Urokinase-type plasminogen activator gene-deficient mice are resistant to T-cell-independent arthritis models. (a) Type II collagen mAb-induced arthritis (CAIA) using Pam-3-Cys as a boost. C57 (n = 10), u-PA-/- (n = 7) mice. P < 0.05, u-PA-/- vs. C57 mice. (b) K/BxN serum transfer model. C57 (n = 7), u-PA-/- (n = 5) mice. P < 0.0001, u-PA-/- vs. C57 mice. (c) Histologic pictures of representative joints from C57BL/6 and u-PA-/- mice with K/BxN serum transfer arthritis. H & E, Safranin O fast green and fibrin(ogen) staining is shown. (d) Quantification of histologic features. P < 0.05, u-PA-/- vs. C57 mice for each histologic feature. Values expressed as mean ± standard error of the mean.