#51-OR
UPREGULATION AND SHEDDING OF HLA-E BY ENDOTHELIAL CELLS UPON INFLAMMATION: A TYPICAL FEATURE OF ENDOTHELIUM.
Stephanie Coupel, MD, PhD, Anne Moreau, MD, Vaclav Horejsi, MD, PhD and Beatrice Charreau, PhD. Nantes France, ITERT, 44093, INSERM U643; Nantes France, CHU H
tel-Dieu, 44093, Service d
Anatomopathologie and Praha Czech Republic, Institute of Molecular Genetics.
HLA-E is broadly defined by a limited polymorphism and cellular expression. HLA-E interacts with the inhibitory receptor CD94/NKG2A expressed on NK and a subset of CD8+T cells. Although HLA-E transcripts have been detected in almost all cell types, only few data report on protein expression in vivo. In the present study, we show that HLA-E expression in human tissues is mainly restricted to endothelial cells (EC). Histology using MEM/E2 mAbs shows HLA-E expression on all EC types (venous, arterial, glomerular, microvascular) and HEV in lymphoid organs. HLA-E is also expressed by B and T lymphocytes in spleen and lymph nodes and by macrophages. In vitro, HLA-E transcripts are present in cultured ECs (HUVEC and human arterial EC, HAEC) and are strongly up-regulated upon activation with the pro-inflammatory cytokines TNFα, IFNγ and IL1β. Increase in mRNA level for HLA-E correlates with enhanced protein expression on EC surface, assessed by flow cytometry and western blotting, and production of soluble HLA-E (sHLA-E) molecules. Western blots revealed the presence, in supernatants of activated ECs, of a band of 37kDa corresponding sHLA-E. Inhibition of mRNA or protein synthesis and blockade of exocytosis prevent shedding of sHLA-E whereas protease inhibitors increase cell surface expression and abrogate shedding of HLA-E. To conclude, our data indicate that, in vascularized organs, expression of HLA-E is restricted to ECs and that EC activation increases HLA-E expression and promotes release of sHLA-E. These findings suggest that HLA-E expressed and released by graft ECs may play a role in allograft immunoregulation.