Binding of fibrinogen to immobilized IL-1β (A) ¹²⁵I-fibrinogen was incubated with IL-1β immobilized on Sepharose beads, and the amount of bound protein was determined as radioactivity associated with the beads following centrifugation and washing. Nonspecific binding was determined in the same way in the presence of a 10-fold molar excess of unlabeled IL-1β. Specific binding was calculated by subtracting the nonspecific from the total bound. Each point represents the mean of 3 different experiments. (B) Scatchard plot. The best fit of the data was determined by analysis using the Ligand program²⁹  and suggests a single binding site.