The CD42b (HIP1) antibody recognizes a heterodimer glycoprotein (GPIbα) that contains an α chain (CD42b, 145 kDa) and a β chain (CD42c, 22 kDa) linked by a disulfide bond forming a noncovalent complex with CD42a (GPIX) and d. CD42b antigen is expressed on platelets and megakaryocytes. The GPIb/IX complex (CD42a-d) serves as a receptor for von Willebrand Factor (vWF) and thrombin, and mediates adhesion of platelets to subendothelium of damaged vascular walls. The absence of the CD42 complex leads to the Bernard-Soulier Syndrome (BSS). The CD42b (HIP1) antibody inhibits the ristocetin-dependent binding of vWF to platelets, ristocetin-induced platelet agglutination, and partially inhibits collagen-induced aggregation.