Molecular basis of NB1 (HNA-2a, CD177) deficiency

Dual role of CD177 + neutrophils in inflammatory bowel disease: a review

Inflammatory bowel disease (IBD) represents a group of recurrent chronic inflammatory disorders associated with autoimmune dysregulation, typically characterized by neutrophil infiltration and mucosal inflammatory lesions. Neutrophils, as the earliest immune cells to arrive at inflamed tissues, play a dual role in the onset and progression of mucosal inflammation in IBD. Most of these cells specifically express CD177, a molecule increasingly recognized for its critical role in the pathogenesis of IBD. Under IBD-related inflammatory stimuli, CD177 is highly expressed on neutrophils and promotes their migration. CD177 + neutrophils activate bactericidal and barrier-protective functions at IBD mucosal inflammation sites and regulate the release of inflammatory mediators highly correlated with the severity of inflammation in IBD patients, thus playing a dual role. However, mitigating the detrimental effects of neutrophils in inflammatory bowel disease remains a challenge. Based on these data, we have summarized recent articles on the role of neutrophils in intestinal inflammation, with a particular emphasis on CD177, which mediates the recruitment, transepithelial migration, and activation of neutrophils, as well as their functional consequences. A better understanding of CD177 + neutrophils may contribute to the development of novel therapeutic targets to selectively modulate the protective role of this class of cells in IBD.

Peripheral priming induces plastic transcriptomic and proteomic responses in circulating neutrophils required for pathogen containment

Neutrophils rapidly respond to inflammation and infection, but to which degree their functional trajectories after mobilization from the bone marrow are shaped within the circulation remains vague. Experimental limitations have so far hampered neutrophil research in human disease. Here, using innovative fixation and single-cell-based toolsets, we profile human and murine neutrophil transcriptomes and proteomes during steady state and bacterial infection. We find that peripheral priming of circulating neutrophils leads to dynamic shifts dominated by conserved up-regulation of antimicrobial genes across neutrophil substates, facilitating pathogen containment. We show the TLR4/NF-κB signaling-dependent up-regulation of canonical neutrophil activation markers like CD177/NB-1 during acute inflammation, resulting in functional shifts in vivo. Blocking de novo RNA synthesis in circulating neutrophils abrogates these plastic shifts and prevents the adaptation of antibacterial neutrophil programs by up-regulation of distinct effector molecules upon infection. These data underline transcriptional plasticity as a relevant mechanism of functional neutrophil reprogramming during acute infection to foster bacterial containment within the circulation.

Human Neutrophil Antigen Genotype and Allele Frequencies in Iranian Blood Donors

Objective

Human neutrophil antigens (HNAs) can be targeted by HNA-allo antibodies and cause a variety of clinical conditions such as transfusion-related acute lung injury (TRALI) and neonatal alloimmune neutropenia (NAIN). The current study is aimed at identifying the genotype and allele frequencies of HNAs in Iranian blood donors.

Methods

A total of 150 blood samples were obtained from healthy blood donors. HNA-1, HNA-3, HNA-4, and HNA-5 were genotyped, using the polymerase chain reaction sequence-specific primer (PCR-SSP) technique. The expression of the HNA-2 antigen on the neutrophil surface was evaluated by flow cytometry.

Results

The allele frequencies of FCGR3B∗1 (encoding HNA-1a), FCGR3B∗2 (encoding HNA-1b), and FCGR3B∗3 (encoding HNA-1c) were 0.34, 0.63, and 0.03, respectively. For HNA-3, the allele frequencies for SLC44A2∗1 (encoding HNA-3a) and SLC44A2∗2 (encoding HNA-3b) were 0.63 and 0.37, respectively. The frequencies of ITGAM∗1 (encoding HNA-4a) and ITGAM∗2 (encoding HNA-4b) alleles were 0.85 and 0.15, respectively. Furthermore, the frequencies of ITGAL∗1 (encoding HNA-5a) and ITGAL∗2 (encoding HNA-5b) alleles were 0.72 and 0.28, respectively. In the studied population, HNA-2 antigen was present on the neutrophil surface in 97.3% of the individuals, while no detectable HNA-2 expression was observed in 2.7% of the individuals. However, no significant difference in HNA-2 expression between different age groups was found.

Conclusion

The present study provides the first report of the HNA allele and genotype frequencies among the Iranian population. All HNAs (HNA-1 to HNA-5) were typed using the PCR-SSP and flow cytometer. In the current cohort study, the determined HNA allele frequencies were similar to the previous reports from British, German, and Danish populations. Considering the presence of different Iranian ethnic groups, further studies with a larger sample size are needed to draw a total picture for HNA allele frequencies.

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.

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.

Molecular Genetics of the Human Neutrophil Antigens

BACKGROUND AND OBJECTIVE

Antibodies to human neutrophil antigens (HNAs) have been implicated in transfusion-related acute lung injury and allo- and autoimmune neutropenia. To date, five HNA systems are assigned, and during the last decades enormous efforts have been undertaken to identify the underlying genes and to characterize the antigens. This review of the literature will provide the current genetic, molecular and functional information on HNAs.

RECENT FINDINGS

New information on alleles and antigens has been added to nearly each of the five HNA systems. HNA-1d has been added as the antithetical epitope to HNA-1c that is located on the glycoprotein encoded by FCGR3B*02 but not by FCGR3B. FCGR3B*04 and *05 now are included as new alleles. A CD177*787A>T substitution was demonstrated as the main reason for the HNA-2-negative phenotype on neutrophils. The target glycoprotein of HNA-3 antibodies could be identified as choline transporter-like protein 2 (CTL2) encoded by SLC44A2. The conformation sensitive epitope discriminates between arginine and glutamine at position 152 resulting in HNA-3a and HNA-3b. An additional Leu151Phe substitution can impair HNA-3a antibody binding. Recently an alloantibody against HNA-4b which discriminates from HNA-4a by an Arg61His exchange of the glycoprotein encoded by the ITGAM gene was reported in neonatal alloimmune neutropenia. An update of the current HNA nomenclature based on the new findings was provided in 2016 by the ISBT Granulocyte Immunobiology Working Party nomenclature subcommittee.

CONCLUSIONS

The molecular basis of each of the five HNA antigen systems has been decoded during the past decades. This enables reliable molecular typing strategies, antibody detection and specification as well as development of new assays based on recombinant antigens. However, research on HNA alleles, antigens, and antibodies is not finally terminated and also in the future will add new findings.

Neonatal Alloimmune Neutropenia

Neonatal alloimmune neutropenia (NAIN, NAIN or NIN) is a neutrophil blood group antagonism, analogous to hemolytic disease of the fetus and newborn (HDFN) and fetal/neonatal alloimmune thrombocytopenia (FNAIT). A limited number of prospective screening studies showed that granulocyte-specific antibodies were detectable in 0.35-1.1% of random postnatal maternal samples and that the incidence of NAIN was below 0.1%. Symptoms vary from none to mild skin infections, omphalitis or more severe infections like pneumonia, sepsis, and meningitis. Treatment of neonatal infection with antibiotics and granulocyte-colony stimulating factor is advised.

Flow-Cytometric Analysis of HNA-2 Expression and Phenotypes Among Thai Blood Donors

BACKGROUND

Antibodies specific to human neutrophil antigen (HNA), especially HNA-2, are implicated in various conditions, including neonatal alloimmune neutropenia, febrile non-hemolytic transfusion reactions, and transfusion-related acute lung injury. The distribution of the HNA-2 phenotype frequencies in the Thai population remains unknown. This study aimed to investigate HNA-2 phenotype frequencies in Thai blood donors and to compare the relationships of sex and age with HNA-2 expression.

METHODS

EDTA blood samples were collected from 220 unrelated healthy Thai blood donors, including 150 males and 70 females, with ages ranging from 20 to 57 years. Polymorphonuclear cells were isolated and stained with monoclonal antibodies clone MEM-166 and clone 2D1, which are specific to human CD177 (HNA-2) and CD45, respectively. HNA-2 expression according to sex and age was analyzed by flow cytometry.

RESULTS

Among the 220 donors, HNA-2-positive and HNA-2-null-phenotype frequencies were 0.995 and 0.005, respectively. Mean antigen expression was significantly higher in women (71.01±15.46%) than in men (64.59±18.85%; P <0.05). No significant differences in HNA-2 expression were found between different age groups. HNA-2 phenotype frequencies were similar to those in Asian, African, American, and Brazilian populations, but were significantly different from those in eastern Japanese, Korean, and French populations (P <0.001).

CONCLUSIONS

This is the first report of HNA-2 phenotype frequencies in a Thai population, and the data will be helpful in predicting the risk of HNA-2 alloimmunization and in recruiting granulocyte panel donors.

Gene silencing and a novel monoallelic expression pattern in distinct CD177 neutrophil subsets

CD177 presents antigens in allo- and autoimmune diseases on the neutrophil surface. Eulenberg-Gustavus et al. show that epigenetic silencing causes CD177^negative neutrophils, whereas a novel pattern of monoallelic CD177 expression results in a variable percentage of CD177^positive neutrophils in bimodal individuals.

CD177 presents antigens in allo- and autoimmune diseases on the neutrophil surface. Individuals can be either CD177-deficient or harbor distinct CD177^neg and CD177^pos neutrophil subsets. We studied mechanisms controlling subset-restricted CD177 expression in bimodal individuals. CD177^pos, but not CD177^neg neutrophils, produced CD177 protein and mRNA. Haplotype analysis indicated a unique monoallelic CD177 expression pattern, where the offspring stably transcribed either the maternal or paternal allele. Hematopoietic stem cells expressed both CD177 alleles and silenced one copy during neutrophil differentiation. ChIP and reporter assays in HeLa cells with monoallelic CD177 expression showed that methylation reduced reporter activity, whereas demethylation caused biallelic CD177 expression. HeLa cell transfection with c-Jun and c-Fos increased CD177 mRNA. Importantly, CD177^pos human neutrophils, but not CD177^neg neutrophils, showed a euchromatic CD177 promoter, unmethylated CpGs, and c-Jun and c-Fos binding. We describe epigenetic mechanisms explaining the two distinct CD177 neutrophil subsets and a novel monoallelic CD177 expression pattern that does not follow classical random monoallelic expression or imprinting.

Characterization of the CD177 interaction with the ANCA antigen proteinase 3

Proteinase 3 is a serine protease found in neutrophil granules and on the extracellular neutrophil membrane (mPR3). mPR3 is a major antigen for anti-neutrophil cytoplasmic antibodies (PR3-ANCAs), autoantibodies causing fatal autoimmune diseases. In most individuals, a subpopulation of neutrophils also produce CD177, proposed to present additional PR3 on the surface, resulting in CD177^neg/mPR3^low and CD177^pos/mPR3^high neutrophil subsets. A positive correlation has been shown between mPR3 abundance, disease incidence, and clinical outcome. We present here a detailed investigation of the PR3:CD177 complex, verifying the interaction, demonstrating the effect of binding on PR3 proteolytic activity and explaining the accessibility of major PR3-ANCA epitopes. We observed high affinity PR3:CD177 complex formation by surface plasmon resonance. Using flow cytometry and a PR3-specific FRET assay, we found that CD177 binding reduced the proteolytic activity of PR3 in vitro using purified proteins, in neutrophil degranulation supernatants containing wtPR3 and directly on mPR3^high neutrophils and PR3-loaded HEK cells. Finally, CD177^pos/mPR3^high neutrophils showed no migration advantage in vitro or in vivo when migrating from the blood into the oral cavity. We illuminate details of the PR3:CD177 interaction explaining mPR3 membrane orientation and proteolytic activity with relevance to ANCA activation of the distinct mPR3 neutrophil populations.

A sequence-specific polymerase chain reaction method for HNA-2 genotyping: homozygous c.843A>T mutation predicts the absence of CD177

BACKGROUND

Human neutrophil antigen-2 is located on a glycosylphosphatidylinositol-anchored receptor, CD177. Humans not expressing CD177 on their neutrophils may, under defined conditions, form isoantibodies. The genetic background for the absence of CD177 is not fully understood, and genetic screening of patients and donors is currently unavailable. A recent study has documented two mutations associated with CD177 absence: a nonsense polymorphism c.843A>T and a single-base deletion c.1011delG.

STUDY DESIGN AND METHODS

First, we aimed to demonstrate that these newly described mutations are indeed associated with the absence of CD177. DNA fragments from isoimmunized, CD177-negative individuals were sequenced (n = 5). An additional five negative and 10 positive individuals were also analyzed. Second, we aimed to establish a sequence-specific primer (SSP) polymerase chain reaction method for easy and rapid detection of these mutations.

RESULTS

None of 10 CD177-positive individuals, but four of 10 CD177-negative individuals were homozygous for the A>T mutation at Position c.843, including three of five isoimmunized individuals. This finding is supportive for the reported association. Surprisingly, and in contrast to the initial report, c.1011delG was not detected in our cohort. Furthermore, a two-step SSP method for c.843A>G was successfully established.

CONCLUSION

c.843A>T, but not c.1011delG, is associated with the absence of CD177 in a significant number of individuals, including CD177-isoimmunized women. The c.843A>T mutation is easily detectable by a newly established SSP, but screening for this mutation will only provide sufficient evidence for a final diagnosis in case of homozygosity for the c.843T allele.

Heterogeneity of Human Neutrophil CD177 Expression Results from CD177P1 Pseudogene Conversion

Most humans harbor both CD177neg and CD177pos neutrophils but 1-10% of people are CD177null, placing them at risk for formation of anti-neutrophil antibodies that can cause transfusion-related acute lung injury and neonatal alloimmune neutropenia. By deep sequencing the CD177 locus, we catalogued CD177 single nucleotide variants and identified a novel stop codon in CD177null individuals arising from a single base substitution in exon 7. This is not a mutation in CD177 itself, rather the CD177null phenotype arises when exon 7 of CD177 is supplied entirely by the CD177 pseudogene (CD177P1), which appears to have resulted from allelic gene conversion. In CD177 expressing individuals the CD177 locus contains both CD177P1 and CD177 sequences. The proportion of CD177hi neutrophils in the blood is a heritable trait. Abundance of CD177hi neutrophils correlates with homozygosity for CD177 reference allele, while heterozygosity for ectopic CD177P1 gene conversion correlates with increased CD177neg neutrophils, in which both CD177P1 partially incorporated allele and paired intact CD177 allele are transcribed. Human neutrophil heterogeneity for CD177 expression arises by ectopic allelic conversion. Resolution of the genetic basis of CD177null phenotype identifies a method for screening for individuals at risk of CD177 isoimmunisation.

Genetic mechanism of human neutrophil antigen 2 deficiency and expression variations

Human neutrophil antigen 2 (HNA-2) deficiency is a common phenotype as 3-5% humans do not express HNA-2. HNA-2 is coded by CD177 gene that associates with human myeloproliferative disorders. HNA-2 deficient individuals are prone to produce HNA-2 alloantibodies that cause a number of disorders including transfusion-related acute lung injury and immune neutropenia. In addition, the percentages of HNA-2 positive neutrophils vary significantly among individuals and HNA-2 expression variations play a role in human diseases such as myelodysplastic syndrome, chronic myelogenous leukemia, and gastric cancer. The underlying genetic mechanism of HNA-2 deficiency and expression variations has remained a mystery. In this study, we identified a novel CD177 nonsense single nucleotide polymorphism (SNP 829A>T) that creates a stop codon within the CD177 coding region. We found that all 829TT homozygous individuals were HNA-2 deficient. In addition, the SNP 829A>T genotypes were significantly associated with the percentage of HNA-2 positive neutrophils. Transfection experiments confirmed that HNA-2 expression was absent on cells expressing the CD177 SNP 829T allele. Our data clearly demonstrate that the CD177 SNP 829A>T is the primary genetic determinant for HNA-2 deficiency and expression variations. The mechanistic delineation of HNA-2 genetics will enable the development of genetic tests for diagnosis and prognosis of HNA-2-related human diseases.

Geno- and phenotyping of human neutrophil antigens

For typing of human neutrophil antigens (HNA) usually genotyping techniques are used, except for HNA-2, which-due to a gene expression defect-requires phenotyping. For genotyping, several techniques have been described. Most reference laboratories use variations of the polymerase chain reaction (PCR) for antigen typing which showed good results in international quality assessment exercises. The granulocyte immunofluorescence test has been the gold standard technique for phenotyping for all HNA antigens except for HNA-3a and -3b phenotyping. The expression of the latter antigens on neutrophils is often better shown by the use of the granulocyte agglutination test.

Differential expression of granulopoiesis related genes in neutrophil subsets distinguished by membrane expression of CD177

Objective

Differential gene expression in CD177⁺ and CD177⁻ neutrophils was investigated, in order to detect possible differences in neutrophil function which could be related to the pathogenesis of ANCA-associated Vasculitides (AAV).

Methods

Neutrophils were isolated from healthy controls (HC) with high, negative or bimodal CD177 expression, and sorted into CD177⁺ and CD177⁻ subpopulations. Total RNA was screened for expression of 24,000 probes with Illumina Ref-8 Beadchips. Genes showing differential expression between CD177⁺ and CD177⁻ subsets in microarray analysis were re-assessed using quantitative-PCR. CD177 expression on neutrophil precursors in bone marrow was analyzed using quantitative PCR and flowcytometry.

Results

The proportion of CD177⁺ cells increased during neutrophil maturation in bone marrow. Fold change analysis of gene expression profile of sorted CD177⁺ and CD177⁻ neutrophils resulted in 14 genes with fold change (fc) >3 difference in expression. Interestingly, 10 of these genes have been reported to change significantly in expression during neutrophil maturation, and most of these genes were granule protein (GP) coding genes. mRNA expression levels measured by RT-PCR of a number of these GP, and of PR3 and MPO were higher in the CD177⁻ neutrophil subset in HC, however, particular granule protein amounts were comparable between CD177⁺ and CD177⁻ neutrophil subsets. AAV patients had higher amounts of CD177⁺ neutrophils, but contrary to neutrophils from HC expression of GP-genes was increased, possibly due to activation.

Conclusion

The neutrophil population can be distinguished by membrane expression of CD177 into subsets that are different in expression of GP mRNA but not in GP protein production. GP gene expression is also elevated in AAV patients, which is not explained by skewed distribution of CD177⁺ and CD177⁻ subsets but may be associated with neutrophil activation during on-going inflammation.

Molecular typing of human platelet and neutrophil antigens (HPA and HNA)

Genotyping is an important tool in the diagnosis of disorders involving allo-immunisation to antigens present on the membranes of platelets and neutrophils. To date 28 human platelet antigens (HPAs) have been indentified on six polymorphic glycoproteins on the surface of platelets. Antibodies against HPAs play a role in foetal and neonatal alloimmune thrombocytopenia (FNAIT), post-transfusion purpura (PTP) and refractoriness to donor platelets. The 11 human neutrophil antigens (HNAs) described to date have been indentified on five polymorphic proteins on the surface of granulocytes. Antibodies to HNAs are implicated with foetal and neonatal alloimmune neutropenia (FNAIN), autoimmune neutropenia (AIN) and transfusion related acute lung injury (TRALI). In this report, we will review the molecular basis and techniques currently available for the genotyping of human platelet and neutrophil antigens.

Genotyping of human neutrophil antigens by polymerase chain reaction sequence-based typing

BACKGROUND

Genotyping for human neutrophil antigen (HNA) systems is required in the investigation of disorders involving alloimmunisation to HNA. We established a polymerase chain reaction sequence-based typing method for genotyping HNA and determined the genotype and allele frequencies of HNA in the Zhejiang Han population of China.

MATERIALS AND METHODS

Four hundred, healthy unrelated Zhejiang Han individuals were recruited. Specific primers for HNA were designed and the polymerase chain reaction amplification conditions were optimised. Amplification amplicons were purified with enzyme digestion and then sequenced.

RESULTS

The frequencies of the FCGR3B*01 and FCGR3B*02 alleles were 0.613 and 0.387; no FCGR3B*03 allele was found. The frequencies of the SLC44A2*1 and SLC44A2*2 alleles were 0.654 and 0.346, respectively, while the frequencies of the ITGAL*1 (HNA-5a) and ITGAL*2 (HNA-5b) alleles were 0.896 and 0.104. Only ITGAM*1 (HNA-4a) allele was found in this study. Six single nucleotide polymorphisms were confirmed on sequenced regions separate from HNA polymorphisms, including FCGR3B (IVS3+39G>A and IVS3+52G>A), CD177(172A>G), SLC44A2 (IVS5-44A>G and IVS7-15T>C) and ITGAM (IVS3+118T>C).

DISCUSSION

The polymerase chain reaction sequence-based typing method for genotyping HNA is reliable. These data of HNA alleles frequencies could contribute to the analysis of alloimmunisation to HNA in China.

CD177 expression on neutrophils: in search of a clonal assay for myeloid neoplasia by flow cytometry

OBJECTIVES

To determine whether the fraction of CD177+ neutrophils might be altered in clonal myeloid disorders, similar to the skewed κ/λ ratio for B-cell lymphomas, and could be used to identify myeloid neoplasms.

METHODS

Blood and bone marrow samples were evaluated for the fraction of CD177+ neutrophils by flow cytometry.

RESULTS

Skewed high neutrophil CD177(%) was not associated with neoplasia, but skewed low neutrophil CD177(%) was highly correlated with clonal myeloid disorders at values less than 40%. Specificity of low neutrophil CD177(%) for clonal myeloid disorders was 87% with a 40% cutoff and 95% with a 30% cutoff. Findings were most pronounced for myelodysplasia, with 52% (11/21) containing fewer than 40% CD177+ neutrophils. Specificity was also suggested by normalization of neutrophil CD177(%) in four patients who reached morphologic remission after therapy for myelodysplasia or acute leukemia.

CONCLUSIONS

Skewed low neutrophil CD177(%) is highly associated with clonal myeloid disorders, particularly myelodysplasia, and may be useful for detecting clonal myeloid disorders.

External quality assessment in molecular immunohematology: the INSTAND proficiency test program

BACKGROUND

Genotyping for red blood cell (RBC), platelet (PLT), and granulocyte antigens is a new tool for clinical pathology, transfusion medicine services, and blood banks. Proficiency in laboratory tests can be established by external quality assessments (EQAs), which are required for clinical application in many health care systems. There are few EQAs for molecular immunohematology.

STUDY DESIGN AND METHODS

We analyzed the participation and pass rates in an EQA for RBC, PLT, and granulocyte antigens. This EQA was distributed by INSTAND, a large nonprofit provider of proficiency tests, twice per year since Fall 2006 as EQA Number 235 Immunohematology A (molecular diagnostic). The coordinators defined at the outset which alleles are mandatory for detection.

RESULTS

The number of participants steadily increased from 51 to 73 per proficiency by Fall 2012. More than 60 institutions utilized this EQA at least once a year. Approximately 80% of them participated in RBC, 68% in PLT, and 22% in granulocyte systems. With the exceptions of RHD (82%) and granulocytes (85%), pass rates exceeded 93%. While the pass rate increased for granulocyte and decreased for the ABO system, the pass rates for the other systems changed little over 6½ years.

CONCLUSIONS

The INSTAND proficiency test program was regularly used for EQA by many institutions, particularly in Central Europe. While the technical standards and pass rates in the participating laboratories were high, there has been little improvement in pass rates since 2006.

External quality assessment of human neutrophil antigen (HNA)-specific antibody detection and HNA genotyping from 2000 to 2012

Since 2000, Quality Assurance (QA) exercises for the detection and identification of granulocyte antibodies and DNA typing for human neutrophil antigens (HNA) have been distributed within the International Granulocyte Immunobiology Workshops, which are linked to International Society of Blood Transfusion. The exercises were standardised at the outset to enable laboratory performance to be monitored. Between 2000 and 2012, nine exercises were distributed to 20 laboratories. Overall, 45 examples of 42 unique samples containing defined granulocyte reactive antibodies were distributed for serological analysis together with 20 samples for HNA genotyping. The level of satisfactory serological performance was initially set at 50% and later increased to 70%, while the 'cut-off' for HNA genotyping was set at 100% after 2008. Failure to achieve the minimum score in the QA exercises in consecutive years resulted in temporary exclusion. In 2000, the 15 participating laboratories had a mean score of 56.1% for serological analysis and 13 laboratories attempted HNA-1a and -1b genotyping, while 11 attempted HNA-1c typing. Steady improvements in proficiency for serological testing and HNA typing occurred in subsequent exercises. In 2012, the mean score for serology was 88.5% and 12/13 laboratories scored 100% for HNA-1a, -1b, -1c, -3a, -3b, -4a, -4bw, -5a and -5bw genotyping. These QA exercises have provided an invaluable tool to monitor and improve the standard of granulocyte immunology investigations for participating laboratories, thereby enhancing performance for both clinical investigations and donor screening programmes to reduce the incidence of TRALI.

Determination of human neutrophil antigen-1, -3, -4 and -5 allele frequencies in English Caucasoid blood donors using a multiplex fluorescent DNA-based assay

BACKGROUND AND OBJECTIVES

A number of DNA-based methods to genotype the alleles coding for HNA have been described, but all require the separate amplification and analysis of each allele. The aim was to develop a DNA-based method for simultaneous detection of HNA-1, HNA-3, HNA-4 and HNA-5 alleles.

MATERIALS AND METHODS

An allele-specific primer extension method was used in combination with magnetic beads from Luminex technology. PCR-sequence-specific primers (SSP) was used to resolve the presence of the HNA-1b allele in samples assigned by the Luminex bead assay as HNA-1a/-1b/-1c or HNA-1b/-1c. HNA allele frequencies were determined in a panel of 140 randomly selected English Caucasoid blood donors.

RESULTS

HNA allelic types were compared with historical results, and 100% concordance was found. Only eight of the 97 samples used in the validation required additional testing by PCR-SSP. Allele frequencies were determined in the blood donor population as follows: 0·318 for HNA-1a, 0·668 for HNA-1b, 0·014 for HNA-1c, 0·768 for HNA-3a, 0·232 for HNA-3b, 0·882 for HNA-4a, 0·118 for HNA-4b, 0·736 for HNA-5a and 0·264 for HNA-5b.

CONCLUSION

A multiplex Luminex bead assay for the simultaneous detection of HNA-1, HNA-3, HNA-4 and HNA-5 alleles is described that enables rapid typing of donors to support HNA alloimmunized patients who require HNA-compatible blood products.

Proteinase 3 contributes to transendothelial migration of NB1-positive neutrophils

Neutrophil transmigration requires the localization of neutrophils to endothelial cell junctions, in which receptor-ligand interactions and the action of serine proteases promote leukocyte diapedesis. NB1 (CD177) is a neutrophil-expressed surface molecule that has been reported to bind proteinase 3 (PR3), a serine protease released from activated neutrophils. PR3 has demonstrated proteolytic activity on a number of substrates, including extracellular matrix proteins, although its role in neutrophil transmigration is unknown. Recently, NB1 has been shown to be a heterophilic binding partner for the endothelial cell junctional protein, PECAM-1. Disrupting the interaction between NB1 and PECAM-1 significantly inhibits neutrophil transendothelial cell migration on endothelial cell monolayers. Because NB1 interacts with endothelial cell PECAM-1 at cell junctions where transmigration occurs, we considered that NB1-PR3 interactions may play a role in aiding neutrophil diapedesis. Blocking Abs targeting the heterophilic binding domain of PECAM-1 significantly inhibited transmigration of NB1-positive neutrophils through IL-1β-stimulated endothelial cell monolayers. PR3 expression and activity were significantly increased on NB1-positive neutrophils following transmigration, whereas neutrophils lacking NB1 demonstrated no increase in PR3. Finally, using selective serine protease inhibitors, we determined that PR3 activity facilitated transmigration of NB1-positive neutrophils under both static and flow conditions. These data demonstrate that PR3 contributes in the selective recruitment of the NB1-positive neutrophil population.

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.

Human neutrophil alloantigen-1a, -1b, -2, -3a and -4a frequencies in Brazilians

Human neutrophil reactive antibodies may cause clinical disorders such as transfusion-related acute lung injury, febrile transfusion reactions, alloimmune neonatal neutropenia, immune neutropenia after stem cell transplantation, refractoriness to granulocyte transfusion, drug-induced neutropenia and autoimmune neutropenia. Using the granulocyte immunofluorescence test by flow cytometry, the phenotypic frequencies of the human neutrophil alloantigens (HNA)-1a, -1b, -2, -3a and -4a were determined in 100 healthy Brazilian persons. Neutrophils were separated from blood samples by sedimentation, centrifugated and incubated with HNA-specific alloantibody plus fluorescein isothiocyanate-labeled F(ab')(2) fragments of anti-human IgG. The results showed that the phenotype frequencies of HNA-1a, -1b, -2a, -3a and -4a were 65%, 83%, 97%, 95% and 94%, respectively. We detected that neutrophils from 17% of Brazilians typed positive only with anti-HNA-1a (HNA-1a/a), 35% only with anti-HNA-1b (HNA-1b/b) and 48% reacted with both antibodies (HNA-1a/b). The frequencies found for HNA-1a and -1b were quite similar to that reported among Africans and American-Africans, but different from those found in Japanese and Chinese. In addition, our data showed that the frequencies of HNA-2, -3a and -4a in Brazilians were comparable with those observed in Caucasians. The determination of HNAs frequencies among populations with distinct racial backgrounds is important not only for anthropological reasons, but also for neonatal typing in suspected cases of alloimmune neutropenia or when patients are severely neutropenic.

Human neutrophil alloantigens systems

Neutrophil alloantigens are involved in a variety of clinical conditions including immune neutropenias, transfusion-related acute lung injury (TRALI), refractoriness to granulocyte transfusions and febrile transfusion reactions. In the last decade, considerable progress has been made in the characterization of the implicated antigens. Currently, seven antigens are assigned to five human neutrophil antigen (HNA) systems. The HNA-1a, HNA-1b and HNA-1c antigens have been identified as polymorphic forms of the neutrophil Fcγ receptor IIIb (CD16b), encoded by three alleles. Recently, the primary structure of the HNA-2a antigen was elucidated and the HNA-2a-bearing glycoprotein was identified as a member of the Ly-6/uPAR superfamily, which has been clustered as CD177. The HNA-3a antigen is located on a 70-95 kDa glycoprotein; however, its molecular basis is still unknown. Finally, the HNA-4a and HNA-5a antigens were found to be caused by single nucleotide mutations in the αM (CD11b) and αL (CD11a) subunits of the leucocyte adhesion molecules (β2 integrins). Molecular and biochemical characterization of neutrophil antigenshave expanded our diagnostic tools by the introduction of genotyping techniques and immunoassays for antibody identification. Further studies in the field of neutrophil immunology will facilitate the prevention and management of transfusion reactions and immune diseases caused by neutrophil antibodies.

Molecular studies reveal that A134T, G156A and G1333A SNPs in the CD177 gene are associated with atypical expression of human neutrophil antigen-2

BACKGROUND AND OBJECTIVES

The human neutrophil antigen-2 (HNA-2) is expressed on a subpopulation of neutrophils as most subjects present a negative plus a positive HNA-2 population of neutrophils. The number of neutrophils expressing HNA-2 is variable and may increase in pregnancy, infections, myeloproliferative disorders and after G-CSF. This study investigated the presence of polymorphisms in the gene encoding HNA-2 (CD177) in individuals presenting different patterns of antigen expression and determined the association of single nucleotide polymorphisms (SNPs) with the heterogeneous HNA-2 expression.

MATERIALS AND METHODS

Flow cytometry was employed to analyse the HNA-2 expression on neutrophils from 135 healthy subjects using two monoclonal antibodies (TAG4, 7D8). Sequencing reactions were performed on subjects whose antigen expression was low (< or = 50%), high (> or = 80%) or atypical (a nonreactive population plus two distinct positive cell populations).

RESULTS

Five SNPs were detected, two of them (A793C, G1084A) were related to a low expression of HNA-2 (P = 0.031 and P = 0.004). Atypical antigen expression was observed in 5.9% (8/135) of the individuals, three nonpregnant women and five men. In these cases, the cDNA sequences revealed three SNPs (A134T, G156A and G1333A) strongly related to this atypical HNA-2 expression (P = 0.004, P = 0.006 and P < 0.0001, respectively).

CONCLUSIONS

Our data show that polymorphisms in the CD177 are associated with variations in the HNA-2 expression and may be the cause of atypical expressions.

Neutrophil-specific antigen HNA-2a, NB1 glycoprotein, and CD177

PURPOSE OF REVIEW

Several advances have been made in characterization of the molecule that carries human neutrophil antigen (HNA)-2a, NB1 glycoprotein, the gene that encodes NB1 glycoprotein, CD177, and the role of antibodies to HNA-2a in transfusion reactions.

RECENT FINDINGS

NB1 glycoprotein binds to the endothelial cell adhesion molecule, platelet endothelial cell adhesion molecule-1 (PECAM-1), and participates in neutrophil transmigration. The overexpression of neutrophil CD177 mRNA has become a useful, but nonspecific biomarker of myeloproliferative diseases, especially polycythemia vera. CD177 mRNA overexpression is also a biomarker of a subset of patients with essential thrombocythemia who are at increased risk of thromboembolic complications. In patients with myeloproliferative disorders CD177 mRNA overexpression is secondary to a gain-of-function mutation in JAK2, JAK2 V617F. NB1 glycoprotein is co-localized on neutrophil plasma membranes with proteinase 3 and a complex of NB1 glycoprotein and proteinase 3 may initiate the activation of neutrophils by antineutrophil cytoplasmic antibodies in patients with Wegener's granulomatosis. The inadvertent transfusion of antibodies to HNA-2a with blood components frequently causes pulmonary transfusion reactions.

SUMMARY

The expression of CD177 is an important biomarker of myeloproliferative diseases, NB1 glycoprotein is a ligand for PECAM-1 and it may have a role in Wegener's granulomatosis, and antibodies to HNA-2a frequently cause pulmonary transfusion reactions.

Human neutrophil alloantigens

OBJECTIVE

This review describes alloantigens currently listed in the human neutrophil alloantigen (HNA) system.

MATERIAL AND METHODS

Review of the literature.

RESULTS

Neutrophil antigens are implicated in a variety of clinical conditions including neonatal immune neutropenia, transfusion-related acute lung injury, refractoriness to granulocyte transfusions, febrile transfusion reactions, immune neutropenia after bone marrow transplantation, autoimmune neutropenia and drug-induced immune neutropenia. Seven antigens have been listed in the HNA system that are assigned to five antigen groups. Six antigens have been characterized biochemically and molecularly so that their primary structure is now known. As shown by regularly performed international granulocyte immunology workshops, a combination of granulocyte agglutination and immunofluorescence tests together with a panel of typed cells is currently the best means of detection.

CONCLUSIONS

Most of the HNA antigens have been well-characterized so that HNA typing as well as the detection of the corresponding antibodies are now reliably possible. This will improve diagnostics of neutrophil antibody-mediated clinical conditions as well as the prevention of transfusion-related acute lung injury.

Leukocyte antigen and antibody detection assays: tools for assessing and preventing pulmonary transfusion reactions

Antibodies to neutrophil and HLA antigens can cause pulmonary transfusion reactions, and in some cases acute lung injury. When evaluating cases of pulmonary transfusion reactions, it is often necessary to test donors for neutrophil and HLA antibodies and also type the recipient for neutrophil and HLA antigens. A variety of enzyme-linked immunosorbent assay (ELISA) and flow cytometry-based solid phase assays are available to test for HLA class I and class II antibodies, but not neutrophil antibodies. Screening for neutrophil antibodies requires the preparation of panels of fresh neutrophils and testing in agglutination, immunofluorescence, or flow cytometry assays. Genotyping of HLA class I and II antigens is performed with a variety of sequence-specific primers, sequenced-specific oligonucleotide probe, and sequence-based typing assays. Neutrophil-specific antigens HNA-1a, -1b, -1c, -4a, and -5a can be genotyped, but not HNA-2a or -3a. Phenotyping of HNA-2a can be performed with CD177 monoclonal antibodies, but the gene encoding HNA-3a has not been identified, and the genomic basis for the HNA-2a-negative phenotype is not known. In conclusion, patients and donors involved with pulmonary transfusion reactions can be quickly typed for HLA antigens and tested for HLA antibodies, but testing for neutrophil antibodies and antigens requires the use of a reference laboratory.

Establishment of cell lines stably expressing HNA-1a, -1b, and -2a antigen with low background reactivity in flow cytometric analysis

BACKGROUND

Antibodies to neutrophil antigens have been implicated in neonatal alloimmune neutropenia, autoimmune neutropenia, and transfusion-related acute lung injury. Most often, neutrophil-specific antibodies are directed toward human neutrophil antigen (HNA)-1 (Fcgamma receptor 3b) and HNA-2a (CD177) in these disorders.

STUDY DESIGN AND METHODS

To detect the alloantibodies in the serum samples, a panel of cell lines was established in which the HNA-1a, HNA-1b (polymorphisms of HNA-1), or HNA-2a gene was transduced with a retrovirus vector to confer stable transgene expression in K562 cells that exhibited low background reactivity to human serum samples obtained from healthy donors in flow cytometric analysis.

RESULTS

It was shown that several well-characterized human serum samples containing antibodies against HNA-1a, -1b, and -2a were unambiguously identified by the established panel cell lines and observed a lower background reactivity and longer shelf life of the K562 panel cell lines compared with isolated neutrophils, which have been used for the cell panel to identify antibodies against HNA in human serum samples.

CONCLUSION

These results indicate that the K562 panel cell lines provide a good panel for detecting HNA-reactive neutrophil antibodies in human serum samples.

NB1 mediates surface expression of the ANCA antigen proteinase 3 on human neutrophils

Antineutrophil cytoplasmic antibodies (ANCAs) with specificity for proteinase 3 (PR3) are central to a form of ANCA-associated vasculitis. Membrane PR3 (mPR3) is expressed only on a subset of neutrophils. The aim of this study was to determine the mechanism of PR3 surface expression on human neutrophils. Neutrophils were isolated from patients and healthy controls, and hematopoietic stem cells from cord blood served as a model of neutrophil differentiation. Surface expression was analyzed by flow cytometry and confocal microscopy, and proteins were analyzed by Western blot experiments. Neutrophil subsets were separated by magnetic cell sorting. Transfection experiments were carried out in HEK293 and HL60 cell lines. Using neutrophils from healthy donors, patients with vasculitis, and neutrophilic differentiated stem cells we found that mPR3 display was restricted to cells expressing neutrophil glycoprotein NB1, a glycosylphosphatidylinositol (GPI)–linked surface receptor. mPR3 expression was decreased by enzymatic removal of GPI anchors from cell membranes and was absent in a patient with paroxysmal nocturnal hemoglobinuria. PR3 and NB1 coimmunoprecipitated from and colocalized on the neutrophil plasma membrane. Transfection with NB1 resulted in specific PR3 surface binding in different cell types. We conclude that PR3 membrane expression on neutrophils is mediated by the NB1 receptor.

CD177: A member of the Ly-6 gene superfamily involved with neutrophil proliferation and polycythemia vera

Genes in the Leukocyte Antigen 6 (Ly-6) superfamily encode glycosyl-phosphatidylinositol (GPI) anchored glycoproteins (gp) with conserved domains of 70 to 100 amino acids and 8 to 10 cysteine residues. Murine Ly-6 genes encode important lymphocyte and hematopoietic stem cell antigens. Recently, a new member of the human Ly-6 gene superfamily has been described, CD177. CD177 is polymorphic and has at least two alleles, PRV-1 and NB1. CD177 was first described as PRV-1, a gene that is overexpressed in neutrophils from approximately 95% of patients with polycythemia vera and from about half of patients with essential thrombocythemia. CD177 encodes NB1 gp, a 58–64 kD GPI gp that is expressed by neutrophils and neutrophil precursors. NB1 gp carries Human Neutrophil Antigen (HNA)-2a. Investigators working to identify the gene encoding NB1 gp called the CD177 allele they described NB1. NB1 gp is unusual in that neutrophils from some healthy people lack the NB1 gp completely and in most people NB1 gp is expressed by a subpopulation of neutrophils. The function of NB1 gp and the role of CD177 in the pathogenesis and clinical course of polycythemia vera and essential thrombocythemia are not yet known. However, measuring neutrophil CD177 mRNA levels has become an important marker for diagnosing the myeloproliferative disorders polycythemia vera and essential thrombocythemia.

CD177 polymorphisms: correlation between high-frequency single nucleotide polymorphisms and neutrophil surface protein expression

BACKGROUND

Human neutrophil antigen-2a (NB1) is located on NB1 glycoprotein, which is expressed on subpopulations of neutrophils. PRV-1 is a gene that is over-expressed in neutrophils from patients with polycythemia rubra vera. The gene encoding NB1 differs from PRV-1 at four nucleotides. The purpose of this study was to determine if PRV-1 and NB1 are alleles of the same gene or two separate genes; and, moreover, if they are alleles, to explore potential correlations to NB1 glycoprotein expression.

STUDY DESIGN AND METHODS

Primer pairs were used to amplify WBC DNA in the regions surrounding the four NB1 polymorphic sites. The four resulting amplicons were sequenced. The size of the neutrophil population in each donor that stained brightly with CD177 antibody was assessed by flow cytometry.

RESULTS

If PRV-1 and NB1 are separate genes, then all people should be heterozygous for the PRV-1/NB1 polymorphisms. Because 11 of 23 donors were homozygous for PRV-1 polymorphisms at all four sites, PRV-1 and NB1 are alleles of the same gene, CD177. When the sequenced exons were compared with PRV-1, 13 single nucleotide polymorphisms (SNPs) that result in amino acid changes were found. The G42C NB1 polymorphism, found in 10 donors, was the most common SNP. The size of the CD177 bright-staining neutrophil population was greater in 42C/C donors than in 42G/G donors (66 +/- 20% vs. 41 +/- 21%, p = 0.004).

CONCLUSIONS

PRV-1 and NB1 are alleles of the polymorphic gene CD177. The most common SNP in bp 42 predicted an amino acid change that may have an effect on protein expression.

Lack of NB1 GP (CD177/HNA-2a) gene transcription in NB1 GP- neutrophils from NB1 GP-expressing individuals and association of low expression with NB1 gene polymorphisms

The human neutrophil NB1 glycoprotein (NB1 GP, HNA-2a, CD177) has gained clinical importance for being involved in pulmonary transfusion reactions and immune neutropenias. The NB1 GP shows the unique feature of being expressed only on a neutrophil subpopulation. Recently, we identified splicing defects responsible for an NB1 GP deficiency. In this study, we have investigated the molecular basis of the heterogeneous expression of NB1 GP by separating the 2 neutrophil subpopulations using immunofluorescence followed by single-cell picking or by fluorescence-activated cell sorter. We found a lack of NB1 mRNA in the NB1 GP- cells that remained constant even after granulocyte colony-stimulating factor (G-CSF) administration. Comparing the cDNA sequences of donors with a large (> 60%) and those with a small (< 40%) NB1 GP-expressing subpopulation, we found 6 polymorphisms. Of the 6, 3 were significantly associated with a small NB1 GP-expressing subpopulation, indicating a genetic basis for NB1 GP nonexpression.

Expression of human neutrophil antigen-2a (NB1) is increased in pregnancy

BACKGROUND

The expression of human neutrophil antigen-2a (HNA-2a) or NB1 is highly variable. This study investigated variations in neutrophil expression of HNA-2a by comparing the expression of epitopes recognized by three HNA-2a-specific CD177 antibodies among healthy adults and pregnant women.

STUDY DESIGN AND METHODS

Flow cytometry was used to compare the neutrophil reactions of three CD177 antibodies (MEM-166, TAG4, and 7D8) among 52 healthy adults. Because HNA-2a expression is greater in women than men, neutrophils were studied from 21 women early in pregnancy and 23 women late in pregnancy.

RESULTS

All three CD177 antibodies reacted with two populations of neutrophils: a brightly staining population and a dimly staining population. Among the 52 healthy adults, there was no difference in the mean size of the brightly reactive population of neutrophils recognized by each antibody (46 +/- 23% for MEM-166, 49 +/- 23% for TAG4, and 49 +/- 23% for 7D8), and all three antibodies were specific for HNA-2a. For all three antibodies the size of the antigen bright neutrophil population was greater on neutrophils collected both early and late in pregnancy than in healthy adults. There was no difference in the size of the antigen bright population among neutrophils tested early and late in pregnancy.

CONCLUSION

HNA-2a antigen expression increases in pregnancy. Some of the variations in neutrophil expression of HNA-2a among individuals is likely due to differences in gene regulation or differences in post-translational protein modifications rather than gene polymorphisms.

Molecular nature of antigens implicated in immune neutropenias

Granulocyte (neutrophil) antibodies can cause autoimmune neutropenia, drug-induced neutropenia, immune neutropenia after bone marrow transplantation, neonatal immune neutropenia, refractoriness to granulocyte transfusions as well as febrile and pulmonary transfusion reactions. In the last decade, considerable progress has been made in the characterization of the implicated antigens. In 1998, the Granulocyte Antigen Working Party of the ISBT introduced a new nomenclature for human neutrophil alloantigens (HNA), which is based on the antigens' glycoprotein location. In the HNA nomenclature the immunogenic (glyco-) proteins are indicated by arabic numbers followed by a letter of the alphabet which identify the (glyco-) proteins' polymorphisms, i.e. the specific antigens. Currently, seven HNA antigens are assigned to five systems. The HNA-1a, HNA-lb and HNA-1c antigens, the former NA1, NA2, and SH antigens, have been identified as polymorphic forms of the neutrophil Fc gamma receptor IIIb (CD16b) encoded by three alleles. Recently, we could elucidate the primary structure of the HNA-2a antigen, the former NB1. We could identify the HNA-2a-bearing glycoprotein as a novel member of the Ly-6/uPAR superfamily which has been clustered meanwhile as CD177. The HNA-3a antigen, the former 5b, is located on a 70-95 kDa glycoprotein. However, its molecular basis is still unknown. Finally, the HNA-4a and HNA-5a antigens, the former MART and OND, were found to be caused by single nucleotide mutations in the alphaM (CD11b) and alphaL (CD11a) subunits of the leucocyte adhesion molecules (beta2 integrins). The glycoproteins CD11b, CD16b, and CD177 have been found to be also frequent targets of autoantibodies - approximately 30% of neutrophil autoantibodies are directed against CD16b. Characterization of granulocyte antigens have expanded our diagnostic tools by the introduction of genotyping techniques and immunoassays for antibody identification. In addition, it allowed new insights in the pathophysiology of immune neutropenias and transfusion reactions. Ongoing studies will further improve the prevention and management of granulocyte antibody-mediated diseases.