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Immunophenotyping and protein profiling of Fontan-associated plastic bronchitis airway casts
Jennifer Racz1, Gerta Mane, Michael Ford
1Department of Clinical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109-1065, USA.
Insights
Plastic bronchitis (PB) airway casts in children with Fontan physiology are inflammatory and contain fibrin, suggesting complex pathogenesis beyond lymph leak. Cellular necrosis and inflammation resolution derangement may contribute to cast formation.
Area of Science:
- Pediatric Cardiology
- Pulmonary Medicine
- Immunology
Background:
- Plastic bronchitis (PB) is a rare, fatal condition characterized by airway cast formation.
- It predominantly affects children with congenital heart disease, particularly after Fontan procedure.
- Current understanding of PB pathogenesis is limited, relying mainly on case reports.
Purpose of the Study:
- To investigate the pathogenesis of plastic bronchitis airway casts.
- Characterize inflammatory cell phenotypes and protein/cytokine profiles within casts.
Main Methods:
- Utilized immunofluorescence confocal microscopy to identify cellular content.
- Employed proteomics to analyze protein composition.
- Conducted cytokine array assays to determine cytokine-chemokine profiles.
Main Results:
- Identified neutrophils, eosinophils, macrophages, and B lymphocytes; T lymphocytes were scarce.
- Fibrin(ogen) and extracellular histone H4 were abundant proteins.
- Cast homogenates exhibited a proinflammatory cytokine profile.
Conclusions:
- Plastic bronchitis casts in Fontan patients are cellular, inflammatory, and fibrin-rich, challenging the lymph leak hypothesis.
- Extracellular histones and low T cell counts suggest impaired inflammation resolution contributes to cast formation.
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.
