The pulmonary innate immune system responds to various airborne microbes. Although its specificity is broad and based on the recognition of pathogen-associated molecular patterns, it is uniquely regulated to limit inflammation and thereby prevent damage to the gas-exchanging alveoli. Macrophages, critical cell determinants of this system, recognize microbes through pattern recognition receptors such as TLRs, which typically mediate proinflammatory responses. The lung collectin, surfactant protein A (SP-A), has emerged as an important innate immune determinant that regulates microbe-macrophage interactions in this environment. In this study, we report the basal and SP-A-induced transcriptional and posttranslational regulation of TLR2 and TLR4 expression during the differentiation of primary human monocytes into macrophages. Despite SP-A’s ability to up-regulate TLR2 expression on human macrophages, it dampens TLR2 and TLR4 signaling in these cells. SP-A decreases the phosphorylation of IκBα, a key regulator of NF-κB activity, and nuclear translocation of p65 which result in diminished TNF-α secretion in response to TLR ligands. SP-A also reduces the phosphorylation of TLR signaling proteins upstream of NF-κB, including members of the MAPK family. Finally, we report for the first time that SP-A decreases the phosphorylation of Akt, a major cell regulator of NF-κB and potentially MAPKs. These data identify a critical role for SP-A in modulating the lung inflammatory response by regulating macrophage TLR activity.

Alveolar macrophages are important host defense cells in the human lung that continuously phagocytose environmental and infectious particles that invade the alveolar space. Alveolar macrophages are prototypical alternatively activated macrophages, with up-regulated innate immune receptor expression, down-regulated costimulatory molecule expression, and limited production of reactive oxygen intermediates (ROI) in response to stimuli. Surfactant protein A (SP-A) is an abundant protein in pulmonary surfactant that has been shown to alter several macrophage (Mφ) immune functions. Data regarding SP-A effects on ROI production are contradictory, and lacking with regard to human Mφ. In this study, we examined the effects of SP-A on the oxidative response of human Mφ to particulate and soluble stimuli using fluorescent and biochemical assays, as well as electron paramagnetic resonance spectroscopy. SP-A significantly reduced Mφ superoxide production in response to the phorbol ester PMA and to serum-opsonized zymosan (OpZy), independent of any effect by SP-A on zymosan phagocytosis. SP-A was not found to scavenge superoxide. We measured Mφ oxygen consumption in response to stimuli using a new oxygen-sensitive electron paramagnetic resonance probe to determine the effects of SP-A on NADPH oxidase activity. SP-A significantly decreased Mφ oxygen consumption in response to PMA and OpZy. Additionally, SP-A reduced the association of NADPH oxidase component p47phox with OpZy phagosomes as determined by confocal microscopy, suggesting that SP-A inhibits NADPH oxidase activity by altering oxidase assembly on phagosomal membranes. These data support an anti-inflammatory role for SP-A in pulmonary homeostasis by inhibiting Mφ production of ROI through a reduction in NADPH oxidase activity.

A crucial step in infection isTuberculosis (TB) remains a significant therapeutic challenge for the early 21st century. The global incidence and prevalence of infection and multidrug resistance and the impact of AIDS and poverty diminish the likelihood that TB will be controlled without a more effective vaccine (9, 15). Therefore, innovative approaches to discovering improved diagnostic methods, therapies, and vaccine candidates are very much needed.