11-21-2006, 12:21 AM
Games parasites play!
Phagocytic cells, like macrophages and neutrophils, are an early line of defense against invading bacteria. However, some bacteria have evolved mechanisms to avoid destruction even after they have been engulfed by phagocytes.
Two examples:
Salmonella enterica is a bacterium that causes food poisoning in humans. Once engulfed by phagocytosis, it secretes a protein that prevents the fusion of its phagosome with a lysosome.
Mycobacteria (e.g., the tubercle bacillus that causes tuberculosis) use a different trick.
When the phagosome is first pinched off from the plasma membrane, it is coated with a protein called "TACO" (for tryptophan-aspartate-containing coat protein).
This must be removed before the phagosome can fuse with a lysosome.
Mycobacteria taken into a phagosome are able, in some way, to keep the TACO coat from being removed.
Thus there is no fusion with lysosomes and the mycobacteria can continue to live in this protected intracellular location
Phagocytic cells, like macrophages and neutrophils, are an early line of defense against invading bacteria. However, some bacteria have evolved mechanisms to avoid destruction even after they have been engulfed by phagocytes.
Two examples:
Salmonella enterica is a bacterium that causes food poisoning in humans. Once engulfed by phagocytosis, it secretes a protein that prevents the fusion of its phagosome with a lysosome.
Mycobacteria (e.g., the tubercle bacillus that causes tuberculosis) use a different trick.
When the phagosome is first pinched off from the plasma membrane, it is coated with a protein called "TACO" (for tryptophan-aspartate-containing coat protein).
This must be removed before the phagosome can fuse with a lysosome.
Mycobacteria taken into a phagosome are able, in some way, to keep the TACO coat from being removed.
Thus there is no fusion with lysosomes and the mycobacteria can continue to live in this protected intracellular location