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Rationale: Imatinib is an inhibitor of platelet-derived growth factor receptors. We have reported that treatment with imatinib inhibited bleomycin-induced pulmonary fibrosis in mice. However, late treatment with imatinib had no effect., Objectives: To clarify why imatinib had no antifibrotic effect when its administration was delayed, we focused on alpha(1)-acid glycoprotein (AGP), because it was reported to bind imatinib and mediate drug resistance., Methods: The concentration of AGP in serum of mice and patients with idiopathic pulmonary fibrosis was measured by radial immunodiffusion testing. The effects of AGP in vitro were evaluated by assaying the growth of lung fibroblasts. We examined the combined effects of erythromycin (EM) or clarithromycin (CAM) on bleomycin-induced pulmonary fibrosis in mice., Measurements and Main Results: Addition of AGP abrogated imatinib-mediated inhibition of the growth of fibroblasts. However, treatment with EM or CAM restored the growth-inhibitory effects of imatinib. The elevated level of AGP was detected in serum and lung homogenates in bleomycin-exposed mice and reached a plateau on Day 14. Imatinib alone did not ameliorate pulmonary fibrosis when treatment was started on Day 15, whereas coadministration of imatinib and EM or CAM significantly reduced the fibrogenesis via inhibition of the growth of fibroblasts in vivo. Serum levels of AGP were higher in patients with idiopathic pulmonary fibrosis than in healthy subjects., Conclusions: AGP is an important regulatory factor modulating the ability of imatinib to prevent pulmonary fibrosis in mice, and combined therapy with imatinib and EM or CAM might be useful for treatment of pulmonary fibrosis.

CD13/aminopeptidase N (E.C.3.4.11.2) is an ectoenzyme located in the outer membrane of a variety of cells. Because aminopeptidase expression was shown to be upregulated by a Th1-related cytokine, IFN-gamma, we examined here the significance of CD13/aminopeptidase N in pulmonary sarcoidosis. The activity of aminopeptidase in bronchoalveolar lavage fluid (BALF) was significantly higher in patients with sarcoidosis than in normal volunteers (NV) and control patients (CP). The activity significantly correlated with lymphocyte percentages and the ratio of CD4+ to CD8+ T lymphocytes in the BALF, and was higher in patients with sarcoidosis with parenchymal involvement than in those without the involvement. CD13/aminopeptidase N protein, which has a molecular mass of approximately 150 kD, was detectable in alveolar macrophages (AM) from patients with sarcoidosis at higher levels than in those from NV. CD13/aminopeptidase N induced in vitro chemotactic migration of human lymphocytes in a concentration range of 10(-)(5) to 10(-)(1) U/ml. The chemotactic activity was greater for CD4+ T lymphocytes than for CD8+ T lymphocytes. The enzymatic activity of CD13/aminopeptidase N was responsible for the chemotactic activity because bestatin, an inhibitor of CD13/aminopeptidase N, abolished the chemotactic activity. Higher chemotactic activity for lymphocytes was detected in the BALF from patients with sarcoidosis than in that from NV, and the activity was significantly decreased by treatment with bestatin. This study indicates that CD13/ aminopeptidase N expressed in AM may have a role in T-lymphocyte involvement in the sarcoid lung and the pathogenesis of alveolitis in this disorder.