Surfactant protein A mediates mycoplasmacidal activity of alveolar macrophages

Mycoplasma pneumoniae is a leading cause of pneumonia and exacerbates other respiratory diseases in humans. mie investigated the potential role of surfactant protein (SP) A in antimycoplasmal defense using alveolar macrophages (AMs) from C57BL/6NCr (C57/BL) mice, which are highly resistant to infections of Mycoplasma pulmonis. C57BL AMs, activated with interferon (IFN)-gamma and incubated with SP-A (25 mu g/ml) at 37 degrees C, produced significant amounts of nitric oxide (.NO; nitrate and nitrite production = 1.1 mu M . h(-1) . 10(5) AMs(-1)) and effected an 83% decrease in mycoplasma colony-forming units (CFUs) by 6 h postinfection. Preincubation of AMs with the inducible nitric oxide synthase inhibitor N-G-monomethyl-L-arginine abolished .NO production and SP-A-mediated killing of mycoplasmas. No decrease in CFUs was seen when IFN-gamma-activated macrophages were infected with mycoplasmas in the absence of SP-A despite significant .NO production (nitrate and nitrite production = 0.6 mu M . h(-1) . 10(5) AMs(-1)). These results demonstrate that SP-A mediates killing of mycoplasmas by AMs, possibly through an .NO-dependent mechanism.