The neutrophil alloantigen HNA-3a (5b) is located on choline transporter-like protein 2 and appears to be encoded by an R>Q154 amino acid substitution

Frequencies of SLC44A2 alleles encoding human neutrophil antigen-3 variants in the African American population

BACKGROUND

The human neutrophil antigen-3 (HNA-3) epitopes reside on the choline transporter-like protein-2 (CTL2). A single-nucleotide substitution (461G>A; Arg154Gln) on the CTL2 gene (SLC44A2) defines the allele SLC44A2*1, which expresses HNA-3a, and SLC44A2*2, which expresses HNA-3b; an additional substitution (457C>T; Leu153Phe) in SLC44A2*1:2 may impact genotyping systems. People who only express HNA-3b may develop anti-HNA-3a. These alloantibodies have been linked to severe transfusion-related acute lung injury, which may be a reason to screen blood donors for SLC44A2*2 homozygosity. For Caucasian and Asian populations, SLC44A2 allele frequencies are known. Our primary objective was to determine the SLC44A2 allele frequencies in the African American population.

STUDY DESIGN AND METHODS

Purified DNA from 334 individuals (202 male, 132 female; 241 African American, 93 Caucasian) was collected. Two real-time polymerase chain reaction assays were developed to genotype all samples; results were confirmed by nucleotide sequencing.

RESULTS

In 241 African American donors, the allele frequency of SLC44A2*1 was 93% (85%-<100%; 95% confidence intervals, Poisson distribution) while SLC44A2*2 was 7% (5%-10%). In 93 Caucasian donors, the allele frequency of SLC44A2*1 was 83% (71%-98%) and SLC44A2*2 was 17% (11%-24%), matching previously reported data for Caucasians but differing from African Americans (p < 0.001, Fisher's exact test).

CONCLUSIONS

This study describes the allele frequencies of the three known HNA-3 variants in an African American population. We found that African Americans have a significantly lower probability of possessing the SLC44A2*2 allele and may thus be less likely to form the clinically relevant anti-HNA-3a.

Full-length recombinant choline transporter-like protein 2 containing arginine 154 reconstitutes the epitope recognized by HNA-3a antibodies

BACKGROUND

Recent reports have shown that the HNA-3a leukocyte antigen, a target for antibodies that cause severe transfusion-related acute lung injury, correlates with an arginine 154 (rather than glutamine) polymorphism in choline transporter-like protein 2 (CTL2) but did not show directly that R154 determines HNA-3a. CTL2 peptides containing R154 are recognized by only half of HNA-3a antibodies studied to date. Constructs that react with all HNA-3a antibodies are needed to fully define the HNA-3a epitope.

STUDY DESIGN AND METHODS

HEK293 cells were transfected with cDNA encoding full-length CTL2 linked to green fluorescent protein (GFP). Transfectants were selected for GFP expression and tested with antibodies specific for HNA-3a and -3b.

RESULTS

Each of 20 HNA-3a antibodies reacted preferentially with HEK293 cells expressing the R154 CTL2 construct. An HNA-3b antibody reacted only with CTL2 (Q154).

CONCLUSIONS

These findings provide direct evidence that R154 in the context of full-length CTL2 is both necessary and sufficient to create the HNA-3a epitope but suggest that posttranslational modifications of the protein, for example, S-S bonds or addition of glycans, are necessary for recognition of HNA-3a by many antibodies. This could complicate development of an assay for large-scale screening of blood donors to detect anti-HNA-3a.

Detection of granulocyte antibodies using simultaneous analysis of specific granulocyte antibodies assay (SASGA)

OBJECTIVE

Granulocyte-associated antibodies can cause several clinical granulocytopenic disorders. The monoclonal-antibody-specific immobilization of granulocyte antigens (MAIGA) is currently used as the standard assay to specify these antibodies. Here we describe an assay for specific analysis of granulocyte antibodies (SASGA) which is able to simultaneously detect and specify granulocyte IgG- and IgM-antibodies using flow cytometry.

METHODS

Bead populations with distinct fluorescence intensities were used as solid phase for immobilization of mAb. Typed granulocytes were incubated with human sera and a mix of three distinct mouse monoclonal antibodies against specific granulocyte antigens (for example CD16, CD11a, HLA class I). After cell lysis and incubation of lysate with beads, goat antibodies against human IgG and IgM antibodies were added. Seventy-one frozen sera of donors and patients previously implicated in transfusion reactions and various underlying disorders were analysed for specific granulocyte-binding antibodies using MAIGA and SASGA.

RESULTS

The SASGA assay was able to simultaneously detect granulocyte-specific antibodies for different glycoproteins. Overall, the results of MAIGA and SASGA were concordant in 92·9%. 5 sera containing anti-HNA-1b (n=2) and -HLA class I (n=3) were not detected by MAIGA, but were recognized by the SASGA. In serial dilution tests with sera containing anti-HNA-1a, -1b, -2a and HLA class I, the SASGA assay detected the antibodies at higher dilutions than MAIGA.

CONCLUSION

The SASGA assay permits reliable detection of specific granulocyte antibodies. Six distinct antibodies can be simultaneously determined. This method will potentially open the way to investigations on additional specific antibodies as it facilitates laboratory diagnosis.

Experimental models of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is defined clinically as acute lung injury occurring within six hours of the transfusion of any blood product. It is the leading cause of transfusion-related death in the United States, but under-recognition and diagnostic uncertainty have limited clinical research to smaller case control studies. In this review we discuss the contribution of experimental models to the understanding of TRALI pathophysiology and potential therapeutic approaches. Experimental models suggest that TRALI occurs when a host, with a primed immune system, is exposed to an activating agent such as anti-leukocyte antibody or a biologic response modifier such as lysophosphatidylcholines. Recent work has suggested a critical role for platelets in antibody-based experimental models and identified potential therapeutic strategies for TRALI.

Genetic variation of the HNA-3a encoding gene

BACKGROUND

Antibodies against the human neutrophil alloantigen-3a (HNA-3a) play an important role in transfusion-related acute lung injury. The HNA-3a and -3b alloantigens result from a single-nucleotide exchange in the choline transporter-like protein 2 gene (CTL2). We sought for additional polymorphisms that might impair antibody binding to or genotyping of the HNA-3a or -3b antigens.

STUDY DESIGN AND METHODS

CTL2-specific complementary DNA (cDNA) fragments were generated from 67 unrelated blood donors followed by DNA sequencing. Polymerase chain reaction with sequence-specific primers (PCR-SSP) was used to test a higher number of donors for relevant new single-nucleotide polymorphisms (SNPs). The granulocyte agglutination test recommended for HNA-3a antibody detection was performed to check HNA-3a antibody binding to the products of the CTL-2 gene variants.

RESULTS

Two new missense mutations were demonstrated in the CTL2 cDNA: a 537C>T* exchange leading to a Leu153Phe amino acid substitution and 988C>T variation predicting Thr301Met change. The inherited 537T variant is located in HNA-3a allele results impaired granulocyte agglutination by four of 14 antibodies tested while 988T remains nearly unaffected.

CONCLUSIONS

The Leu153Phe exchange next to the HNA-3a/b defining amino acid position can impede the binding of HNA-3a alloantibodies. The HNA-3a genotyping by PCR-SSP might produce misleading results in HNA-3ab heterozygous individuals with the additional CTL2-537T variation of the HNA-3a antigen. These findings must account for the development of new screening assays.

HNA-3a-specific antibodies recognize choline transporter-like protein-2 peptides containing arginine, but not glutamine at Position 154

BACKGROUND

Antibodies specific for the neutrophil antigen HNA-3a cause severe, sometimes fatal transfusion-related acute lung disease (TRALI) when transfused, but it has not been possible to screen blood donors for anti-HNA-3a because using neutrophils as targets was impractical and molecular properties of the antigen were unknown. Recently it was shown that HNA-3a is carried on choline transporter-like protein-2 (CTL2) and that the HNA-3a/b phenotype is closely correlated with an R154Q amino acid polymorphism in CTL2. However, it has not been shown by direct experiment that R154 is essential for the HNA-3a epitope.

STUDY DESIGN AND METHODS

Preliminary attempts to express recombinant full-length CTL2 (R154) recognized by anti-HNA-3a were unsuccessful. We therefore tested HNA-3a-specific antibodies from donors implicated in TRALI reactions for reactivity against chemically synthesized linear and cyclic CTL2 peptides containing R154 or Q154.

RESULTS

Nine of 20 HNA-3a antibodies recognized the R154, but not the Q154 version of a cyclic 36-residue CTL2 peptide (D131-K166). However, 11 others failed to distinguish between the two versions of this peptide.

CONCLUSION

The findings provide direct evidence that R154 in the context of CTL2 D131-K166 is necessary to create the HNA-3a epitope but, in the context of cyclic CTL2 peptide D131-K166, is sufficient to detect only about one-half of the HNA-3a-specific antibodies implicated in TRALI. It is likely that fragments of CTL2 longer than can be made on a large scale with an automated synthesizer will be needed to produce a target capable of detecting all examples of anti-HNA-3a in donated blood.

Isoforms, expression, glycosylation, and tissue distribution of CTL2/SLC44A2

Antibodies to the solute carrier protein, CTL2/SLC44A2, cause hearing loss in animals, are frequently found in autoimmune hearing loss patients, and are implicated in transfusion-related acute lung injury. We cloned a novel CTL2/SLC44A2 isoform (CTL2 P1) from inner ear and identified an alternate upstream promoter and exon 1a encoding a protein of 704 amino acids which differs in the first 10-12 amino acids from the known exon 1b isoform (CTL2 P2; 706 amino acids). The expression of these CTL2/SLC44A2 isoforms, their posttranslational modifications in tissues and their localization in HEK293 cells expressing rHuCTL2/SLC44A2 were assessed. P1 and P2 isoforms with differing glycosylation are variably expressed in cochlea, tongue, heart, colon, lung, kidney, liver and spleen suggesting tissue specific differences that may influence function in each tissue. Because antibodies to CTL2/SLC44A2 have serious pathologic consequences, it is important to understand its distribution and modifications. Heterologous expression in X. laevis oocytes shows that while human CTL2-P1 does not transport choline, human CTL2-P2 exhibits detectable choline transport activity.

The frequencies of human neutrophil alloantigens in the Chinese Han population of Guangzhou

BACKGROUND

Antibodies against polymorphic structures on human neutrophil antigens (HNAs) play a role in alloimmune-mediated neutropenia and are the leading cause of antibody-mediated transfusion-related acute lung injury (TRALI). This study aimed to determine the frequencies of HNAs in the major Han ethnic group living in Guangdong Province, Southern China.

STUDY DESIGN AND METHODS

A total of 493 healthy Chinese Han blood donors from Guangzhou were recruited. DNA samples were isolated and typed for all five HNA-1, -2, -3, -4, and -5 systems using allele-specific polymerase chain reaction approaches. Results were compared with available data from other Chinese cohorts and other Asian and Caucasian populations.

RESULTS

In this cohort, the gene frequency for HNA-1a (0.667) was approximately twice that of HNA-1b (0.333). In contrast to Caucasian populations, HNA-1a represents the most frequent allele in the Chinese population. HNA-3 system genotyping revealed comparable frequencies for HNA-3a (0.738) and -3b (0.262) in Chinese and Caucasian populations. Homozygous HNA-3 bb individuals were found in 5.64% of our cohort. HNA-4 genotyping revealed no HNA-4 bb homozygous individuals. In contrast, HNA-5 bb homozygous individuals represented 2.43% of the population. Typing the HNA-2 system for the single-nucleotide polymorphism C42G showed that the C-allele (69%) is overrepresented and is associated with an increased number of HNA-2a-positive neutrophil subpopulations.

CONCLUSION

This study describes for the first time the frequencies of all HNA systems, including the newly identified HNA-3, within one cohort of Chinese Han population. Comparison with Caucasian populations may allow assessment of anti-HNA alloimmunization and estimation of alloimmune neutropenia and TRALI incidence in Chinese populations.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

The frequency and specificity of human neutrophil antigen antibodies in a blood donor population

BACKGROUND

Transfusion-related acute lung injury (TRALI) has been associated with both human leukocyte antigen (HLA) and human neutrophil antigen (HNA) antibodies. HNA antibody frequency, specificity, and demographic associations have not been well defined in the blood donor population.

STUDY DESIGN AND METHODS

A subset of 1171 donors (388 nontransfused males, 390 HLA antibody-negative females with three or more pregnancies, and 393 HLA antibody-positive females with three or more pregnancies) from a larger Leukocyte Antibody Prevalence Study was tested for immunoglobulin (Ig)G and IgM HNA antibody using a granulocyte immunofluorescence flow cytometry assay. Additional testing on selected samples included monoclonal antibody immobilization of granulocyte antigen-flow cytometry and granulocyte genotyping.

RESULTS

Eight samples were HNA antibody positive (prevalence, 0.7%; 95% confidence interval [CI], 0.3%-1.3%]). Three HNA antibodies (one IgG and two IgM) were found in nontransfused males (prevalence, 0.8%; 95% CI, 0.2%-2.2%); all were panreactive or nonspecific. One HLA antibody-negative previously pregnant female had an IgG HNA antibody with HNA-1a specificity (prevalence, 0.3%; 95% CI, 0.01%-1.4%). Four HLA antibody-positive previously pregnant females demonstrated HNA antibodies, three IgG and one IgM (prevalence, 1%; 95% CI, 0.3%-2.6%). Two of these were HNA-1a specific, one HNA-4a specific, and one nonspecific.

CONCLUSIONS

HNA antibodies occur with low frequency in the donor population and are present in both male and female donors. Despite the implementation of TRALI reduction strategies, HNA antibodies are still present in donor blood products. Although our data do not create a case for urgent implementation of donor HNA antibody testing, future new developments for high-throughput HNA antibody screening, including for HNA-3a, may warrant reconsideration.