Fibrinogen is degraded by MMP9 [39] [40] [41] , and the fibrinogen degradation fragments have been shown to be biologically important molecules with numerous proinflammatory actions [42] . We reasoned that the generation of the SJIA urine biomarker peptides, including those derived from fibrinogen, may be an outcome of the actions of inflammatory mediators on protease expression and regulation, generating a disease-specific degradation pattern of source proteins, such as fibrinogen.