Purification and characterization of carcinoembryonic antigen-related antigens in normal adult feces.

We tried to purify carcinoembryonic antigen (CEA)-related antigens in normal human feces and found that, besides nonspecific cross-reacting antigen (fecal NCA), there are three other molecular species of CEA-related antigens which have been inclusively called normal fecal antigen (NFA). These were designated normal fecal antigen 1 (NFA-1), normal fecal antigen 2 (NFA-2), and normal fecal cross-reacting antigen (NFCA), respectively. Among these antigens, NFA-1, NFA-2, and fecal NCA were isolated in pure form. NFCA has not yet been obtained in pure form but was identified as an antigen different from three other antigens. All antigens were glycoprotein in nature and migrated electrophoretically in the beta region. Their molecular weights were estimated to be 20,000 to 30,000 for NFA-1, 160,000 to 170,000 for NFA-2, and 80,000 to 90,000 for NCA, respectively. NFA-2 had amino acid and carbohydrate compositions similar to those of CEA. The results obtained by immunodiffusion analyses of antigenic determinants indicate that CEA and NFA-2 can be divided into four antigenic moieties: the first one is distinctive for CEA (cancer determinant) or NFA-2 (NFA-2-distinctive determinant); the second one corresponds to NFA-1 (NFA-1 determinant); and the remaining two moieties are present on NFCA, one of which is characteristic for NFCA (NFCA determinant) and the other of which is shared with NCA (NCA-common determinant).