[Hypersensitivity pneumonitis monitored with serum KL-6, a marker of interstitial pneumonia]

A 44-year-old man was hospitalized because of exertional dyspnea that had progressed for one month. A chest X-ray film showed bilateral small nodular and reticular shadows. The patient presented with a positive inflammatory reaction and hypoxemia. Bronchoalveolar davage fluid had a high lymphocyte fraction and a low CD4/CD8 ratio. Trichosporon cutaneum antibodies were detected, and a specimen obtained by transbronchial lung biopsy showed alveolitis with granuloma formation. The patient reacted positively on a provocation test that was done by having him stay home for 5 days. Summer-type hypersensitivity pneumonitis was diagnosed, and a steroid was administered because of the prolonged abnormal chest roentgenographic findings. KL-6, a mucinous high-molecular-weight glycoprotein that is expressed on Type II pneumonocytes, was retrospectively used as a marker of pneumonitis. A new kit for enzyme-linked immunoassay (ED046) was used to measure the serum KL-6 level. The serum KL-6 level peaked approximately 10 days after the patient was admitted to the hospital and was thus kept away from antigens, and also after the provocation test. The steroid treatment was started, the KL-6 level decreased gradually. Within 2 months after steroid treatment began, the dose of the steroid was reduced and the KL-6 level decreased below the upper limit of normal. The KL-6 level remained low thereafter; it was not influenced by liver dysfunction or other inflammatory processes. However, the C-reactive protein level decreased rapidly after provocation and thereafter immediately returned to almost zero. The lactate dehydrogenose level peaked 8 days after provocation and decreased rapidly after steroid treatment. These results suggest that the serum KL-6 level provides new information regarding the clinical course and treatment of interstitial pneumonia. In addition KL-6 may be useful form monitoring disease activity, especially while tapering the dose of steroids in patients with interstitial pneumonia.