Relative affinities of IL6RIL6 chimera and IL-6 + sIL-6R mixture for gp130. Scatchard plot of the dose-dependent binding of the IL6RIL6 chimera alone (⧫) or of free sIL-6R in the presence of a constant amount of IL-6 (▪). Binding measured on immobilized pure soluble gp130 as described in Materials and Methods. Calculated kd were 6 × 10⁻¹¹ mol/L for IL6RIL6 chimera and 2.5 × 10⁻¹⁰ mol/L for the sIL-6R + IL-6 mixture.