Lung surfactant apoprotein (LSP) content of sputum samples from patients with chronic airway diseases

Abstract

LSP contents of sputum samples from patients with chronic airway diseases were measured by an enzyme-linked immunosorbent assay (ELISA) kit which was designed by Kuroki et al to examine whether a substance identical to lung surfactant contained in alveolar lining layer, is also contained in respiratory tract fluid or not in the ELISA kit. One antibody to LSP was conjugated to peroxidase and another one to LSP was fixed onto a bead. A neo-anionic detergent, Triton X-100 and an anionic detergent, sodium dodecyl sulfate (SDS) were added to extraction medium to separate LSP from lung surfactant, and LSP reaction of sputum sample was maximal when the ratio of Triton X-100 to SDS was in range of 1 to 4. Airway mucous glycoprotein (AMG) purified from sputum sample did not show any LSP reaction. In CsCl density gradient ultracentrifugation of whole sputum, the LSP reaction was detectable only in the top fraction with density of about 1.40 and AMG was located in the fraction with a density of about 1.50. These results indicate that the LSP reaction of sputum sample is not due to false reaction caused by nonspecific binding of viscous AMG to the two antibodies to LSP, but to the existence of LSP. Therefore it was concluded that lung surfactant is contained in respiratory tract fluid. In general, the LSP concentrations in sputum samples were lower in purulent sputa than in mucoid or mucopurulent sputa, and lower in patients with diffuse panbronchiolitis and bronchiectasia than in those with pulmonary emphysema and chronic bronchitis. It was shown that LSP was hydrolyzed by neutrophil leucocyte homogenate. These results suggest that LSP content of sputum is influenced by various factors such as infection and disease in the respiratory tract, and thus is useful to estimate pathological states of chronic airway diseases.