Vascular endothelial cells evade apoptosis triggered by human leukocyte antigen-DR ligation mediated by allospecific antibodies.
BACKGROUND
Human leukocyte antigen (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 monoclonal antibodies (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 interferon (IFN)-gamma-treated ECs was quantitatively lower (3-5-fold) than that on B cells. Whereas anti-HLA-DR monomorphic mAbs induced apoptosis of B cells (approximately 22%), no significant apoptosis of IFN-gamma-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, as evident in the modulation of tyrosine phosphorylation and protein kinase (PK)C-alpha/beta and PKB/Akt activation. Our results suggest that HLA-DR ligation induces both common and divergent signaling events in ECs and B cells.


CONCLUSIONS
Collectively, our data suggest that, in contrast with 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.
Le Bas-Bernardet
Stéphanie
S
Institut National de la Santé et de la Recherche Médicale, Unité 643 Immunointervention en Allo et Xénotransplantation, Hôtel-Dieu, Nantes, France.
Coupel
Stéphanie
S
Chauveau
Annabelle
A
Soulillou
Jean-Paul
JP
Charreau
Béatrice
B
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D001158:Arteries / Q000166:cytology; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006684:HLA-DR Antigens / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D007518:Isoantibodies / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology
D000911:Antibodies, Monoclonal; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; D007518:Isoantibodies; D007371:Interferon-gamma