Fig. 4

Hypothesis for M1/M2/foreign body giant cell (FBGC) formation. Cellular stress induced by a foreign body may be the driving force for macrophage differentiation. Reactive oxygen species (ROS) may also be a key factor for macrophage differentiation. Slow or nondegradable grafts accumulate stress in the macrophages. To reduce intracellular stress, increasing the volume of cytoplasm via cellular fusion can be a useful strategy for survival. If the graft is degraded appropriately, intracellular stress is reduced thereafter. M2 transition will occur after reduced stress