Entry and intracellular replication of Mycobacterium tuberculosis in cultured human microvascular endothelial cells

• Published in: Microbial pathogenesis 2006-08, Vol.41 (2), p.119-124
• Main Authors: Mehta, Parmod K., Karls, Russell K., White, Elizabeth H., Ades, Edwin W., Quinn, Frederick D.
• Format: Article
• Language: English
• Subjects: Bacterial Adhesion - physiology; Bacterial diseases; Bacterial Infections - microbiology; Biological and medical sciences; Cell Growth Processes - physiology; Cell Line; Endothelial Cells - metabolism; Endothelial Cells - microbiology; Endothelial Cells - pathology; Endothelium; Fundamental and applied biological sciences. Psychology; Human bacterial diseases; Humans; Infectious diseases; Intercellular Adhesion Molecule-1 - biosynthesis; M. tuberculosis; Medical sciences; Microbiology; Microscopy, Electron - methods; Mycobacterium tuberculosis; Mycobacterium tuberculosis - growth & development; Mycobacterium tuberculosis - physiology; Pathogenesis; Pulmonary Alveoli - blood supply; Pulmonary Alveoli - metabolism; Pulmonary Alveoli - pathology; Tuberculosis and atypical mycobacterial infections; Tuberculosis, Pulmonary - metabolism; Tuberculosis, Pulmonary - microbiology; Tuberculosis, Pulmonary - pathology
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/j.micpath.2006.05.002

Establishment of pulmonary Mycobacterium tuberculosis infection requires evasion of host innate defenses. In the lung alveoli, epithelial cells naturally resist uptake by the inhaled bacilli while macrophages patrol the epithelial surface and phagocytose foreign microbes. Alveolar microvascular endothelial cells, however, have not been examined as a potential point of direct interaction with the bacilli. It has been shown with other bacterial and viral lung pathogens that the lung endothelial cells are not only a point of interaction, but a source for intracellular replication and chronic infection by the pathogen. To investigate if endothelial cells are susceptible to M. tuberculosis infection, we examined attachment, internalization, and intracellular replication of M. tuberculosis bacilli in an immortalized human lung microvascular endothelial cell line (HULEC). By 6 h post-infection, 12% of infecting bacilli were associated with the HULEC monolayer cells. This was twice the association observed following a similar infection with cells from a human foreskin microvascular endothelial cell line (HMEC-1). As measured by survival after the addition of a high extracellular concentration of the aminoglycoside amikacin, approximately one-third of the associated bacilli were internalized and unavailable to the drug in both cell lines. Using electron microscopy, large numbers of bacilli were visible in the vacuoles of HULEC cells after 48 h post-infection; the presence of bacterial septa between adjacent mycobacteria suggests intracellular replication. These in vitro findings support the hypothesis that lung endothelial cells have the potential to participate in in vivo lung infections.