Mechanism of foreign body granuloma.

Foreign body granulomas are seen in response to relatively inert foreign bodies, in the absence of T cell–mediated immune responses. Typically, foreign body granulomas form around materials such as talc (associated with intravenous drug abuse), sutures, or other fibers that are large enough to preclude phagocytosis by a macrophage but are not immunogenic. Epithelioid cells and giant cells are apposed to the surface of the foreign body. The foreign material can usually be identified in the center of the granuloma, particularly if viewed with polarized light, in which it may appear refractile.