1371 NEONATAL LUNG DEFENSES AFTER SURFACTANT THERAPY

Abstract

Artificial surfactant has been used to treat Hyaline Membrane Disease (HMD), but its effect on phagocytic function in the neonatal lung is poorly defined. A mixture of 70% phosphatidylcholine/30% phosphatidylglycerol w/w was diluted in sterile phosphate-buffered saline (PBS) and sonicated. Either 4 mg/Kg of this mixture or an equal volume (100 μl) of PBS was instilled into the surgically exposed trachea of less than 12 hr old rabbits. One hr after instillation, in vivo bacterial clearance was studied by exposing the groups to a Streptococcus agalactiae type Ia (GBS) aerosol and the numbers of viable GBS-compared in the left lung at 0 and 4 hrs after infection. Results follow: Intrapulmonary killing of GBS was significantly lower in surfactant vs control (p<0.05). Additional litters were divided and treated with either surfactant or PBS, and alveolar macrophages (AM) recovered 1 hr later by lavage. Phagocytosis was ascertained using FITC-labeled GBS opsonized in newborn rabbit serum (50 GBS:AM) by a fluorescence quenching method. The percentage of phagocytic AM (x = 91.4 vs 93.0) and GBS/phagocytic AM (x = 16.9 vs 18.6) were similar in surfactant vs PBS animals. Surfactant therapy may impair bacterial killing by newborn AM.