Immunological Heterogeneity of Carcinoembryonic Antigen" Purification

Two antigens cross-reactive with carc inoembryonic antigen (CEA) and distinct from the nonspecif ic cross-react ing antigen were identified in meconium by double immunodiffusion with a conventional goat ant i -CEA antiserum. These two antigens together competi t ively inhibited cross-react ing antibodies against them in CEA radioimmunoassay and contr ibuted to the measurement of meconium CEA levels which averaged 6 times higher than that determined with anti-CEA specif ic 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 adsorpt ion to an immunoadsorbent containing a cross-react ive murine monoclonal ant ibody to CEA. Preliminary character izat ion of the purified meconium antigen showed it to be a glycoprotein, migrating as an ~x-globulin and having a molecular size similar to that of CEA (Mr 185,000 v e r s u s 200,000) . Antigenically, it lacks at least one determinant present on CEA and differs further from CEA by being weakly reactive with concanaval in A and resistant to proteolyt ic digestion with Pronase E. Although these propert ies of meconium antigen suggest that it may be nonspecif ic cross-react ing antigen 2, addit ional chemical and antigenic studies are required to establish its relationship to CEA and other CEA-related antigens in meconium.