File:ER mediated phagocytosis.gif
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Image of ER-mediated phagocytosis
Phagocytosis is initiated by the binding of particles — inert materials, microorganisms or dead cells — to receptors at the cell surface, possibly in short pseudopodia already present at the surface of cells such as macrophages (B). Signalling events rapidly lead to cytoskeletal (mainly actin) reorganization and concomitant pseudopodia extension. Although most of the models of phagocytosis present the plasma membrane as the main source of membrane for phagosome formation (by an invagination process) (Aa), other endomembranes have been shown to contribute to this process. Recycling endosomes, recruited to the cell surface by a process referred to as focal exocytosis (Ab), have been identified as a potential source of membrane for phagosome formation. Another important source of membrane shown to be involved in phagocytosis is the endoplasmic reticulum (ER), in a process known as ER-mediated phagocytosis (Ac). Several reports have shown that proteins usually present on the plasma membrane, and on recycling endosomes (RAB4 and RAB11) and on ER (calreticulin and calnexin), are also present on phagosomes, indicating the potential involvement of all of these membranes in phagocytosis. In some cases, lysosomes (Ly) and azurophil granules (AG), their counterparts in neutrophils, have been shown to fuse with the plasma membrane during phagocytosis (Ad). After their formation, phagosomes fuse sequentially with early endosomes, late endosomes and lysosomes. Interestingly, domains labelled with lysosomal-associated membrane protein (LAMP) (C) or calnexin (D) can be observed on isolated phagosomes, indicating the dual contribution of endocytic and ER-derived membranes in the biogenesis of these compartments.
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|current||18:26, 29 May 2014||600 × 560 (106 KB)||Z3399239||==ER_mediated_phagocytosis.gif== Image of ER-mediated phagocytosis Phagocytosis is initiated by the binding of particles — inert materials, microorganisms or dead cells — to receptors at the cell surface, possibly in short pseudopodia already pres...|