Tissue factor (TF), the primary cellular initiator of the coagulation protease cascade, is implicated in having important roles in hemostasis, thrombogenesis, inflammation, and the cellular immune response, although the cytologic distribution of TF in tissues has yet to be described. This study used epitope-defined monoclonal antibodies to human tissue factor for immunohistochemical localization of TF in normal human tissues. TF was selectively expressed in tissues and was associated with cells rather than extracellular matrix. It was anatomically sequestered from blood, being undetectable in endothelium and peripheral blood cells. TF was present in vascular adventitia, organ capsules, epidermis, and mucosal epithelium. Most dermal and submucosal fibroblasts were negative. Except for alveolar macrophages and possibly dendritic cells of some lymphoid follicles, tissue macrophages did not express TF; (expression was demonstrable in LPS stimulated monocytes). Cerebral cortex, renal glomeruli, and cardiac myocytes were additional sites of prominent TF expression. Based on the cellular distribution of TF, it is hypothesized that intravascular initiation of coagulation requires induced expression by intravascular cells, and that the normal distribution of TF represents a hemostatic "envelope" ready to activate coagulation when vascular integrity is disrupted.

Selective cellular expression of tissue factor in human tissues. Implications for disorders of hemostasis and thrombosis.

Localization of human tissue factor antigen by immunostaining with monospecific, polyclonal anti-human tissue factor antibody

Protease-activated receptor (PAR)-1 is a cellular receptor for thrombin that is activated after proteolytic cleavage. The contribution of PAR-1 to inflammatory cell–mediated renal injury was assessed in murine crescentic glomerulonephritis (GN). A pivotal role for thrombin in this model was demonstrated by the capacity of hirudin, a selective thrombin antagonist, to attenuate renal injury. Compared with control treatment, hirudin significantly reduced glomerular crescent formation, T cell and macrophage infiltration, fibrin deposition, and elevated serum creatinine, which are prominent features of GN. PAR-1–deficient (PAR-1−/−) mice, which have normal coagulation, also showed significant protection from crescentic GN compared with wild-type mice. The reductions in crescent formation, inflammatory cell infiltration, and serum creatinine were similar in PAR-1−/− and hirudin-treated mice, but hirudin afforded significantly greater protection from fibrin deposition. Treatment of wild-type mice with a selective PAR-1–activating peptide (TRAP) augmented histological and functional indices of GN, but TRAP treatment did not alter the severity of GN in PAR−/− mice. These results indicate that activation of PAR-1 by thrombin or TRAP amplifies crescentic GN. Thus, in addition to its procoagulant role, thrombin has proinflammatory, PAR-1–dependent effects that augment inflammatory renal injury.

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Protease-Activated Receptor 1 Mediates Thrombin-Dependent, Cell-Mediated Renal Inflammation in Crescentic Glomerulonephritis

The plasminogen/plasmin system has the potential to affect the outcome of inflammatory diseases by regulating accumulation of fibrin and other matrix proteins. In human and experimental crescentic glomerulonephritis (GN), fibrin is an important mediator of glomerular injury and renal impairment. Glomerular deposition of matrix proteins is a feature of progressive disease. To study the role of plasminogen and plasminogen activators in the development of inflammatory glomerular injury, GN was induced in mice in which the genes for these proteins had been disrupted by homologous recombination. Deficiency of plasminogen or combined deficiency of tissue type plasminogen activator (tPA) and urokinase type plasminogen activator (uPA) was associated with severe functional and histological exacerbation of glomerular injury. Deficiency of tPA, the predominant plasminogen activator expressed in glomeruli, also exacerbated disease. uPA deficiency reduced glomerular macrophage infiltration and did not significantly exacerbate disease. uPA receptor deficiency did not effect the expression of GN. These studies demonstrate that plasminogen plays an important role in protecting the glomerulus from acute inflammatory injury and that tPA is the major protective plasminogen activator.

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Plasminogen and plasminogen activators protect against renal injury in crescentic glomerulonephritis.

. The majority of patients with rapidly progressive crescentic glomerulonephritis show histologic features of extensive necrosis and focal and segmental proliferation with fibrin production, but little or absent Ig deposition in the glomerulus. This subcategory of the disease, labeled “pauci-immune” glomerulonephritis, has recently been shown to be associated with the presence of antineutrophil cytoplasmic antibody in the patient9s circulation (but not within the glomerulus). The absence of the effectors of humoral immunity at the site of renal injury led to this investigation of the contribution of cell-mediated immunity to the glomerular injury in this form of glomerulonephritis. In 15 patients presenting acutely with pauci-immune glomerulonephritis, CD3-positive T cells (3.7 ± 2.5 [mean ± SD] cells per glomerular cross section, [c/gcs]), CD45RO-positive T cells (2.7 ± 1.9 c/cgs), macrophages (7.3 ± 6.1 c/gcs), fibrin (3+), and endothelial-associated tissue factor were demonstrated to be prominent in glomeruli. These mediators were absent in a group of 12 patients with thin basement membrane disease and only occasionally observed in a group of eight patients with “humorally mediated” (noncrescentic) glomerulonephritis. Thus, in pauci-immune glomerulonephritis, there is the development of significant cell-mediated immunity with activated T cells, macrophages, tissue factor, and fibrin at the site of glomerular injury, suggesting that this glomerular disease is most likely a manifestation of T cell-directed cognate immune injury.

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Prominence of Cell-Mediated Immunity Effectors in “Pauci-Immune” Glomerulonephritis

Mechanisms for initiation of glomerular fibrin deposition were studied using renal tissue obtained from two patients with rapidly progressive, crescentic glomerulonephritis. Histological examination showed extensive glomerular monocyte infiltration and fibrin deposition in both patients. Sonicated cell suspensions of isolated glomeruli from these patients contained markedly augmented levels of procoagulant activity (PCA) compared with the levels found in normal glomeruli. This PCA was characterized as tissue factor by its functional dependence on Factors VII and V, independence of Factors VIII and XII, inhibition by concanavalin A and phospholipase C, and association with cell membranes. Its coagulant activity was also inhibited by a specific monoclonal anti-human tissue factor antibody. Tissue factor could be identified in glomeruli from these two patients by indirect immunofluorescence using this antibody. These studies implicate extrinsic pathway activation via tissue factor in intraglomerular deposition of fibrin in these patients. Activated monocytes, known to be a potent source of procoagulant activity and seen in large numbers within glomeruli from these patients, are a likely source of this tissue factor.

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J P Dowling

Papers

Glomerular Procoagulant Activity in Human Proliferative Glomerulonephritis