Antibodies Specific for MHC Class II Antigens Cause TRALI Directly in a Two-Event in Vivo Model

Abstract

AbstractAbstract 845Transfusion-related acute lung injury (TRALI) is the most common life threatening adverse event related to the transfusion of blood products. Antibodies to HLA class II antigens have been implicated in clinical TRALI, and in situ animal modeling has demonstrated that antibodies to HLA class II antigens bind to Human monocytes that express the cognate antigen resulting in the release of soluble mediators, which induce neutrophil (PMN)-mediated ALI in isolated rat lungs. This mechanism of TRALI is complex, used Human reagents in rodent lungs, and must meet a number of constraints. We hypothesize that the initial clinical event(s) predisposing to TRALI must 1) change the antigen surface expression of PMNs so that they express HLA class II antigens and 2) activate the pulmonary endothelium so that the subsequent transfusion of an antibody specific to the expressed surface antigen bind and activate the PMNs resulting in endothelial damage, capillary leak, and TRALI. Methods:Sprague Dawley rats underwent three different first events: 1) saline given intraperitoneally (IP) followed by a 2–24 hour waiting period, 2) endotoxin (LPS) [2 mg/kg] given IP with a 2 hour waiting period, or 3) interferon-γ(INF-γ) [3 μg/kg] + M-CSF [20 μg/kg] given IP with a 24 hour waiting period along with tumor necrosis factor-α (TNF-α) [65 ng/kg] given intravenously (IV) at 22 hours, following INF-γ/M-CSF injection, with a 2 hour incubation period. A femoral cut down was made, the vessels cannulated, and either blood was removed to assess rat MHC Class II (OX6) surface antigen expression on PMNs with blockade of the Fc receptors to obviate non-specific binding plus isotypic controls or OX6 (150 μg/kg) antibodies were infused as a second event followed by Evans blue dye (EBD) [30 mg/kg] IV injection, at 6 hours blood was obtained, and a bronchoalveolar lavage (BAL) performed to quantify capillary leak/ALI. Results:both INF-γ/M-CSF/TNF-α and LPS increased OX6 surface expression vs. buffer-treated control (Table 1). Both TNFa and LPS cause activation of the pulmonary endothelium resulting in PMN sequestration (data not shown). In rats that received either INF-γ/M-CSF/TNF-α or LPS, the infusion of OX6 antibodies caused significant lung leak of EBD (Table 2). In conclusion, if the initial insult(s) in TRALI induces surface expression of class II antigens on the PMNs and activated the pulmonary endothelium, then infusion of class II antibodies caused ALI. Such a pathogenesis may be appropriate for clinical TRALI and provides a much simpler explanation for class II antibody-mediated ALI.Table 1:OX6 binding to Rat PMNs (MFI)ControlLPSIFNγ (3 μg/kg)/MCSF (20μg/kg)/TNFα (65 ng/kg)OX6-PE198±33364±371037±618Table 2:MHC Class II cause Lung Injury (% EBD in BALF)2nd Event1st EventNSLPS (2 mg/kg)IFNγ (3 μg/kg)/MCSF (20μg/kg)/TNFα (65 ng/kg)NS0.05±0.010.11±0.020.09±0.02Mouse IgG0.09±0.030.08±0.03N/AOX6 (150 ug/kg)0.05±0.010.18±0.06*,+0.18±0.04*,+*p<0.05 from NS as 1st Event;+p<0.05 from NS as 2ndEvent (Non-parametric Independent comparisions, post-hoc Newman-Keuls) Disclosures:Silliman:Pall Corporation: Honoraria, Research Funding.