BACKGROUND Cryopreservation in dimethyl sulfoxide and storage at −80 °C extends the shelf life of platelets to at least 2 years, allowing greater availability in rural and military areas. While cryopreserved platelets (CPPs) have been extensively characterized for coagulation and thrombin generation, reports on the mechanism of adverse reactions to CPPs transfusion are scarce. Here, we tested the hypothesis that CPPs facilitate phagocytosis by Kupffer cells and subsequently promote the inflammatory response in Kupffer cells. STUDY DESIGN AND METHODS P‐selectin expression, glycoprotein Ibα clustering and phosphatidylserine (PS) surface exposure on platelets stored at 22 °C, 4 °C and − 80 °C for 3 days were examined by flow cytometry. The phagocytosis of mepacrine‐labeled platelets coincubated with THP‐1 cells was examined by flow cytometry and confocal microscopy, and the release of cytokines from THP‐1 cells was measured by enzyme‐linked immunosorbent assay. RESULTS CPPs showed a marked enhancement of exposed PS but dramatically reduced glycoprotein Ibα expression and clustering compared with platelets stored at 4 °C. Activation of THP‐1 cells was stronger by CPPs than by platelets stored at 22 °C and 4 °C. CPP interference tests using annexin V and anti–P‐selectin showed that CPPs induced increases in PS‐ and P‐selectin–mediated phagocytosis, as well as secretion of the proinflammatory cytokine tumor necrosis factor‐α, and interleukins IL‐1β and IL‐6, but a decrease in transforming growth factor‐β production in THP‐1 cells. Surface‐exposed PS was more effective than P‐selectin for the activation of THP‐1 cells. CONCLUSION CPPs triggered PS and P‐selectin–mediated phagocytosis by macrophages and stimulated the inflammatory response of macrophages.

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