Biliary glycoprotein (BGP) expression on T cells and on a natural-killer-cell sub-population

Human T and natural-killer (NK) cells, that are thought to be the major cytotoxic effector-cell populations in the defence against neoplastic cells, were isolated from blood and decidua in order to analyze their expression of carcinoembronic-antigen-(CEA)-family-member proteins. Biliary glycoprotein (BGP,CD66a) was the only member of the carcinoembryonic antigen family detected. While freshly isolated T-cells expressed low amounts of BGP, freshly isolated NK cells were negative. After in vitro stimulation for 3 days, T cells up-regulated their BGP expression and a sub-group of NK cells (CD16- CD56+), known to predominate in decidua revealed de novo expression of BGP. In contrast, stimulated CD16+ CD56+ NK cells, which occur exclusively in the blood, remained negative. The expression of BGP could be shown on the protein level by using a panel of 12 well-defined MAbs and on the transcription level in rt-PCR and subsequent oligonucleotide hybridization. Interestingly, rIL-2-stimulated T cells expressed 3-fold higher levels of BGP compared with those seen after stimulation with phytohemagglutinin (PHA). PHA, on the other hand, induced a higher expression of HLA-DR, an activation marker of T cells. The differential regulation implies a distinct function of BGP and HLA-DR.