Fig. 2. Mβ2-dependent phagocytosis is mediated by RhoA. Mβ2 integrin binds ligands poorly in resting phagocytes. External stimuli induce an inside-out signalling pathway that activates the small GTP-binding protein Rap1, which results in the induction of structural changes in Mβ2 and increased affinity for its ligand, the C3bi complement fragment that coats phagocytic preys. The capture of a C3bi-opsonised particle by Mβ2 integrins generates forces that pull the particle inside the cell along a Rho-dependent actin-polymerisation pathway that involves Rock and mDia (outside-in signalling). See text for details.