Clinical aspects and typing of platelet alloantigens

A first WHO reference reagent for the detection of anti-human platelet antigen-15b

Background and Objectives

Alloantibodies to human platelet antigen‐15b (anti‐HPA‐15b) have been detected in mothers with foetal–neonatal alloimmune thrombocytopenia and in multiply transfused patients. Assays used to detect this antibody, which aids in disease diagnosis, can be unreliable and vary in sensitivity. The objective was to generate a stable, lyophilized anti‐HPA‐15b preparation and evaluate its suitability as a World Health Organization (WHO) reference reagent for use in the quality control of platelet alloantibody detection assays. Results from an international collaborative study to evaluate the preparation were used to assign a minimum potency at which laboratories can be expected to detect the antibody.

Materials and Methods

Recalcified plasma containing anti‐HPA‐15b was aliquotted, lyophilized and coded 18/220. Twenty‐five laboratories in 16 countries tested doubling dilutions of the reconstituted material in glycoprotein‐specific assays such as the monoclonal antibody–specific immobilization of platelet antigen assay and reported the last positive (or endpoint) dilution.

Results

Twenty‐four laboratories (96%) detected antibodies with HPA‐15b specificity in preparation 18/220. Reported endpoint dilutions were normally distributed with a modal dilution of 1 in 16 and ranged from 1 in 2 to 1 in 128. Only two laboratories (8%) failed to detect anti‐HPA‐15b at 1 in 8 dilution.

Conclusions

When diluted 1 in 8, most laboratories detected anti‐HPA‐15b in preparation 18/220 using HPA‐15bb platelets but not with HPA‐15aa platelets. The participants agreed this to be an appropriate dilution for assignment as the minimum potency. In October 2020, the WHO Expert Committee on Biological Standardization approved 18/220 as an International Reference Reagent.

A new efficient tool for non-invasive diagnosis of fetomaternal platelet antigen incompatibility

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the consequence of platelet destruction by maternal alloantibodies against fetal human platelet antigens (HPA). This may result in intracranial haemorrhages (ICH) or even fetal death. Currently, fetal HPA genotyping is performed using invasive procedures. Here, we carried out a proof-of-concept study for non-invasive prenatal diagnosis of fetal platelet genotyping in four HPA systems (HPA-1, -3, -5 and-15) by droplet digital polymerase chain reaction (ddPCR) using cell-free DNA extracts from the plasma of 47 pregnant women with suspected, or history of, FNAIT. Results showed that 74% (35/47) of pregnant women presented incompatibility in at least one HPA system, and 38% (18/47) of cases presented HPA-1 incompatibility, including nine women with multiple incompatibilities. ICH occurred in one case of profound fetal thrombocytopenia with HPA-15 incompatibility, confirming the need for non-invasive prenatal genotyping in systems other than HPA-1. Fetal HPA genotypes predicted by ddPCR were confirmed in all FNAIT cases after amniocentesis or delivery. Fetal HPA genotyping on maternal plasma based on ddPCR is a fast, safe and reliable non-invasive method. This technique will be useful for the early identification of pregnancies at high risk of FNAIT requiring antenatal management to minimize the risk of fetal/neonatal haemorrhage.

Polymorphisms of the human platelet antigen-1, -2, -3, -5, and -15 systems and acute cellular liver transplant rejection

The human platelet antigen (HPA)-1, -2, -3, -5, and -15 systems are characterized as polymorphic alloantigens expressed on platelets and endothelial cells. In this retrospective study, we investigated, whether HPA-1, -2, -3, -5, and -15 incompatibilities are associated with acute cellular liver transplant rejection. A total of 96 Caucasian liver transplant recipients and corresponding donors were analyzed, 43 with biopsy proven acute cellular rejection (BPAR) and 53 without acute cellular rejection (No-BPAR). Polymorphisms of mentioned HPA systems were determined by polymerase chain reaction-sequence specific primers (PCR-SSP). Our data demonstrate that acute cellular rejection episodes were associated with HPA-3 incompatibility (58% HPA-3 incompatibility in BPAR group vs. 32% HPA-3 incompatibility in No-BPAR group, p=0.013). Furthermore, the frequency of HPA-3bb genotype was significantly higher in BPAR recipients as compared to No-BPAR recipients (30% vs 6%, p=0.002). On the other hand, there was no association between acute cellular rejection and the other tested HPA systems. We conclude that in the Caucasian population the HPA-3 system confers susceptibility to acute cellular rejection after liver transplantation.

[Thirty years of platelet immunology in fetal and neonatal alloimmune thrombocytopenia management, current situation]

Fetal and neonatal allo-immune thrombocytopenia (FNAIT) is considered as a rare disease due to the incidence (1/1000-1/2000 births). The major complication of severe thrombocytopenia is bleeding and particularly intra-cranial hemorrhage and neurologic sequelae following. Serology and molecular biology developments have reconfigured the platelet immunology diagnosis. Anti-HPA-1a allo-immunisation is responsible for more than 80% FNAIT cases with a high recurrence rate of severe bleeding complications. Therapeutic management has changed over the coming years from an invasive concept associating fetal blood sampling and in utero platelet transfusion to a non invasive treatment by intravenous immunoglobulins injection (IVIg). The purpose of this article is to provide an update on FNAIT management in the light of current developments over the past 30years.

[Platelet transfusion role in neonatal immune thrombocytopenia]

Neonatal immune thrombocytopenia represent less than 5% of cases of early thrombocytopenia (early-onset<72hours post-delivery). As in adults, thrombocytopenia in neonates is defined as a platelet count less than 150G/L. They are either auto- or allo-immune. Thrombocytopenia resulting from transplacental passage of maternal antibodies directed to platelet membrane glycoproteins can be severe. The major complication of severe thrombocytopenia is bleeding and particularly intra-cranial haemorrhage and neurologic sequelea following. However, auto- and allo-immune thrombocytopenia have very different characteristics including the treatment management. In fact, this treatment is based on platelet transfusion associated or not to intravenous immunoglobulin administration. The purpose of this article is to remind platelet transfusion's place in neonatal immune thrombocytopenia in terms of recently published French guidelines and international practices.

Allele frequencies of human platelet antigens in Banjar, Bugis, Champa, Jawa and Kelantan Malays in Peninsular Malaysia

OBJECTIVES

The major aims of this study are to characterise and compile allelic data of human platelet antigen (HPA)-1 to -6 and -15 systems in five Malay sub-ethnic groups in Peninsular Malaysia.

BACKGROUND

HPAs are polymorphic glycoproteins expressed on the surface of platelet membranes and are genetically differentiated across ethnogeographically unrelated populations.

METHODS

Blood samples were obtained with informed consent from 192 volunteers: Banjar (n = 30), Bugis (n = 37), Champa (n = 51), Jawa (n = 39) and Kelantan (n = 35). Genotyping was done using polymerase chain reaction-sequence specific primer method.

RESULTS

In general, frequencies of HPAs in the Malay sub-ethnic groups are more similar to those in Asian populations compared with other more distinct populations such as Indians, Australian Aborigines and Europeans.

CONCLUSIONS

This study provides the first HPA datasets for the selected Malay sub-ethnic groups. Subsequent analyses including previously reported HPA data of Malays, Chinese and Indians revealed details of the genetic relationships and ancestry of various sub-populations in Peninsular Malaysia. Furthermore, the comprehensive HPA allele frequency information from Peninsular Malaysia provided in this report has potential applications for future study of diseases, estimating risks associated with HPA alloimmunization and for developing an efficient HPA-typed donor recruitment strategy.

Sequence-Based Typing for Platelet alloantigens

Human platelet antigen (HPA) typing is largely performed by use of DNA-based techniques in patients that require assessing the risk of HPA alloimmunization. In this chapter, HPA typing by sequencing-based typing (SBT) techniques is described.

Establishment of reference panel for human platelet antigen genotyping

BACKGROUND AND OBJECTIVES

Human platelet antigens (HPAs) are platelet-specific alloantigens associated with polymorphisms of platelet surface glycoproteins (GPs), and they can induce alloantibodies when individuals lacking a particular polymorphism are exposed to them via pregnancy or transfusion. Immune responses to HPAs are involved in the pathogenesis of several clinical syndromes. HPA genotyping is therefore important for clinical diagnosis and laboratory research. This study aims to establish a reference panel for HPA genotyping.

MATERIALS AND METHODS

Genomic DNA extracted from human blood was used as the template for amplifying HPA (1a-5a and 15a) gene fragments using specific primers. The amplified products were cloned into pGM-T vectors, which were transformed into competent TOP10 cells. After clone screening and amplification, the plasmids were extracted and sequenced. Next, the gene fragments HPA-1b-5b and 15b were obtained by site-directed mutagenesis using the corresponding HPA-1a-5a and 15a plasmids as template DNA.

RESULTS

We successfully constructed reference plasmids for HPA genotyping with HPA-1a-5a, 15a, HPA-1b-5b and 15b. The DNA sequences were consistent with those published in GenBank.

CONCLUSION

Obtaining reference DNA for low-frequency HPAs is very difficult, and the successful construction of reference plasmids for the six HPA systems may solve this problem. Establishment of this panel has laid the foundation for future research on HPA genotyping.

Simultaneous genotyping of HPA-17w to -21w by PCR-SSP in Chinese Cantonese

Studies have reported the polymorphism of human platelet antigen (HPA)-17w, -18w, -19w, -20w, and -21w. However, the distribution of these five antigens in Chinese Cantonese is still unknown. In this study, we designed new sequence-specific primers for HPA-19w to -21w and used published primers for HPA-17w and -18w to develop a polymerase chain reaction with the sequence-specific primers (PCR-SSP) method for simultaneously genotyping HPA-17w to -21w. A total of 820 unrelated Cantonese apheresis platelet donors in Guangzhou were involved in this study. Among the five HPAs, complete a/a homozygosity was observed for HPA-17w to -20w with an allele frequency of 1.0000. For HPA-21w, nine individuals (9/820, 1.10%) were found to be HPA-21a/bw heterozygous and the allele frequencies of HPA-21a and HPA-21bw were 0.9945 (1631/1640) and 0.0055 (9/1640), respectively. The reliability of the PCR-SSP method was determined by comparing with the genotyping results by DNA sequencing, and no inconsistencies were observed between the two methods. This study provides a reliable PCR-SSP method for simultaneously genotyping HPA-17w to -21w and could improve HPA-matched platelet transfusion in Chinese Cantonese.

Co-stimulation with LPS or Poly I:C markedly enhances the anti-platelet immune response and severity of fetal and neonatal alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a life-threatening bleeding disorder caused by maternal antibodies against fetal/neonatal platelets. FNAIT is also linked with miscarriages, although the incidence and mechanisms of fetal death have not been well studied. IntegrinαIIbβ3 (GPIIbIIIa) and the GPIbα complex are major glycoproteins expressed on platelets and are also major antigens targeted in autoimmune thrombocytopenia (ITP), but reported cases of anti-GPIb-mediated FNAIT are rare. Bacterial and viral infections have been causally linked with the pathogenesis of immune-mediated thrombocytopenia (ITP); however, it is unknown whether these infections contribute to the severity of FNAIT. Here, immune responses against platelet antigens were examined by transfusing wild-type (WT) mouse platelets into β3-/- or GPIbα-/- mice. To mimic bacterial or viral infections, lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid (Poly I:C) were injected intraperitoneally following platelet transfusions. The FNAIT model was established by breeding the immunised female mice with WT male mice. We demonstrated for the first time that the platelet GPIbα has lower immunogenicity compared to β3 integrin. Interestingly, co-stimulation with LPS or Poly I:C markedly enhanced the immune response against platelet GPIbα and caused severe pathology of FNAIT (i.e. miscarriages). LPS or Poly I:C also enhanced the immune response against platelet β3 integrin. Our data suggest that bacterial and viral infections facilitate the anti-platelet GPIbα response, which may lead to a severe non-classical FNAIT (i.e. miscarriage but not neonatal bleeding) that has not been adequately reported in humans.

Human platelet antigen alleles in 998 Taiwanese blood donors determined by sequence-specific primer polymerase chain reaction

Polymorphism of human platelet antigens (HPAs) leads to alloimmunizations and immune-mediated platelet disorders including fetal-neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura (PTP), and platelet transfusion refractoriness (PTR). HPA typing and knowledge of antigen frequency in a population are important in particular for the provision of HPA-matched blood components for patients with PTR. We have performed allele genotyping for HPA-1 through -6 and -15 among 998 platelet donors from 6 blood centers in Taiwan using sequence-specific primer polymerase chain reaction. The HPA allele frequency was 99.55, and 0.45% for HPA-1a and -1b; 96.49, and 3.51% for HPA-2a and -2b; 55.81, and 44.19% for HPA-3a and -3b; 99.75, and 0.25% for HPA-4a and -4b; 98.50, and 1.50% for HPA-5a and -5b; 97.75 and 2.25% for HPA-6a and -6b; 53.71 and 46.29% for HPA-15a and -15b. HPA-15b and HPA-3a, may be considered the most important, followed by HPA-2, -6, -1, -5, and -4 systems, as a cause of FNAIT, PTP, and PTR based on allele frequency. HPA-4b and HPA-5b role cannot be excluded based on their immunogenicity. A larger-scale study will now be conducted to confirm these hypotheses and to establish an apheresis donor database for the procurement of HPA-matched apheresis platelets for patients with PTR.

High-throughput simultaneous genotyping of human platelet antigen-1 to -16 by using suspension array

BACKGROUND

Comprehensive and accurate detection of human platelet antigens (HPAs) plays a significant role in diagnosis and prevention of the platelet (PLT) alloimmune syndromes and ensuring clinical safety of patients undergoing PLT transfusion. The majority of the available methods are incapable of performing high-throughput simultaneous detection of HPA-1 to -16, and the accuracy of many methods needs to be further enhanced.

STUDY DESIGN AND METHODS

We have developed a new HPA-genotyping method for simultaneous detection of HPA-1 to -16 based on suspension array technology. A total of 216 samples from Chinese Han donors in Xi'an were genotyped using the developed method, and all the samples again were genotyped using polymerase chain reaction (PCR) sequence-based typing (PCR-SBT), which is considered the gold standard.

RESULTS

All 216 samples were successfully genotyped for HPA-1 to -16 using both our method and PCR-SBT. Results showed that the genotype and allele frequencies obtained using our method were fully consistent with those obtained using PCR-SBT.

CONCLUSION

Our method provides accurate, high-throughput, and simultaneous genotyping of HPA-1 to -16 and will serve as the foundation for large-scale clinical genotyping of HPAs and for the establishment of an HPA-typed PLT donor registry.

Crosstalk between Platelets and the Immune System: Old Systems with New Discoveries

Platelets are small anucleate cells circulating in the blood. It has been recognized for more than 100 years that platelet adhesion and aggregation at the site of vascular injury are critical events in hemostasis and thrombosis; however, recent studies demonstrated that, in addition to these classic roles, platelets also have important functions in inflammation and the immune response. Platelets contain many proinflammatory molecules and cytokines (e.g., P-selectin, CD40L, IL-1β, etc.), which support leukocyte trafficking, modulate immunoglobulin class switch, and germinal center formation. Platelets express several functional Toll-like receptors (TLRs), such as TLR-2, TLR-4, and TLR-9, which may potentially link innate immunity with thrombosis. Interestingly, platelets also contain multiple anti-inflammatory molecules and cytokines (e.g., transforming growth factor-β and thrombospondin-1). Emerging evidence also suggests that platelets are involved in lymphatic vessel development by directly interacting with lymphatic endothelial cells through C-type lectin-like receptor 2. Besides the active contributions of platelets to the immune system, platelets are passively targeted in several immune-mediated diseases, such as autoimmune thrombocytopenia, infection-associated thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. These data suggest that platelets are important immune cells and may contribute to innate and adaptive immunity under both physiological and pathological conditions.

Prevalence of the HPA-18w to -21w alleles in the Chinese Han population

Recently, four new platelet alloantigen (HPA) systems HPA-18w to-21w were identified. However, genotyping for HPA-18w to -21w alleles was rarely reported. Here, we established a polymerase chain reaction sequence-based typing (PCR-SBT) method and investigated the distribution of HPA-18w to -21w alleles in the Chinese Han population. The specific primers of HPA-18w, -19w, -20w and -21w were designed, and the PCR products were bidirectionally sequenced. 855 randomly selected platelet donors were genotyped for HPA-18w to -21w with the PCR-SBT method. The results showed that all individuals were monomorphic for HPA-18w to HPA-20w with a/a homozygous frequency of 1.0 and absence of HPA-18bw to -20bw alleles. The frequencies of the HPA-21a/21a and HPA-21a/21b genotypes were 0.981(839/855) and 0.019(16/855), respectively. Seven mutations were confirmed on sequenced region separate from HPA polymorphisms, including ITGA2 (IVS17+48G>A and IVS17+72G>A), ITGA2B (IVS19-26C>G) and ITGB3 (IVS4+234C>T, IVS11-19 T>C, IVS11-104T>C and GT repeats from IVS11-131 to IVS11-109). These data will provide useful information for diagnosis, prevention and treatment of alloimmune thrombocytopaenia.

The maternal immune response to fetal platelet GPIbα causes frequent miscarriage in mice that can be prevented by intravenous IgG and anti-FcRn therapies

Fetal and neonatal immune thrombocytopenia (FNIT) is a severe bleeding disorder caused by maternal antibody-mediated destruction of fetal/neonatal platelets. It is the most common cause of severe thrombocytopenia in neonates, but the frequency of FNIT-related miscarriage is unknown, and the mechanism(s) underlying fetal mortality have not been explored. Furthermore, although platelet αIIbβ3 integrin and GPIbα are the major antibody targets in immune thrombocytopenia, the reported incidence of anti-GPIbα-mediated FNIT is rare. Here, we developed mouse models of FNIT mediated by antibodies specific for GPIbα and β3 integrin and compared their pathogenesis. We found, unexpectedly, that miscarriage occurred in the majority of pregnancies in our model of anti-GPIbα-mediated FNIT, which was far more frequent than in anti-β3-mediated FNIT. Dams with anti-GPIbα antibodies exhibited extensive fibrin deposition and apoptosis/necrosis in their placentas, which severely impaired placental function. Furthermore, anti-GPIbα (but not anti-β3) antiserum activated platelets and enhanced fibrin formation in vitro and thrombus formation in vivo. Importantly, treatment with either intravenous IgG or a monoclonal antibody specific for the neonatal Fc receptor efficiently prevented anti-GPIbα-mediated FNIT. Thus, the maternal immune response to fetal GPIbα causes what we believe to be a previously unidentified, nonclassical FNIT (i.e., spontaneous miscarriage but not neonatal bleeding) in mice. These results suggest that a similar pathology may have masked the severity and frequency of human anti-GPIbα-mediated FNIT, but also point to possible therapeutic interventions.

Human platelet antigen allele frequencies and new mutations on platelet glycoprotein genes in the Chinese Han population

BACKGROUND AND OBJECTIVES

The frequencies of human platelet antigens (HPAs) vary between different populations. In this study, we determined the HPA allele frequencies in the Chinese Han population and identified situation of incompatibility possibly leading to alloimmunisation.

METHODS

A total of 750 volunteer blood donors of the Chinese Han population were genotyped for HPA-1 to -17w systems. HPA genotyping was determined by polymerase chain reaction sequence-based typing.

RESULTS

Among the 17 HPA systems, the allele frequency is different from other populations. We noted the absence of HPA-7bw to HPA-14bw, HPA-16bw and HPA-17bw alleles in the population. The estimated incompatibility probabilities regarding platelet antigens 1 to 6w and 15 systems after transfusion of random donor platelet were from 0·004 to 0·373. Thirteen glycoprotein alleles were observed in the population. In addition, we identified 16 novel mutations on the glycoprotein genes separated from HPA polymorphisms, including GP1BA (517-525delAAC), ITGA2B (2722C>T and IVS26+85T>C), ITGA2 (1521C>T, 2474T>G and IVS20+10 G>C), ITGB3 (1476G>A, IVS10+19C>A, 1813G>A, IVS11+21G>A, IVS11+152A>G and IVS11-104T>C), GP1BB (IVS1-79G>A, IVS1-27C>T and 129G>A) and CD109 (2139A>G). Five of them could lead to amino acid deletion, substitution or premature stop codon in corresponding glycoprotein.

CONCLUSIONS

There was a high degree of polymorphism of the membrane glycoprotein genes related to human platelet alloantigen-1 to -17w systems in the Chinese Han population. These data could have some impact on the diagnosis, prevention and treatment of alloimmune thrombocytopenia.

New paradigms in the management of alloimmune refractoriness to platelet transfusions

PURPOSE OF REVIEW

Following transfusion or pregnancy, a significant number of patients develop antibodies to class I human leukocyte antigen. Some will exhibit platelet transfusion refractoriness, defined as inappropriately low platelet count increments after two or more consecutive transfusions. Unfortunately, failure of at least two products is required before an immunologic work-up is undertaken. Among those diagnosed with immune refractoriness, there is no standard method for identifying platelet products likely to be effective.

RECENT FINDINGS

Recent advances in detection and identification of human leukocyte antigen antibody may permit pretransfusion screening of selected patients and provide guidance in choosing the optimal product. An approach more like that for red cell alloimmunized patients, in which one provides products guided solely by the antibody profile, is preferable to selection based on educated guesswork when human leukocyte antigen identical units are unavailable, and offers some advantages over platelet crossmatching.

SUMMARY

This review presents a literature-based algorithm with which to approach the management of platelet refractory individuals, focusing on newer technology to maximize the post-transfusion yield of matched units. Strategies are presented that allow selection of more effective products for difficult, broadly alloimmunized individuals, including patients who have developed antibodies to human platelet antigens.

Collaborative studies to establish the first World Health Organization International Standard for detection of human antibody against human platelet antigen-3a

BACKGROUND AND OBJECTIVES

The platelet-specific antibody anti-human platelet antigen-3a (anti-HPA-3a) is involved in neonatal alloimmune thrombocytopenia, post-transfusion purpura, and platelet refractoriness. However, HPA-3a antibodies are often difficult to detect, probably because the antigen is labile. This report describes the production of a freeze-dried preparation of pooled human plasma, coded 03/190, containing IgG antibodies against the HPA-3a. The material is intended for use as a minimum sensitivity reagent in glycoprotein-specific assays currently used for anti-HPA-3a detection. Laboratories can use it to assess the sensitivity of their 'in-house' assays for anti-HPA-3a and to calibrate local controls for routine use in each batch of tests.

MATERIALS AND METHODS

Plasma containing anti-HPA-3a was obtained from a mother of two babies both born with severe thrombocytopenia, and following dilution it was freeze dried in glass ampoules.

RESULTS

Two collaborative studies demonstrated that the candidate material contained anti-HPA-3a and human leucocyte antigen (HLA) class I antibodies, but no other HPA antibodies that might confuse the detection of the anti-HPA-3a. The minimum dilution that should give a positive result was determined to be 1 : 8 by two further international collaborative studies involving a total of 49 laboratories in 23 countries.

CONCLUSION

The material also contains HLA antibodies and is suitable for use only in techniques that are glycoprotein specific (i.e. monoclonal antibody immobilization of platelet antigens and enzyme-linked immunosorbent assay) where only HPA antibodies will be detected. This standard will allow laboratories to measure their sensitivity of detection of anti-HPA-3a and will also allow those laboratories with relatively insensitive techniques to monitor their performance as they improve their methodology.

A systematic review and survey of the management of unexpected neonatal alloimmune thrombocytopenia

BACKGROUND

Unexpected neonatal alloimmune thrombocytopenia (NAIT) may have devastating consequences and its management is challenging. To design future trials, evidence from the literature and existing best practice need review.

STUDY DESIGN AND METHODS

This study was a cross-sectional survey of neonatal units in Germany and Canada to determine management strategies of NAIT and a systematic search for randomized controlled trials (RCTs).

RESULTS

Management of NAIT differs substantially between countries with regard to platelet (PLT) thresholds for screening, initiation of therapy, and treatment. Seventy-seven percent of Canadian physicians versus 68 percent of German physicians screen preterm and term infants, at a PLT threshold of 30 x 10(9) to 100 x 10(9) per L. In preterm infants, 60 percent of Canadian neonatologists commence treatment at a PLT count of between 30 x 10(9) and 50 x 10(9) per L. In Germany 32 percent of the physicians start treatment at this level and 25 percent use a threshold of between 10 x 10(9) and 20 x 10(9) per L. In term infants, 6 percent of the Canadian physicians and 16 percent of the German physicians use even lower treatment triggers of between 5 x 10(9) and 10 x 10(9) per L. In the presence of bleeding, 61 percent of German physicians await the arrival of antigen-negative PLTs, while 64 percent of Canadian neonatologists prefer intravenous immunoglobulin or random-donor PLTs (81%). Maternal PLTs are utilized by 31 percent of physicians in both countries. No RCTs were identified.

CONCLUSION

In the absence of RCTs, management of unexpected NAIT differs between countries. Clinicians and transfusion services may use the results of our study to develop collaborative protocols, redefine preferred hospitalwide strategies, and design future controlled trials.

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.

Foetal and neonatal alloimmune thrombocytopaenia

Foetal/neonatal alloimmune thrombocytopaenia (NAIT) results from maternal alloimmunisation against foetal platelet antigens inherited from the father and different from those present in the mother, and usually presents as a severe isolated thrombocytopaenia in otherwise healthy newborns. The incidence has been estimated at 1/800 to 1/1000 live births. NAIT has been considered to be the platelet counterpart of Rh Haemolytic Disease of the Newborn (RHD). Unlike RHD, NAIT can occur during a first pregnancy. The spectrum of the disease may range from sub-clinical moderate thrombocytopaenia to life-threatening bleeding in the neonatal period. Mildly affected infants may be asymptomatic. In those with severe thrombocytopaenia, the most common presentations are petechiae, purpura or cephalohaematoma at birth, associated with major risk of intracranial haemorrhage (up to 20% of reported cases), which leads to death or neurological sequelae. Alloimmune thrombocytopaenia is more often unexpected and is usually diagnosed after birth. Once suspected, the diagnosis is confirmed by demonstration of maternal antiplatelet alloantibodies directed against a paternal antigen inherited by the foetus/neonate. Post-natal management involves transfusion of platelets devoid of this antigen, and should not be delayed by biological confirmation of the diagnosis (once the diagnosis is suspected), especially in case of severe thrombocytopaenia. Prompt diagnosis and treatment are essential to reduce the chances of death and disability due to haemorrhage. Due to the high rate of recurrence and increased severity of the foetal thrombocytopaenia in successive pregnancies, antenatal therapy should be offered. However, management of high-risk pregnancies is still a matter of discussion.

Fetoneonatal alloimmune thrombocytopenia (FNAIT): Our experience

OBJECTIVE

Fetoneonatal alloimmune thrombocytopenia (FNAIT) is a relatively rare clinical syndrome characterized by marked thrombocytopenia shortly after birth. It occurs when fetal platelets are destroyed, after sensitization, by a transplacental passage of maternal antibodies directed against a fetal platelet alloantigen inherited from the father. This article reviews some pathophysiologic and clinical aspects of FNAIT.

METHODS

We also present our experience with the management of 12 newborns affected with a symptomatic form of this disorder in order to verify what would be the best diagnostic and therapeutic protocols.

RESULTS

Antibody identification in maternal serum showed 9 anti-HPA-1a (75% of cases), 2 anti-HPA-1b (17%) and 1 anti-HPA-1a+anti-Gp IV+anti-HLA class I (8%).

CONCLUSION

Sixteen human platelet alloantigen (HPA) systems have been identified, six major (from HPA 1 to 5 and HPA 15) and ten rare or private, each composed of two allelic antigens (named "a" or "b", according to major or minor frequency in the population). All HPA systems, including private or low frequency, may play a role in determining FNAIT. Unfortunately FNAIT cannot be prevented, in fact no one of maternal parameters is predictive of thrombocytopenia or its magnitude.

Les thrombopénies fœtales et néonatales allo-immunes : problèmes en suspens

The allo-immune thrombocytopenias are the major cause of severe thrombocytopenia in the fetus and the neonate. The frequency of this affection has been evaluated to be 1 out of 800 to 1000 live births. The deleterious consequences of severe thrombocytopenia are intracranial hemorrhages leading to death or neurological sequelae. Progress in platelet immunology and antenatal medicine has allowed a better diagnosis of this affection and development of the antenatal management of high-risk pregnancies. Nevertheless there are unsolved questions, particularly concerning the mechanism of the maternal immunization, the laboratory difficulties for the identification of the alloantibodies, the absence of antenatal management standardization.

Fetal-neonatal alloimmune thrombocytopenia and unexpected Glanzmann thrombasthenia carrier: report of two cases

BACKGROUND

Discrepancy between phenotyping and genotyping during the investigation of maternofetal alloimmunization leads to the identification of defects on genes encoding membrane glycoproteins (GPs) IIb and IIIa.

STUDY DESIGN AND METHODS

Human platelet (PLT) alloantigen (HPA)-1 and -3 PLT phenotypes and genotypes were performed by use of, respectively, the monoclonal antibody-specific immobilization of PLT antigens and the polymerase chain reaction (PCR)-sequence-specific priming techniques for up to 2400 families with thrombocytopenic newborn. When a discrepancy was detected, genomic DNA from the mother was amplified for coding sequences of either the GPIIb or GPIIIa genes. The genetic abnormality responsible for the discrepancy was determined by direct sequencing of the PCR products.

RESULTS

Two cases of discrepancy were identified among 2400 families tested. In the first case, Mother L, serologically assigned as HPA-1b-homozygous, was genotyped HPA-1a/1b. In the second case, Mother S, serogically defined HPA-3b-homozygous, was genotyped HPA-3a/3b. DNA sequence analysis revealed for Mother L a T(1447)-->C a point mutation within exon 10 of the GPIIIa gene and for Mother S a C(480)-->G point mutation within exon 4 of the GPIIb gene. These mutations reported in Glanzmann thrombasthenia (GT) patients account for nonexpression of the implicated allele on the PLT surface. Thus, the mothers are GT carriers. Alloantibodies, hallmarks of immunization, were not detected in the maternal serum samples.

CONCLUSION

Although this situation is rarely encountered, it is important to combine phenotyping and genotyping to avoid false PLT typing assignation and erroneous diagnosis when alloimmunization might occur.

Relevance of the HPA-15 (Gov) polymorphism on CD109 in alloimmune thrombocytopenic syndromes

BACKGROUND

Alloantibodies against the human platelet (PLT) alloantigen (HPA)-15 system residing on CD109 can cause fetal and neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura, and PLT transfusion refractoriness. The detection of antibodies against HPA-15, however, is hampered by the variable low expression and instability of the CD109 molecule during preparation and storage.

STUDY DESIGN AND METHODS

This study analyzed the occurrence of HPA-15 alloantibodies in 1403 patients: 930 FNAIT and 473 polytransfused (PT) patients by modified monoclonal antibody specific immobilization of PLT antigens (MAIPA) assay with well-defined phenotyped PLTs. A DNA typing technique was developed to confirm the phenotypes of PLT donors. B-cell lines were established as sources of reference DNA.

RESULTS

Genotyping of 407 unrelated blood donors revealed the gene frequencies 0.512 and 0.488 for HPA-15a and -15b, respectively. Based on the selection of PLTs expressing high amounts of CD109 on the surface (mean fluorescence intensity ratio 4-5 on expression peak on Days 2-4 after apheresis) antibody screening by the MAIPA assay was performed. In total, 16 (1.1%) HPA-15 alloantibodies were found comprising four anti-HPA-15a and 12 anti-HPA-15b. Anti-HPA-15b without other PLT-reactive antibodies were detectable in three serum samples of PT patients. The incidence of HPA-15 alloimmunization in PT patients was significantly higher than in mothers with FNAIT (3.0% vs. 0.22%). In relation to all detected HPA-specific antibodies, HPA-15 is responsible for 6.2 percent of alloimmunizations.

CONCLUSION

These observations indicate that alloimmunization against HPA-15 should be considered as a cause for immune thrombocytopenia, particularly in patients receiving multiple PLT transfusions.

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.

Association of PLA2 polymorphism of the ITGB3 gene with early fetal loss

To study the association between early fetal loss and the presence of the PLA2 polymorphism of the ITGB3 gene we conducted a case-control study on 98 cases (i.e., women in fertile age, who experienced at least one episode of early fetal loss) and 38 healthy controls. PLA2 polymorphism was present in 44.2% of cases and 18.4% of controls, and cases with one (n = 24) event had an odds ratio (OR) = 2.7 (95% confidence interval [CI] 0.7-10.0), with two events (n = 52) an OR = 3.8 (95% CI 1.3-11.5), and with three (n = 16) or four abortions (n = 6) had a combined OR = 4.4 (95% CI 1.2-17.0), compared to controls, indicating that PLA2 polymorphism may be implicated in an inherited form of thrombophilia, and to early fetal loss.

Estimation and predictive use of the corrected count increment—a proposed clinical guideline

BACKGROUND AND OBJECTIVE

Platelets are frequently given inappropriately. The accepted indication is symptomatic thrombocytopaenia due to bone marrow failure. In contrast replacement therapy is contraindicated in immune mediated peripheral sequestration because it is almost always ineffective and also aggravates the already rapid rate of the clearance due to superimposed isoimmunisation. Furthermore circulating levels, rather than the clinical situation, customarily trigger the request and would typically be at 20 x 10(9)/l. Usage is under evaluated and, accordingly, current practice has been scrutinised and a guideline proposed that is applicable to user and vendor alike.

DESIGN AND METHODOLOGY

Prospectively a consecutive series of eligible cases were selected and, with informed consent, all relevant information recorded. Specific observations were haematologic status, quality of the product and the impact of previous exposure to blood fractions on outcome. Additionally, factors that influence response were documented and included disseminated intravascular coagulation, splenomegaly and concurrent use of intravenous Amphotericin B. The absolute numbers infused, the increase in peripheral value recorded and this ratio which is designated as corrected count index generated in each instance.

RESULTS

The CCI was computed for each of the 85 megaunits given to 29 individuals and subsequently estimated for the entire sample population using regression analysis. Each of the variables was used to test the hypothesis that such a figure might differ depending on patient sub-population. This approach was accurate in 60% of the time and predicates a more rational use of donor characteristics. The cardinal measurement is that supplied by the transfusion service which can be used as a basis for clinically important predictors of anticipated benefit.

CONCLUSION

This data, in keeping with international practice, leads to the recommendation that commercial and other services routinely measure and specify absolute numbers. The clinicians, reciprocally, should always confirm this figure and then match anticipated to observed outcome. Failure to carry out these simple procedures lead to gross over utilisation of this expensive intervention, risks unnecessary sensitisation and furthers persistence with sub-optimum administration.

Real-time PCR genotyping of human platelet alloantigens HPA-1, HPA-2, HPA-3 and HPA-5 is superior to the standard PCR-SSP method

Genotyping of the human platelet alloantigens (HPA) is useful for the diagnosis and therapy of the patients with alloimmune thrombocytopenic syndromes, such as post-transfusion refractoriness to platelets, post-transfusion thrombocytopenic purpura and foetomaternal alloimmune thrombocytopenia. We have developed, optimized and validated a new method for simultaneous genotyping of HPAs - HPA-1, HPA-2, HPA-3 and HPA-5 - by using the real-time polymerase chain reaction (PCR) based on TaqMan technology. Its performances were compared to those of the standard PCR-sequence-specific primers (SSP) method by testing 120 DNA samples. Several discrepancies between the two methods have been observed, especially in the HPA-3 genotyping. Evidently, the PCR-SSP method produced several false positive results due to its technical drawbacks. Based on our comparison, we believe that the new real-time TaqMan PCR assay for the HPA-1, HPA-2, HPA-3 and HPA-5 genotyping is faster, more reliable and reproducible, compared to the standard PCR-SSP.

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.

Eleven human platelet systems studied in the Vietnamese and Ma'ohis Polynesian populations

The frequencies of human platelet antigens (HPA) are variable among different ethnic groups. Platelet phenotyping and genotyping in different populations are important to the clinical implications of antiplatelet alloimmunization. No report on HPA prevalence has been published concerning the Vietnamese Kinh and Ma'ohis Polynesian populations. Recent anthropological and genetic marker studies suggest that these two groups have a common origin in East Asia, so we have conducted a combined study concerning the frequency of HPA-1 to HPA-11w systems (excluding HPA-8w) and Gov in these two populations. The results demonstrate a similar pattern of prevalence between Ma'ohis and most of the Asian populations. However, it should be noted that the frequency of HPA-2 is closer to northern Caucasian frequencies than to Asian frequencies. The population of Kinh shows an HPA distribution that is closer to the Chinese population than to the northeastern Thais except for HPA-3, closer to the Indonesian population. Given HPA-3 gene frequency distribution fetomaternal incompatibility could occur more frequently with the risk of alloantibody production.

[Fetal-neonatal alloimmune thrombocytopenia]

Fetal-neonatal alloimmune thrombocytopenia is the commonest cause of severe thrombocytopenia in the newborn. This disorder is due to the destruction of fetal platelets by a maternal platelet-specific antibody caused by fetal-maternal incompatibility. The most serious complication is intracranial hemorrhage (10-30 % of newborns), which may cause death (10 % of the reported cases) or irreversible neurological sequelae (20 %). The diagnosis is usually made after birth when most affected neonates have petechiae, purpura or overt bleeding. The degree of severity varies according to platelet count. Current methods allow detection of maternal platelet alloantibodies (usually HPA-1a). Clinical grounds and the exclusion of other causes of neonatal thrombocytopenia are required to establish an accurate diagnosis. Recurrence of this disease is very high and has prompted clinicians to develop antenatal prophylactic programs in subsequent pregnancies. However, the optimal treatment of at-risk pregnancies remains controversial. The early diagnosis of this process allows effective therapy based on the infusion of compatible platelets and IgG immunoglobulins when hemorrhage is not obvious. Antenatal management of subsequent pregnancies can prevent recurrence of thrombocytopenia and intracranial hemorrhage. The aim of this review is to draw pediatricians' attention to the importance of this probably under-diagnosed disease in which early diagnosis can prevent potentially severe complications.

Collaborative studies to establish the first WHO Reference Reagent for detection of human antibody against human platelet antigen-5b

BACKGROUND AND OBJECTIVES

This report describes the production of a freeze-dried preparation of pooled human plasma, coded 99/666, containing immunoglobulin G (IgG) antibodies against human platelet antigen 5b (HPA-5b).

MATERIALS AND METHODS

The material is intended for use as a minimum sensitivity reagent in the assays currently used for detection of antibodies to HPA-5b. Laboratories can use it to assess the sensitivity of their 'in-house' assays for antibodies to HPA-5b and to calibrate local controls for routine use in each batch of tests.

RESULTS

Two collaborative studies demonstrated that the two candidate materials contained antibodies to HPA-5b and that there were no other HPA or human leucocyte antigen (HLA) antibodies which might confuse the detection of antibodies to HPA-5b. The two samples were pooled and freeze-dried in 1-ml ampoules.

CONCLUSIONS

The minimum dilution of the antibody against 5b required to yield a positive result was determined, by two international collaborative studies involving a total of 49 laboratories in 26 countries, to be 1 in 2.

Platelet antigens. The role of human platelet alloantigens (HPA) in blood transfusion and transplantation

In this review, we describe the platelet surface molecules with special focus on the polymorphic glycoproteins giving rise to the human platelet alloantigen (HPA) system. We list the platelet glycoprotein complexes GPIa/IIa, GPIIb/IIIa, GPIb/V/IX and some other molecules, the corresponding genes that encode them and we describe their polymorphisms as well as their physiological function. Based on data obtained by serological and molecular methods, we explain how ancestral HPA alloepitopes have developed into the modern variants. We also describe the tissue distribution of these proteins, which seems to be wider than thought initially, and discuss the significance of the HPA encoding genes distribution in various populations. Methods for their determination are then described briefly Since HPA alloepitopes can induce antibodies with resulting clinical conditions such as: post-transfusion refractoriness to platelets (PTR); post-transfusion thrombocytopenic purpura (PTTP); and fetomaternal alloimmune thrombocytopenia (FMAIT), the mechanism of this alloimmunization and its prevention is described. Although the humoral arm is more important from the clinical viewpoint, the activation of the cytotoxic arm by HPA alloepitopes is also possible. These polymorphisms also seem to have a role in certain other clinical circumstances, therefore their impact on cardiovascular diseases and haemostatic disorders as well as their role in the transplantation of solid organs and bone marrow is addressed. We conclude that during the last decades, the research of the platelet membrane molecules contributed considerably to the diagnostics, prevention and therapy of the blood coagulation and haemostatic disorders, to the management of the neonatal thrombocytopenias, transfusion-related thrombocytopenias, refractoriness to platelet transfusions and autoimmune disorders. It also changed our view on the role of HPA alloepitopes in bone marrow and solid organ transplantation. In the future, this accumulated knowledge will be useful for the development of the cell-based therapies and immune modulation of both acquired and hereditary diseases.

Genotyping for platelet-specific antigens: techniques for the detection of single nucleotide polymorphisms

Accurate typing of patients for platelet-specific (human platelet) antigens (HPA) is required in several different clinical situations, and blood services need to maintain panels of HPA-typed apheresis platelet donors and whole-blood donors to support HPA alloimmunized patients. Six clinically relevant HPA alloantigen systems have been described and, in addition, a significant number of HPA alloantigens with a highly skewed allele frequency or of very low immunogenicity have been reported. Certain well-characterized biallelic systems such as Gov have not as yet been included in the HPA nomenclature but are included in this review. Biochemical studies have identified the platelet membrane proteins on which the HPA antigens are localized. Cloning of the genes encoding these proteins and the realization that there is adequate mRNA in fresh platelets has led to identification of the molecular basis of HPA antigens over the last decade. All but one of the biallelic platelet-specific alloantigen systems are based on a single nucleotide polymorphism in the DNA sequence, corresponding to a single amino acid substitution in the encoded primary protein sequence. The discovery of the genetic basis of the alloantigens has allowed the development of polymerase chain reaction-based techniques for HPA genotyping using genomic DNA. The genetic basis of the HPA alloantigens, the most commonly used genome typing techniques and their pitfalls, and future developments, are discussed in this review.

A functional platelet fibrinogen receptor with a deletion in the cysteine-rich repeat region of the beta(3) integrin: the Oe(a) alloantigen in neonatal alloimmune thrombocytopenia

This report describes a new low-frequency alloantigen, Oe(a), responsible for a case of neonatal alloimmune thrombocytopenia (NAIT). In a population study none of 600 unrelated blood donors was an Oe(a) carrier. By immunochemical studies the Oe(a) antigen could be assigned to platelet glycoprotein (GP) IIIa. Sequencing of GPIIIa complementary DNA from an Oe(a) (+) individual showed deletion of a lysine residue at position 611 (DeltaLys(611)). Analysis of 20 Oe(a) (-) and 3 Oe(a) (+) individuals showed that the DeltaLys(611) form of GPIIIa was related to the phenotype. Anti-Oe(a) reacted with the DeltaLys(611), but not with the wild-type isoforms on stable transfectants expressing GPIIIa, indicating that DeltaLys(611) directly induces the expression of Oe(a) epitopes. Under nonreducing conditions the Pro(33)DeltaLys(611) variant migrated with a slightly decreased molecular weight compared to the Pro(33)Lys(611) isoform suggesting that DeltaLys(611) has an influence on the disulfide bonds of GPIIIa. The Pro(33)DeltaLys(611) GPIIIa could undergo conformational changes and bind to fibrinogen in a similar manner as the Pro(33)Lys(611) isoform. No difference was found in the tyrosine phosphorylation of pp125(FAK), suggesting that DeltaLys(611) has no effect on integrin function. In contrast to all other low-frequency antigens, the DeltaLys(611) isoform was associated with the HPA-1b, but not with the high frequency HPA-1a allele. Comparison with GPIIIa DNA from nonhuman primates indicated that the HPA-1a allele represents the ancestral form of GPIIIa. It can be assumed that the Oe(a) form did arise as a result of a mutational event from an already mutated GPIIIa allele.

Preparation of single chain variable fragment of MG7 mAb by phage display technology

AIM: To develop the single chain variable fragment of MG₇ murine anti-human gastric cancer monoclonal antibody using the phage display technology for obtaining a tumor-targeting mediator.

METHODS: mRNA was isolated from MG₇ producing murine hybridoma cell line and converted into cDNA. The variable fragments of heavy and light chain were amplified separately and assembled into ScFv with a specially constructed DNA linker by PCR. The ScFvs DNA was ligated into the phagmid vector pCANTAB5E and the ligated sample was transformed into competent E. Coli TG1. The transformed cells were infected with M13K07 helper phage to form MG₇ recombinant phage antibody library. The volume and recombinant rate of the library were evaluated by means of bacterial colony count and restriction analysis. After two rounds of panning with gastric cancer cell line KATOIII of highly expressing MG₇-binding antigen, the phage clones displaying ScFv of the antibody were selected by ELISA from the enriched phage clones. The antigen binding affinity of the positive clone was detected by competition ELISA. HB2151 E.coli was transfected with the positive phage clone demonstrated by competition ELISA for production of a soluble form of the MG₇ ScFv. ELISA assay was used to detect the antigen-binding affinity of the soluble MG₇ ScFv. Finally, the relative molecular mass of soluble MG₇ ScFv was measured by SDS-PAGE.

RESULTS: The V-H, V-L and ScFv DNAs were about 340 bp, 320 bp and 750 bp, respectively. The volume of the library was up to 2 × 10⁶ and 8 of 11 random clones were recombinants. Two phage clones could strongly compete with the original MG₇ antibody for binding to the antigen expressed on KATOIII cells. Within 2 strong positive phage clones, the soluble MG₇ ScFv from one clone was found to have the binding activity with KATOIII cells. SDS-PAGE showed that the relative molecular weight of soluble MG₇ ScFv was 32.

CONCLUSION: The MG₇ ScFv was successfully produced by phage antibody technology, which may be useful for broadening the scope of application of the antibody.

Platelet alloantibodies in transfused patients

BACKGROUND

Patients receiving cellular blood components may form HLA antibodies and platelet-specific alloantibodies.

STUDY DESIGN AND METHODS

Serum samples from a cohort of 252 patients with hematologic or oncologic diseases who are receiving cellular blood components were studied for platelet-reactive antibodies. Specificity of platelet alloantibodies was determined with a panel of typed platelets

RESULTS

Platelet-reactive antibodies were detected in the sera of 113 patients (44.8% of 252), HLA antibodies in the sera of 108 (42.9%), and platelet-specific antibodies in the sera of 20 (8%). The following platelet-specific antibodies were identified: anti-HPA-5b (n = 10), anti-HPA-1b (n = 4), anti-HPA-5a (n = 2), anti-HPA-1a (n = 1), anti-HPA-2b (n = 1), anti-HPA-1b+5b (n = 1), and anti-HPA-1b+2b (n = 1). Fifteen sera from the 108 patients with anti-HLA (13.9%) contained additional platelet-specific alloantibodies, while in 5 sera, platelet-specific alloantibodies only were detected: anti-HPA-5b (n = 4) and anti-HPA-1a (n = 1). Of the 108 sera with HLA antibodies, 29 (26.9%) showed discordant results when studied with the lymphocytotoxicity test and the glycoprotein-specific immunoassay. Ten sera contained panreactive antibodies against platelet glycoproteins (GP) IIb/IIIa, GPIa/IIa, and/or GPIb/IX. Alloimmunization occurred in 58.3 percent of female patients with previous pregnancies, but in only 23.3 percent of those without previous pregnancies (p = 0.0049).

CONCLUSION

Platelet alloantibody specificities in transfused patients (predominantly anti-HPA-5b and -1b with antigen frequencies <30% among whites) differ significantly from those observed in patients with neonatal alloimmune thrombocytopenia or posttransfusion purpura, in whom anti-HPA-1a (antigen frequency >95%) is the most prevalent specificity. HLA antibody detection yields discordant results when the lymphocytotoxicity assay and a glycoprotein-specific immunoglobulin-binding assay are used.

Immune thrombocytopenia in the foetus and the newborn: diagnosis and therapy

Thrombocytopenia is a common condition in intensive care units. However the frequency of neonatal thrombocytopenia in all newborns (< 150 x 10(9)/L) has been estimated at 1-4%. Foetal/neonatal immune thrombocytopenia due to the transplacental passage of maternal antiplatelet IgG is a transient passive disease in an otherwise healthy newborn. The major risk of severe thrombocytopenia is intracranial haemorrhage (ICH) leading to death or neurological impairment. The principal aim in the management of the affected infants is to prevent the deleterious consequences of severe thrombocytopenia. Autoimmune thrombocytopenic purpura (AITP) in pregnant women can induce moderate or severe thrombocytopenia in the foetus or the newborn whatever the mother's disease status. Foetal thrombocytopenia can occur as early as 20 weeks of gestation. The frequency of ICH has been estimated to be 1-3% of cases. Foetal thrombocytopenia cannot be prevented. After birth, thrombocytopenia usually worsens during the first days of life. Postnatal management is usually ly of intravenous immunoglobulins. Neonatal alloimmune thrombocytopenia is considered to be the platelet counterpart of haemolytic disease of the newborn. Severe bleeding in the central nervous system and death (10% of cases) or neurological sequelae (20% of cases) may occur. The incidence of neonatal alloimmune thrombocytopenia has been estimated at 1 per 800-1000 live births. After birth, maternal platelet transfusion is the treatment of choice. Due to the high risk of recurrence of foetal thrombocytopenia in subsequent pregnancies, protocols for antenatal management including maternal therapy with intravenous immunoglobulins and/or corticosteroids, or in utero transfusion have been proposed.

Platelet polymorphisms in thrombotic disorders

Plaque rupture and/or endothelial damage lead to exposure of von Willebrand factor (VWF) and collagen which facilitate the adhesion of circulating platelets via glycoprotein (GP) GPIb-IX-V and integrin alpha2 beta1, respectively, to the damaged vessel wall. This process activates the platelets and leads to a conformational change of a second integrin alphaIIb beta3 that facilitates fibrinogen binding and platelet aggregation. Thrombin generated at the blood-plaque interface converts fibrinogen to fibrin, which stabilizes thrombus growth. Therefore, any genetic differences that might alter surface expression or activity of these receptors could influence the risk for adverse outcome as a result of the hemostatic process. In the last five years, there has been a rapid accumulation of literature concerning the relationship between genetic variations in platelet glycoproteins and risk for coronary heart disease. In this study, we have presented a comprehensive review of the impact of platelet receptor polymorphisms and thrombotic risk.