INDUCTION OF FLARE-UP REACTIONS IN RAT ANTIGEN-INDUCED ARTHRITIS

Flare-up reactions were induced in the rat chronic antigen-induced art hritis model (AIA), similar to those in mice and rabbits. After two co nsecutive immunizations (500 mu g each, Day -21 and -14) with methylat ed bovine serum albumin (mBSA) in complete Freund's adjuvant (CFA), a biphasic primary arthritis was induced on Day 0 by intra-articular (i. a.) injection of 100 mu g mBSA. The acute arthritic phase lasted 1 wee k, followed by chronic, mild joint swelling. Flare-up could then be in duced on Day 40 by a second i.a. injection of 10-100 mu g mBSA into th e knee, with maximal hare-up reaction 2 days following the i.a. inject ion, and a return to chronic levels within 2 weeks. On Day 6 after ind uction of the flare-up, the inflamed joint showed massive cartilage an d bone destruction; high numbers of alpha beta-T-cell-receptor-positiv e cells and macrophages, but only a few IL-2-receptor-carrying cells w ere detected in the inflamed synovial membrane. Induction of a second flare-up, 40 days after the first one, was possible by i.a. injection of 100 mu g mBSA. Unlike in the mouse model, intravenous injection of up to 10 mg mBSA failed to induce flare-ups in the chronically inflame d joint.