Phagocytosis: A Fundamental Process in Immunity

Figure 5

Initial engagement of phagocytic receptors. Aggregation FcγRIIa by an IgG opsonized particle initiates signaling. Receptor ITAMs (red rectangles) are phosphorylated by Src-family kinases (SFK) and recruit Syk. This leads to inside-out signaling for integrin (CR3) activation via the GTPase Rap. Activated integrin binds to adaptor molecules such as talin, vinculin, and kindlin-3 and connect to the actin cytoskeleton. Activated integrins also bind to the particle (via multiple possible ligands [113]) and form a diffusion barrier that excludes larger molecules, such as the transmembrane phosphatase CD45. This allows other Fc receptors to be engaged and increase the signaling for phagocytosis.