PHOSPHATIDYLINOSITOL 3-KINASE/AKT MEDIATED PHOSPHORYLATION OF BAD IN HUMAN AORTIC ENDOTHELIAL CELLS EXPOSED TO SUB SATURATING CONCENTRATIONS OF ANTI-HLA CLASS I ANTIBODIES CONFERS RESISTANCE AGAINST ANTIBODY-COMPLEMENT MEDIATED CELL DEATH.

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PHOSPHATIDYLINOSITOL 3-KINASE/AKT MEDIATED PHOSPHORYLATION OF BAD IN HUMAN AORTIC ENDOTHELIAL CELLS EXPOSED TO SUB SATURATING CONCENTRATIONS OF ANTI-HLA CLASS I ANTIBODIES CONFERS RESISTANCE AGAINST ANTIBODY-COMPLEMENT MEDIATED CELL DEATH.
Kishore Narayanan Ph.D. , Donna Phelan B.S. and Thalachallour Mohanakumar Ph.D. . St. Louis MO, USA, Washington University School of Medicine, 63110, Surgery ; St. Louis MO, USA, Washington University School of Medicine, 63110, Pathology and Immunology and St. Louis MO, USA, Barnes-Jewish Hospital, 63110, HLA Laboratory .

It is known that allografts transplanted across ABO incompatibility or HLA-sensitization results in an antibody mediated rejection response known as hyperacute rejection. However, in certain circumstances, xenografts and allografts have been shown to survive despite the presence of circulating antigraft antibodies and complement. We developed an in vitro model using serum containing polyclonal anti-HLA class I antibodies obtained from highly sensitized patients and analyzed their ability to provide signals following binding to human aortic endothelial cells (EC). Using this model, we show herein that EC undergo caspase 3-dependent cell death by apoptosis upon exposure to saturating concentrations of anti-HLA class I antibodies and complement. In contrast, exposure of ECs to sub-saturating concentrations of anti-HLA class I antibodies conferred resistance towards antibody-complement mediated lysis. Further, it induced PI-3 kinase and Akt activities that facilitate the phosphorylation of Bad. The accommodated endothelium bound to fewer peripheral blood mononuclear cells and this was correlated by a significant reduction in the expression of the adhesion molecules ICAM-1 and VCAM-1. In addition, accommodated ECs exhibited significant increase in the expression of anti-apoptotic genes Bcl-xL, Bcl-2 and Heme Oxygenase-1. In conclusion exposure of sub-saturating concentrations of anti-HLA class I antibodies results in the induction of a novel signal transduction pathway that confers resistance to endothelial cells against antibody-complement mediated cell death.