Pulmonary surfactant and tuberculosis

Mycobacterium tuberculosis comes in contact with pulmonary surfactant, alveolar macrophages and type II epithelial cells. Alveolar type II epithelial cells secrete pulmonary surfactant, a complex mixture of phospholipids and proteins lining the alveolar surface, while alveolar macrophages are involved in surfactant catabolism. Surfactant proteins SP-A and SP-D modulate phagocytosis of M. tuberculosis by alveolar macrophages. We have reported that mice with decreased surfactant catabolism resulting from GM-CSF deficiency are highly susceptible to acute aerosol infection with 100 cfu of M. tuberculosis. Here, we evaluated the lungs of WT, GM-CSF-deficient, and GM-CSF-corrected mice surviving six months after sub-acute aerosol infection of 5-10 cfu M. tuberculosis. We show that GM-CSF-deficient mice develop intra-bronchial and intra-alveolar tuberculosis lesions with numerous mycobacteria, inflammatory cells, and extracellular proteinaceous material containing surfactant protein B ( SP-B). In contrast, WT and GM-CSF-corrected mice develop typical epithelioid granulomas containing lymphocytes, SP-B positive cells, and M. tuberculosis bacilli inside macrophages. Our findings support the concept that whole pulmonary surfactant is an important component of host mycobacterial infection in the distal lung. (C) 2009 Elsevier Ltd. All rights reserved.