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.