Fibrin deposits are associated with greater cartilage calcification. (a) Representative images of fibrin immunohistochemical staining and Alizarin red staining for calcium-containing crystals on consecutive sections of cartilage explants from end-stage RA patients. Staining was analysed in the low, medium, and high degraded cartilage areas of each patient. Pictures from one representative patient per group are shown. Scale bar = 50 μm. n = 4. (b) Correlation graphs between cartilage damage scores (AU) and calcification scores (AU), and between fibrin deposit scores (AU) and calcification scores (AU). Linear regression and Pearson correlation tests. *p < 0.05, **p < 0.01. n = 4. (c) Representative Alizarin red staining of WT murine chondrocytes stimulated for 24 h with CPP and increasing concentrations of Fg. Scale bar = 100 μm. (d) Corresponding quantification of calcium content in cell monolayer and (e) IL-6 secretion in cell supernatant. Two-way ANOVA post hoc Bonferroni correction. n = 3 experiments. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. (f) qRT-PCR of the indicated calcification genes in murine chondrocytes stimulated for 4 h with CPP and 500 ug/ml Fg. Two-way ANOVA post hoc Bonferroni correction. n = 3 experiments. *p < 0.05, ****p < 0.0001. (g) qRT-PCR of the indicated matrix genes in murine chondrocytes stimulated for 4 h with CPP and 500 ug/ml Fg. Two-way ANOVA post hoc Bonferroni correction. n = 3 experiments. **p < 0.01, ****p < 0.0001.