CHARACTERIZATION OF A SPECIES OF NONSPECIFIC CROSS-REACTING ANTIGEN (NCA) EXPRESSED BY HUMAN MONOCYTIC CELL-LINES - STRUCTURE AND EXPRESSION DURING CELL-DIFFERENTIATION

It has been documented that human monocytes/macrophages are reactive w ith antibodies directed to carcinoembryonic antigen (CEA) and non-spec ific cross-reacting antigens (NCAs), a group of glycoproteins antigeni cally cross-reactive with CEA, yet the molecules responsible for this antigenic activity have not been fully clarified. In the present study , among 7 myelomonocytic cell lines tested, 2 monoblastoid lines, U-93 7 and THP-1, were found to express NCA-50/90, a glycosyl-phosphatidyli nositol-anchored cell-adhesion molecule chiefly expressed on granulocy tes. The 2 cell lines showed a reaction pattern with 5 distinct anti-C EA and anti-NCA monoclonal antibodies, similar to that of CHO transfec tants expressing recombinant NCA-50/90. Immunoprecipitation and SDS-PA GE analyses identified glycoproteins of about 95 and 55 kDa in U-937 a nd THP-1 cells, respectively. Deglycosylation of the 2 antigens with N -glycanase gave the same apparent molecular mass of about 45,000, whic h was also the same as that of the deglycosylated form of the recombin ant NCA-50/90. Upon Northern-blot analysis, only one band of approxima tely 2.5 kb was detected in both cell lines with a cDNA probe for NCA- 50/90, which has a broad specificity to the CEA gene family members. c DNA cloning demonstrated that the 2.5-kb clones encode the peptide of NCA-50/90. The expression of NCA-50/90 by U-937 and THP-1 was down-reg ulated at both the protein and mRNA levels during cell differentiation from monoblastoid to monocyte/macrophage-like cells induced by stimul ation with phorbol 12-myristate 13-acetate. Our observations suggest t hat NCA-50/90 is a differentiation antigen of cells of the monocyte/ma crophage lineage as well as of the granulocyte lineage. (C) 1994 Wiley -Liss, Inc.