Three novel β3 domain-deletion peptides for the sensitive and specific detection of HPA-4 and six low frequency β3-HPA antibodies

Summary.  Background:  Antibodies against human platelet antigens (HPA) are clinically important in fetal–maternal alloimmune thrombocytopenia, refractoriness to platelet transfusions and post-transfusion purpura. Of the 16 HPAs, nine are located on the β3 subunit of the αIIbβ3 integrin. Antibody detection is generally based on platelet-derived αIIbβ3 from HPA-genotyped donors. Recombinant allelic β3 peptides, expressed at high levels would improve consistency in antibody detection, but the expression of soluble and monomeric integrins expressing complex dependent epitopes has previously proved challenging. Objectives:  We aimed to generate three recombinant β3 peptides for the detection of antibodies against HPA-4, HPA-8bw and five of the six remaining low frequency β3 alloantigens. Methods:  The removal of the specificity-determining loop from the βA domain and fusion of truncated β3 to calmodulin was exploited to obtain expression of monomeric protein. Using site-directed mutagenesis, the mutations for HPA-4b and HPA-8bw were introduced in the ITGB3*001 haplotype. A third peptide for the detection of antibodies against HPA coded by non-synonymous single nucleotide polymorphisms of low frequency was generated by the introduction of five mutations forming the basis of HPA-6bw, -7bw, -10bw, -11bw, and -16bw antigens. Results:  Reactivity of the three peptides with β3-specific murine monoclonal antibodies and human HPA-1a phage antibodies confirmed the structural integrity of the recombinant fragments, and reactivity with a unique panel of polyclonal anti-HPA sera confirmed expression of the relevant HPA epitopes. Conclusions:  These data demonstrate that β3 integrin domain-deletion fragments are suitable molecular targets for HPA antibody detection.     

Immunization against a low-frequency human platelet alloantigen in fetal alloimmune thrombocytopenia is not a single event: characterization by the combined use of reference DNA and novel allele-specific cell lines expressing recombinant antigens

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by maternal immunization against a fetal platelet (PLT) alloantigen. In cases of FNAIT attributed to low-frequency PLT alloantigens, the laboratory diagnosis is often hampered by the lack of adequate PLTs. STUDY DESIGN AND METHODS: Three families with maternal immunization against fetal PLT antigens were analyzed. In Family 1, previous immunization of another female or woman has been observed. In Families 2 and 3, newborns presented with the typical clinical picture of FNAIT. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing with reference to DNA from Epstein-Barr virus-transformed B-lymphoblastoid cell lines. Antibodies were characterized by glycoprotein (GP)-specific immunoassay with a panel of stable Chinese hamster ovary cell lines expressing low-frequency alloantigens. RESULTS: In three families, maternal immunization associated with the low-frequency alloantigens human PLT antigen (HPA)-8bw (Sra), HPA-11bw (Groa), and HPA-13bw (Sita) was identified. Maternal serum samples showed positive reactions in an antigen capture assay with cell lines carrying recombinant GP IIb/IIIa (HPA-8bw and -11bw) or GPIa/IIa (HPA-13bw), respectively. These results could be confirmed by genotyping analysis of fathers and newborns. CONCLUSION: This study demonstrates that cases of FNAIT attributed to low-frequency PLT alloantigens cannot be regarded as single events. The availability of reference DNA and cell lines expressing recombinant PLT alloantigens can facilitate their identification.     

Management and outcome of 200 cases of fetomaternal alloimmune thrombocytopenia

BACKGROUND: Fetomaternal alloimmune thrombocytopenia (FMAIT) is the commonest cause of severe thrombocytopenia in term neonates but its management remains controversial. STUDY DESIGN AND METHODS: A 7-year prospective observational study of 200 cases of FMAIT evaluated the relationship between human platelet antigen (HPA) antibody specificity, clinical presentation, morbidity, mortality, and therapeutic interventions in the antenatal and postnatal period, with long-term follow-up of neonates with intracranial hemorrhage (ICH). RESULTS: In 1148 referrals for FMAIT, HPA antibodies were confirmed in 200 (17%). The commonest specificities were anti-HPA-1a, 150 (75%); anti-HPA-5b, 31 (15.5%); and anti-HPA-15b, 8 (4%). Of 123 (62%) cases (two sets of twins) with no previous history of FMAIT, intrauterine deaths occurred in 5: anti-HPA-1a alone, 3; in combination with anti-HPA-5b, 1; and anti-HPA-15b, 1. Of the 120 live neonates, 103 had severe thrombocytopenia and 17 (14%) developed ICH (anti-HPA-1a, 13; anti-HPA-5b, 3; anti-HPA-15b, 1). Postnatal care varied widely with 37 percent of neonates receiving random rather than HPA-1a and -5b-negative platelets. Of the remaining 77 cases with a history of FMAIT, 40 received intrauterine transfusions. Six (15%) of these fetuses died in utero and an additional 2 developed ICH postnatally. Of the 19 children with ICH, 1 (anti-HPA-15b) died on Day +1, and neurologic sequelae persist in 13 (mean follow-up, 2.5 years). CONCLUSION: HPA-1a antibodies are most commonly implicated in severe thrombocytopenia but HPA-5b and HPA-15b antibodies can also result in poor outcome. Postnatal transfusion management is extremely variable, and fetal transfusions are associated with significant morbidity and mortality.     

PCR with sequence-specific primer-based simultaneous genotyping of human platelet antigen-1 to -13w

BACKGROUND: Accurate human platelet antigen (HPA) typing is important for patients with diagnosis of alloimmune thrombocytopenic syndromes and provision of HPA-matched blood components for these patients. STUDY DESIGN AND METHODS: Thirteen sequence-specific primers (SSPs) designed on the basis of known published polymorphisms for HPA-1 to HPA-13w, respectively, were employed for simultaneous HPA genotyping. All PCR amplifications were carried out with identical cycling conditions in 96-well plates containing primer mixtures. A total of 300 blood samples from unrelated volunteer donors in Taiwan were included in the study. RESULTS: All primers had specific amplification products. The typing results were available within 4 hours each time for up to four blood samples tested. Among the 13 HPAs, HPA-3 had the greatest heterozygosity with a gene frequency of 0.3267, 0.4967, and 0.1767 for HPA-3a/HPA-3a, HPA-3a/HPA-3b, and HPA-3b/HPA3-b, respectively. For the remaining 12 HPAs, the predominance of a/a homozygosity was noted for HPA-1, -2, -4, -5, and -6, with a frequency ranging from 0.9200 to 0.9967. The frequency of a/a homozygosity was 1.0000 for HPA-7w to -13w, except for HPA-10w, for which one case was observed to be HPA-10aw/HPA-10bw heterozygous. Excluding HPA-3, b/b homozygosity was noted in only one case (HPA-6b/HPA-6b). The prevalence rates of HPA-1 to -13w in this study were consistent with previous reports using different methods. CONCLUSION: An extended, streamlined PCR-SSP protocol for simultaneous genotyping of HPA-1 to HPA-13w was established. This allows fast and reliable diagnosis of alloimmune thrombocytopenia, and is readily applicable to large-scale genetic population studies.     

Anti-HPA-9bw (Maxa) fetomaternal alloimmunization, a clinically severe neonatal thrombocytopenia: difficulties in diagnosis and therapy and report on eight families

BACKGROUND: Fetal or neonatal alloimmune thrombocytopenia (FMAIT) results from a maternal alloimmunization against fetal platelet (PLT) antigens. In Caucasian persons, HPA-1a is the most frequently implicated antigen. During the past few years, FMAIT has been reported associated with rare or private antigens. STUDY DESIGN AND METHODS: Since the first documented case of FMAIT due to anti-HPA-9bw (Max(a)), no additional cases have been reported. Here a retrospective analysis is presented of the cases referred to our laboratories in recent years. The diagnosis was performed by genotyping and identification of the maternal alloantibody by the monoclonal antibody-specific immobilization of PLT antigens (MAIPA) technique. RESULTS: Parental genotyping showed HPA-9bw (Max(a)) mismatch as the sole antigenic incompatibility in seven of eight families. Because the father was found to be HPA-9bw (Max(a)) heterozygous in all the cases, the infant or fetus was genotyped to ascertain the diagnosis. The maternal alloantibody was identified in the MAIPA technique. These data strongly suggest, however, that recognition of the HPA-9bw (Max(a)) epitope is not uniform. The neonatal thrombocytopenia was severe in most cases with bleeding. The outcome was good in all the cases but one. CONCLUSION: This analysis confirms that anti-HPA-9bw (Max(a)) FMAIT is not uncommon and was found to be approximately 2 percent of our confirmed FMAIT cases. It is a clinically severe syndrome that requires prompt diagnosis, albeit difficult, and maternal PLT transfusion therapy. Laboratory investigation of a suspected FMAIT case should be carried out in a specialist laboratory well-experienced in optimal testing. Appropriate management and antenatal therapy should be considered for successive pregnancies to prevent fetal bleeding.     

The natural history of maternal immunization against foetal platelet alloantigens

Foetomaternal alloimmune thrombocytopenia (FMAIT) occurs when maternal antibodies of an antigen-negative mother cause destruction of sensitized foetal platelets. In Caucasian populations, 6-12% of human platelet antigen (HPA)-1a-negative women develop anti-HPA-1a, and the incidence of clinically affected cases is estimated to be 10-20% of immunized women. This study was performed in order to elucidate the rate of maternal immunization, incidence of FMAIT and the likely outcome of the condition in Asians. Excluding two or more pregnancies during the period, serum samples from 24 630 pregnant women, mainly Japanese, were screened for antibodies against platelet alloantigens by means of mixed passive haemagglutination (MPHA) (Anti-HPA-MPHA, Olympus, Tokyo). Antibodies were detected in 0.91% (223/24 630) of the women's samples and the immunization rate was correlated with the number of pregnancies. Antibody specificity included anti-HPA-4b (49), anti-HPA-5a (three), anti-HPA-5b (168), anti-HPA-4b + 5b (one) and anti-Nak(a) (CD36) (two). No alloimmunization was observed within the HPA-1, HPA-2, HPA-3 or HPA-6 systems. Among HPA-4b- or HPA-5b-negative women, 24% or 14% estimated, respectively, had antibodies and 26% (10/38) or 10% (12/125) of neonates, respectively, born to these mothers developed thrombocytopenia. Two neonates born to mothers having anti-HPA-4b developed generalized purpura. No cases of intracranial bleeding or death due to FMAIT were recorded. Generalized purpura due to FMAIT occurs in one in 9359 (95% CI: 1 in 77 519-1 in 2591) pregnancies solely because of HPA-4b incompatibility.     

Detection of human platelet antigen-1a alloantibodies in cases of fetomaternal alloimmune thrombocytopenia using recombinant β3 integrin fragments coupled to fluorescently labeled beads

BACKGROUND: Testing for alloantibodies against human platelet antigens (HPAs) is essential for the clinical diagnosis of fetomaternal alloimmune thrombocytopenia (FMAIT), posttransfusion purpura, and platelet (PLT) refractoriness. Most of the methods currently used for HPA alloantibody detection rely on the availability of panels of HPA‐typed PLTs and some rely on validated monoclonal antibodies (MoAbs) against the PLT glycoproteins. Recombinant β3 integrins displaying the HPA‐1a (rHPA‐1a) or HPA‐1b (rHPA‐1b) epitopes have been produced as an alternative source of antigen. The suitability of these integrin fragments was evaluated for the development of an HPA‐1a alloantibody screening assay, using Luminex xMAP technology. STUDY DESIGN AND METHODS: A 3‐plex bead assay was developed by coupling biotinylated rHPA‐1a, rHPA‐1b, and recombinant glycoprotein VI to LumAvidin microspheres. Forty patient samples referred for FMAIT diagnostic testing, which were previously screened by the MoAb‐specific immobilization of PLT antigens (MAIPA) assay, were used to assess the assay. RESULTS: The rHPA‐1a‐ and rHPA‐1b‐coupled beads were able to detect HPA‐1a and HPA‐1b alloantibodies in all patient samples tested that were previously confirmed to contain HPA‐1‐specific antibodies. Furthermore, HLA Class I antibodies did not cross‐react with the coupled beads. CONCLUSION: The 3‐plex bead assay can be used to detect HPA‐1a antibodies with sufficient specificity and sensitivity for use in the clinical setting of FMAIT. The development of other recombinant integrin fragments with the use of Luminex xMAP technology may assist in providing more rapid HPA antibody detection, enabling prompt diagnosis of alloimmune PLT disorders.     

Human platelet antigen-specific alloantibodies implicated in 1162 cases of neonatal alloimmune thrombocytopenia

BACKGROUND: Neonatal alloimmune thrombocytopenia (NATP) caused by fetomaternal mismatch for human platelet (PLT) alloantigens (HPAs) complicates approximately 1 in 1000 to 1 in 2000 pregnancies and can lead to a serious bleeding diathesis, intracranial hemorrhage, and sometimes death of the fetus or neonate. As a national reference center for NATP investigations, our experience with this entity over a 12-year period was reviewed. STUDY DESIGN AND METHODS: The laboratory records of all cases of suspected NATP referred for evaluation from January 1, 1990, to December 31, 2002, were analyzed. The spectrum of PLT alloantibody specificities identified was compared with an earlier reported series of serologically verified NATP cases. RESULTS: HPA-specific alloantibodies were identified in 1162 (31%) of 3743 sera of mothers of infants with clinically suspected NATP. Maternal HPA-1a (PlA1) alloimmunization accounted for the majority (79%) of confirmed NATP cases, with HPA-5b (Bra), HPA-3a (Baka), and HPA-1b (PLA2) alloantibodies accounting for 9, 2, and 4 percent of cases, respectively. In addition, an increase in the number of cases in which multiple HPA-specific alloantibodies were present in maternal sera was observed during the study period. CONCLUSION: Although, as with the earlier series, maternal HPA-1a alloimmunization was the dominant cause of NATP, the identification of an increasing number of cases due to alternative HPA polymorphisms suggests that investigation for HPA-1 incompatibility alone is no longer sufficient to fully evaluate clinically suspect NATP cases.     

Establishment of an HPA-1- to -16-typed platelet donor registry in China

In order to determine gene frequencies of human platelet antigen (HPA) and establish a panel of accredited HPA-1a, -2a, -4a, -5a and -6a-negative donors as well as an HPA-typed platelet donor registry, a total of 1000 Chinese donors of Han nationality (500 from north China and 500 from south China) were typed for HPA-1 through -16 using a DNA-based polymerase chain reaction with sequence-specific primers genotyping method. The gene frequencies of HPA-1b, -2b, -3b, -4b, -5b, -6bw, -10bw and -15b were 0.0060, 0.0485, 0.4055, 0.0045, 0.0140, 0.0135, 0.0005 and 0.4680, respectively. The HPA-7bw, -8bw, -9bw, -11bw, -12bw, -13bw, -14bw and -16bw alleles were not found. The HPA-2b and -5b homozygous donors were detected at low frequencies. The HPA mismatch probabilities potentially leading to alloimmunization in random platelet transfusion vary with a region from 0.1% to 37% depending on the distribution patterns of common and less common alleles in each system. This study provides a useful HPA-typed plateletpheresis donor registry in China and could improve platelet antibody detection and HPA-matched platelet transfusion in alloimmune thrombocytopenic patients.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for genotyping of human platelet-specific antigens

BACKGROUND: Genotyping of single-nucleotide polymorphisms (SNPs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an emerging technique, where finally tools for end users have become available to design primers and analyze SNPs of their own interest. This study investigated the potential of this technique in platelet (PLT) genotyping and developed a validated method for genotyping of clinical relevant human PLT antigens (HPAs).
STUDY DESIGN AND METHODS: A multiplex assay using MALDI-TOF MS to analyze six HPA loci (HPA-1, HPA-2, HPA-3, HPA-4, HPA-5, and HPA-15) simultaneously in a single reaction was applied for the genotyping of 100 DNA samples from a cohort of plateletpheresis donors and a patient population (n = 20) enriched for rare alleles. The genotyping results using MALDI-TOF MS were validated by the comparison with the results from typing by polymerase chain reaction with sequence-specific primers and conventional DNA sequencing.
RESULTS: Both homozygous and heterozygous genotypes of HPA-1 to -5 and -15 of the 120 individuals were easily identified by a six-plexed assay on MALDI-TOF MS. The three approaches achieved a 100 percent concordance for the genotyping results of the six HPA loci.
CONCLUSION: Compared to conventional methods, the MALDI-TOF MS showed several advantages, such as a high velocity, the ability to perform multiplexed assays in a single reaction, and automated high-throughput analysis of samples. This enables cost-efficient large-scale PLT genotyping for clinical applications.     

Low-avidity HPA-1a alloantibodies in severe neonatal alloimmune thrombocytopenia are detectable with surface plasmon resonance technology

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is mostly caused by maternal alloantibodies directed against the human platelet alloantigen (HPA)-1a. Currently, the serologic diagnosis of FNAIT is based on the characterization of the HPA alloantibodies in monoclonal antibody–based antigen-capture assays (e.g., MAIPA assay). Accumulated current evidence indicated that such assays may overlook some HPA-1a antibodies.
STUDY DESIGN AND METHODS: This study employed surface plasmon resonance (SPR) technology using immunoaffinity-purified glycoprotein IIb/IIIa isoforms immobilized on biosensor chips to study the binding kinetics of HPA-1a alloantibodies from different FNAIT cases in real time.
RESULTS: Analysis of HPA-1a alloantibodies from FNAIT cases (n = 9) in SPR showed a moderate relative response (22.2-69.7 resonance units [RU]) and slow antibody dissociation. After the dissociation phase, varying amounts of bound antibodies (41%-79%) remained on the chip. In contrast in HPA-1a alloantibodies from a patient suffering from posttransfusion purpura, a high relative response (∼490 RU) was observed at the end of the association phase and no dissociation of antibody binding was detectable. Of particular relevance, by the use of this SPR technique, HPA-1a alloantibodies were detected in two severe FNAIT cases that had determined as false negative by MAIPA assay. In SPR, these HPA-1a alloantibodies showed low-avidity nature characterized by gradual dissociation of antibody during the association phase and complete detachment of antibody binding after the dissociation phase. This high "off-rate" character of low-avidity HPA-1a alloantibodies indicates that such antibody binding is easily detachable by the extensive washing procedure of the MAIPA.
CONCLUSIONS: Our results demonstrated that the SPR method can facilitate the diagnosis of clinically relevant low-avidity HPA-1a antibodies.     

浙江汉族人群血小板抗原1-16多态性调查

目的了解浙江汉族人群血小板抗原1-16多态性分布。方法采用PCR-SSP方法对120份浙江无血缘关系汉族样本作HPA-1—16等位基因分型。结果HPA-1b、-2b、-3b、-6bw、-15b的基因频率分别为0.0125、0.0542、0.3833、0.0125、0.4833,未检出HPA-4b、-5b、-7bw、-8bw、-9bw、-10bw、-11bw、-12bw、-13bw、-14bw、-16bw等位基因。浙江汉族人群HPA-3、15抗原系统血小板随机输注错配概率分别为0.36、0.37。结论浙江汉族人群HPA多态性分布与中国其他地区汉族人群比较没有差异,HPA-3和15系统多态性较丰富,因此在随机血小板输注或胎母之间比较容易发生同种免疫反应。     

A single-nucleotide polymorphism in the human ITGB3 gene is associated with the platelet-specific alloantigen Vaa (HPA-17bw) involved in fetal maternal alloimmune thrombocytopenia

BACKGROUND: The previously reported platelet (PLT)-specific antigen, Va^a, was defined by an alloantibody detected in the serum sample of a mother who delivered an infant displaying symptoms of severe fetal maternal alloimmune thrombocytopenia (FMAIT). This PLT antigen was localized to the integrin αIIbβ3 (GPIIbIIIa) but its genetic basis was not defined.
STUDY DESIGN AND METHODS: Genomic ITGA2B (αIIb) and ITGB3 (β3) DNA from a Va^a-positive individual were sequenced to identify potential polymorphisms underlying the Va^a antigen. Recombinant β3 integrin carrying the putative mutation was then used to assess serologic reactivity with the original maternal Va^a antiserum.
RESULTS: A single-nucleotide polymorphism (SNP; C622>T) in exon 5 of ITGB3 resulting in the replacement of threonine with methionine at residue 195 of the mature β3 was identified. Calmodulin-tagged soluble recombinant β3 encoding Met195 was produced in S2 cells and found to react specifically with the Va^a antiserum.
CONCLUSION: With the use of a combination of DNA sequencing and recombinant antigen expression, the molecular basis of the PLT-specific Va^a antigen (HPA-17bw), a low-frequency antigen implicated in FMAIT, has been resolved. These data further demonstrate the value of using recombinant β3 peptides for the detection of rare but clinically relevant antibodies.     

Blockade of maternal anti-HPA-1a–mediated platelet clearance by an HPA-1a epitope–specific F(ab')2 in an in vivo mouse model of alloimmune thrombocytopenia

BACKGROUND: Neonatal alloimmune thrombocytopenia (NAIT) is most commonly caused by transplacental passage of maternal human platelet-specific alloantigen (HPA)-1a antibodies that bind to fetal platelets (PLTs) and mediate their clearance. SZ21, a monoclonal antibody (MoAb) directed against PLT glycoprotein IIIa, competitively inhibits the binding of anti-HPA-1a alloantibodies to PLTs in vitro. The purpose of this investigation was to determine whether SZ21 F(ab')₂ fragments might be therapeutically effective in inhibiting or displacing maternal HPA-1a antibodies from the fetal PLT surface and preventing their clearance from circulation.
STUDY DESIGN AND METHODS: Resting human PLTs from HPA-1ab heterozygous donors were injected into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Purified F(ab')₂ fragments of SZ21 or control immunoglobulin G (IgG) were injected intraperitoneally 30 minutes before introduction of HPA-1a antibodies. Blood samples were taken periodically and analyzed by flow cytometry to determine the percentage of circulating human PLTs.
RESULTS: Anti-HPA-1a IgG from NAIT cases were able to efficiently clear HPA-1a–positive PLTs from murine circulation. Administration of SZ21 F(ab')₂ fragments not only inhibited binding of HPA-1a antibodies to circulating human PLTs, preventing their clearance, but also displaced bound HPA-1a antibodies from the PLT surface.
CONCLUSION: F(ab')₂ fragments of HPA-1a–selective MoAb SZ21 effectively inhibit anti-HPA-1a–mediated clearance of human PLT circulating in an in vivo NOD/SCID mouse model. These results suggest that agents that inhibit binding of anti-HPA-1a to PLTs may have therapeutic potential in the treatment of NAIT.     

Platelet alloantigen frequencies in Amazon Indians and Brazilian blood donors

The frequencies of human platelet-specific alloantigens (HPAs) vary between different ethnic groups, and genotyping using DNA techniques has been preferred over immunophenotyping methods for population studies. Using a polymerase chain reaction with allele-specific primers (PCR-ASP) method, we determined the allelic polymorphisms of five HPA systems among 174 unrelated individuals of two different Brazilian ethnic groups including Amazon Indians (n = 95) and blood donors (n = 79). Comparison of the calculated gene frequencies of the two alleles of HPA-1, -2, -3, -4 and -5 systems for Amazon Indians and Brazilian blood donors showed that gene frequencies obtained for the two alleles of HPA-1 (P<0.001), HPA-2 (P = 0.001) and HPA-5 (P<0.001) were significantly different between the two groups of individuals. All natives tested carried the HPA-2a and the HPA-5a alleles, but the HPA-1b and HPA-4b alleles are absent from the Indian population. It was also observed that all blood donors carried the HPA-1a, HPA-4a and HPA-5a alleles. In conclusion, the present data indicate differences in the frequency of the HPA systems between Amazon Indians and Brazilian subjects who present a high rate of racial admixture. While the frequencies of the HPA-1 and HPA-5 genes seen in Amazon Indians are similar to those reported for Oriental populations, the frequencies of the HPAs alleles in Brazilian blood donors are comparable to those reported for populations in North America and Europe.     

献血者血小板1-16抗原基因遗传多态性分析及已知HPA型供者数据库的建立

本研究的目的是分析人类血小板抗原（human platelet antigen,HPA）基因多态性,根据分布频率来判断HPA抗原不配合比率以及抗体产生的机会,确定有临床意义的血小板抗原系统,并建立邯郸地区血小板基因频率数据库和供者库.采用SSP-PCR方法对邯郸地区148名随机献血者进行HPA1-16抗原32个等位基因的检测分析,并与不同人群的分布频率进行比较.结果表明：每个样本均检测到HPA-1a、2a、4a-14a、16a基因;HPA-4a、7a-14a、16a呈现单态性,未检测出相应的等位基因HPA-b;对于HPA-1、-2、-5、-6主要以a/a纯合子为多,a/a基因型频率分别是0.9595、0.8108、0.9865、0.9797,没有b/b纯合子出现.在HPA1-16中,具有最高杂合度的是HPA-15,基因型HPA15a/15a、HPA15a/15b、HPA15b/15b频率分别是0.2230、0.5270、0.2500;HPA-3在其次,基因型HPA3a/3a、HPA3a/3b、HPA3b/3b频率分别是0.3851、0.5135、0.1014.经x2检验,结果符合Hardy-Weinberg遗传平衡定律.邯郸地区随机献血者HPA1-5系统基因频率与石家庄地区相似（P＞0.05）;与我国台湾人群进行HPA1-13、HPA-15的比较,HPA-1、-2、-6具有明显的不同（P＜0.05）,其它相似（P＞0.05）;与韩国人群进行HPA1-8的比较,除HPA-3具有明显不同外（P＜0.05）,其余均相似（P＞0.05）;与美国黑人进行HPA1-5的比较,HPA-1、-2、-5具有明显的差异（P＜0.05）;与英国人进行HPA1-11的比较,HPA-1、-5具有明显的不同（P＜0.05）.结论：北方地区中国人群HPA-2、-3、5、-15系统具有多态性,且HPA抗原分布不配合比率较高,这必然造成免疫暴露的机会增加,提示在临床上可能具有重要的免疫学意义.同时,在此次研究数据的基础上建立了邯郸地区血小板基因频率数据库和血小板已知型供者库.     

The first two cases of neonatal alloimmune thrombocytopenia associated with the low-frequency platelet antigen HPA-21bw (Nos) in Japan

BACKGROUND: Neonatal alloimmune thrombocytopenia (NAIT) is a disorder characterized by maternal alloimmunization against paternal fetal platelet antigens. Two healthy, unrelated Japanese women each gave birth to a child with severe NAIT. STUDY DESIGN AND METHODS: To elucidate the maternal causes of NAIT, we conducted serologic and genetic studies in these two NAIT infants. RESULTS: The serologic experiments localized the antigens to the glycoprotein (GP) IIIa subunit of the GPIIb/IIIa complex. Sequence‐based typing studies subsequently identified a G>A mutation at Nucleotide 1960 (a glutamic acid > lysine substitution at Position 628) in the 11th exon of the GPIIIa gene. This mutation was recently identified in a report as HPA‐21bw. Next, it was determined that the cause of NAIT in both cases was the HPA‐21bw antigen, as shown by the mothers' antibodies reacting with the mutated GPIIIa‐transfected cells, but not with transfectants expressing wild‐type GPIIIa. A molecular genetic screening for the HPA‐21bw allele among Japanese donors showed that its genetic frequency in the population was 0.53% (10/1888), indicating that HPA‐21bw occurs at a low but appreciable frequency in the population. Furthermore, in a retrospective study of 50 previous NAIT cases of unknown causes, we found one NAIT case associated with the HPA‐21bw antibody. The two NAIT cases in this study represent the first ones to be associated with HPA‐21bw in Japan. CONCLUSION: We identified the HPA‐21bw allele from two unrelated Japanese infants with severe NAIT. We identified 10 individuals (1.06%) positive for the HPA‐21bw allele from a genetic screening of 944 Japanese blood donors.     

Simultaneous genotyping of human platelet antigens (HPA) 1 through 6 using new sequence-specific primers for HPA-5

BACKGROUND: Polymerase chain reaction using sequence-specific primers is widely used for genotyping human platelet antigens (HPA). However, the results of HPA-5 genotyping are still problematic.
STUDY DESIGN AND METHODS: New sequence-specific primers were designed for HPA-5 that, together with already published primers, allow simultaneous genotyping of HPA-1, -2, -3, -4, -5 , and -6 . The reliability of the described protocol was determined by using reference DNA samples as well as samples from healthy blood donors.
RESULTS: All primers produced specific amplification products. The genotype and the previously ascertained phenotype of the tested specimens were in concordance in all cases.
CONCLUSION: The described polymerase chain reaction protocol allows rapid, reliable, simultaneous genotyping of HPA-1, -2, -3, -4, -5 , and -6 .     

Multicolor real-time polymerase chain reaction genotyping of six human platelet antigens using displacing probes

BACKGROUND: Several genotyping methods for six clinically relevant human platelet antigens (HPAs) have been reported. A four-color real-time polymerase chain reaction (PCR) method using displacing probes for genotyping of the six HPAs is described. STUDY DESIGN AND METHODS: Primers and four differently fluorophor-labeled displacing probes were designed and synthesized to detect single-nucleotide polymorphisms responsible for each of the HPA-1, -2, -3, -4, -5, and -15 genotypes. Two HPA systems were analyzed in a single PCR procedure. After validation with samples of known genotypes, a total of 150 blood samples from healthy donors were genotyped. The results were compared with PCR with sequence-specific primers (SSP), PCR-restriction fragment length polymorphism (RFLP), and/or direct DNA sequencing. The frequencies of each HPA allele were calculated. RESULTS: Unequivocal real-time PCR genotyping results were obtained with minimal manual manipulation and carryover contamination. All 150 blood samples were correctly genotyped as confirmed by PCR-SSP, PCR-RFLP, and/or direct DNA sequencing. The allelic frequencies of HPA-1 through -5 and -15 among the Chinese population in Xiamen were comparable with those previously reported with Chinese living in other territories. For each specimen, genotyping of all six HPA biallelic systems was achieved in three tubes of PCR within 90 minutes and with material cost of no more than $1. CONCLUSION: Genotyping of HPA with real-time PCR using displacing probes is more rapid and reliable compared with PCR-SSP and PCR-RFLP methods and is more affordable than existing real-time PCR-based HPA genotyping assays. Thus, our approach is more suitable for routine HPA analysis and ideal for both urgent clinical testing and high-throughput screening.     

Association of human platelet antigens polymorphisms with the levels of serum fibrosis marks in chronic hepatitis C patients

BackgroundHost genetic polymorphisms influence the fibrosis progression of chronic hepatitis C (CHC) patients. Previous studies have shown the association of human platelet antigens (HPAs) polymorphisms with CHC. However, little is known regarding the association of HPAs polymorphisms with the fibrosis progression of CHC. The aim of this study was to determine the association of HPA -2, -3, -5 and -15 polymorphisms with the levels of serum fibrosis marks in CHC patients.MethodsThe HPA -2, -3, -5 and -15 were genotyped by 5ˊ-nuclease assay in 211 CHC patients, while the serum concentration of hyaluronic acid (HA), collagen IV (CIV), amino-terminal pro-peptide of type III procollagen (PIIINP), and laminin (LN) from the same samples were measured by time resolved fluorescence immunoassay.ResultsThe level of serum LN was significantly lower in CHC patients with HPA-15aa genotype compared to those with HPA-15ab/bb (P = 0.032) but did not differ among HPA-2, -3 and -5 genotypes. There were no difference in HA, CIV and PIIINP levels among HPA-2, -3,-5 and -15 genotypes.ConclusionsThis study demonstrates that HPA-15 aa polymorphism is associated lower serum LN in CHC, which suggests that HPA -15 aa may be involved in the fibrosis progression of CHC.