Experimental granulomatous inflammation: the ultrastructure of the reaction of guinea pigs to bentonite injection.

Bentonite, a silicate, induces a classical non-immunological foreign body reaction when injected intradermally into guinea pigs. The cellular response consists of a mass of macrophages and large macrophage polykaryons, surrounded and infiltrated by an extensive fibrous reaction. The bentonite granuloma shows no signs of intercellular organisation of the reacting cells. Study of its ultrastructure suggests a low turnover lesion with a stable, long-lived cell population. The bentonite granuloma is contrasted with the tuberculous, immunologically mediated epithelioid cell granuloma produced in sensitised guinea pigs.