Role of glycoprotein Ibα in phagocytosis of platelets by macrophages

BACKGROUND: Platelet (PLT) storage at 0 to 4 degrees C suppresses bacterial multiplication, but induces clusters of glycoprotein (GP) Ib alpha that trigger their phagocytosis by macrophages and reduce their survival after transfusion. A method was sought that detects cold-induced changes in GPIb alpha involved in phagocytosis. STUDY DESIGN AND METHODS: Human PLTs were isolated and stored for up to 48 hours at 0 degrees C. Binding of a phycoerythrin (PE)-labeled antibody directed against amino acids (AA) 1-35 on GPIb alpha (AN51-PE) was compared with phagocytosis of PLTs by matured monocytic THP-1 cells, analyzed by fluorescence-activated cell sorting. RESULTS: Freshly isolated PLTs were detected as a single population of AN51-PE-positive particles and showed less than 5 percent phagocytosis. Cold storage led to a decrease in AN51-PE binding and an increase in phagocytosis. N-Acetylglucosamine, known to interfere with macrophage recognition of GPIb alpha clusters, restored normal AN51-PE binding to cold-stored PLTs and suppressed phagocytosis. CONCLUSIONS: It is concluded that binding of an antibody against AA 1-35 on GPIb alpha reflects changes in GPIb alpha that make PLTs targets for phagocytosis by macrophages.