IL-1β showed a saturable and specific binding to polymerized fibrin. (A) Binding of ¹²⁵I-IL-1β to polymerized fibrin. ¹²⁵I-IL-1β was added to a solution of 100 μg/mL fibrinogen and clotted by the addition of 0.5 U/mL thrombin. Bound and unbound IL-1β were then separated by vacuum filtration, and nonspecific binding was determined in the presence of 10-fold molar excess of IL-1β. Specific binding was calculated by subtracting nonspecific from total binding. Each point represents the mean of 3 different experiments. (B) Scatchard plot. The best fit of the data was determined using the Ligand program²⁹  and indicated the presence of single binding site.