Molecular Genetics of the Human Neutrophil Antigens

Analysis of maternal Fc gamma receptor IIIb isoantibodies using immunomagnetic negative selected neutrophils

BACKGROUND AND OBJECTIVES

The isolation of neutrophils and subsequent detection of anti-human neutrophil antigens (HNA) antibodies are crucial in clinical medicine for the diagnosis of autoimmune neutropenia, neonatal alloimmune neutropenia (NAIN) and transfusion-related acute lung injury (TRALI). This study reports two cases of maternal anti-Fc-gamma-receptor-IIIb (FcγRIIIb) isoimmunization without NAIN symptoms and compares the efficiency of immunomagnetic negative selection (IMNS) with traditional dextran/Ficoll for neutrophil isolation in HNA serological assays.

MATERIALS AND METHODS

Investigating two cases of maternal anti-FcγRIIIb isoimmunization, neutrophils from three donors were isolated from 8 mL of whole blood using IMNS and dextran/Ficoll. Serological assays included the granulocyte agglutination and immunofluorescence test, monoclonal antibody immobilization of granulocyte antigens and the LABScreen Multi (One Lambda). IMNS and dextran/Ficoll were compared in terms of cell yield, viability, time, cost and purity.

RESULTS

Maternal anti-FcγRIIIb isoantibodies with FCGR3B gene deletion were detected in both cases. Newborns and fathers exhibited specific gene combinations: FCGR3B*02/FCGR3B*02 (Case 1) and FCGR3B*02/FCGR3B*03 (Case 2). IMNS outperformed dextran/Ficoll, yielding four times more neutrophils (average neutrophil counts: 18.5 × 103/μL vs. 4.5 × 103/μL), efficiently removing non-neutrophil cells and reducing processing time (30-40 min vs. 70-90 min), although it incurred a higher cost (2.7 times).

CONCLUSION

Two cases of maternal anti-FcγRIIIb isoantibodies, unrelated to NAIN, were identified. Although neutropenia has not been described in these cases, we emphasize the importance of identifying asymptomatic cases with the potential for severe neutropenia. Additionally, IMNS is introduced as a rapid, high-yield, high-purity neutrophil isolation technique, beneficial for serological assays detecting anti-HNA antibodies.

Comparison of real-time quantitative PCR and two digital PCR platforms to detect copy number variation in FCGR3B

The importance of structural genetic variants, such as copy number variations (CNVs), in modulating human disease is being increasingly recognized. Several clinical conditions require investigation of human neutrophil antigen (HNA-1), which is encoded by the Fc gamma receptor IIIb gene (FCGR3B), including suspicion of neutropenia, infections, and proactive testing of blood component donors to reduce the potential risk in transfusion. In this study, we compared real-time quantitative polymerase chain reaction (qPCR) with two digital PCR (dPCR) platforms, namely droplet digital PCR and an array-based platform, to determine copy numbers (CNs) in FCGR3B. We initially tested 400 anonymous blood donors with qPCR using a commercially available TaqMan probe assay (Applied Biosystems) on a Quant Studio 12 Flex. CNs was determined for all 400 tested individuals with CNs ranging from zero to four. Zero copies were detected in 0.2% (1/400), one copy was detected in 3.8% (15/400), two copies were detected in 87.8% (351/400), three copies were detected in 8.0% (32/400), and four copies were detected in 0.2% (1/400) of tested individuals. From this cohort, we selected 32 donors with CNs from zero to four for analyses with Digital Real-Time PCR (dPCR) using Lab on an array (LOAA) on an On-Point analyzer from Optolane Technologies Inc. and the Droplet Digital PCR (ddPCR) platform from Bio-Rad Laboratories. We compared the obtained CNs of FCGR3B on the three platforms and found full concordance between the CNs obtained. We therefore conclude that all three platforms can be used for quantification of CNs for FCGR3B, and although dPCR has some advantages over qPCR, it was not necessary for reliably estimating CNs of the FCGR3B gene.

High-resolution HLA genotyping identifies risk alleles in both class I and II for primary autoimmune neutropenia in early childhood in a Danish cohort

HLA studies in patients with autoimmune neutropenia (AIN) have shown very consistent results for the association with HLA class II alleles at low resolution. This study aimed to examine the association of both HLA class I and class II at high resolution to clarify the contribution of risk alleles to the disease. A total of 107 AIN patients were genotyped for six loci of HLA class I (HLA-A, -B and -C) and class II (HLA-DRB1, -DQB1, and -DPB1) genes by a high-resolution (3-field, 6-digit) analysis and compared with HLA typing of 1000 healthy controls. Compared with the controls, the allele frequencies were significantly higher in AIN patients for A*02:17:01G, C*01:02:01G, DRB1*10:01:01G, DRB1*14:01:01G, DRB1*16:01:01G, DQB1*05:02:01G, and DQB1*05:03:01G but lower significant for C*03:04:01G, DRB1*04:01:01G, DRB1*13:02:01G, DQB1*03:02:01G, and DQB1*06:04:01G. Frequently associated two-locus haplotypes were found to be DRB1*10:01:01G-DQB1*05:01:01G and DRB1*16:01:01G-DQB1*05:02:01G, while the S2 (Q- or D-KRAA) shared epitope (SE) was associated with lower risk. A unique association with HLA alleles was observed between patients with specific anti-HNA-1a antibodies and broad-reacting anti-FcγRIIIb. Anti-HNA-1a antibody-positive patients were associated with C*01:02:01G, DRB1*01:01:01G, DRB1*16:01:01G, DQB1*05:01:01G, DQB1*05:02:01G, DQB1*06:04:01G, and DPB1*10:01:01G; the two-locus haplotypes DRB1*01:01:01G-DQB1*05:01:01G and DRB1*16:01:01G-DQB1*05:02:01G; and the S3P (Q- or R-RRAA) SE. Anti-FcγRIIIb antibody-positive patients were associated with the alleles A*02:17:01G, DRB1*10:01:01G, and DQB1*05:02:01G; the haplotypes DRB1*10:01:01G-DQB1*05:01:01G and DRB1*11:01:02G-DQB1*05:02:01G; and the S3D (DRRAA) SE. The different associations regarding FcγRIIIb antibody specificities could indicate disease heterogeneity.

Clinical significance of human neutrophil antigen-1 antibodies in children with neutropenia

Primary autoimmune neutropenia in young children is characterized by chronic neutropenia and positivity for antibodies against human neutrophil antigens (HNAs). This study analyzed the clinical characteristics of 402 children with neutropenia to identify differences between those with and without HNA-1 antibodies (HNA1abs). HNAabs in sera were detected by granulocyte immunofluorescence testing using flow cytometry. Relative fluorescence intensity (RFI) values were used to divide patients into positive (PG, n = 302), borderline (BG, n = 34), and negative (NG, n = 66) groups. The antibodies reacted to HNA-1a alone (59%), HNA-1b alone (1%), and HNA-1a/1b (40%). The PG had a significantly lower absolute neutrophil count before definitive diagnosis and a 1.6- to 2-times greater risk of hospitalization during neutropenia than the other groups. The median duration of neutropenia was longest in the PG at 25 months, followed by 20 months in the BG and 14 months in the NG. This large-scale cohort characterizes clinically distinct groups using the RFI value for HNA1abs in young children with neutropenia. Detection of HNA1abs may aid in understanding the clinical characteristics of children with neutropenia.

World human neutrophil antigens investigation survey

BACKGROUND AND OBJECTIVES

Human neutrophil antigens (HNAs) are categorized into five systems: HNA-1 to HNA-5. Given the importance of neutrophils in immunity, we sought to create awareness of the role of HNA diagnostic services in managing immune neutropenia and transfusion-related acute lung injury. To provide health communities all around the world with access to these services, we conducted a survey to create a directory of these HNA diagnostic services.

MATERIALS AND METHODS

An Excel table-based survey was created to capture information on the laboratory's location and was emailed to 55 individuals with known or possible HNA investigation activity. The collected data were then summarized and analysed.

RESULTS

Of contacted laboratories, the surveys were returned from 23 (38.2%) laboratories; 17 have already established HNA diagnostic (of them 12 were regular participants of the International Granulocyte Immunobiology Workshop [ISBT-IGIW]), 4 laboratories were in the process of establishing their HNA investigation and the remaining 2 responder laboratories, did not conduct HNA investigations. In established laboratories, investigation for autoimmune neutropenia (infancies and adults) was the most frequently requested, and antibodies against HNA-1a and HNA-1b were the most commonly detected.

CONCLUSION

The directory of survey respondents provides a resource for health professionals wanting to access HNA diagnostic services. The present study offers a comprehensive picture of HNA diagnostics (typing and serology), identifying weak points and areas for improvement for the first time. Identifying more laboratories involved in HNA diagnostics with limited access to international societies in the field will globally improve HNA diagnostics.

Integrin Subunit Alpha M, ITGAM Nonsynonymous SNP Is Associated with Knee Osteoarthritis among Thais: A Case-Control Study

Knee osteoarthritis (OA), which is one of the most common degenerative joint diseases, presents a multifactorial etiology, involving multiple causative factors including genetic and environmental determinants. Four human neutrophil antigen (HNA) systems can be determined using each HNA allele by single-nucleotide polymorphisms (SNPs). However, there are no data on HNA polymorphisms and knee OA in Thailand, so we investigated the association of HNA SNPs and knee OA in the Thai population. In a case-control study, detection of HNA-1, -3, -4, and -5 alleles by polymerase chain reaction with sequence-specific priming (PCR-SSP) was performed in participants with and without symptomatic knee OA. Logistic regression models were used to estimate the odds ratio (OR) and 95% confidence interval (CI) between cases and controls. Among 200 participants, 117 (58.5%) had knee OA; 83 (41.5%) did not and were included as controls in this study. An integrin subunit alpha M (ITGAM) nonsynonymous SNP, rs1143679, was markedly associated with symptomatic knee OA. The ITGAM*01*01 genotype was identified as an important increased risk factor for knee OA (adjusted OR = 5.645, 95% CI = 1.799-17.711, p = 0.003). These findings may contribute to our understanding of the application prospects for therapeutic approaches to knee OA.

Genetic variations in low-to-medium-affinity Fcγ receptors and autoimmune neutropenia in early childhood in a Danish cohort

Autoimmune neutropenia (AIN) in early childhood is caused by autoantibodies directed against antigens on the neutrophil membrane and is a frequent cause of neutropenia in children. Association of AIN with Fcγ receptor (FCGR) 3B variants is well described. In this study, we investigate genetic variations in the FCGR locus and copy number variation of FCGR3B. A total of 130 antibody-positive AIN patients, 64 with specific anti-HNA-1a antibodies and 66 with broad-reacting anti-FcγRIIIb antibodies, were genotyped with a multiplex ligation probe assay and compared with healthy controls. Positive findings were confirmed with real-time q-PCR. We determined copy numbers of the FCGR2 and FCGR3 genes and the following SNPs: FCGR2A Q62W (rs201218628), FCGR2A H166R (rs1801274), FCGR2B I232T (rs1050501), FCGR3A V176F (rs396991), haplotypes for FCGR2B/C promoters (rs3219018/rs780467580), FCGR2C STOP/ORF and HNA-1 genotypes in FCGR3B (rs447536, rs448740, rs52820103, rs428888 and rs2290834). Generally, associations were antibody specific, with all associations being representative of the anti-HNA-1a-positive group, while the only association found in the anti-FcγRIIIb group was with the HNA-1 genotype. An increased risk of AIN was observed for patients with one copy of FCGR3B; the HNA genotypes HNA-1a, HNA-1aa or HNA-1aac; the FCGR2A 166H and FCGR2B 232I variations; and no copies of FCGR2B 2B.4. A decreased risk was observed for HNA genotype HNA-1bb; FCGR2A 166R; FCGR2B 232T; and one copy of FCGR2B promoter 2B.4. We conclude that in our Danish cohort, there was a strong association between variation in the FCGR locus and AIN. The findings of different genetic associations between autoantibody groups could indicate the presence of two different disease entities and disease heterogeneity.

Genetic landscape of human neutrophil antigen variants in India from population-scale genomes

Antibodies against human neutrophil antigens (HNAs) play a significant role in various clinical conditions such as neonatal alloimmune neutropenia, transfusion-related acute lung injury, and other nonhemolytic transfusion reactions. This study aims to identify the genotype and allele frequencies of HNAs in the healthy Indian population. Ten genetic variants in four human genes encoding alleles of HNAs class I-V approved by the International Society of Blood Transfusion-Granulocyte Immunobiology Working Party were used in the analysis. Genetic variants from whole genome sequences of 1029 healthy Indian individuals corresponding to HNA alleles were analyzed. The frequencies of the variants were compared with global population datasets using an in-house computational pipeline. In HNA class I, allele frequencies of FCGR3B*01, FCGR3B*02, and FCGR3B*03 encoding HNA-1a, HNA-1b, and HNA-1c were 0.07, 0.8, and 0.13, respectively. HNA class 3 alleles namely SLC44A2*01 (encoding HNA-3a) and SLC44A2*02 (encoding HNA-3b) were found at allele frequencies of 0.78 and 0.22, respectively. The frequencies of ITGAM*01 encoding HNA-4a and ITGAM*02 encoding HNA-4a were 0.95 and 0.05, respectively. Furthermore, allele frequencies of HNA class 5 alleles were 0.32 for ITGAL*01 (encoding HNA-5a) and 0.68 for ITGAL*02 (encoding HNA-5b). Interestingly, it was also found that rs2230433 variant deciding the HNA class 5 alleles, was highly prevalent (78.2%) in the Indian population compared with other global populations. This study presents the first comprehensive report of HNA allele and genotype frequencies in the Indian population using population genome datasets of 1029 individuals. Significant difference was observed in the prevalence of HNA5a and HNA5b in India in comparison to other global populations.

Human neutrophil antigen 3 genotype impacts neutrophil-mediated endothelial cell cytotoxicity in a two-event model of TRALI

BACKGROUND

Antibodies against human neutrophil antigen (HNA)-3a are associated with severe cases of transfusion-related acute lung injury (TRALI). The HNA-3 system is located on choline transporter-like 2 (CTL-2) protein. CTL-2 is encoded by the gene SLC44A2 and a single-nucleotide polymorphism c.461G>A results in two antigens: HNA-3a and HNA-3b. Three HNA-3 genotypes/ phenotypes exist: HNA-3aa, HNA-3bb, and HNA-3ab. Two different pathways of anti-HNA-3a TRALI have been described: a two-hit neutrophil-dependent pathway and a one-hit neutrophil-independent pathway. However, it is not clear whether HNA-3ab heterozygous patients have a lower risk of anti-HNA-3a-mediated TRALI compared to HNA-3aa homozygous patients.

MATERIALS AND METHODS

Healthy volunteers were genotyped for HNA-3 by real-time polymerase chain reaction, and phenotyped for HNA-3a by granulocyte immunofluorescence test (GIFT) and granulocyte agglutination test (GAT) against two donor sera containing anti-HNA-3a antibodies. The two sera were also used in in vitro models of human pulmonary microvascular endothelial cell (HLMVEC) cytotoxicity to investigate pathways of TRALI development.

RESULTS

For both anti-HNA-3a sera, GIFT results matched the genotype, with a lower GIFT ratio for HNA-3ab neutrophils compared to HNA-3aa neutrophils, whereas GAT results showed no difference in agglutination. HLMVEC cytotoxicity was not observed in a one-hit neutrophil-independent model but was observed in a two-hit neutrophil-dependent model. Differences in cytotoxicity were observed between the two anti-HNA-3a sera used. Consistent with reduced HNA-3a antigen density as measured by GIFT, HNA-3ab neutrophils mediated less HLMVEC cytotoxicity than HNA-3aa neutrophils.

CONCLUSION

HNA-3 genotype and HNA-3a antigen expression impacted the severity of anti-HNA-3a-mediated HLMVEC cytotoxicity in a two-hit neutrophil-dependent model of TRALI. Different HNA-3a antibodies might also impact the magnitude of HLMVEC cytotoxicity.

Effect of stimulated platelets in COVID-19 thrombosis: Role of alpha7 nicotinic acetylcholine receptor

Since early 2020, SARS-CoV-2-induced infection resulted in global pandemics with high morbidity, especially in the adult population. COVID-19 is a highly prothrombotic condition associated with subsequent multiorgan failure and lethal outcomes. The exact mechanism of the prothrombotic state is not well understood and might be multifactorial. Nevertheless, platelets are attributed to play a crucial role in COVID-19-associated thrombosis. To date, platelets' role was defined primarily in thrombosis and homeostasis. Currently, more focus has been set on their part in inflammation and immunity. Moreover, their ability to release various soluble factors under activation as well as internalize and degrade specific pathogens has been highly addressed in viral research. This review article will discuss platelet role in COVID-19-associated thrombosis and their role in the cholinergic anti-inflammatory pathway. Multiple studies confirmed that platelets display a hyperactivated phenotype in COVID-19 patients. Critically ill patients demonstrate increased platelet activation markers such as P-selectin, PF4, or serotonin. In addition, platelets contain acetylcholine and express α7 nicotinic acetylcholine receptors (α7nAchR). Thus, acetylcholine can be released under activation, and α7nAchR can be stimulated in an autocrine manner and support platelet function. α7 receptor is one of the most important mediators of the anti-inflammatory properties as it is associated with humoral and intrinsic immunity and was demonstrated to contribute to better outcomes in COVID-19 patients when under stimulation. Hematopoietic α7nAchR deficiency increases platelet activation and, in experimental studies, α7nAchR stimulation can diminish the pro-inflammatory state and modulate platelet reactiveness via increased levels of NO. NO has been described to inhibit platelet adhesion, activation, and aggregation. In addition, acetylcholine has been demonstrated to decrease platelet aggregation possibly by blocking the e p-38 pathway. SARS-CoV-2 proteins have been found to be similar to neurotoxins which can bind to nAChR and prevent the action of acetylcholine. Concluding, the platelet role in COVID-19 thrombotic events could be explained by their active function in the cholinergic anti-inflammatory pathway.

Genetic epidemiology of human neutrophil antigen variants suggests significant global variability

Human neutrophil antigens possess significant clinical implications especially in the fields of transfusion and transplantation medicine. Efforts to estimate the prevalence of genetic variations underpinning the antigenic expression are emerging. However, there lacks a precise capture of the global frequency profiles. Our article emphasizes the potential utility of maintaining an organized online repository of evidence on neutrophil antigen-associated genetic variants from published literature and reports. This, in our opinion, is an emerging area and would significantly benefit from the awareness and understanding of population-level diversities.

Human neutrophil antigen 2 sequence-based typing: Joining the hunt for the CD177 answer

BACKGROUND AND OBJECTIVES

Isoantibodies to human neutrophil antigen 2 (CD177) have been associated with several clinical conditions but to date the molecular basis for altered or non-expression has not been determined. Reliance on phenotyping and crossmatch to investigate these neutropenic clinical cases are inconvenient for the patients and demanding of resources within the laboratory. Therefore, a molecular approach has been introduced to address both issues.

MATERIALS AND METHODS

A DNA panel of 100 randomly selected blood donors were collected and supplemented with 18 DNA samples from blood donors previously shown to be CD177 null. All DNA samples were sequence-based typed for all exons and observed polymorphisms recorded. The DNA from two families previously investigated for neonatal alloimmune neutropenia due to CD177 isoantibodies were also analysed.

RESULTS

The incidence of CD177 null could be associated with a known exon 7 single-nucleotide polymorphism in 16/21 known CD177 null samples, which is consistent with previously published findings. Two additional mutations that may lead to null expression were also identified, of which one may be novel. In both family investigations, this same mutation could also be observed in the maternal DNA sample.

CONCLUSION

Based on these observations, introduction of CD177 genotyping into routine use would identify null expression in over 75% (16/21) of associated cases. In turn, this could significantly reduce the need for supplementary testing and associated inconvenience to patients while permitting increased efficiency of laboratory testing. An added benefit would potentially elucidate other clinically relevant mutations and associated antigenic targets.

Association between human leukocyte antigens (HLAs) and human neutrophil antigens (HNAs) and autoimmune neutropenia of infancy in Danish patients

BACKGROUND

Autoimmune neutropenia of infancy (AIN) is a frequent cause of neutropenia in children. The disease is caused by antibodies against epitopes on the immunoglobulin G (IgG) Fc receptor type 3b (FcγIIIb). We investigated the possible association of human neutrophil antigens (HNA), human leukocyte antigen (HLA)-DR, and HLA-DQ alleles with AIN and the association of these genotypes with the presence of autoantibodies.

METHODS

Eighty AIN cases with a median age of 13.5 months were included. Controls were healthy unrelated Danish blood donors. Anti-HNA-1a autoantibodies were detected using a flow cytometric granulocyte immunofluorescence test (Flow-GIFT) with phenotyped donor cells for detection of antibody specificity. Molecular determination of HNA genotypes was determined using real-time polymerase chain reaction (q-PCR). High-resolution HLA-DRB1 and HLA-DQB1 were determined by next-generation sequencing.

RESULTS

Antibodies against HNA-1a were detected in 51% (n = 41) of AIN patients, and anti-HNA-1b was detected in 3% (n = 2) of cases. In 46% of cases, the antibodies were anti-FcγIIIb-reactive. FCGR3B*01+,*02-,*03- was more common (odds ratio, 6.70; P < .0001), and FCGR3B*01-,*02+,*03- was less common (odds ratio, 0.30; P < .0001) among AIN cases. HNA-1a antibodies were significantly more frequent among AIN cases with the FCGR3B*01+,*02-,*03- genotype (odds ratio, 3.86; P < .007). The HLA-DRB1*14 - HLA-DQB1*05:03 haplotype was significantly more common (odds ratio, 7.44; P < .0001) in AIN patients.

CONCLUSION

The HLA haplotype HLA-DRB1*14 - DQB1*05:03 is associated with Danish AIN cases. Among Danish AIN patients, anti-HNA-1a is the most common autoantibody, and the antibody is more common in cases with the FCGR3B*01+,*02-,*03- genotype.

Choline transporter-like proteins 1 and 2 are newly identified plasma membrane and mitochondrial ethanolamine transporters

The membrane phospholipids phosphatidylcholine and phosphatidylethanolamine (PE) are synthesized de novo by the CDP-choline and CDP-ethanolamine (Kennedy) pathway, in which the extracellular substrates choline and ethanolamine are transported into the cell, phosphorylated, and coupled with diacylglycerol to form the final phospholipid product. Although multiple transport systems have been established for choline, ethanolamine transport is poorly characterized and there is no single protein assigned a transport function for ethanolamine. The solute carriers 44A (SLC44A) known as choline transporter-like proteins-1 and -2 (CTL1 and CTL2) are choline transporter at the plasma membrane and mitochondria. We report a novel function of CTL1 and CTL2 in ethanolamine transport. Using the lack or the gain of gene function in combination with specific antibodies and transport inhibitors we established two distinct ethanolamine transport systems of a high affinity, mediated by CTL1, and of a low affinity, mediated by CTL2. Both transporters are Na⁺-independent ethanolamine/H⁺ antiporters. Primary human fibroblasts with separate frameshift mutations in the CTL1 gene (M1= SLC44A1^ΔAsp517 and M2= SLC44A1^ΔSer126) are devoid of CTL1 ethanolamine transport but maintain unaffected CTL2 transport. The lack of CTL1 in M2 cells reduced the ethanolamine transport, the flux through the CDP-ethanolamine Kennedy pathway, and PE synthesis. In contrast, overexpression of CTL1 in M2 cells improved ethanolamine transport and PE synthesis. These data firmly establish that CTL1 and CTL2 are the first identified ethanolamine transporters in whole cells and mitochondria, with intrinsic roles in de novo PE synthesis by the Kennedy pathway and intracellular redistribution of ethanolamine.

Serologic and molecular studies to identify neonatal alloimmune neutropenia in a cohort of 10,000 neonates

Neonatal alloimmune neutropenia (NAIN) is caused by maternal alloimmunisation to fetal human neutrophil antigens (HNAs). This study investigated maternal HNA/HLA alloantibodies involved with NAIN and identified the frequency of NAIN in Brazilian neonates. Neonatal neutropenia (neutrophil count < 1.5 × 10⁹ /L) was investigated in samples from 10,000 unselected neonates, resulting in 88 neutropenic newborns (NBs) and their 83 mothers. Genotyping was performed by PCR-SSP (HNA-1/-4) and PCR-RFLP (HNA-3/-5). Serologic studies were performed by GAT (granulocyte agglutination test), Flow-WIFT (white blood cells immunofluorescence test) and LABScreen-Multi-HNA-Kit (OneLambda®) (LSM). Neonatal neutropenia was identified in 88/10,000 (0·9%) NBs. Genotyping revealed 60·2% maternal-fetal HNA incompatibilities (31·8% for HNA-1; 14·8% for HNA-3; 15·9% for HNA-4; 21·6% for HNA-5). Serologic studies revealed 37·3% of mothers with positive results with at least one technique. The detected anti-HNA specificities were confirmed in eight positive cases related to HNA-1/-3 systems. In cases with maternal-fetal HNA-4/-5 incompatibility, no specific neutrophil alloantibodies were found but anti-HLA I/II were present. Anti-HNA-2 was not identified. This is a large Brazilian study which involved the investigation of antibodies against all five HNA systems in neutropenia cases and showed a frequency of NAIN in 8/10,000 neonates. Among the HNA antibodies identified, we highlight the anti-HNA-1d and anti-HNA-3b, antibodies unusual in alloimmunised women, and rarely related to NAIN cases.

Multicenter Study on Differential Human Neutrophil Antigen 2 Expression and Underlying Molecular Mechanisms

Background

The human neutrophil antigen 2 (HNA-2), which is expressed on CD177, is undetectable in 3-5% of the normal population. Exposure of these HNA-2_null individuals to HNA-2-positive cells can cause immunization and pro-duction of HNA-2 antibodies, which can induce immune neutropenia and transfusion-related acute lung injury. In HNA-2-positive individuals, neutrophils are divided into a CD177^pos. and a CD177^neg. subpopulation. The molecular background of HNA-2 deficiency and the bimodal expression pattern, however, are not completely decoded.

Study Design

An international collaboration was conducted on the genetic analysis of HNA-2-phenotyped blood samples, including HNA-2-deficient individuals, mothers, and the respective children with neonatal immune neutropenia and regular blood donors.

Results

From a total of 54 HNA-2_null individuals, 43 were homozygous for the CD177 *787A>T substitution. Six carried the CD177 *c.1291G>A single nucleotide polymorphism. All HNA-2-positive samples with >40% CD177^pos. neutrophils carried the *787A wild-type allele, whereas a lower rate of CD177^pos. neutrophils was preferentially associated with *c.787AT heterozygosity. Interestingly, only the *c.787A allele sequence was detected in complementary DNA (cDNA) sequence analysis carried out on all *c.787AT heterozygous individuals. However, cDNA analysis after sorting of CD177^pos. and CD177^neg. neutrophil subsets from HNA-2-positive individuals showed identical sequences, which makes regulatory elements within the promoter unlikely to affect CD177 gene transcription in different CD177 neutrophil subsets.

Conclusion

This comprehensive study clearly demonstrates the impact of single nucleotide polymorphisms on the expression of HNA-2 on the neutrophil surface but challenges the hypothesis of regulatory epigenetic effects being implicated in the bimodal CD177 expression pattern.

Human neutrophil antigens: Nature, clinical significance and detection

Granulocytes are an essential part of both the innate and adaptive immune systems. Human neutrophil antigens (HNAs) are a family of epitopes that are located on glycoproteins that are mostly expressed on human granulocytes. Antibodies that recognize these epitopes have been associated with neutropenia, transfusion complications, haematopoietic stem cell transplant nonengraftment and renal transplant rejection. Currently, there are fourteen recognized HNA alleles across five antigen systems (HNA-1 through HNA-5), the molecular basis of which are located on the genes FCGR3B, CD177, SLC44A2, ITGAM and ITGAL, respectively. Elucidation of the associated genes has permitted the development of testing strategies for HNA typing and aided understanding of the associated epitopes. This review will outline the associated clinical conditions that require HNA investigation and how these are performed in specialized laboratories. Investigations provided are both reactive for patients with a variety of existing or suspected neutropenias and proactive in the testing of blood component donors in order to reduce the potential risk to patients who require transfusion.

Leukocyte-Reactive Antibodies in Female Blood Donors: The Austrian Experience

Introduction

Antibody-mediated transfusion-related acute lung injury (TRALI) is caused by antibodies against human leukocyte antigens (HLAs) or human neutrophil antigens (HNAs), and is one of the most serious complications associated with transfusion medicine. Prevention strategies like testing allo-exposed female blood donors have not yet been introduced nationwide in Austria. To assess the need and feasibility of routine leukocyte antibody testing, the prevalence of leukocyte-reactive antibodies in an Austrian female donor population was been determined using classical cell-based methods which were compared with a high-throughput bead-based method.

Methods

Sera from 1,022 female blood donors were screened using a granulocyte aggregation test (GAT) and a white blood cell immunofluorescence test (WIFT) after retesting and specification of positive samples by granulocyte immunofluorescence test (GIFT) and monoclonal antibody-specific immobilization of granulocyte antigens (MAIGA). Potential HLA reactivities were confirmed using the microbeads assay LabScreen^TM Mixed. The results in 142 donor sera and 38 well-defined reference sera were investigated by the microbeads assay LabScreen^TM Multi and compared with classical cell-based methods.

Results

Reactivity with either granulocytes and/or lymphocytes was detected in 79 sera (7.7%), with the majority being HLA-specific. Antibodies against HNA were obtained in 7 samples (0.7%). The aggregating potential of the detected antibodies was observed in 9 cases (0.9%). Most of the leukocyte-reactive antibodies occurred at a donor age of between 35 and 59 years (n = 61). LabScreen Multi showed good agreement (κ = 0.767) for HNA antibody detection by cell-based assays, but double/multiple specificities (100% of 7 anti-HNA-1b sera) as well as false-negative results (40% of 15 HNA-3-specific sera) occurred.

Discussion

Leukocyte-reactive antibody screening is advised in Austrian female donors for safe blood transfusion, including single-donor convalescent plasma treatment of COVID-19 that may be implemented soon. For the introduction of LabScreen Multi, the combination with GAT should be considered to ensure correct anti-HNA-3a detection.

Targeted exome sequencing designed for blood group, platelet, and neutrophil antigen investigations: Proof-of-principle study for a customized single-test system

BACKGROUND

Immunohematology reference laboratories provide red blood cell (RBC), platelet (PLT), and neutrophil typing to resolve complex cases, using serology and commercial DNA tests that define clinically important antigens. Broad-range exome sequencing panels that include blood group targets provide accurate blood group antigen predictions beyond those defined by serology and commercial typing systems and identify rare and novel variants. The aim of this study was to design and assess a panel for targeted exome sequencing of RBC, PLT, and neutrophil antigen-associated genes to provide a comprehensive profile in a single test, excluding unrelated gene targets.

STUDY DESIGN AND METHODS

An overlapping probe panel was designed for the coding regions of 64 genes and loci involved in gene expression. Sequencing was performed on 34 RBC and 17 PLT/neutrophil reference samples. Variant call outputs were analyzed using software to predict star allele diplotypes. Results were compared with serology and previous sequence genotyping data.

RESULTS

Average coverage exceeded 250×, with more than 94% of targets at Q30 quality or greater. Increased coverage revealed a variant in the Scianna system that was previously undetected. The software correctly predicted allele diplotypes for 99.5% of RBC blood groups tested and 100% of PLT and HNA antigens excepting HNA-2. Optimal throughput was 12 to 14 samples per run.

CONCLUSION

This single-test system demonstrates high coverage and quality, allowing for the detection of previously overlooked variants and increased sample throughput. This system has the potential to integrate genomic testing across laboratories within hematologic reference settings.

Neonatal alloimmune neutropaenia: Experience from an Australian paediatric health service

AIM

To describe the presenting features and investigation findings in infants diagnosed with neonatal alloimmune neutropaenia (NAIN) within an Australian paediatric health network. The secondary aim was to describe the management and resolution of neutropaenia in infants with NAIN.

METHODS

A retrospective cohort study was conducted at Monash Children's Hospital, Melbourne, Australia. Infants referred to the Victorian Transplantation and Immunogenetics Service for evaluation of NAIN were identified and medical records were reviewed. Descriptive statistical analysis of infants' clinical outcomes, investigation findings and management was performed.

RESULTS

Nine infants were diagnosed with NAIN between December 2004 and June 2017. Overall incidence of NAIN was around 1 per 10 000 births. Median gestational age was 38 (range 35-40) weeks and birthweight was 2920 (2300-4445) g. Median age at NAIN work-up was 7 (2-33) days. Prior to investigation for NAIN, median absolute neutrophil count was 0.2 (0.01-0.6) × 10⁹ cells/L. The post-natal ward was the source of presentation in most infants (78%). All except one infant were admitted to a neonatal unit and commenced on intravenous antibiotics (89%). Six infants were asymptomatic but received antibiotics for risk of infection (75%). Granulocyte-colony stimulating factor was administered to 44% of infants due to neutropaenia with presumed or confirmed infection. NAIN resolved at median age of 32 (6-200) days.

CONCLUSIONS

Infants with NAIN frequently presented with severe, unexpected neutropaenia without major infection. Intravenous antibiotic therapy and granulocyte-colony stimulating factor use was common in this cohort.

A novel nonsense mutation found in the CD177 gene of Thai individuals with the HNA-2 null phenotype

OBJECTIVES

The aim of this study is to explore the molecular basis and to develop a simple sequence-specific primer polymerase chain reaction (PCR-SSP) technique for screening genotypes associated with the human neutrophil antigen-2 (HNA-2) null phenotype among Thai blood donors.

BACKGROUND

Single-nucleotide polymorphisms (SNPs) c.787A>T of the CD177 gene is well known to be primarily demonstrated as a genetic determinant for HNA-2 deficiency.

METHODS

The SNPs in the CD177 gene (exons 7 and 9) of 49 Thai blood donors with the known percentage of CD177 expression by flow cytometry including 48 HNA-2 positive and 1 HNA-2 null individuals were identified by long-range PCR amplification and sequencing. Moreover, screening for the c.1254G>A mutation was developed using an in-house PCR-SSP technique and tested among 771 unrelated donor samples.

RESULTS

A HNA-2 null sample from the first cohort was heterozygous for c.787A/T and homozygous for c.1291G/G, namely, a 787A-1291G/787T-1291G (AG/TG) genotype. Interestingly, we could identify SNP c.1254G>A (rs188387562, p. Trp418Ter) that caused a nonsense mutation of the CD177 gene in exon 9. This individual might have the 787A-1254A-1291G/787T-1254G-1291G genotype. From the second cohort (771 unrelated donors), the 1254GG homozygote was the most common (96.37%), followed by the 1254GA heterozygote (3.50%) and 1254AA homozygote (0.13%). Blood samples of two individuals with 787AT-1254GA-1291GG and 787AA-1254AA-1291GG genotypes were tested and the HNA-2 antigen expressions were 0.03% and 0.16% in rank.

CONCLUSIONS

The c.787A>T is a primary genetic hallmark to determine the HNA-2 null phenotype. Additional screening of the novel c.1254G>A in combination with c.787A>T is a suitable, convenient and effective diagnosis among Thais.

Towards a Regional Registry of Extended Typed Blood Donors: Molecular Typing for Blood Group, Platelet and Granulocyte Antigens

BACKGROUND

The provision of compatible blood products to patients is the most essential task of transfusion medicine. Besides ABO and Rh, a number of additional blood group antigens often have to be considered for the blood supply of immunized or chronically transfused patients. It also applies for platelet antigens (HPA) and neutrophil antigens (HNA) for patients receiving platelet or granulocyte concentrates. Here, we describe the molecular screening for a number of blood group, HPA, and HNA alleles. Based on the screening results we are building up a regional blood donor registry to provide extended matched blood products on demand.

METHODS

We developed and validated TaqMan™ PCR and PCR-SSP methods for genetic markers defining 37 clinically relevant blood group antigens (beyond ABO and Rh), 10 HPA, and 11 HNA. Furthermore, we describe a feasible method for fast molecular screening of the HNA-2null phenotype. All data were statistically evaluated regarding genotype distribution. Allele frequencies were compared to ExAC data from non-Finnish Europeans.

RESULTS

Up to now more than 2,000 non-selected regular blood donors in south-west Germany have been screened for blood group, HPA, and HNA alleles. The screening results were confirmed by serology and PCR-SSP methods for selected numbers of samples. The allele frequencies were similar to non-finnish Europeans in the ExAC database except for the alleles encoding the S, HPA-3b and HNA-4b antigens, with significantly lower prevalence in our cohort, as well as the LU14 and the HNA-3b antigens, with a higher frequency compared to the ExAC data. We identified 71 donors with rare blood groups such as Lu(a+b-), Kp(a+b-), Fy(a-b-) and Vel-, and 169 donors with less prevalent HPA or HNA types.

CONCLUSION

Molecular screening for blood group alleles by using TaqMan™ PCR is an effective and reliable high-throughput method for establishing a rare donor registry.