Hyaluronate and Type III Procollagen Peptide Concentrations in Bronchoalveolar Lavage Fluid As Markers of Disease Activity in Farmer's Lung

Ten patients were studied during an acute episode of farmer's lung. Prominent findings were an impaired diffusion capacity (on average only 51% of predicted) and substantially increased amounts of hyaluronate and type III procollagen peptide recovered during bronchoalveolar lavage; mean concentrations of these constituents in lavage fluid were 547 (range 137-1125) and 9.7 (2.8-19.4) micrograms/l, respectively. In bronchoalveolar lavage fluid from healthy controls (n = 21) hyaluronate concentrations were less than 15 micrograms/l and procollagen peptide concentrations less than 0.2 micrograms/l. Lavage fluid concentrations of these potential markers of fibroblast activation declined during the recovery phase of farmer's lung; four to 10 weeks after admission (n = 7) mean concentrations of hyaluronate and procollagen peptide were 154 (range 38-650) and 4.4 (0.6-15.8) micrograms/l, respectively. At clinical remission six to 14 months after admission concentrations of these markers had returned almost to normal, though slightly increased concentrations were still evident in about half the patients (n = 7). At that time lung volumes were normal but diffusion capacity remained slightly subnormal. It was concluded that in farmer's lung release of hyaluronate and type III procollagen peptide reflects activity of the disease. Increased synthesis of these connective tissue components continuing in a patient avoiding mouldy plant material may signal an increased risk of developing fibrotic lung disease. The abnormal accumulation of hyaluronate in the smaller airways in acute farmer's lung may be expected to immobilize water and thereby provide a possible mechanism of the interstitial inflammatory lung oedema with associated impaired gas diffusion. This hypothesis is supported by the relation found between hyaluronate in lavage fluid and reduced diffusion capacity.