Collagen 4 binding to VWF depends on multimeric structure and intact VWF A1 domain. Binding of VWF samples to collagen 4 was measured by ELISA and results are expressed as the ratio of collagen 4 binding to VWF:Ag. (A) VWF:CB4/VWF:Ag ratios for human plasma samples from healthy controls (n = 246) and type 3 VWD subjects (n = 24) as well as type 2A (n = 43) and type 2B subjects (n = 19) lacking high-molecular-weight multimers. (B) VWF:CB4/VWF:Ag ratios for recombinant VWF constructs expressed in HEK293T cells with either full-length human VWF sequence or VWF containing the indicated sequence variation (n = 3 separate transfections for each construct). Error bars show mean ± 1 SD.