Tuberculosis continues to be an enormous world health problem. Delineation of the specific interactions between the adapted intracellular lung pathogen M. tuberculosis (M.tb) and host alveolar macrophages (AMs) in the innate immune response will be important for the development of novel treatment strategies and vaccines. The macrophage mannose receptor (MR) mediates phagocytosis of M.tb. It is highly expressed on AMs and a marker of a unique differentiation state (alternative activation) that includes increased phagocytosis and decreased oxidative responses. AMs are bathed in surfactant protein A (SP-A) and surfactant protein D (SP-D), important lung innate immune molecules. We have determined that SP-A enhances M.tb phagocytosis by upregulating MR function and downregulating macrophage oxidative responses. AMs originate from circulating monocytes that immigrate into the pulmonary microenvironment. We find that SP-A added during monocyte differentiation in vitro leads to a unique phenotype, including enhanced MR and CD14 expression and oxidative responses. In contrast to SP-A, the lesser abundant SP-D agglutinates M.tb and reduces M.tb phagocytosis by macrophages by blocking a microbial ligand for the MR. Our central hypothesis is that M.tb is an efficient respiratory pathogen because it is particularly adapted for survival in the AM whose function is regulated by surfactant components. SP-A, through its action on phagocytes, may enhance the susceptibility of these cells for M.tb entry and growth. ? ? Our AIMs are to: 1) To determine the mechanism (s) underlying SP-A-induced up-regulation of MR activity (A) and inhibition of respiratory responses (B) in macrophages. 2) To determine the impact of SP-A, SP-D, and surfactant lipids on the intracellular survival of M.tb in human macrophages. 3) To determine the effects of SP-A on monocyte differentiation to macrophages and the response of these cells to M.tb. Studies will examine those phenotypic and functional attributes characteristic of AM, focusing on regulation of MR activity, the respiratory response, and intracellular survival of M.tb. 4) To determine the role of two key macrophage biochemical mediators in SP-A-induced changes in MR activity and oxidative responses: Protein Kinase C (PKC) and Phosphoinositide-3-kinase (PI3K). ? ? We will use microscopy techniques and biochemical assays to assess SP-A's effects on MR trafficking, oxidative responses and SP-A signaling in human macrophages. We will use an in vitro assay of monocyte differentiation to characterize SP-A's effects. Our overall goal will be to better understand the role of surfactant components as regulators of macrophage biology and their impact on M.tb pathogenesis. ? ?
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