Induction of a silica air-pouch granuloma in rat

An inflammatory reaction was induced by the injection of crystalline silica into a subcutaneous air pouch formed on the dorsa of rats. The degree of inflammation depended on the quantity of silica injected and on the time interval between air pouch formation and silica injection. The silica provoked exudation of fluid, accumulation of polymorphonuclear and mononuclear leucocytes and the formation of a granuloma. These parameters reached peak values by day 4 whilst the serum acute phase protein levels peaked on day 1. Cyclophosphamide, indomethacin and prednisolone inhibited fluid accumulation but only cyclophosphamide inhibited cell infiltration. The increase in wet and dry granuloma weight was suppressed only by steroid treatment. The suitability of this model as a screen for anti-inflammatory compounds is discussed.