Prospective, Longitudinal Study of Plastic Bronchitis Cast Pathology and Responsiveness to Tissue Plasminogen Activator

Conclusions-In this study, we demonstrated abnormal pulmonary lymphatic perfusion in most patients with plastic bronchitis. Interruption of the lymphatic flow resulted in significant improvement of symptoms in these patients and, in some cases, at least temporary resolution of cast formation.

Tissue factor (TF) initiates the extrinsic coagulation cascade and is a high-affinity receptor for coagulation factor VII. TF also participates in protease-activated receptor (PAR)1 and PAR2 activation. Human epithelial basal cells were previously purified on the basis of TF expression. The purpose of this study was to determine if tracheobronchial epithelial basal cell-associated TF drives coagulation and/ or activates PARs to promote basal cell functions. We used human tracheobronchial tissues to isolate human airway epithelial cells using specific cell surface markers by flow cytometry and studied TF expression by immunostaining. TF-dependent fibrin network formation was observed by confocal and scanning electron microscopy. TF knockdown was done using short hairpin RNA, and TF mRNA was measured using quantitative RT-PCR. We found that 97 6 5% of firstpassage human tracheobronchial epithelial cells were basal cells, and 100% of these basal cells expressed TF. Basal cell-associated TF was active, but TF activity was dependent on added extrinsic coagulation cascade factors. TF inhibition caused basal cell apoptosis and necrosis. This was due to two parallel but interdependent TFregulated processes: failure to generate a basal cell-associated fibrin network and suboptimal PAR1 and PAR2 activity. The data indicate that membrane surface TF mediates airway epithelial basal cell attachment, which maintains cell survival and mitotic potential. The implications of these findings are discussed in the context of basal cell-associated TF activity in normal and injured tissues and of the potential for repair of airway epithelium in lung disease.Keywords: tissue factor; epithelium; clotting; fibrin; tracheobronchial Tissue factor (TF) is a transmembrane cell receptor and cofactor for factor VII (FVII) and serves biological functions beyond its established role in blood coagulation (1). TF may act as a transmembrane signaling molecule by activating and delivering coagulation factors for signaling, and the TF-coagulation FVIIa complex activates G protein-coupled receptors, including the protease-activated receptors (PARs) (2). Under pathologic conditions, TF can be expressed by circulating blood elements (monocytes, neutrophils, and platelets) and by an associated elevated number of cell-derived circulating microparticles. The role of TF in epithelial cell function is much less well understood than its role in the circulation and in hemostasis.In acute lung injury, increased coagulation and decreased fibrinolysis result in diffuse alveolar fibrin deposition, potentially increasing lung inflammation (3). Recent evidence indicates that the damaged alveolar epithelium expresses TF (4) and that FVII-activating protein expression is increased (5). Alveolar procoagulant microparticles are also elevated (6), and intrinsic elevation of tissue factor pathway inhibitor (TFPI) expression is insufficient to inhibit this procoagulant effect (7). Coagulation pathologies also occur in conducting airways. For example, the sulfur mustard ana...

Rationale: Plastic bronchitis (PB) is a rare and deadly condition that is characterized by the formation of airway casts. It most frequently occurs in children with underlying congenital heart disease that has been surgically palliated by the Fontan procedure. The Fontan circulation results in above-normal central venous pressure, and it has been hypothesized that the formation of airway casts is due to lymph leak. Knowledge of plastic bronchitis pathogenesis is poor and stems mostly from published case reports.Objectives: To garner information about cast pathogenesis by characterizing inflammatory cell phenotypes in existing formalin-preserved, paraffin-embedded samples and generating protein and cytokine-chemokine profiles of airway cast homogenates.Methods: We used immunofluorescence confocal microscopy, state-of-the-science proteomics, and a cytokine array assay to immunophenotype cellular content and to generate protein and cytokine profiles of plastic bronchitis airway casts, respectively.Measurements and Main Results: Neutrophils, eosinophils, macrophages, and B lymphocytes were identified in cast samples; there were notably fewer T lymphocytes. Fibrin(ogen) was an abundant protein in the cast proteome. Histone H4 was also abundant, and immunofluorescence microscopy demonstrated it to be mostly extracellular. The cytokine profile of plastic bronchitis casts was proinflammatory.Conclusions: Plastic bronchitis airway casts from children with Fontan physiology are composed of fibrin and are cellular and inflammatory in nature, providing evidence that their formation cannot be explained simply by lymph leak into the airways. Consequences of cellular necrosis including extracellular histones and the apparent low number of T cells indicate that a derangement in inflammation resolution likely contributes to cast formation.