An immunologic study of the apoproteins of rat lung surfactant

An immunologic analysis of lung surfactant-associated proteins, designed to detect surfactant-specific protein(s), was performed. Rat lung surfactant was isolated and purified and was used to raise antisera in rabbits. The antisera were found to react with both rat serum and lung surfactant. Antibodies against rat serum proteins were removed from the IgG fraction of the antiserum by means of affinity chromatography using rat serum linked to Sepharose 4B. The specificity of the purified IgG thus prepared (surfactant-specific IgG) was checked by immunodiffusion analysis and by immunoperoxidase and immunofluorescence staining of sections of lungs obtained from adult, newborn, and fetal rats. Immunodiffusion analysis revealed a single precipitin line against rat lung surfactant, but no reactivity with rat serum proteins. After immunoperoxidase staining, only few cells were positive in 19-day-old fetal lungs, but the number of stained cells increased rapidly in the succeeding gestational days. In newborn and adult rats, both alveolar cells and the alveolar-lining layer stained positively for surfactant-specific protein(s). Affinity columns, prepared with surfactant-specific IgG, were used to purify surfactant-specific proteins from isolated rat surfactant. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the surfactant-specific protein, after chemical reduction, revealed two major protein subunits, having molecular weights of 38,000 and 32,000. The 38,000-dalton protein subunit was also seen on sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the surfactant isolated from monkey lung lavages and human amniotic fluid.