Study Reveals New Insight Into Transfusion-Related Acute Lung Injury

Roxanne Nelson

December 21, 2009

December 21, 2009 (New Orleans, Louisiana) — Transfusion-related acute lung injury (TRALI) is a leading cause of transfusion-related morbidity and mortality, and characterized by acute noncardiogenic pulmonary edema and compromised respiratory status. Although the etiology of TRALI is not fully understood, many cases of TRALI are likely caused by antibodies to leukocyte antigens in blood components.

New translational research presented here at the American Society of Hematology 51st Annual Meeting might help lead to a reduction of this serious transfusion-related complication.

TRALI is now known to be caused by human neutrophil antigen (HNA)-3a-negative specific antibodies, and about 4% to 5% of the general population is at risk because they are HNA-3a-negative, explained Joel Anne Chasis, MD, associate professor of hematology/oncology at the University of California in San Francisco, and a staff scientist at the Lawrence Berkeley National Laboratory.

Dr. Chasis, who was not involved in the study, told Medscape Oncology that this new research describes a genome-wide survey that found a single-nucleotide polymorphism (SNP) that correlates with the HNS-3a-negative phenotype. The hope is that this research will eventually lead to strategies to screen both individuals and donated blood for presence of the HNA-3a-antibodies, which are capable of causing TRALI, Dr. Chasis explained.

Acute Lung Injury

TRALI is defined as an acute lung injury occurring during or within 6 hours of a transfusion, and is most often caused by leukocyte antibodies that are present in the blood-donor product. The leukocyte antibodies are thought to interact with recipient neutrophils, resulting in the activation and aggregation in pulmonary capillaries, the release of local biologic response modifiers causing capillary leak, and lung injury, according to the study's lead author, Brian R. Curtis, MS, MT(ASCP)SBB, technical director of the Platelet & Neutrophil Immunology Laboratory, BloodCenter of Wisconsin, in Milwaukee.

"It continues to be the number 1 cause of transfusion-related mortality reported to the [US Food and Drug Administration]]," said Mr. Curtis, who presented the findings during a late-breaking abstract session. Antibodies that have been implicated in TRALI include donor human leukocyte antigen (HLA) class I, HLA class II, and/or neutrophil-specific antibodies, and even though a number of neutrophil-specific antibodies have been reported, the most common is directed at the HNA-3a antigen.

He pointed out that even though HNA-3a/b antigens were discovered 45 years ago, the protein carrier and the molecular composition of the antigens themselves remains unknown. But with the recognition that HNA-3a-specific antibodies are especially prone to cause severe and often fatal TRALI, the importance of defining the HNA-3a/b antigens has become imperative, said Mr. Curtis.

CTL2 Implicated

In this study, Mr. Curtis and colleagues attempted to determine the protein carrier for HNA-3a, and conducted a genome-wide SNP scanning of the DNA from 8 HNA-3a-negative people and 107 unrelated normal people. They observed that each of the HNA-3a-negative people were homozygous (AA) for a SNP (G>A) located at nt542 of the SLC44A2 gene encoding the choline transporter-like protein (CTL)2 (P < .000001 corrected for the number of SNPs surveyed). Conversely, this was true for only 5 of the normal individuals.

This particular SNP (rs2288904) was the only one in SLC44A2 that correlated with the HNA-3a-negative phenotype, and predicted an extracellular amino acid substitution (R>Q154) in the mature protein, he said.

To validate their SNP analyses, the researchers directly sequenced DNA encoding CTL2 and found that, without exception, nt542G and nt542A correlated only with the phenotypes HNA-3a and HNA-3b.

Next, they performed sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and subjected the candidate bands to mass spectrometric analysis to obtain direct evidence that HNA-3a is carried on CTL2. After 3 independent assays, they observed that peptides derived from CTL2 spanned the entire length of the protein. Therefore, they concluded that the "HNA-3a antigen results from the substitution of G for A at nt542 of the SLC44A2 gene, leading to the insertion of R for Q at position 154 in the first extracellular loop of CTL2."

Although the function of CTL2 remains unknown, the researchers noted that "cross-linking of the antigen by anti-HNA-3a in neutrophils triggers an explosive activation of primed cells." This action indicates that CTL2 is functional within this type of cell, and thus provides a possible explanation for the severe TRALI reactions that have been observed in patients transfused with CTL2-specific antibodies.

"Elucidation of the molecular basis of HNA-3a/b should facilitate our ability to detect the antibodies in blood donors using recombinant proteins or fragments of the protein that target the antibody," concluded Mr. Curtis. "We can currently genotype individuals now and rapidly identify HNA-3-negative individuals as part of a diagnostic assessment of TRALI in cases that occur, and also identify persons at risk."

This could potentially reduce the risk for this complication in future blood donation, he added.

The authors have disclosed no relevant financial relationships.

American Society of Hematology (ASH) 51st Annual Meeting: Abstract LBA 4. Presented December 8, 2009.

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