UVB Light Exposed Human Platelets Mediate Acute Lung Injury In a Two-Event Mouse Model of Transfusion

Abstract 3354

Transfusion related acute lung injury (TRALI) has occurred in patients whose underlying condition led to an inflamed endothelium, and who were transfused with a transfusion product that contained either HLA or HNA antibodies or biologic modifiers such as lipids or antigens from stored cells. Similar two-event reactions can be modeled in animals pretreated with lipopolysaccharide (LPS) and infused with similar types of antibodies or media from stored transfusion products. The first event induces activation of the endothelium and sequestration of neutrophils in the lungs while the second event activates neutrophils to cause local tissue damage. In some animal models of acute lung damage platelet depletion reduces the lung damage while in other models infusion of activated platelets potentiates it. Ultraviolet B (UVB) light has been used on platelet transfusion products to prevent alloimmunization or with chemical sensitizers to reduce pathogens. Such processing may damage platelets and potentiate their storage lesion. UVB exposed human platelets (HPs) were evaluated in a two-event animal model of acute lung injury (ALI) where the sensitizing event was LPS and the second event was infusion of HPs or UVB HPs (2.4 J/cm²). Immunodeficient (SCID) mice were used to minimize the species difference (Piper et al., Transfusion 47:1540-9, 2007). UVB exposure of HPs increased their p-selectin expression (control 17.8±0.3% vs. UVB 35.9±3.2%) and reduced their JC-1 dye ratio indicating mitochondrial damage (8.9±0.7 control vs 1.9±1.2 UVB). Internal organ distribution of intravenous (IV) infused HPs was followed with whole animal imaging, confocal microscopy and with pathophysiological changes in bronchoalveolar lavage fluid (BALF). In LPS-treated mice, UVB HPs labeled with fluorescent dye had more accumulation in lungs compared to untreated HPs (29±12% vs 15±5% respectively; % of total fluorescence recovered), while the accumulation in lungs of healthy animals was equivalent for both UVB treated and untreated HPs. In separate experiments, LPS pretreated mice were infused with UVB exposed HPs or control HPs, and lungs were examined by histology and with confocal microscopy for fluorescent staining for CD41 and CD62 expression. Histology sections revealed extensive changes in lungs, such as thickening of the alveolar septa and obliteration of lung architecture in LPS animals infused with UVB HPs as compared to healthy animals infused with control HPs or with HPs treated with UVB. Confocal microscopy with specific antibodies identified HP accumulation in lungs of LPS treated animals infused with UVB exposed HPs. However, HP accumulation in lungs did not occur with control HPs or in healthy mice. Accumulation of UVB HPs in lungs of LPS pretreated mice was associated with increased (3-4 fold compared to control HPs) protein concentration and leukocyte accumulation in BALF. Increased alveolar permeability to protein and leukocyte accumulation in alveoli is associated with acute lung damage. To examine whether lung damage occurred due to presence of UVB HPs in the lungs or due to biologic mediators released into plasma from UVB exposed HPs we separated plasma from HPs post UVB treatment and infused the UVB plasma alone. Plasma isolated from UVB HPs did not alter BALF protein levels or leukocyte counts even though the UVB HPs did. In conclusion, UVB HPs can accumulate in lungs of LPS primed animals and are associated with lung damage as indicated by histological changes and increased protein and WBCs in BALF fluid. The ALI is associated with direct platelet accumulation in the lungs but not with biologic modifiers released into plasma. Our animal model of ALI suggests that HPs exposed to high doses of UVB could mediate similar effects in patients predisposed to TRALI with sepsis or other causes of endothelial cell inflammation. The findings and conclusions in this abstract have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy.