Monoclonal, anti-domain and anti-peptide antibodies assign the molecular weight 160,000 granulocyte membrane antigen of the CD66 cluster to a mRNA species encoded by the biliary glycoprotein gene, a member of the carcinoembryonic antigen gene family.

mAb directed against the CD66 cluster of granulocyte differentiation Ag recognize Ag of the carcinoembryonic Ag family. A major Ag in extracts from granulocyte membranes bound by CD66 antibodies exhibits a relative molecular mass of 160,000. According to recent data, this Ag may be a product of the biliary glycoprotein (BGP) gene that belongs to the CEA gene family. As a result of alternative splicing, the BGP gene is transcribed into at least seven distinct mRNA species. To identify splice variants of BGP, antisera were raised against the A2 domain expressed in bacteria and to a peptide comprising the C-terminal 23 amino acids encoded by the 3' exon of the BGP gene. The antisera and an mAb specific for members of the BGP family were used to identify potential BGP splice variants in granulocyte membranes. For comparison, the binding of antibodies to Ag purified from human bile was investigated. In the membrane preparation from granulocytes, the only Ag identified by the mAb, the domain antiserum and the peptide antiserum, was the Ag of M(r) 160,000 recognized by a CD66 antibody. These results indicate that the M(r) 160,000 granulocyte membrane Ag of the CD66 cluster is the product of the BGP-specific mRNA containing all coding sequences of the BGP gene. Among two major biliary glycoproteins present in human bile, the M(r) 115,000 Ag contains the A2 domain, whereas the domain is lacking in the "classical" biliary glycoprotein of M(r) 85,000. None of the bile Ag bound the peptide antiserum.