Immunochemical Differences Among Carcinoembryonic Antigen in Tumor Tissues and Related Antigens in Meconium and Adult Feces

We have isolated carcinoembryonic antigen (CEA)-related antigens from meconium and compared them with those in adult feces. Two CEA-related antigens were detected in meconium [nonspecific cross-reacting antigen 2 (NCA-2) and meconium nonspecific cross-reacting antigen] while four CEA-related antigens were found in adult feces [normal fecal antigen 1, normal fecal antigen 2 (NFA-2), normal fecal cross-reacting antigen, and fecal nonspecific cross-reacting antigen, respectively]. By conventional anti-CEA antisera, NCA-2 in meconium, NFA-2 in adult feces, and CEA in tumor tissues were indistinguishable from each other, but they could be distinguished by specific antibody preparations against a determinant unique to CEA (CEA-distinctive determinant) or to NFA-2 (NFA-2-distinctive determinant). Neither the CEA-distinctive determinant nor the NFA-2-distinctive determinant was detected on the NCA-2 molecule. No antigenic determinants unique to NCA-2 have been detected with the anti-NCA-2 antisera which we have prepared thus far. The molecular weight of purified NCA-2 was estimated to be 150,000 to 170,000 as compared to 160,000 to 170,000 for NFA-2 and 170,000 to 180,000 for CEA. NCA-2 had amino acid and carbohydrate compositions similar to those of CEA and NFA-2. All NFA-2 preparations and about one-half of the CEA preparations were sensitive to Pronase E digestion, which released two antigen fragments from these molecules, but NCA-2-preparations were resistant to such digestion.