7_340_2

7_340_2 - Under the Radar Screen: How Bugs Trick Our Immune...

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Marie-Eve Paquet and Gijsbert Grotenbreg Whitehead Institute for Biomedical Research Under the Radar Screen: How Bugs Trick Our Immune Defenses Session 2: Phagocytosis
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Salmonella • Gram negative bacteria that can cause diseases such as typhoid fever or gastroenteritis in humans or other animals. • Salmonella are facultative intracellular bacteria. • Their survival is linked to their ability to “hide” within a variety of cell type. • They penetrate cells through a mechanism similar to phagocytosis but can also penetrate non-phagocytic cells. • Their genes encode for several proteins that are necessary to assemble a complex apparatus termed the “type III secretion system” (TTSS). • The TTSS allows Salmonella to inject effectors into the cell and promote its uptake by phagocytic and non phagocytic cells.
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Phagocytosis vs Macropinocytosis Salmonella triggers uptake through membrane ruffling similar to macropinocytosis. Macropinocytosis allows to pick up smaller particles and large droplets of liquid. There is no specific recognition involved in macropinocytosis. Phagocytosis is exclusively performed by certain cells such as macrophages or neutrophils. It is usually mediated by cell surface receptors The micropinosome tends to be larger than the phagosome but they both eventually mature and fuse with the endocytic compartment.
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• Shared question: How does Salmonella modify the phagosome so that it can survive in it ? • Shared approaches: Both use microscopy 1st paper is from 1994 and uses light microscopy to observe the phagosome maturation 2nd paper is from 2004 and uses confocal microscopy to observe similar phenomenon (try to get a color print out) 2nd paper uses fluorescence to detect the proteins of interest. Fluorescence can be “added” to a protein through a fluorescently labeled antibody that recognizes the protein or a fluorescent tag (such as the green fluorescent protein or GFP) can be fused to the protein of interest through protein engineering). They also use FRAP=fluorescence recovery after photobleaching to measure the ability of molecules
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This note was uploaded on 11/11/2011 for the course BIO 7.344 taught by Professor Bobsauer during the Spring '08 term at MIT.

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7_340_2 - Under the Radar Screen: How Bugs Trick Our Immune...

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