Immunological similarity of NCA (non-specific cross-reacting antigen) in feces with alpha 1-acid glycoprotein.
We have recently suggested that carcinoembryonic antigen (CEA) may contain alpha 1-acid glycoprotein (AG) antigenic determinant. In the present work we examined a protein with CEA-like activity in the feces of healthy subjects (NCA) for immunological cross-reactivity with AG. When the perchloric acid extract of feces was fractionated on a Sephadex G-200, two fractions (large and small molecular weight) were obtained. The large molecular weight fraction had higher CEA activity than the small one. The perchloric acid (PCA) extract of feces was subjected to affinity chromatography using anti-CEA bound to Sepharose, and the bound protein was labelled with 125I, and then fractionated on a Sephadex G-200 column. Two radioactive peaks, Peak 1 corresponding to an approximate Mr of 180 000 and Peak 2, corresponding to an approximate Mr of 60 000 were found. Both peaks showed immunoreactivity with either anti-CEA or anti-AG. This experiment suggests the presence of two kinds of CEA-reactive proteins in feces: one which may be a big protein with immunological similarity to AG and a second which appears to be a hydrolysed fragment of this protein.