Intracellular Bacillary Burden Reflects a Burst Size for Mycobacterium tuberculosis In Vivo

PLoS Pathogens

Gregory Hendricks¹  Teresa Repasy²  Hardy Kornfeld²  Jinhee Lee²  Nuria Martinez²  Simeone Marino³  Denise E. Kirschner³  Stephen Baker⁴  Darrell N. Kotton⁵  Andrew A. Wilson⁵ 

[1] Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America;Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America;Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America;Department of Quantitative Health Science, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America;Pulmonary Center, Boston University School of Medicine, Boston, Massachusetts, United States of America

关键词: Mycobacterium tuberculosis;    Neutrophils;    White blood cells;    Tuberculosis;    Macrophages;    Aerosols;    Cell staining;    Apoptosis;   

DOI  :  10.1371/journal.ppat.1003190

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

We previously reported that Mycobacterium tuberculosis triggers macrophage necrosis in vitro at a threshold intracellular load of ∼25 bacilli. This suggests a model for tuberculosis where bacilli invading lung macrophages at low multiplicity of infection proliferate to burst size and spread to naïve phagocytes for repeated cycles of replication and cytolysis. The current study evaluated that model in vivo, an environment significantly more complex than in vitro culture. In the lungs of mice infected with M. tuberculosis by aerosol we observed three distinct mononuclear leukocyte populations (CD11b− CD11c+/hi, CD11b+/lo CD11clo/−, CD11b+/hi CD11c+/hi) and neutrophils hosting bacilli. Four weeks after aerosol challenge, CD11b+/hi CD11c+/hi mononuclear cells and neutrophils were the predominant hosts for M. tuberculosis while CD11b+/lo CD11clo/− cells assumed that role by ten weeks. Alveolar macrophages (CD11b− CD11c+/hi) were a minority infected cell type at both time points. The burst size model predicts that individual lung phagocytes would harbor a range of bacillary loads with most containing few bacilli, a smaller proportion containing many bacilli, and few or none exceeding a burst size load. Bacterial load per cell was enumerated in lung monocytic cells and neutrophils at time points after aerosol challenge of wild type and interferon-γ null mice. The resulting data fulfilled those predictions, suggesting a median in vivo burst size in the range of 20 to 40 bacilli for monocytic cells. Most heavily burdened monocytic cells were nonviable, with morphological features similar to those observed after high multiplicity challenge in vitro: nuclear condensation without fragmentation and disintegration of cell membranes without apoptotic vesicle formation. Neutrophils had a narrow range and lower peak bacillary burden than monocytic cells and some exhibited cell death with release of extracellular neutrophil traps. Our studies suggest that burst size cytolysis is a major cause of infection-induced mononuclear cell death in tuberculosis.

【 授权许可】

CC BY