Abstract
Platelet-derived adherence-inhibiting factor (AIF) has been known to regulate the neutrophil binding to type IV collagen through the competitive inhibition of the binding. However, it has been not clear whether AIF affects the neutrophil adherence to endothelial cells. In this study, we have examined the effect of AIF on neutrophil adherence to confluently-cultured human umbilical vein endothelial cell monolayers (HUVEC) . AIF inhibited neutrophil adherence to resting, TNF-α- or thrombinstimulated HUVEC by about 54%, 44%, 75%, respectively. When the AIF-binding sites of HUVEC were estimated using 125I-AIF, resting endothelial cells have about 2500 sites/cell, and the binding sites were increased up to about 9300 or 3400 sites/cell, respectively, after stimulation with TNF-α or thrombin. To analyze the AIF-binding proteins, resting, TNF-α or thrombin-stimulated HUVEC were surface-labeled with 125I, and the extracts were chromatographed on AIF-affinity columns. Western blot analysis of the radio-active fractions from the columns revealed that E-selectin and P-selectin molecules were upregulated in stimulated HUVEC. These above observations suggest the possibility that AIF binds to E-and P-selectins of endothelial cells, and regulates neutrophil adherence to endothelial cells.
