A RAPID COLORIMETRIC ASSAY FOR CARCINOEMBRYONIC ANTIGEN (CEA)-MEDIATED CELL-ADHESION AND ANALYSIS OF CEA DOMAINS INVOLVED IN THE ADHESION

A colorimetric microadhesion assay that allows the quantitative determ ination of carcinoembryonic antigen (CEA)-mediated homophilic cell adh esion to CEA immobilized on 96-well polyvinyl chloride plates is descr ibed. Chinese hamster ovary (CHO) cells transfected with a full-length CEA cDNA were used as indicator cells. After dislodging nonadherent c ells, specifically bound cells were quantified by a colorimetric analy sis based on the ability of live cells to reduce the dye 3-(4,5 -dimet hylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to a blue forma zan product. The domains of CEA responsible for the homophilic cell ad hesion were analyzed by inhibition assays using anti-CEA monoclonal an tibodies whose reactive domains were already known. The involvement of domain N and possibly subdomain A3 of CEA in the homophilic cell adhe sion has been suggested.