IMMUNOGOLD LOCALIZATION OF SP-A IN LUNGS OF INFANTS DYING FROM RESPIRATORY-DISTRESS SYNDROME

Prematurely born infants can develop the neonatal respiratory distress syndrome (PDS) because of a deficiency of pulmonary surfactant. This lipoprotein complex synthesized by type II pneumocytes has different u ltrastructural forms-intra- and extracellular lamellar bodies, which w ithin the alveoli are transformed into tubular myelin, and this in tur n gives rise to the surface monolayer, the functionally active form of surfactant. We have previously shown that at autopsy RDS lungs lack t ubular myelin and have decreased immunoreactivity for antisera to surf actant protein A (SP-A), an important component of tubular myelin. The refore, we proposed a role for SP-A in the conversion of lamellar bodi es to tubular myelin and in the pathogenesis of RDS. To explore this p ossibility further, we compared in 14 RDS and 14 control lungs the dis tribution of SP-A in ultrathin sections, using affinity-purified rabbi t anti-human-SP-A IgG and goat anti-rabbit IgG-conjugated with 10 nm c olloidal gold particles. In controls, gold label was present in lamell ar bodies, endoplasmic reticulum, on the cytoplasmic membrane of type II cells, and on lamellar bodies and tubular myelin either within alve oli or macrophages. In RDS lungs, reduced label was present in the sam e intracellular compartments and organelles, except in tubular myelin, which is absent. It is postulated that if SP-A is indeed necessary fo r the conversion of lamellar bodies to tubular myelin, in RDS either t here is a deficiency of adequate amounts of functional SP-A or some ot her important component of surfactant is missing.