Abstract
The effect of the bridge heterologous combination of antiserum and enzyme-labeled steroid on sensitivity in heterogeneous enzyme immunoassay of cortisol has been investigated. The enzyme labeling of cortisol was carried out by the N-succinimidyl ester method. Four cortisol derivatives possessing different bridges at C-4 were covalently linked to β-galactosidase at various molar ratios of steroid to enzyme. The anti-cortisol antisera 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 specificity was dependent upon the length of the bridge. It was found that the heterologous system using the steroid-enzyme conjugate obtained from a hapten having a shorter bridge than that used for antibody production resulted in an increase in sensitivity of the assay, whereas the use of a longer bridge was ineffective. This phenomenon can be explained in terms of the steric interaction between antibody and labeled enzyme.
