CD66a antigen, also known as biliary glycoprotein (BGP), is a member of the carcinoembryonic antigen (CEA) family and of the immunoglobulin super-family. CD66a, CD66b, CD66c and CD66d are known to be expressed by hematopoietic cells. CD66a antigen is also expressed in epithelia, in certain endothelia and in cells of the myeloid lineage. In liver, expression occurs in hepatocytes along the bile canaliculi. Apical membranous expression of the antigen is reported to occur in enterocytes, superficial absorptive cells of the colon, epithelia of oesophageal and Brunner's glands, bile ducts and gall bladder, pancreatic ducts, proximal tubules of the kidney, prostate, endometrium and mammary ducts.