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Phagocytosis
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Phagocytosis
is the internalisation of solid particles into the cells.
The first line of defence against invading bacteria is
phagocytosis by the professional phagocytes, neutrophils and
macrophages, however, other cells (non-professional phagocytes) are also
capable of phagocytosis. It
is increasingly clear that there are at least two types of phagocytosis
involved in bacterial internalisation, each associated with its own
signal transduction machinery and cytoskeletal components.
Receptor mediated phagocytosis (RMP) involve WASP and Arp2/3 (May
et al, 2000), and non-RMP that is
probably just macropinocytosis (Brumell et
al, 1999).
Non-RMP involves hyper-ruffling of the cell membrane and inert
latex beads as well as normally non-invasive bacteria can enter the cell
while this is going on. Non-RMP
is thought to be like macropinocytosis
as clathrin coated structures are seen.
The process of both type of phagocytosis is altered by pathogenic
bacteria, Yersinia, Shigella
and Salmonella switch on non RMP, while EPEC secretes a toxin that
triggers tyrosine dephosphorylation paralysing the phagocytic function (Goosney
et al, 1999).
Normally, the phagosome produced by RMP fuses with lysosome soon
after internalisation. This
releases hydrolytic enzyme into the phagolysosome to digest and destroy
the contents. |
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