Serum secretory leukoprotease inhibitor (SLPI) is synthesized and secreted by serous cells in airway glands, and the serum level is speculated to reflect airway gland hyperplasia. To test this hypothesis, we measured the serum SLPI in 38 clinically stable patients with chronic bronchitis (3F and 35M; 58±2 years, mean±S.E.M.) (group CB), 24 patients with Sjögren's syndrome (24F; 52±3 years) (group SG), and compared it with 12 healthy control subjects (6F and 6M; 54±3 years) (group CN) using an enzyme-linked immunosorbent assay (ELISA). The serum SLPI from group CB (105±8 ng/ml) was significantly higher than that from group CN (60±2 ng/ml) and further, it significantly correlated with sputum volume per day. Although the mean value of serum SLPI from group SG (64±5 ng/ml) was not different from that from group CN, serum SLPI significantly correlated with the duration of respiratory symptoms (cough and/or sputum) in group SG. In conclusion serum SPLI level reflects airway gland hyperplasia, suggesting that SLPI measurement is a possible laboratory method to estimate airway glandular hyperplasia.
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