Competitive inhibition of ¹²⁵I–PSGL-1 binding to immobilized mPS by fluid-phase mPS, sPS, or Lec-EGF. Microtiter wells were coated with mPS (5 μg/mL) and then blocked with HSA. To each well was added a fixed concentration of ¹²⁵I–PSGL-1 with increasing concentrations of unlabeled mPS, sPS, or Lec-EGF. After incubation for 1 hour at room temperature, specific binding of ¹²⁵I–PSGL-1 was determined as described in the Materials and Methods. Each point represents the mean ± SD of triplicate assays in a single experiment. Similar results were obtained in three other experiments using different preparations of unlabeled fluid-phase mPS, sPS, and Lec-EGF.