S100A8 and arthritic joint disease: To investigate whether serum levels of S100A8/A9 are prognostic for disease outcome, serum S100A8/A9 levels were measured in IL-1Ra–/– mice (n = 37) every 2 weeks starting at week 4 when arthritis has not developed yet, and compared to levels in age-matched BALB/c control mice (n = 8).