Impaired Recognition of Mycobacterium tuberculosis by Alveolar Macrophages From Diabetic Mice

Abstract

Background: Diabetes mellitus is associated with increased tuberculosis risk and severity. We previously reported that tuberculosis susceptibility in diabetic mice results from a delay in innate immune response to inhaled Mycobacterium tuberculosis, leading to delayed adaptive immune priming and, consequently, a higher plateau lung bacterial burden and greater immune pathology.

Methods: We tested the capacity of alveolar macrophages from diabetic mice to phagocytose M. tuberculosis ex vivo and promote T-cell activation in vivo.

Results: Alveolar macrophages from diabetic mice had reduced expression of CD14 and macrophage receptor with collagenous structure (MARCO), which recognize the bacterial cell wall component trehalose 6,6'-dimycolate (TDM). Diabetic alveolar macrophages exhibited reduced phagocytosis of M. tuberculosis or TDM-coated latex beads. This alveolar macrophage phenotype was absent in peritoneal and bone marrow-derived macrophages. Transfer of infected alveolar macrophages from diabetic mice into nondiabetic recipients confirmed an intrinsic alveolar macrophage defect that hindered T-cell priming. The diabetic alveolar macrophage phenotype depended in part on expression of the receptor for advanced glycation end products.

Conclusions: Reduced MARCO and CD14 expression contributes to defective sentinel function of alveolar macrophages, promoting tuberculosis susceptibility in diabetic hosts at a critical early step in the immune response to aerosol infection.

Keywords: CD14; MARCO; Mycobacterium tuberculosis; alveolar macrophages; diabetes; phagocytosis.