In contrast to the findings with the systemic models, the monoarticular arthritis models - namely antigen-induced arthritis (AIA) [6] and methylated bovine serum albumin/interleukin-1 (mBSA/IL-1) arthritis [7], both of which use mBSA as the antigen and involve an intra-articular (i.a.)injection - develop more severe disease in the absence of u-PA. This evidence concerns the gene IL1B and arthritic joint disease.