Competition of radioiodinated SLPI binding to monocytes. 0.5 nmol/L radioiodinated SLPI was added to 12 × 10⁶ monocytes in binding buffer with increasing amounts of competitors overnight at 4°C. Cells were washed twice with PBS and cell pellets were assayed for ¹²⁵I emission. Data shown are the mean of triplicate values ± SD, and are representative of experiments performed ≥3 times. (A) Competitors included monoclonal anti-CD14 (▪), anti–human cathepsin G (⋄), anti–human neutrophil elastase (▵), or unlabeled SLPI (•). (B) Competitors included PI (▵), mutein Gly⁷² (♦), or mutein Phe⁷² (⋄). (C) Competotors included domain 1 of SLPI (Dom 1, ♦) and domain 2 of SLPI (Dom 2, ⋄).