The Xia.G5 antibody reacts with mouse GPIbalpha (CD42b), a platelet/megakaryocyte-specific polypeptide that is part of the GPIb-V-IX complex. The antibody binds to the N-terminal 45 kDa domain of GPIb alpha, which contains the s for different ligands of the receptor, including vWf, thrombin, and P-selectin. GPIb alpha is proteolytically cleaved (glycocalicin) during platelet activation.