Aberrant appearance of lung surfactant protein A in sera of patients with idiopathic pulmonary fibrosis and its clinical significance.

Pulmonary surfactant protein A (SP-A) is known to be a major phospholipid-associated glycoprotein in pulmonary surfactant, which is specific to the lung. In this study, the SP-A concentrations in sera of patients with various lung diseases were determined using an enzyme-linked immunosorbent assay. Patients with idiopathic pulmonary fibrosis (IPF) and pulmonary alveolar proteinosis (PAP) exhibited prominently high concentrations of serum SP-A compared to those of other lung diseases and healthy volunteers, although there were significant increases in serum SP-A concentrations in patients with pulmonary tuberculosis, chronic pulmonary emphysema, diffuse panbronchiolitis and bacterial pneumonia compared to those of healthy volunteers. Successive measurement in 2 patients with IPF showed that serum SP-A levels reflect the disease activity of IPF. In patients with IPF, serum SP-A concentrations were significantly correlated with those of serum lactate dehydrogenase, whereas there were no significant correlations of serum SP-A concentrations with erythrocyte sedimentation rate, arterial oxygen saturation, vital capacity and carbon monoxide diffusing capacity. Determination of serum SP-A will contribute to diagnosing IPF and PAP, and may reflect the disease activity of IPF.