When thioether derivatives were used for enzyme labeling, the effectiveness of heterology on assay sensitivity was dependent upon the length of the bridge. It was found that the heterologous system using the enzyme-labeled steroid obtained from a hapten having a bridge shorter than that used for antibody production resulted in an increase in sensitivity of the assay, whereas the use of a longer bridge was not effective. This finding is in good agreement with that obtained in our previous study on enzyme immunoassay for cortisol.