Platelet-derived growth factor in bronchiolitis obliterans-organizing pneumonia

Bronchiolitis obliterans-organizing pneumonia (BOOP) is a disorder characterized by intraluminal proliferation of connective tissue in distal air spaces. As part of a general investigation of the role of growth factors in this process, the present study examined the expression of the mitogen, platelet-derived growth factor (PDGF), and one of its receptors, PDGFR-beta, in this disease. Serial sections of lung biopsy specimens from 20 patients with BOOP and 10 control subjects were stained with antibodies against PDGF, PDGFR-beta, and the monocyte/macrophage marker CD68. Stereologic point counting showed that PDGF(+) cells represented 4.6+/-1.6% (mean+/-SD) of the volume occupied by lung tissue in BOOP and 2.1+/-0.7% in the control subjects (p <0.0001). In both groups the positive cells were tissue macrophages, and CD68(+) macrophages accounted for 10.7+/-4.7% of the lung tissue in BOOP as compared with 5.4+/-3.7% in the control subjects (p <0.005). PDGFR-beta immunoreactivity was present in some alveolar epithelial cells in BOOP, but was absent in control subjects. We conclude that PDGF(+) cells and CD68(+) macrophages are found in greater numbers in lungs with BOOP, and an increased expression of PDGFR-beta epitopes was observed in some patients with BOOP. We speculate that these molecules are important in the pathogenesis of the destructive fibroproliferative process that characterizes this disease.