Effects of Surfactant Lipids and Surfactant Protein A on Host Defense Functions of Rat Alveolar Macrophages

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Abstract
Survanta is commonly used as replacement therapy in newborn infants suffering from surfactant deficiency. We investigated the effects of Survanta and surfactant-like liposomes in the presence and absence of surfactant protein A (SP-A) on host defense functions of rat alveolar macrophages (AM). Phagocytosis of Streptococcus pneumoniae by AM was significantly inhibited in the presence of 100 μg/mL of Survanta. The ability of SP-A to enhance phagocytosis of S. pneumoniae was significantly compromised upon exposure to either Survanta or liposomes, although the overall level of phagocytosis remained higher than in the absence of SP-A. This inhibitory effect was not overcome by opsonization of the bacteria with SP-A before incubation with Survanta and AM. We also found that the ability of SP-A to mediate the association of group B Streptococcus with AM was compromised to a significant degree when exposed to either Survanta or liposomes in concentrations of 150 and 250 μg/mL. However, at most concentrations of Survanta or liposomes tested, the presence of SP-A resulted in significantly higher levels of bacterial association. These data show that Survanta and surfactant-like lipids suppress host defense functions of AM in the presence and absence of SP-A in vitro, although SP-A continues to enhance host defense functions overall.