Fig. 1. Five phases of the formation of foreign body granulomas.

The foreign body response begins rapid neutrophil infiltration, which is with the instantaneous adsorption of various host proteins to the foreign material. The foreign material immediately acquires a layer of host proteins prior to interacting with host cells. Circulating monocytes in the blood slowly migrate to the surrounding tissues and differentiate into macrophages. In cases where the particle volume is greater than the macrophage volume, macrophage aggregation is required and foreign body giant cells are formed. Macrophages secrete factors that recruit and activate fibroblasts, and a fibrous capsule develops around the material. FBGC, foreign body giant cell.