Acquired Zwa antigen on Zwa negative platelets demonstrated by western blotting.

Zwa-negative platelets that had been incubated in random donor AB plasma for several hours and subsequently cryopreserved, were found to be Zwa-positive when tested 3 years later by Western blotting. Following this serendipitous observation, we demonstrated that the Zwa antigen could be passively adsorbed onto the membrane of Zwa-negative platelets incubating for 4 h in the plasma from Zwa-positive donors. This observation supports the hypothesis that passive acquirement of Zwa antigens is a pathogenic mechanism for inducing post-tranfusion purpura, and suggests that Zwa-negative platelets should not be stored in Zwa-positive plasma before transfusion.