engleski

The Francisella tularensis pathogenicity island protein, IglD, plays a role in bacterial escape into the cytoplasm

The Francisella tularensis pathogenicity island is essential for intramacrophage growth. The Francisella tularensis-containing phagosome (FCP) matures to the late endosome like stage that does not fuse to lysosome, followed by bacterial escape into the cytoplasm. Here we show that the Francisella pathogenicity island (FPI) protein, IglD is essential for intracellular replication in U937 and human monocytes derived macrophages (hMDMs). Histopathological studies on BALB/c mice show that the wild type (wt) strain causes sever bronchopneumonia and pulmonary apoptosis with systemic spread and robust replication in the liver and spleen. In contrast, mild or no histopahological changes are detected in the organs of mice after infection with the iglD mutant. Intracellular trafficking studies show that at 15min after infection, ~80% of the phagosome harboring the wt or the iglD mutant colocalize with LAMP-2 marker. At 30 min after infection, only 50% of the iglD mutant-containing phagosomes acquire LAMP-2. At 30 min after infection, phagosomes harboring the wt strain do not acquire the lysosomal enzyme Cathepsin D while ~40% of the phagosomes harboring the iglD mutant co-localize with lysosomes. As a positive control, we used iglC mutant since iglC mutant-containing phagosomes colocalize with both LAMPs and Cathepsin D. We show that despite the severe defect in intracellular replication within macrophages the iglD mutant strain escapes into the cytoplasm at a faster rate then the wt strain by 30 and 60 min after infection, in vitro and in vivo. Our data show that the intracellular iglD mutant belongs to two subpopulations, one that fuses to lysosomes while the other escapes into the cytoplasm more rapidly than the wt strain.

pathogenicity island; Francisella

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