Affiliation:
1. Division of Infectious Diseases, Department of Medicine, UCLA School of Medicine, Center for Health Sciences, Los Angeles, California 90095
Abstract
ABSTRACT
Knowledge of whether
Mycobacterium tuberculosis
resides within a relatively impermeable membrane-bound vacuole or is free within the cytoplasm within its host cell is central to an understanding of the immunobiology of this intracellular parasite but is a matter of controversy. To explore this issue, we assessed the accessibility of medium-size protein molecules (Fab fragments of 50,000 Da) to
M. tuberculosis
within human macrophages. We infected the macrophages with wild-type or green fluorescent protein-expressing
M. tuberculosis
, microinjected Fab fragments directed against a major surface antigen of
M. tuberculosis
into the host cell, and assayed the accessibility of the bacteria to the Fab fragments by both immunofluorescence microscopy and immunogold electron microscopy. Whereas microinjected intact immunoglobulin G molecules against cytoplasmic early endosomal antigen 1 readily stained this antigen, microinjected Fab fragments against
M. tuberculosis
did not stain the bacterium within its phagosome. In contrast, microinjected Fab fragments against
Listeria monocytogenes
, an intracellular bacterium known to permeabilize its phagosomal membrane, strongly stained this bacterium. Our study shows that
M. tuberculosis
resides in an isolated phagosome that is relatively impermeable to cytoplasmic constituents.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
32 articles.
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