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Transfusion-related acute lung injury (TRALI) is a hazardous transfusion complication with an associated mortality of 5% to 15%. We previously showed that stored (5 days) but not fresh platelets (1 day) cause TRALI via ceramide-mediated endothelial barrier dysfunction. As biological ceramides are hydrophobic, extracellular vesicles (EVs) may be required to shuttle these sphingolipids from platelets to endothelial cells. Adding to complexity, EV formation in turn requires ceramide. We hypothesized that ceramide-dependent EV formation from stored platelets and EV-dependent sphingolipid shuttling induces TRALI. EVs formed during storage of murine platelets were enumerated, characterized for sphingolipids, and applied in a murine TRALI model in vivo and for endothelial barrier assessment in vitro. Five-day EVs were more abundant, had higher long-chain ceramide (C16:0, C18:0, C20:0), and lower sphingosine-1-phosphate (S1P) content than 1-day EVs. Transfusion of 5-day, but not 1-day, EVs induced characteristic signs of lung injury in vivo and endothelial barrier disruption in vitro. Inhibition or supplementation of ceramide-forming sphingomyelinase reduced or enhanced the formation of EVs, respectively, but did not alter the injuriousness per individual EV. Barrier failure was attenuated when EVs were abundant in or supplemented with S1P. Stored human platelet 4-day EVs were more numerous compared with 2-day EVs, contained more long-chain ceramide and less S1P, and caused more endothelial cell barrier leak. Hence, platelet-derived EVs become more numerous and more injurious (more long-chain ceramide, less S1P) during storage. Blockade of sphingomyelinase, EV elimination, or supplementation of S1P during platelet storage may present promising strategies for TRALI prevention.

Transfusion-related acute lung injury (TRALI) is a syndrome of respiratory distress upon blood transfusion and is the leading cause of transfusion-related fatalities. Whether the gut microbiota plays any role in the development of TRALI is currently unknown. We observed that untreated barrier-free (BF) mice suffered from severe antibody-mediated acute lung injury, whereas the more sterile housed specific pathogen-free (SPF) mice and gut flora-depleted BF mice were both protected from lung injury. The prevention of TRALI in the SPF mice and gut flora-depleted BF mice was associated with decreased plasma macrophage inflammatory protein-2 levels as well as decreased pulmonary neutrophil accumulation. DNA sequencing of amplicons of the 16S ribosomal RNA gene revealed a varying gastrointestinal bacterial composition between BF and SPF mice. BF fecal matter transferred into SPF mice significantly restored TRALI susceptibility in SPF mice. These data reveal a link between the gut flora composition and the development of antibody-mediated TRALI in mice. Assessment of gut microbial composition may help in TRALI risk assessment before transfusion.

Transfusion related acute lung injury (TRALI) is a syndrome of respiratory distress which occurs within 6 hours of blood transfusion. It is the leading cause of transfusion-related fatalities and the pathogenesis is incompletely understood. In the majority of the cases, anti-leukocyte antibodies present in the transfused blood product, in combination with recipient predisposing risk-factors such as inflammation, are implicated to be responsible for the onset of TRALI. Unfortunately, no therapies are available for TRALI. Recently, using novel murine models of TRALI, CD4+T cells were found to be important protector cells against antibody-mediated TRALI and administration of interleukin (IL)-10 was demonstrated to be a successful treatment strategy for TRALI, rescuing mice therapeutically from pulmonary edema, the hallmark of acute lung injury (Kapur et al, Blood 2017, 129(18):2557-2569). Whether the gut microbiome plays any role in the development of TRALI is currently unknown. For that purpose, we compared the biological TRALI response in mice housed in a barrier-free (BF) setting versus mice housed in a specific pathogen-free (SPF) environment. We utilized our TRALI model in which C57BL/6 mice were first depleted of CD4+ T cells in vivo followed by injection of anti-major histocompatibility complex class I antibodies (clones 34-1-2s and AF6-88.5.5.3). The TRALI response was analyzed after 90 minutes for several parameters including pulmonary edema (lung wet-to-dry weight ratios, W/Ds), rectal temperatures (indicative of systemic shock), plasma levels of macrophage inflammatory protein (MIP)-2 (murine homologue of IL-8, a neutrophil chemoattractant), levels of pulmonary neutrophils (major effector cells in TRALI) and lung histology. We observed that after one week of housing, baseline rectal temperatures of BF mice significantly increased from 38.7o C to 39.5° C (p Disclosures Semple: Rigel: Consultancy; Novartis: Consultancy; Amgen: Consultancy; UCB: Consultancy.