A model of persistent antigen-induced chronic inflammation in the rat air pouch

Continuing antigen-induced inflammation was established in a subcutaneous air pouch in rats by recurrent local challenge. The animals were sensitized using bovine serum albumin in Freund's complete adjuvant and were challenged 14 days later by injection of the antigen in a solution containing sodium carboxymethylcellulose into the air pouch to produce allergic inflammation. A single antigenic challenge induced acute inflammation with a predominantly polymorph infiltration in the first 48 h. Later samples showed a low-grade mononuclear response which persisted for 4-5 days. Repeated challenge produced chronic inflammation with an accentuated mononuclear response. Connective tissue activation involving fibronectin and collagen was seen as the inflammation progressed, and this was associated with production of ferritin by mononuclear cells. Discontinuation of challenge injections resulted in resolution of the granuloma. We suggest this model can be used to investigate the mechanisms involved in chronic inflammatory diseases with an immunological component and to evaluate the effects of therapeutic intervention upon chronic allergic inflammation.