CD40 ENGAGEMENT ON ENDOTHELIAL-CELLS PROMOTES TISSUE FACTOR-DEPENDENTPROCOAGULANT ACTIVITY

The CD40 molecule expressed on endothelial cells has been shown to tra nsduce activation signals resulting in upregulation of adhesion molecu les. Herein, we studied the impact of CD40 engagement on the induction of tissue factor (TF)-dependent procoagulant activity (PCA) at the su rface of human umbilical vein endothelial cells (HUVECs). First, we fo und that co-incubation of HUVECs with 3T6 fibroblasts transfected with the CD40L gene (3T6-CD40L) resulted in a clear induction of PCA which was not observed with control untransfected fibroblasts. The specific ity of this finding was established bl: inhibition experiments using m onoclonal antibodies (mAbs) blocking CD40 or CD40L. PCA induced by CD4 0 ligation was TF-related as it was not observed in factor VII-deficie nt plasma and was associated with the accumulation of TF mRNA. To inve stigate the role of CD40/CD40L interactions in the induction of endoth elial cell PCA by lymphocytes, interferon (IFN)-gamma-stimulated EC we re incubated with T cells in the absence or presence of anti-CD40 or a nti-CD40L mAb. The 60-70% inhibition of PCA induced by these mAbs but not their isotype-matched control indicated that the CD40 pathway is i nvolved in the induction of PCA resulting from interactions between ac tivated HUVECs and T cells. We conclude that activation signals elicit ed by CD40 engagement on endothelial cells result in the induction of TF-dependent PCA. The CD40/CD40L pathway might therefore be involved i n the development of prothrombic states during diseases associated wit h endothelial cell and T cell activation.