Osteopontin levels are elevated in patients with eosinophilic pneumonia

Background and objective: Osteopontin is a key cytokine involved in pro‐inflammatory T helper type 1 (Th1)‐associated immune responses, which has recently been implicated in allergic diseases. We investigated the pathogenic role of osteopontin in eosinophilic pneumonia. Methods: The concentrations of osteopontin and Th1‐ or Th2‐associated cytokines were measured in BAL fluid (BALF) from 41 patients with eosinophilic pneumonia, including those with acute (AEP, n = 12), chronic (CEP, n = 16), or drug‐induced eosinophilic pneumonia (DEP, n = 13). The results were compared with those from patients with other interstitial lung diseases. Immunocytochemistry and double immunofluorescence labelling were performed to determine the cellular source of osteopontin. Results: Osteopontin was significantly elevated in BALF from patients with eosinophilic pneumonia as compared with BALF from patients with drug‐induced interstitial pneumonia, hypersensitivity pneumonitis, idiopathic interstitial pneumonia, or sarcoidosis, and also compared with BALF from healthy volunteers. Osteopontin concentrations elevated at the time of exacerbation decreased during clinical improvement, either spontaneously or as a result of corticosteroid therapy. Elevated concentrations of CXCL10, CCL17 and IL‐10 were also detected in BALF from patients with eosinophilic pneumonia. Osteopontin concentrations in BALF of AEP patients were correlated with IL‐5, as well as IL‐10, CCL11, CCL17 and CXCL10 concentrations. In AEP and DEP patients, serum osteopontin concentrations were also elevated. Double immunofluorescence labelling showed that in patients with eosinophilic pneumonia, osteopontin was expressed in lung eosinophils. Conclusions: Osteopontin is likely to contribute to the development of inflammation in patients with eosinophilic pneumonia.