To determine how the different pathogenic mechanisms leading to arthritis development in the different models (systemic immune complex-driven versus local trauma induced by i.a. injection) may explain the contrasting requirement for u-PA (as was found for plasminogen using the CIA model with an i.a. injection of type II collagen [21]), we have used a similar approach, combining the K/BxN immune complex-driven arthritis model with an i.a. injection of saline. This evidence concerns the gene PLG and arthritic joint disease.