Antibody binding of galsulfase during infusion. Blood-plasma samples were collected from patient 2 and patient 6 just before start of galsulfase infusion (0 min) and at time points thereafter. The open symbols present the total galsulfase activity measured in the plasma; the closed symbols present the amount of activity remaining after Protein-A-Sepharose-mediated immunoprecipitation of antibody-bound ARSB. The difference between the curves represents the proportion of antibody-bound enzyme. The activity in the supernatant was measured with paranitrocatecholdisulfate and is expressed in nmol/10 μl per hour.