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BACKGROUND: We recently reported that infusion of ultraviolet light B (UVB)-exposed human platelets (HPs) can be the second event that mediates acute lung injury (ALI) in a two-event mouse model of transfusion-related acute lung injury (mTRALI). We have now identified changes in HPs induced by UVB light and responses of the recipient animal that mediate the mTRALI.

STUDY DESIGN AND METHODS: Effects of UVB on HPs were monitored by flow cytometry and aggregation. HPs exposed to UVB, with or without inhibitors to specific biochemical pathways, were infused into lipopolysaccharide (LPS)-primed severe combined immunodeficient (SCID) mice. ALI was monitored by protein elevations in bronchoalveolar lavage fluid (BALF).

RESULTS: UVB increased fibrinogen binding and potentiated HP aggregation. Infusion of UVB HPs into LPS-primed SCID mice led to macrophage inflammatory protein 2 (MIP-2) elevations in plasma and BALF and resulted in ALI. Protein kinase C (PKC) inhibitors prevented UVB-induced HP changes in vitro and reduced MIP-2 elevation and mTRALI in vivo. Blocking of fibrinogen binding to HP αIIbβ3 with c7E3 monoclonal antibody prevented mTRALI. MIP-2 elevation in vivo in response to UVB HPs was essential for ALI since blocking of MIP-2 receptor in vivo prevented mTRALI.

CONCLUSION: PKC signaling mediates UVB-induced HP fibrinogen binding and aggregation in vitro. The host animal responds to an infusion of UVB HPs by MIP-2 elevation that mediates downstream mTRALI. Elucidation of molecular mechanisms in UVB HP–mediated mTRALI may provide insight into pulmonary adverse events reported with UV-irradiated pathogen-reduced platelets.