Effect of chondroitinase ABC and heparinase III treatment on PF4-dependent IgG binding to platelets. Chondroitinase ABC treatment (filled bar) significantly reduced PF4-dependent binding of the HIT-mimetic monoclonal KKO (left) and IgG in 3 SRA-positive HIT sera (right). Ordinate depicts IgG binding to platelets relative to control digestion (no enzyme). Treatment with heparinase III (open bar) was without effect except for a 7% reduction in IgG binding observed with a single HIT sample. Values shown are the means of triplicate determinations +1.0 standard deviation. HPA-1a is a serum sample containing antibody to platelet-specific antigen HPA-1a. NC, pooled normal serum. Asterisks indicate significance of differences between enzyme-treated and untreated samples (***P < .001; **P < .01; *P < .05).