Tissue localization of transforming growth factor-β1 in pulmonary eosinophilic granuloma

Pulmonary eosinophilic granuloma is characterized by infiltration of the lungs with fibronodular lesions containing specialized Langerhans' cells. In some patients, progressive pulmonary fibrosis leads to significant respiratory impairment. Transforming growth factor-β1 (TGF-β1) promotes fibrosis by enhancing the synthesis of extracellular matrix components. The role of TGF-β1 in promoting fibrosis in the setting of pulmonary eosinophilic granuloma is currently unknown. We used immunohistochemistry to evaluate the extent and distribution of TGF-β1 and the extracellular matrix components type I collagen and decorin, a TGF-β1-binding proteoglycan. Lung biopsies from 11 patients with pulmonary eosinophilic granuloma were evaluated. In biopsies with active inflammatory lesions containing Langerhans' cells, hyperplastic type 2 pneumocytes and alveolar macrophages within and surrounding the fibronodular lesions contained abundant TGF-β1. Langerhans' cells were consistently devoid of immunoreactive TGF-β1. Active inflammatory lesions also exhibited staining for decorin, in a loosely organized distribution. Advanced fibrotic lesions of eosinophilic granuloma, containing minimal inflammatory cells and few or no Langerhans' cells, exhibited weak or absent staining for TGF-β1 within either hyperplastic type 2 pneumocytes or alveolar macrophages. The fibroconnective tissues of these advanced fibrotic lesions consistently revealed dense staining for decorin. Through their actions on extracellular matrix protein accumulation, TGF-β1 and the TGF-β1-binding proteoglycan decorin may modulate fibrotic repair accompanying pulmonary eosinophilic granuloma.