Open AccessInvolvement of the autophagy pathway in trafficking of M ycobacterium tuberculosis bacilli through cultured human type II epithelial cells
Author(s) -
Fine Kari L.,
Metcalfe Maureen G.,
White Elizabeth,
Virji Mumtaz,
Karls Russell K.,
Quinn Frederick D.
Publication year - 2012
Publication title -
cellular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.542
H-Index - 138
eISSN - 1462-5822
pISSN - 1462-5814
DOI - 10.1111/j.1462-5822.2012.01804.x
Subject(s) - endosome , autophagy , biology , mycobacterium tuberculosis , intracellular parasite , microbiology and biotechnology , intracellular , bacilli , phagosome , tuberculosis , bacteria , apoptosis , biochemistry , medicine , pathology , genetics
Summary Interactions between M ycobacterium tuberculosis bacilli and alveolar macrophages have been extensively characterized, while similar analyses in epithelial cells have not been performed. In this study, we microscopically examined endosomal trafficking of M . tuberculosis strain E rdman in A 549 cells, a human type II pneumocyte cell line. Immuno‐electron microscopic ( IEM ) analyses indicate that M . tuberculosis bacilli are internalized to a compartment labelled first with R ab5 and then with R ab7 small GTP ase proteins. This suggests that, unlike macrophages, M . tuberculosis bacilli traffic to late endosomes in epithelial cells. However, fusion of lysosomes with the bacteria‐containing compartment appears to be inhibited, as illustrated by IEM studies employing LAMP ‐2 and cathepsin‐ L antibodies. Examination by transmission electron microscopy and IEM revealed M . tuberculosis ‐containing compartments surrounded by double membranes and labelled with antibodies against the autophagy marker L c3, providing evidence for involvement and intersection of the autophagy and endosomal pathways. Interestingly, inhibition of the autophagy pathway using 3‐methyladenine improved host cell viability and decreased numbers of viable intracellular bacteria recovered after 72 h post infection. Collectively, these datasuggest that trafficking patterns for M . tuberculosis bacilli in alveolar epithelial cells differ from macrophages, and that autophagy is involved this process.