Activation of NF-κB in human endothelial cells induced by monoclonal and allospecific HLA antibodies

Chronic graft rejection, characterized by a gradual occlusion of grafted vessels, is the most serious complication following heart and kidney transplantation. Although often associated with chronic production of anti-HLA and anti-endothelial antibodies, the precise role of antibodies in chronic rejection remains uncertain. Here we have investigated whether HLA-specific antibodies, either monoclonal or derived from patients, cause endothelial cell activation. Thus we investigated tyrosine phosphorlyation, NF-kappa B activation and cell proliferation in human umbilical Vein endothelial cells (HUVEC) or microvascular endothelial cells from adult human heart (CMEC), Ligation of monomorphic determinants of MHC class I molecules (using the mAb W6/32) on the surface of HUVEC caused an increase in tyrosine phosphorylation of proteins of mel. wt similar to 75-80 kDa, Similarly, ligation of monomorphic determinants on both CMEC and HUVEC resulted in increased NF-kappa B binding compared to controls (by 74.4 and 52.5%, P = 0.001) and this was enhanced by addition of secondary antibody. Two HLA-specific mAb resulted in a 277 and 170% increase in NF-kappa B-binding activity compared to controls, Four patient samples containing HLA antibodies were used against HLA-specific HUVEC and four samples were incubated with HUVEC bearing irrelevant antigens, Patient sera alone enhanced NF-kappa B binding by 27-186%, but only when added to HUVEC bearing relevant antigens, W6/32 and allospecific antibodies from patients significantly enhanced HUVEC proliferation, measured by uptake of [H-3]thymidine. In conclusion, activation of NF-kappa B by human anti-HLA antibodies demonstrates their potential role in pathogenesis of chronic vascular occlusive disease following transplantation.