title: Hypoxia increases membranal and secreted HLA-DR in endothelial cells, rendering them T-cell activators.
abstract: Transplantation involves preoperative ischemic periods that contribute to endothelial cell (EC) dysfunction and T-cell activation, leading to graft rejection. As hypoxia is a major constituent of ischemia, we evaluated its effect on the ability of ECs to express HLA-DR, which is required for presentation of antigens to T cells, and by itself serves as an important target for allogeneic T cells. Primary human umbilical vein ECs (HUVEC) and the human endothelial cell line EaHy926 were incubated in normoxia or hypoxia (PO(2) < 0.3%). Hypoxia increased the membranal expression (by 4-6 fold, P < 0.01) and secretion (by sixfold, P < 0.05) of HLA-DR protein, without influencing the accumulation of its mRNA. Alternative splicing, attenuated trafficking, or shedding from the plasma membrane were not observed, but the lysosomal inhibitor bafilomycin A1 reduced HLA-DR secretion. Hypoxia-induced endothelial HLA-DR elevated and diminished the secretion of IL-2 and IL-10, respectively, from co-cultured allogeneic CD4(+) T cells in a HLA-DR-dependent manner, as demonstrated by the use of monoclonal anti-HLA-DR. Our results indicate a yet not fully understood post-translational mechanism(s), which elevate both membranal and soluble HLA-DR expression. This elevation is involved in allogeneic T-cell activation, highlighting the pivotal role of ECs in ischemia/hypoxia-associated injury and graft rejection.
authors.affiliation: Immunology Research Unit, Carmel Medical Center, The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel.
authors.forename: Nitza
authors.initials: N
authors.lastname: Lahat
authors.forename: Haim
authors.initials: H
authors.lastname: Bitterman
authors.forename: Lea
authors.initials: L
authors.lastname: Weiss-Cerem
authors.forename: Michal A
authors.initials: MA
authors.lastname: Rahat
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology*; D006084:Graft Rejection; D006684:HLA-DR Antigens / Q000096:biosynthesis* / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D007249:Inflammation; D008213:Lymphocyte Activation; D010100:Oxygen / Q000378:metabolism; D011863:Radioimmunoassay / Q000379:methods; D013601:T-Lymphocytes / Q000166:cytology*
chemical_list: D006684:HLA-DR Antigens; D010100:Oxygen