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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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