A beta-galactosidase linked immunoassay for the analysis of antigens on individual cells

Antibodies conjugated to enzymes such as horseradish peroxidase or alkaline phosphatase are widely used to detect antibody binding to individual cells or tissue sections through the deposit of insoluble colored reaction products. However, the presence of endogenous enzyme activity, especially in lymphomyeloid cell populations, necessitates the use of inhibitors which can be shown to decrease the sensitivity of the assay, a particular problem when monoclonal antibodies are used. As no endogenous beta-galactosidase activity can be demonstrated in lymphomyeloid cells, a cytoimmunoenzyme assay based on this enzyme should provide a preferable system for cytological investigations of antigens in these cells. Such as assay was developed using azo coupling of 2 alternative substrates with different diazonium salts to produce rapid and specific precipitation of reaction products of different colors. The sensitivity of the beta-galactosidase cytoimmunoenzyme assay was shown to be comparable with that of assays using FITC or peroxidase coupled antibodies.