IntroductionThe leukocyte antigens 5a and 5b (now designated HNA-3b and HNA-3a) constitute a biallelic antigen system identified by van Leeuwen et al in 1964 using antibodies from multiparous women that agglutinated leukocytes of normal persons. 1 Despite the passage of more than 40 years, molecular properties of the HNA-3 antigens have not been defined. Characterization of HNA-3a has become particularly important with the recognition that HNA-3a-specific antibodies are prone to cause severe, often fatal, transfusion-associated acute lung injury (TRALI). [2][3][4][5] Here, we provide evidence that HNA-3a is carried on choline transporter-like protein 2 (CTL2), a member of the choline transporter-like family of membrane glycoproteins, and that the antigen results from a single nucleotide polymorphism (SNP) in exon 7 of the CTL2 gene (SLC44A2) encoding R154 (HNA-3a) or Q154 (HNA-3b) in the first extracellular loop of the mature protein.
Methods
Antibodies and antibody detectionHNA-3a-specific antibodies were from donors implicated in TRALI reactions. 3,6 Isolation of neutrophils, T and B lymphocytes, and platelets from normal donor blood, detection of antibodies reactive with these cells by flow cytometry and agglutination, and immunoprecipitation of membrane proteins have been described previously. [7][8][9]
SNP analysisGenotyping of DNA from 8 unrelated HNA-3a-negative persons was performed using the Human Genome-Wide SNP Array 6.0 (Affymetrix). Genotypes were assigned using Birdseed 2.0. 10 Quality control studies, including assessment of call rate, investigation of potential genetic relationships among samples, and examination of data to identify potential departures from expected levels of heterozygosity, were completed using plink. 11 Eigenstrat was used to assess geographic ancestry in combination with HapMap CEU, YRI, JPT, and CHB samples. 12 All samples had high call rates (Ͼ 98%) with high-quality genotype data. The 8 HNA-3a-negative persons appeared to be of recent European descent and were quite similar in ancestry to the HapMap CEU samples. Association studies were performed using the 8 HNA-3a-negative samples as cases and unrelated European samples from HapMap3 as controls, with significance assessed using 100 000 permutations; thus, the smallest possible P value in permutation analysis was P ϭ 1 ϫ 10 Ϫ6 .
DNA sequencingGenomic DNA was amplified by the polymerase chain reaction using primers designed to amplify exon 7 of the CTL2 gene SLC44A2 (reference sequence National Center for Biotechnology Information database; www.ncbi.nlm.nih.gov/nucore/NM_001145056.1). Primer sequences are available on request. Automated sequence analysis of polymerase chain reaction products was performed in both directions with the Big Dye Terminator version 3.1 Cycle Sequencing kit on an ABI 3130XL genetic analyzer (Applied Biosystems). 13
Mass spectrometryHNA-3a-specific antibody was incubated with HNA-3a-positive leukocytes and subjected to immunoprecipitation. An Inside Blood analysis of this article appears at the fr...