Studies on Quantitative Change, Localization and Clinical Significance of Surfactant Protein A (SP-A) in Idiopathic Interstitial Pneumonia

Pulmonary surfactant consists of phospholipids and four surfactant proteins, designated as SP-A, -B, -C, -D. SP-A is a major surfactant associated glycoprotein which is specific to the lung. In this study, we measured SP-A in sera and in bronchoalveolar lavage (BAL) fluid in patients with idiopathic interstitial pneumonia (IIP), using ELISA, and compared those to various clinical data. Moreover, we investigated the local state of SP-A in HP lesions, using lung biopsied materials. Serum SP-A levels correlated with serum lactate dehydrogenase (LDH) activity, and serum SP-A in patients with accelerated erythrocyte sedimentation rate (ESR) was significantly higher than that in patients without accelerated ESR. Serum SP-A in patients with more than three years survival was also significantly higher than that in patients who died in less than three years, suggesting that serum SP-A value reflects the disease activity of IIP. Immunohistochemical studies showed that SP-A was not detected in bronchioles where alveoli had collapsed, and many hyperplastic type II cells strongly expressed SP-A in alveolar ducts and this was thought to be associated with high levels of serum SP-A. However, the quantity of SP-A in tissue homogenates significantly decreased in IIP compared to that in normal lung, and SP-A in BAL fluid negatively correlated to those in sera. Western blot analyses showed that there were no abnormal SP-As compared to normal control either in lung homogenates or in BAL fluids. We concluded that serum SP-A concentrations increase in accordance with the activity of IIP since alveolar to vascular leakage was accelerated in IIP