#49-OR
HLA-DR LIGATION MEDIATED BY ALLOSPECIFIC ANTIBODIES DO NOT TRIGGER APOPTOSIS OF VASCULAR ENDOTHELIAL CELLS.
Stephanie Le Bas-Bernardet, PhD, Stephanie Coupel, MD, Annabelle Chauveau, Jean-Paul Soulillou, MD, PhD and Beatrice Charreau, PhD. Nantes France, CHU H
tel-Dieu, 44093, INSERM UMR643.
Background – HLA-DR ligation mediates cell death of antigen-presenting cells (APC), including mature B cells, macrophages, and dendritic cells. This study investigates the apoptotic effects of HLA class II ligation mediated by anti-HLA antibodies on activated human vascular graft endothelial cells (ECs).
Methods – HLA class II expression was examined by flow cytometry using a panel of HLA-typed vascular ECs isolated from transplant donors, and compared with that of B lymphocytes. The apoptotic effects of anti-HLA-DR mAbs were investigated using viability assays, DNA content analysis, and annexin-V labeling. Intracellular signaling pathways mediated by HLA-DR ligation on ECs were examined by western blotting.
Results – Even with optimal stimulation, the expression of HLA-DR on IFN-γ-treated ECs was quantitatively lower (3–5-fold) than that on B cells. Whereas anti-HLA-DR monomorphic mAbs induced apoptosis of B cells (~22%), no significant apoptosis of IFN-γ-activated (DR-positive) ECs (< 5%), collected from the same donor, was observed under the same conditions. Similarly, specific polymorphic anti-HLA-DR11 or -DR16 antibodies were unable to induce EC apoptosis. Nevertheless, antibody-binding to HLA-DR on ECs is sufficient to induce intracellular signaling, evident in the modulation of tyrosine phosphorylation and PKCα/βII activation. Our results suggest that HLA-DR ligation induces both common and divergent signaling events in ECs and B cells.
Conclusion – Collectively, our data suggest that, in contrast to professional APC, graft ECs evade apoptosis mediated by HLA-DR ligation, not as a result of moderate HLA-DR expression but rather as a result of a specific signaling pathway.