Glycosylation and cold platelet storage.

Platelets, unlike red blood cells and plasma, are stored at room temperature because platelets transfused after refrigeration at 4 degrees C are rapidly cleared from the circulation. Storage at room temperature promotes bacterial proliferation, however, and transfusion-transmitted bacteremia has become an increasing problem. Traditionally, the cold storage lesion has been attributed to a change in platelet shape from disc to sphere, but Hoffmeister et al. revisited this issue and have shown that the shape change induced by cold storage does not result in poor platelet survival. Instead, they showed that poor survival results from a virtually irreversible clustering of alpha subunits of glycoprotein Ib (GPIbalpha)) on the platelet surface. In a series of elegant papers, these researchers change the way we view platelet clearance. That is, they show that exposed, terminal, beta-linked N-acetylglucosamine (beta-GlcNAc) residues on clustered GPIbalpha are recognized by the lectin domain of type 3 complement receptors on liver macrophages, leading to rapid clearance by phagocytosis. They also demonstrate that phagocytosis of chilled platelets can be inhibited--and in vivo survival prolonged--by enzymatically galactosylating the terminal beta-GlcNAc residues on GPIbalpha. Disguising the exposed beta-GlcNAc residues on the N-glycans of the clustered GPIbalpha molecules by galactosylation is a promising approach to storing platelets at 4 degrees C without affecting platelet function. Cold storage would limit bacterial proliferation and extend the duration of platelet storage, reducing the incidence of transfusion-transmitted bacteremia and improving the availability of this scarce resource.