EXPRESSION OF THE TRANSPORTER FOR ANTIGEN PROCESSING-1 (TAP-1) GENE IN SUBPOPULATIONS OF HUMAN TROPHOBLAST CELLS

Heterodimers of transporter for antigen processing proteins, Tap-1 and Tap-2, are essential components of the pathway that leads to expressi on of conventional HLA-A, -B class I transplantation antigens on cell surfaces. In this study, expression of the Tap-1 gene in trophoblast c ells, some of which display novel and unconventional HLA class I molec ules that include HLA-G and an HLA-C-like antigen, was investigated by using in situ hybridization to identify Tap-1 mRNA and immunohistoche mistry to detect Tap-1 protein. The experiments were done on semiseria l sections of paraformaldehyde-fixed tissues. In first trimester place ntas, expression of the Tap-1 gene correlated with expression of HLA c lass I antigens in trophoblast cells. HLA-G/C positive extravillous cy totrophoblast cells exhibited high intensity in situ hybridization sig nals for Tap-1 mRNA and strong staining with anti-Tap-1 whereas Tap-1 gene products were rarely detected in HLA class I antigen negative syn cytiotrophoblast and villous cytotrophoblast cells. Relationships were less definitive in term tissues. Although Tap-1 protein was detectabl e in extravillous cytotrophoblast cells (chorionic cytotrophoblast cel ls) as expected, HLA class I negative syncytiotrophoblast contained lo w intensity hybridization and immunostaining signals. Collectively, th e data suggest that (1) as with conventional HLA class I antigens in o ther types of cells, the pathway leading to expression of novel HLA cl ass I antigens in trophoblast cells includes transport of peptides by Tap-1, and that (2) deficiencies in Tap-1 might account in (whole or i n) part for the failure of some trophoblast cells to express HLA class I antigens. (C) 1996 W. B. Saunders Company Ltd