Immunological heterogeneity of carcinoembryonic antigen: purification from meconium of an antigen related to carcinoembryonic antigen

Abstract

Two antigens cross-reactive with carcinoembryonic antigen (CEA) and distinct from the nonspecific cross-reacting antigen were identified in meconium by double immunodiffusion with a conventional goat anti-CEA antiserum. These two antigens together competitively inhibited cross-reacting antibodies against them in CEA radioimmunoassay and contributed to the measurement of meconium CEA levels which averaged 6 times higher than that determined with anti-CEA specific antibody. A purification method for one of these antigens, tentatively designated meconium antigen, is described and uses a combination of ethanol fractionation, ion-exchange and molecular sieve chromatography, and adsorption to an immunoadsorbent containing a cross-reactive murine monoclonal antibody to CEA. Preliminary characterization of the purified meconium antigen showed it to be a glycoprotein, migrating as an alpha-globulin and having a molecular size similar to that of CEA (Mr 185,000 versus 200,000). Antigenically, it lacks at least one determinant present on CEA and differs further from CEA by being weakly reactive with concanavalin A and resistant to proteolytic digestion with Pronase E. Although these properties of meconium antigen suggest that it may be nonspecific cross-reacting antigen 2, additional chemical and antigenic studies are required to establish its relationship to CEA and other CEA-related antigens in meconium.