Fig. 2

An overview of phagocytic and non-phagocytic pathways. a Phagocytosis occurs in macrophages through an actin-based mechanism involving interaction with various specialized cell surface receptors (such as mannose, IgG and complement receptors). The foreign particles recognized by specific receptors are internalized to form endocytic vesicles called phagosomes. The fusion of phagosomes with the lysosomal compartment leads to the formation of phagolysosomes, where the foreign particles are enzymatically degraded. b Clathrin-mediated endocytosis involves the formation of vesicles from triskelion clathrin-coated regions of the plasma membrane. After internalization, the clathrin are recycled back to the plasma membrane followed by movement of ingested materials from early endosome to late endosome, which finally fuse with lysosome to form the lysosome-endosome hybrid. The materials are then degraded by the low pH and enzyme-rich environment of the endo-lysosomal vesicle. C) Caveolin-mediated endocytosis involves internalization through caveolin (a dimeric protein) enriched invaginations. The cytosolic caveolin vesicle delivers its contents to endosomes to form caveosomes, which can transported along the cytoskeleton to the endoplasmic reticulum/golgi complex. D) Macropinocytosis involves the formation of large vesicles called macropinosomes, which occurs through actin filament driven plasma membrane protrusions. Through this pathway, the contents are degraded following fusion with the lysosomal compartment [28]. Reproduced with permission from Stern et al. (2012, BioMed Central) and had been partially adapted from Hillaireau and Couvreur (Cell. Mol. Life Sci. 2009, 66, 2873–2896)