Obligatory Role for Interleukin-13 in Obstructive Lesion Development in Airway Allografts

Abstract

The pathogenesis of bronchiolitis obliterans (BO), a common and devastating obliterative disorder of small airways following lung transplantation, remains poorly understood. Lesions are characterized in their early stages by lymphocyte influx that evolves into dense fibrotic infiltrates. Airway specimens taken from patients with histological BO revealed infiltrating myofibroblasts, which strongly expressed the signaling chain of the high affinity interleukin-13 (IL-13) receptor IL-13R␣1. Because IL-13 has proinflammatory and profibrotic actions, a contributory role for IL-13 in BO development was examined using murine models of orthotopic and heterotopic tracheal transplantation. Compared with airway isografts, allografts exhibited a significant increase in relative IL-13 mRNA and protein levels. Allogeneic tracheas transplanted into IL-13-deficient mice were protected from BO in both transplant models. Flow cytometric analysis of orthotopic transplant tissue digests revealed markedly fewer infiltrating mononuclear phagocytes and CD3؉ T lymphocytes in IL-13-deficient recipients. Furthermore, protection from luminal obliteration, collagen deposition, and myofibroblast infiltration was observed in heterotopic airways transplanted into the IL-13 ؊/؊ recipients. Transforming growth factor-␤1 expression was significantly decreased in tracheal allografts into IL-13 ؊/؊ recipients, compared to wild-type counterparts. These human and murine data implicate IL-13 as a critical effector cytokine driving cellular recruitment and subsequent fibrosis in clinical and ex- Bronchiolitis obliterans syndrome (BOS) is the major factor limiting quality of life as well as long-term survival after lung transplantation. BO is a histological diagnosis, characterized by fibrosis and obliteration of the small airways.1 BOS, the clinical correlate of BO, is diagnosed by irreversible deterioration of pulmonary function in the absence of other causes.2 BOS is seen in up to 60% of lung transplant recipients by 5 years after transplantation. There are currently no meaningful therapeutic interventions, providing a compelling rationale to understand fully BOS pathogenesis as this may lead to development of new therapeutic approaches.Data from human as well as animal studies suggest associations between inflammatory cells/mediators and BOS. Lymphocytic bronchitis is considered a risk factor for development of BOS in humans, 3 and lymphocytic infiltration precedes development of luminal obliteration in animal models of tracheal transplantation. 4,5 Similarly, several markers of inflammation (eg, neutrophilia,(6)(7)(8)7 and monocyte chemoattractant protein-1 (MCP-1/ CCL2) 8,9 ) are predictive of development of BO in humans. However, the failure of immunosuppressive therapy and anti-inflammatory agents to demonstrate efficacy in preventing or treating this disease has focused attention on BOS as a fibroproliferative response to airway epithelial injury. Evidence for this is provided by studies suggesting a role for transforming growth factor-␤ (TGF-...

Resident Tissue-Specific Mesenchymal Progenitor Cells Contribute to Fibrogenesis in Human Lung Allografts

“…26 Previously, myofibroblasts in human BO lesions expressed IL-13 receptor ␣1, the receptor chain necessary for signaling by IL-13. 4 LR-MSCs demonstrated significant expression of this receptor by both flow cytometry and immunofluorescence microscopy ( Figure 2, A nofluorescence (P Ͻ 0.0001, Figure 2C). Immunoblot analysis demonstrates increased expression of both ␣-SMA and collagen I protein in LR-MSCs treated with IL-13 compared with untreated controls (P ϭ 0.016 and P ϭ 0.034, respectively; Figure 2D).…”

“…The profibrotic type 2 helper T cell cytokine IL-13 is critical in the development of luminal obliteration in animal models of BO, 4,26 and increased levels of IL-13 are present in BAL fluid of human lung transplant recipients with BOS. 26 Previously, myofibroblasts in human BO lesions expressed IL-13 receptor ␣1, the receptor chain necessary for signaling by IL-13.…”

“…Immunohistochemical (IHC) staining with ␣-SMA was performed according to standard clinical laboratory procedures, as previously described. 4 Human clone (FOXF1 ORFeome Collaboration Clone; I.D.1000 -67187, accession No. EU832158) was purchased from Open Biosystems (Huntsville, AL).…”

“…Western blot analysis for ␣-SMA and collagen I was performed as previously described, 4,19 using monoclonal ␣-SMA (clone 1A4; Dako) at 1:1000 dilution and rabbit polyclonal antibody to collagen I (Cedarlane Laboratories, Burlington, ON, Canada) at 1:500 dilution.…”

“…2 Subepithelial and/or intraluminal infiltration by myofibroblasts, differentiated mesenchymal cells with augmented collagen secretory and contractile functions, 3 is noted in human biopsy specimens that demonstrate BO. 4 BO presents clinically as an obstructive ventilatory defect termed BO syndrome (BOS). 5 BOS is the major cause of graft failure and long-term mortality, with no effective treatment options.…”