Phosphatidylserine vesicles inhibit phagocytosis of erythrocytes with a symmetric transbilayer distribution of phospholipids

Summary

In the plasma membrane of erythrocytes, the phospholipids are asymmetrically distributed between the two leafits of the Mlayer. Erythrocytes that have lost this asymmetric distribution are more readily phagocytosed in virtu by macrophages. Surface expowre of phosphatldylserine (PS), normally restricted to the Inner ieaft8t of the bliayer, has been suggested as a signal by which macrophages recognize erythrocytes. To test whether lipldsymmetric erythrocytes are recognized by this mechanism, artificial lipid vesicles made of PS were tested for their ability to Inhibit phagocytosis. 5774 mouse macrophages, which preferentially phagocytose PS vesicles, were Incubated with a mixture of llpid-symmetric erythrocytes and veslcles. PS vesicles reduced phagocytosls of llpid-symmetric erythrocytes to the level of lipid-asymmetric erythrocytes, whereas phosphatldylcholine vesicles had only a limited effect. These results support a role for PS in recognition of erythrocytes and lend credence to the more general hypothesis that PS is involved in the recognition of all blood cells by the reticuloendothelial system.

Key Words:

• Erythrocytes
• membrane phospholipid asymmetry
• phagocytosis
• phosphatidylserine
• recognition signals