BACKGROUND: We have previously explored the clinical significance of urinary tissue factor (uTF) in patients with glomerulonephritis (GN) and malignancy. However, the functional and structural properties and putative cell of origin of uTF are poorly documented. In these studies we investigate these aspects of uTF.<br/><br/>METHODS: Functional and structural properties of uTF were investigated using a one stage kinetic chromogenic assay, an enzyme-linked immunoabsorbent assay (ELISA) and transmission electron microscopy (TEM) on urine samples collected from healthy controls (n=69). The distribution of uTF and anionic phospholipid in the kidney were studied in sections from normal areas of nephrectomy specimens, using an immunoperoxidase technique. These were stained for tissue factor (TF) antigen and recombinant Annexin V.<br/><br/>RESULTS: We found uTF to be present on subcellular particles as visualized by TEM. These particles contained anionic phospholipid as evidenced by binding to Annexin V fluorescein isothiocyanate (FITC). Although TF is present in urine in a functional and antigenic form no association was observed between the two. Using immunoperoxidase-based techniques, the cytoplasm of both distal and proximal tubules (but not glomerular cells) was positive for TF antigen and Annexin V.<br/><br/>CONCLUSION: uTF is found on subcellular particles which provide lipid for its functional activity. Both uTF and its associated vesicles are found in the renal tubular cells
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