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Complement activation in stored platelet concentrates

Activation of platelets during preparation and/or storage of platelet concentrates in plastic containers at room temperature has recently been recognized. Many different biologic causes of this activation have been postulated. Activated complement, as a multi‐enzyme system, is one of the possible sources of molecules leading to platelet activation. To detect complement activation, functional complement activity and the generation of complement‐derived ligands were investigated in platelet concentrate supernatant plasma during 5 days of storage at room temperature. Hemolytic tests for functional classical and alternative pathway activity were used, as was the kinetic test for complement‐ mediated inhibition of immune complex precipitation. The presence of C3 activation products (C3, C3c, C3dg) was investigated in plasma by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Western blotting procedures and on platelets by immunofluorescence. Activation of complement was evident during storage, and C3c and C3d fragments were clearly demonstrated in plasma. The amount of C3d fragments on platelets gradually rose during the first 3 days of storage. At the end of 5 days of storage, the platelets became C3d negative. There are two possible mechanisms of C3d disappearance‐shedding and/or further degradation of C3d fragments. Those results indicated that complement activation and the generation of complement‐dependent ligand‐receptor interaction may be mechanisms for platelet activation in concentrates stored at room temperature.