Measurements of recombinant IL-1RA. Measurements of recombinant IL-1RA, using 0.75 (triangles), 1.5 (squares) and 2.25 (diamonds) nanogram of anti-IL-1RA capturing antibody printed on nitrocellulose membranes, and a combination of either 500 or 166.67 ng/ml anti-IL-1RA detection antibody and 10% or 20% amplification reagents in spot-ELISA. Each data point consists of 10 measurements (N = 10). Each line presents an average mean of measurements obtained from duplicate. X-axis: Recombinant IL-1RA in ng/ml. Y-axis: Staining intensity defined as the mean pixel intensity measured on a 0–255 grey scale.