Human platelet-specific alloantigens: update

Frequency of human platelet antigens (HPA) in the Greek population as deduced from the first registry of HPA-typed blood donors

BACKGROUND AND OBJECTIVES

Human platelet antigens (HPA) play a central role in foetal and neonatal alloimmune thrombocytopenia (FNAIT), post-transfusion purpura and some cases of platelet therapy refractoriness. The frequency distribution of HPA had not been studied in the Greek population before we started to create a registry of HPA-typed apheresis platelet donors. The aim of this study was the determination of the frequency of various HPA in the Greek population, through the establishment of a registry of typed donors.

MATERIALS AND METHODS

Here, we report on the first 1000 platelet donors of Greek origin who gave informed consent and were genotyped for 12 pairs of antithetical HPA by Single Specific Primer-Polymerase Chain Reaction (SSP-PCR), including HPA-1, HPA-3, HPA-5 and HPA-15. Antigen frequencies are reported, and allele frequencies were calculated and compared with other European and non-European populations. Tested donors cover all ABO and Rhesus D antigen spectrum.

RESULTS

Antigen and allele frequencies are very similar to other White populations. The frequency of HPA-1bb is 2.9% in our study, and the frequency of HPA-2b, HPA-4b, HPA-9b and HPA-15b is also slightly higher than in other literature reports, while the frequency of HPA-15b was found higher than that of HPA-15a.

CONCLUSION

We report antigen and allele frequencies for a large array of clinically significant HPA for the first time in the Greek population. Frequencies are consistent with other European populations. This registry of HPA-typed platelet donors, available to donate on demand, is an important asset for the treatment of FNAIT cases in Greece.

Platelet antibodies in immune thrombocytopenia and related conditions

Platelet autoantibodies are a common finding in immune thrombocytopenia (ITP) and in rare cases of antibody-mediated platelet function (“acquired thrombasthenia”). In drug-induced immune thrombocytopenia, antibodies react with platelets only in the presence of the offending drug. Alloantibodies reacting with platelets are induced by transfusion of cellular blood products or during pregnancy. They are responsible for fetal/neonatal alloimmune thrombocytopenia (FNAIT), they are able to cause febrile, nonhemolytic transfusion reactions and they give rise to insufficient platelet increments following platelet transfusions. Two rare transfusion reactions: post-transfusion purpura (PTP) and passive alloimmune thrombocytopenia (PAT) are triggered by platelet alloantibodies. This review discusses the clinical value of tests for platelet antibodies in various clinical situations related to insufficient primary hemostasis.

Timely diagnosis and treatment of neonatal alloimmune thrombocytopenia caused by anti HPA-3a antibody: A case report

RATIONALE

Neonatal alloimmune thrombocytopenia (NAIT) caused by anti HPA-3a antibody is rare, and the clinical features of the syndrome are not specific.

PATIENT CONCERNS

A male infant was noted to be irritable and physical examination revealed the presence of petechiae and bruising on the right arm and thigh after born.

DIAGNOSES

Platelet antibodies were investigated using the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay, platelet genotyping (HPA 1-17) was performed by polymerase chain reaction technique with sequence-specific primers (PCR-SSP). The HPA genotype of the newborn was HPA-3a/b, while that of his mother and his father were HPA-3b/b and HPA-3a/a, respectively. The sera of newborn contained antibody against the platelet of newborn's father. The HPA antibody of the newborn was identified as anti HPA-3a. The newborn was confirmed as a patient of NAIT caused by anti HPA-3a antibody.

INTERVENTIONS

A single dose of intravenous immunoglobulin (IVIG) 1 g/kg was administered from day 3 to day 7.

OUTCOMES

At follow-up 3 months after discharge from the hospital, the baby was developing normally and had a normal platelet count (361 × 109/L).

LESSONS

NAIT caused by anti HPA-3a antibody is rare, and we believe this study can provide insights for diagnosing prospective cases. Prognosis of NAIT caused by HPA3a seems to be favorable if diagnosed and treated in a timely manner.

Human platelet antigens are associated with febrile non-hemolytic transfusion reactions

BACKGROUND

Febrile non-hemolytic transfusion reaction (FNHTR) is the most common type of transfusion reactions, and it could be reduced by transfusing patients with leukocyte-poor blood products. However, FNHTR still occur in certain patients transfused with leukocyte-poor red blood cell (LPR) products. It is examined whether human platelet antigen (HPA) could be a potential membrane antigen that plays a role in FNHTR.

METHODS

A total of 120 inpatient subjects who transfused with LPR (60 in FNHTR group, 60 in control group) were typed for HPA-2, HPA-3, and HPA-15 using sequence specific primer-polymerase chain reaction (SSP-PCR) and electrophoresis.

RESULTS

HPA-2 unmatched rate between donors and patients in FNHTR group was 18%, and only 3% unmatched rate was observed in control group (p=0.0082). FNHTR group was further classified according to the imputability. There was a significant difference (p=0.0041) between FNHTR (probable imputability, infection) group and control group, and more significant difference (p=0.0008) was seen between FNHTR (probable imputability, febrile neutropenia) group and control group.

CONCLUSIONS

Those results indicated that HPA-2 might play roles on inducing FNHTR in patients suffering from infectious diseases and febrile neutropenia. HPA-2 genotyping between donors and recipients might be worth integrating in pre-transfusion testing to increase transfusion safety.

Human Platelet Polymorphism can be a genetic marker associated with HIV/HCV coinfection

To evaluate the associations of HPA polymorphisms -1, -3, and -5 with HIV/HCV coinfection were included in this study 60 HIV/HCV-coinfected patients from the Sao Paulo State health service centers. Data reported by Verdichio-Moraes et al. (2009: J. Med Virol 81:757-759) were used as the non-infected and HCV monoinfected groups. Human Platelet Polymorphism genotyping was performed in 60 Patients co-infected with HIV/HCV by PCR-SSP or PCR-RFLP. HIV subtyping and HCV genotyping was performed by RT-PCR followed sequencing. The data analyses were performed using the χ2 test or Fisher's Exact Test and the logistic regression model. Patients coinfected with HIV/HCV presented HCV either genotype 1 (78.3%) or non-1 (21.7%) and HIV either subtype B (85.0%) or non-B (15%). The Human Platelet Polymorphism-1a/1b genotype was more frequent (P < 0.05) in HIV/HCV coinfection than in HCV monoinfection and the allelic frequency of Human Platelet Polymorphism-5b in the Patients coinfected with HIV/HCV was higher (P < 0.05) than in HCV monoinfected cases and non-infected individuals. These data suggest that the presence of specific HPA allele on platelets could favor the existence of coinfection. On the other hand, Human Platelet Polymorphism-5a/5b was more frequent (P < 0.05) in HIV/HCV coinfected and HCV monoinfected groups than in the non-infected individuals, suggesting that this platelet genotype is related to HCV infection, regardless of HIV presence. Results suggest that the Human Platelet Polymorphism profile in HIV/HCV coinfected individuals differs from the one of both HCV monoinfected and non-infected population. So, the Human Platelet Polymorphism can be a genetic marker associated with HIV/HCV coinfection.

Gene frequencies of human platelet alloantigens 1-5 in two Arab populations

BACKGROUND

Polymorphisms of the human platelet alloantigens (HPA) arise from single base pair substitutions in alleles and lead to changes in amino acids of glycoproteins expressed on platelets. The aim of this study was to determine the gene frequencies of the five common HPA (HPA-1 to -5) in Egyptians and Jordanians and to compare these data with those established for other populations.

MATERIALS AND METHODS

HPA genotyping was done by polymerase chain reaction with sequence-specific primers.

RESULTS

The gene frequencies obtained in Egyptians were: HPA-1a/b, 0.767/0.233; HPA-2a/b, 0.759/0.241; HPA-3a/b, 0.704/0.296; HPA-4a/b, 1/0; HPA-5a/b, 0.728/0.272, while the frequencies in Jordanians were: HPA-1a/b, 0.821/0.179; HPA-2a/b, 0.877/0.123; HPA-3a/b, 0.660/0.340; HPA-4a/b, 1/0; HPA-5a/b, 0.795/0.205. The observed gene frequencies in both populations were in Hardy-Weinberg equilibrium. The gene frequencies for HPA-2b and HPA-5b among Egyptians were the highest reported among Arabs. Except for HPA-2, there were no significant differences in the distribution of HPA-1 to -5 between the two populations.

CONCLUSION

The distributions of HPA alleles among Egyptians and Jordanians are similar to those reported for other Arabs. This study reports the first data on gene frequencies of HPA in Egyptians and Jordanians.

Allelic polymorphisms of human platelets-specific alloantigens in South Tunisian population

OBJECTIVES

Human platelet-specific alloantigens (HPA) are polymorphic epitopes which vary among ethnic groups.

BACKGROUND

In Tunisia, HPA frequencies were determined in North and centre; however, the pattern of HPA in South Tunisian population is not been studied yet. The aim of this work was to determine allelic frequencies of HPA-1, -3, and -5 systems in south Tunisian population, in order to estimate the risk of anti-platelet allo-immunization and to create a register of HPA-typed blood donors.

METHODS

Our study concerned 212 unrelated healthy, regular blood donors from southern Tunisia. Allelic polymorphisms of each system were determined using a polymerase chain reaction with sequence-specific primers.

RESULTS

Genotype frequencies a/a, a/b, and b/b were, respectively, 0.670, 0.288, and 0.042 for HPA-1 system, 0.430, 0.462, and 0.108 for HPA-3 system, and 0.750, 0.241, and 0.009 for HPA-5 system. The allele frequencies were 0.814 and 0.186 for HPA-1a and -1b alleles; 0.660 and 0.340 for HPA-3a and -3b alleles and 0.870, and 0.130 for HPA-5a and -5b alleles.

DISCUSSION

The reported frequencies are more similar to those of Caucasians than those of north Tunisian population.

[Is a non-invasive management allowed for maternofetal alloimmune thrombocytopenia? Experience over a 10-year period]

OBJECTIVES

Our purpose was to study a non-invasive management of fetomaternal alloimmune thrombocytopenia (FMAIT).

PATIENTS AND METHODS

Between 1996 and 2005, 18 women were treated. The population was divided into 2 groups: patients with a history of intracranial haemorrhage (ICH) in the older sibling received weekly intravenous immunoglobulin (IVIG) therapy to the mother (1 g/kg per week) without initial cordocentesis whereas patients with a history of neonatal thrombocytopenia did not undergo any treatment.

RESULTS

All pregnancies with a previous FMAIT were monitored with serial ultrasound scans without cordecentesis. 15 patients had HPA-1, 2 HPA-3 and 1 HPA-5 immunizations. Weekly intravenous immunoglobulin therapy was administered in 5 patients with a history of ICH in the older sibling. Two of these delivered thrombocytopenic children; one had a platelet count < 50 x 10(9)/l. For the 13 women (one twin) who had a sibling with neonatal thrombocytopenia, 11/14 newborns had a platelet count < 50 x 10(9)/l. Predelivery fetal blood sampling were performed in 8/18 pregnancies. The neonatal periods of the 19 children were uncomplicated and no ICHs were observed.

DISCUSSION AND CONCLUSION

Our results suggest that a non-invasive strategy avoiding serial cordocentesis may be an effective therapy in patients who are at risk of fetal and neonatal alloimmune thrombocytopenia.

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.

Human platelet alloantigens (HPAs): PCR-SSP genotyping of a UK population for 15 HPA alleles

Alloimmunization to human platelet alloantigens (HPAs) is responsible for neonatal alloimmune thrombocytopenia (NAIT), post-transfusional purpura (PTP) and platelet transfusion refractoriness. HPAs may also have a role as histocompatibility antigens in transplantation as well as associations with cardiac disease. We have developed a polymerase chain reaction-sequence-specific primer (PCR-SSP) assay capable of detecting 15 HPA allelic variants. As part of the validation of the assay, 134 UK renal donors were genotyped to determine HPA allele frequencies in the UK population. The HPA allele frequencies obtained are consistent with those of the other European studies: GP1A*1 (HPA-5a) and GP1A*2 (HPA-5b), 0.914 and 0.086, respectively; GP1BA*1 (HPA-2a) and GP1BA*2 (HPA-2b), 0.925 and 0.075; GP2B*1 (HPA-3a) and GP2B*2 (HPA-3b), 0.627 and 0.373; GP3A*1 (HPA-1a) and GP3A*2 (HPA-1b), 0.840 and 0.161. The rare alleles GP2B*3 (HPA-9bw) and GP3A*3 to *8 (HPA-4b, -6b, -7bw, -8bw, -10bw and -11bw, respectively) were all absent. This comprehensive HPA genotyping assay allows rapid, accurate and reproducible results at low cost.

HPA-5b (Bra ) neonatal alloimmune thrombocytopenia in Quebec: incidence and clinical outcome in 31 cases

BACKGROUND

Clinical detection of neonatal allo-immune thrombocytopenia (NAITP) is often less than the incidence predicted in prospective studies. The aims of this study were to calculate the observed and expected incidence of NAITP in Quebec, Canada, and to evaluate the clinical outcome of infants with anti-HPA-5b NAITP.

STUDY DESIGN AND METHODS

Records from 1998 to 2002 of the only PLT serology laboratory for the province of Quebec were reviewed, as were hospital charts of all HPA-5 cases. The number of expected NAITP cases was estimated with known alloantigen gene frequencies.

RESULTS

Ninety cases of NAITP were identified. The clinical detection rate was 1 in 4100, with 9 to 30 percent of expected HPA-1a and 11 to 23 percent of expected HPA-5b NAITP cases detected. Seventy-eight percent of cases of HPA-5b NAITP were asymptomatic. Sixty-three percent of all deliveries but 94 percent of HPA-5b cases occurred in hospitals performing cord blood PLT counts.

CONCLUSION

The NAITP detection rate was 25 to 50 percent of the rate reported in prospective trials. The less severe clinical presentation of NAITP owing to HPA-5b was confirmed. The frequent routine determination of cord blood PLT counts may explain increased detection of asymptomatic NAITP involving anti-HPA-5b.

Adhesion molecules and atherosclerosis

One early phase of atherosclerosis involves the recruitment of inflammatory cells from the circulation and their transendothelial migration. This process is predominantly mediated by cellular adhesion molecules, which are expressed on the vascular endothelium and on circulating leukocytes in response to several inflammatory stimuli. Selectins (P, E and L) and their ligands (mainly P-selectin ligand) are involved in the rolling and tethering of leukocytes on the vascular wall. Intercellular adhesion molecules (ICAMs) and vascular cell adhesion molecules (VCAM-1), as well as some of the integrins, induce firm adhesion of inflammatory cells at the vascular surface, whereas platelet endothelial cellular adhesion molecules (PECAM-1) are involved in extravasation of cells from the blood compartment into the vessel and underlying tissue. For most of the cellular adhesion molecules, except integrins, soluble forms have been identified in the circulation although their origins are not fully understood. Several lines of evidence support a crucial role of adhesion molecules in the development of atherosclerosis and plaque instability. Expression of VCAM-1, ICAM-1 and L-selectin has been consistently observed in atherosclerotic plaques. There is accumulating evidence from prospective studies for a predictive role of elevated circulating levels of sICAM-1 in initially healthy people, and of sVCAM-1 in patients at high risk or with overt CAD. A large number of common polymorphisms has been identified in the genes encoding the different adhesion molecules, but studies investigating their relationship either with soluble forms or with CAD are still sparse and often based on small samples. Further research is needed to firmly establish the potential clinical and therapeutic utilities of (soluble) adhesion molecules, but results in both fields hold the promise that in future, adhesion molecules might add information for clinical risk prediction and serve as therapeutic targets.

Resistance in vitro to low-dose aspirin is associated with platelet PlA1(GP IIIa) polymorphism but not with C807T(GP Ia/IIa) and C-5T kozak (GP Ibα) polymorphisms

OBJECTIVES

We investigated whether three platelet gene polymorphisms, Pl(A1/A2), C807T, and C-5T Kozak (encoding, respectively, for platelet membrane glycoproteins (GP) IIIa, GP Ia/IIa, GP Ibalpha), could contribute to the resistance to a low dose of aspirin (160 mg/day).

BACKGROUND

Aspirin antiplatelet effect is not uniform in all patients, and the mechanism by which some patients are in vitro resistant to aspirin remains to be determined. However, it has been suggested that polymorphisms of platelet membrane glycoproteins might contribute to aspirin resistance.

METHODS

Ninety-eight patients on aspirin (160 mg/day) for at least one month were enrolled. Aspirin resistance was measured by the platelet function analyzer (PFA)-100 analyzer; genotyping of the three polymorphisms was performed using a polymerase chain reaction-based restriction fragment-length polymorphism analysis.

RESULTS

Using a collagen/epinephrine-coated cartridge on the PFA-100, the prevalence of aspirin resistance was 29.6% (n = 29). Aspirin-resistant patients were significantly more often Pl(A1/A1) (86.2%; n = 25) than sensitive patients (59.4%; n = 41; p = 0.01). Of the 29 patients, 25 were reevaluated after having taken 300 mg/day aspirin for at least one month. Only 11 patients still have nonprolonged collagen epinephrine closure time, and these were all Pl(A1/A1). No relation was found between resistance status and C-5T Kozak or C807T genotypes.

CONCLUSIONS

Platelets homozygous for the Pl(A1) allele appear to be less sensitive to inhibitory action of low-dose aspirin. This differential sensitivity to aspirin may have potential clinical implications whereby specific antiplatelet therapy may be best tailored according to the patient's Pl(A) genotype.

Update on leucodepletion, HLA and platelet serology at Lisbon Regional Blood Centre

The characteristic performance of some leucodepletion processes at the Lisbon Regional Blood Centre is presented. The current position on HLA and platelet serology is briefly described.

[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.

Expression of low-frequency Ala108Pro substitution in the platelet glycoprotein Ibbeta gene

We determined the gene frequency of the glycoprotein (GP) Ibbeta Ala108Pro substitution. The Pro108 allele was not found in 208 healthy Japanese and 200 healthy Caucasians. In vitro expression studies showed surface expression of the GPIbbeta Pro108 variant, suggesting the possibility of the involvement of the substitution as an alloantigen.

Rapid and reliable genotyping of human platelet antigen (HPA)-1, -2, -3, -4, and -5 a/b and Gov a/b by melting curve analysis

BACKGROUND

The probability for occurrence of neonatal alloimmune thrombocytopenic purpura (NAITP) depends largely on the frequency of each individual phenotype in various populations. In caucasians, antibodies to human platelet antigen (HPA)-1a are the major cause of neonatal alloimmune thrombocytopenic purpura, whereas in the Japanese population, antibodies to HPA-4b is most frequently involved in NAITP. Conventional PCR techniques for platelet antigen genotyping rely on sequence-specific primers (SSPs) and detection by gel electrophoresis, a method which is laborious and time consuming. New PCR technology, measuring the match of a hybridization probe with its target and thereby allowing simultaneous detection of both alleles, provides an efficient tool for genotyping of the HPA systems.

STUDY DESIGN AND METHODS

A total of 105 healthy blood donors were genotyped for HPA-1, -2, -3, -4, and -5 a/b and Gov a/b with new primers and probes designed for mutation detection by melting curve analysis (using LightCycler technology). Donor DNA was independently genotyped by an allele-specific assay, using SSPs, in a reference laboratory.

RESULTS

There was full concordance between the two genotyping methods, and genotype frequencies were comparable with previous studies in caucasians.

CONCLUSION

We present rapid and reliable detection systems for HPA-1, -2, -3, -4, and -5 a/b and Gov a/b based on mutation detection of both alleles simultaneously by melting curve analysis. As the Gov system has been reported to have similar frequency of involvement in alloimmune thrombocytopenia as HPA-5, the opportunity for genotyping should aid the diagnosis of such patients.

Human platelet alloantigen polymorphism in Glanzmann's thrombasthenia and its impact on the severity of the disease

Glanzmann's thrombasthenia (GT) is an autosomal recessive disorder of platelets caused by the deficiency or abnormality of platelet receptors. Several platelet alloantigen systems reside on glycoprotein (GP) IIb and GPIIIa, of which the human platelet antigen 1 (HPA-1) system is important. Studies have shown that, in the normal population, the HPA-1b phenotype results in increased platelet aggregation and increased fibrinogen binding, increasing the risk of myocardial infarction. GT produces severe bleeding, but in a subset of patients has a relatively milder course. Forty-one GT patients and 100 healthy control subjects were genotyped for platelet alloantigens HPA-1 to HPA-6, using PCR-ASA (polymerase chain reaction-allele-specific amplification), and for GPIIb-IIIa expression and fibrinogen binding using flow cytometric techniques. Platelet alloantigen distributions were similar in the patient and control groups. With the exception of the two HPA-1b/1b homozygous patients (> 10%), 25 GT patients had less than 5% aggregation to 6 micro mol/l ADP, and 16 patients showed between 5% and 10% aggregation to 6 micro mol/l ADP. Seven out of 37 patients with HPA-1a/1a phenotype showed 1-5% fibrinogen binding and GPIIb-IIIa receptors. The two HPA-1b/1b patients showed 34.6% and 32% fibrinogen binding and > 10% GPIIb-IIIa receptors. This study determined the platelet alloantigen distribution in a large cohort of unrelated GT patients from western India. GT patients homozygous for HPA-1b/1b had higher levels of platelet aggregation and fibrinogen binding as well as a milder course, as evidenced by infrequent epistaxis and no transfusion requirement to date.

Isoimmunization against CD36 (glycoprotein IV): description of four cases of neonatal isoimmune thrombocytopenia and brief review of the literature

BACKGROUND

Platelet CD36 (glycoprotein [GP] IV) deficiency occurs in 3 to 5 percent of persons of Asian or African ancestry. A subset of these individuals is at risk for immunization against CD36, but the magnitude of this problem and its significance in transfusion medicine have not yet been clarified.

STUDY DESIGN AND METHODS

Clinical and laboratory aspects of neonatal thrombocytopenia involving five infants born to four CD36- mothers were characterized. The CD36 gene was sequenced in three mothers. The literature concerning isoimmunization against CD36 was reviewed and summarized.

RESULTS

Isoantibodies reactive with CD36 on normal platelets and platelets from the fathers were identified in each of the four mothers. Two African-American mothers were homozygous for a 1264TG mutation in the CD36 gene. A mother of Italian ancestry was homozygous for a previously unidentified deletion of exons 1 through 3. Previously reported cases of isoimmunization against CD36 were reviewed and summarized.

CONCLUSION

Isoimmunization against CD36 can cause neonatal isoimmune thrombocytopenia (NITP), refractoriness to platelet transfusions, and post-transfusion purpura. Immunization against this glycoprotein (GP) should be considered in patients with apparent alloimmune platelet disorders not explained by immunization against recognized platelet-specific alloantigens, especially in persons of African, Asian, and, possibly, Mediterranean ancestry.

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.

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.

Iron deficiency anaemia in young women

OBJECTIVES

The expression density of GPIaIIa, the primary platelet collagen receptor (integrin alpha2beta1), is linked to two polymorphisms (GPIa-807C/T and HPA-5a/b). During evolution a gene shift from the genotypes GPIa-807CC-HPA-5bb to the genotypes GPIa-807CT-HPA-5aa has taken place. The aim of the study was to assess whether iron deficiency anaemia (e.g. increased blood loss) in young women could be associated with a specific genotype, indicating a role as potential evolutionary selection factor.

STUDY DESIGN

Women between 18 and 40 yr of age presenting for their first blood donation were asked about alimentary habits and use of oral contraception. Haemoglobin and serum ferritin were measured and the GPIa-C807T and HPA-5 genotypes were determined.

RESULTS

Two hundred women were included and grouped according to the WHO definition for iron deficiency anaemia (haemoglobin <121 g L(-1) and ferritin <15 microg L(-1)). Eight women fulfilled both WHO-criteria for iron deficiency anaemia, 145 women fulfilled none. No differences regarding age, use of oral contraceptives, alimentary habits, and HPA-5 were found between the groups. The GPIa-807CC genotype was strongly over-represented in the WHO-anaemic women as compared to the non-WHO-anaemic women (87.5% vs. 33.1%, P=0.003).

CONCLUSION

Iron deficiency anaemia in young women might have been the evolutionary disadvantage causing the gene shift from GPIa-807CC to 807CT.

Neonatal alloimmune thrombocytopenia in the Irish population: a discrepancy between observed and expected cases

AIMS

To estimate the rate of detection of neonatal alloimmune thrombocytopenia (NAITP) in the Irish population, to investigate clinical presentation and outcome in affected infants, and to determine the extent, if any, to which this condition is underdiagnosed at present.

METHODS

Cases were collected in a retrospective fashion from a review of platelet serology laboratory records from January 1992 to December 2000. Clinical data were obtained from hospital records. Testing for maternal antiplatelet antibody was by one or more of the following: the platelet suspension immunofluorescence test, a commercial antigen capture enzyme linked immunosorbent assay (GTI-PakPlus), and the monoclonal antibody immobilisation of platelet antigens assay. Platelet antigen typing was by the polymerase chain reaction technique with sequence specific primers.

RESULTS

Twenty seven serologically verified cases of NAITP were identified in 18 families. Maternal antibody to human platelet antigen 1a accounted for 25 of the 27 confirmed cases. Twenty one of 26 infants were born with severe thrombocytopenia. Nineteen of 27 infants had bleeding manifestations at birth. Petechiae and bruising were most commonly observed (n = 17). There were no documented cases of intracranial haemorrhage in this group but systematic cranial ultrasound was not performed.

CONCLUSIONS

Screening studies in predominantly white populations have estimated the incidence of NAITP to be between 1 in 1000 and 1 in 2000 live births. With 50 000 births each year in Ireland, these results give a clinical detection rate for NAITP of just 1 case in 16 500 live births, strongly suggesting that NAITP is currently underdiagnosed. Antenatal screening to detect women at risk of having babies with NAITP is now scientifically feasible and should be considered.

Frequency distribution of antigens in the human platelet antigen-1 system in the western Indian population

BACKGROUND

Neonatal alloimmune thrombocytopenic purpura (NAITP) occurring because of fetomaternal incompatibility in the human platelet antigen-1 (HPA-1) system is increasingly being detected worldwide. Several studies have reported the frequency and distribution of HPA-1 alleles in different countries and ethnic populations. A paucity of data regarding the frequency of the antigens in the HPA-1 system in the Indian population prompted an undertaking of this study. The molecular method of genotyping the platelet antigens is preferred to serology. It will enable future prenatal diagnosis in mothers suspected to have NAITP so that they can be managed better.

STUDY DESIGN AND METHODS

Five hundred six unrelated subjects were screened for the alleles in the HPA-1 system, of which 185 were healthy males and 321 were females. DNA was extracted from the peripheral blood WBCs of these subjects, followed by PCR amplification and agarose gel electrophoresis of the PCR-amplified products.

RESULTS

Four hundred two out of 506 subjects (79.44%) were found to be homozygous for HPA-1a. Ninety-nine subjects (19.57%) were heterozygous HPA-1a/HPA-1b, and five subjects out of 506 (0.99%) were homozygous for HPA-1b.

CONCLUSION

Homozygosity for HPA-1b exists in the Indian population at a frequency of 0.99 percent, whereas homozygosity for HPA-1a is present in approximately 79 percent of the population. Hence, 0.98 x 0.79 of the females (0.77%) in the reproductive age group are likely to be pregnant with an HPA-1a-positive fetus, leading to a setting in which NAITP might develop. The development of NAITP also depends on the HLA type of the mother; nevertheless, the number of pregnancies in which the fetus is at risk for NAITP in India is quite significant.

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.

Post-transfusion alloimmunization to granulocytes and platelets in Japanese patients as determined by the MPHA method

The current occurrence of alloimmunization to granulocytes and platelets after blood transfusion is unclear due to the fact that antibody assays are cumbersome. Using the MPHA method with extracted granulocyte and platelet antigens, a randomized, blinded trial was conducted to investigate three types of alloantibodies in 431 Japanese patients receiving leukocyte-depleted blood transfusions prepared with or without our latest leukocyte-reduction filter. The frequency of granulocyte, platelet and HLA class I alloantibodies was 0.44%, 0.44% and 16.74%, respectively, in patients receiving non-filtered products and 0%, 0% and 0.49%, respectively, in patients receiving filtered products. The granulocyte antibody reacted with an antigen approximately of 51 KDa. The platelet-specific alloantibody was associated with GPIIb/IIIa and GPIa/IIa. The important factors affecting alloimmunization were the transfusion dose and the use of unfiltered platelet products.

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.

Platelet-specific alloantigens in cadaveric renal transplantation. A prospective study. Effect of HPA-5b mismatch in acute vascular rejection of renal allografts

This prospective study comprised 166 renal allograft-recipient pairs that were studied for human platelet alloantigens (HPA) 1-3 and 5, which have been shown to be expressed by adhesion molecules of the vascular endothelium. Four of the five (80%) HPA-5a5a regraft recipients developing acute vascular rejection (AVR) had received an HPA-5b-incompatible graft in contrast to one of the 32 (3%) regraft recipients without rejection. The occurrence of AVR was not explained by the degree of HLA mismatches. All four regraft recipients of an HPA-5b-mismatched graft with AVR were HLA-A3,B7, and the combination of HLA-A3 and/or B7 match and an HPA-5b-mismatched graft was associated with AVR. No antibodies against HPA-5b were detected in the patients with AVR of an HPA-5b-mismatched graft. These preliminary findings suggest that HPA-5b is a minor histocompatibility antigen involved in the development of AVR.

The management of alloimmune neonatal thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAITP), defined as thrombocytopenia (platelet count < 150 x 10(9)/l) due to transplacentally acquired maternal platelet alloantibodies, occurs in approximately 1 per 1200 live births in a Caucasian population. In such a population, the majority (> 75 percent) of cases are due to fetomaternal incompatibility for the platelet specific alloantigen, HPA-1a (P1A1, Zwa). Incompatibility for the HPA-5b (Bra) alloantigen is the next most frequent cause of NAITP in Caucasians; much less common is NAITP due to incompatibility for HLA, blood group ABO or other platelet-specific antigens. In non-Caucasian populations (e.g. Orientals) HPA-1a incompatibility is a rare cause of NAITP and other alloantigens e.g. HPA-4b (Penb, Yuka) are implicated. The greatest clinical challenge relates to the antenatal management of pregnant women alloimmunized to the HPA-1a (P1A1, Zwa) antigen, and particularly the subset of such women who have a history of a previously affected infant with severe thrombocytopenia and/or intracranial hemorrhage (ICH). The risk of antenatal ICH in the fetus of such women is high enough to merit intervention, either weekly infusion of high-dose intravenous immunoglobulin G (IVIG) with or without corticosteroids given to the mother (the preferred approach in North American centres), or repeated in-utero fetal platelet transfusions (the preferred treatment approach in some European centres). Post-natal management of severely affected infants centres on the rapid provision of compatible antigen-negative platelets harvested from the mother or a phenotyped donor. The value of antenatal screening programs to detect 'at risk' alloimmunized women during pregnancy continues to be debated.

B-lymphoblastoid cell lines as a source of reference DNA for human platelet and neutrophil antigen genotyping

BACKGROUND

Human platelet and neutrophil antigens (HPAs, HNAs) are targets for platelet or granulocyte antibodies causing immune thrombocytopenia or neutropenia, respectively. Currently, genotyping is replacing phenotyping as the preferred method of diagnosis of immune cytopenia. To establish a reliable genotyping analysis, however, the availability as reference DNA of genomic DNA from persons of known genotype is essential.

STUDY DESIGN AND METHODS

By the use of Epstein-Barr virus transformation, panels of B-lympho-blastoid cell lines (B-LCLs) from HPA- and HNA-phenotyped individuals were developed. Genomic DNA was isolated from these cell lines and tested as reference DNA for genotyping of persons for HPAs and HNAs.

RESULTS

DNA derived from these B-LCLs was typed by polymerase chain reaction-restriction fragment length polymorphism and -sequence-specific primers. The results were in accordance with the genotyping from peripheral blood cells. These results were confirmed by 24 laboratories in Germany in a blind study.

CONCLUSION

The inexhaustible source of reference DNA derived from B-LCLs allowed the evaluation of reliable HPA and HNA genotyping for quality control purposes. It should facilitate the development of DNA typing in blood centers and clinical laboratories.

Prenatal treatment of severe fetomaternal alloimmune thrombocytopenia

Prenatal treatment of fetomaternal alloimmune thrombocytopenia (FMAIT) in previously affected families is of great clinical importance. We report here our experience in the prenatal treatment of 15 severely thrombocytopenic fetuses. Thrombocytopenia was in 13 cases due to immunization to HPA-1a, in one case to HPA-5b, and in one case to HPA-6b. Thirteen fetuses received altogether 34 intrauterine platelet transfusions, seven of them in combination with maternal-administered intravenous gammaglobulin (IVIG) and two in combination with IVIG and prednisone. Six of the 13 fetuses had only one transfusion just prior to delivery. In our experience, IVIG seemed to be less effective than reported; only two fetuses of eight treated initially with weekly maternal-administered IVIG responded, and these were the mildest affected cases in the study. On the other hand, owing to the short survival time, weekly platelet transfusions could only partly maintain a safe platelet count in the four fetuses treated with serial intrauterine platelet transfusions. The number of transfusions needed to be limited because of the high cumulative risk associated with repeated procedures. Three of 34 intrauterine platelet transfusions were associated with near-loss of three different fetuses due to prolonged fetal bradycardia after the transfusion. In conclusion, overall neonatal outcome was good, with no mortality; among the study group there was no intracranial haemorrhage (evaluated by postnatal ultrasonography) compared with one case in their untreated siblings. However, the problem of the optimal treatment of FMAIT remains to be solved. For the moment, the treatment of choice is a combination of maternal IVIG and platelet transfusions in severely affected cases. Serial fetal blood samplings (FBS) are needed in order to monitor the fetus with sufficient care.

Frequencies of platelet-specific alloantigen systems 1-5 in three distinct ethnic groups in Brazil

The human platelet antigen (HPA) systems are related to immune platelet disorders as well as to the development of occlusive vascular disease. Several distinct biallelic HPA systems are known, and a heterogeneous distribution of HPA alleles has been described among distinct ethnic groups. In this study we genotyped 320 carefully selected individuals from three distinct ethnic groups in Brazil (Caucasians, Blacks and Amazonian Indians) for the HPA-1, -2, -3, -4 and -5 systems. A similar prevalence for all HPA alleles was found in Brazilians of Caucasian and Black descent. These data contrast with those reported for similar ethnic groups in other countries. Among the Amazonian Indians, no b allele of the HPA-1, -4 and -5 systems was identified. The data presented here could be useful in the diagnosis of alloimmune platelet disease, in genetic counselling and in the development of screening programmes for HPA-related diseases.

The 2 Gene Coding Sequence T807/A873 of the Platelet Collagen Receptor Integrin 2β1 Might Be a Genetic Risk Factor for the Development of Stroke in Younger Patients

The polymorphisms C807T and G873A of the platelet integrin 2β1 (collagen receptor glycoprotein [GP] Ia-IIa) are linked to the expression density of this receptor. The GPIa T807/A873 allele causes a higher receptor expression, enhancing platelet binding to collagen. This might present a genetic predisposition for the development of thromboembolic complications. In this case-control study, the genotypes of the GPIa C807T polymorphism and presence of conventional risk factors (hypertension, diabetes mellitus, and smoking) were compared in stroke patients and patients without cerebrovascular disease (non-CVD patients) ≤50 years of age (n = 45 and 41, respectively) and in stroke patients and non-CVD patients more than 50 years of age (n = 182 and 129, respectively. In patients ≤50 years of age, the T807 allele was the only overrepresented variable (P = .023; odds ratio, 3.02; 95% confidence interval, 1.20 to 7.61) and an independent risk factor, whereas the presence of conventional risk factors was similar between stroke patients ≤50 years of age and non-CVD patients ≤50 years of age. Large epidemiological studies should prove whether the platelet collagen receptor GPIa-IIa T807 allele is an independent risk factor for the development of stroke in younger patients.

The 2 Gene Coding Sequence T807/A873 of the Platelet Collagen Receptor Integrin 2β1 Might Be a Genetic Risk Factor for the Development of Stroke in Younger Patients

The polymorphisms C807T and G873A of the platelet integrin 2β1 (collagen receptor glycoprotein [GP] Ia-IIa) are linked to the expression density of this receptor. The GPIa T807/A873 allele causes a higher receptor expression, enhancing platelet binding to collagen. This might present a genetic predisposition for the development of thromboembolic complications. In this case-control study, the genotypes of the GPIa C807T polymorphism and presence of conventional risk factors (hypertension, diabetes mellitus, and smoking) were compared in stroke patients and patients without cerebrovascular disease (non-CVD patients) ≤50 years of age (n = 45 and 41, respectively) and in stroke patients and non-CVD patients more than 50 years of age (n = 182 and 129, respectively. In patients ≤50 years of age, the T807 allele was the only overrepresented variable (P = .023; odds ratio, 3.02; 95% confidence interval, 1.20 to 7.61) and an independent risk factor, whereas the presence of conventional risk factors was similar between stroke patients ≤50 years of age and non-CVD patients ≤50 years of age. Large epidemiological studies should prove whether the platelet collagen receptor GPIa-IIa T807 allele is an independent risk factor for the development of stroke in younger patients.

Association of the Platelet Glycoprotein Ia C807T Gene Polymorphism With Nonfatal Myocardial Infarction in Younger Patients

Recently, we have shown that two alleles of the glycoprotein (GP) Ia gene, designated C807 and T807, are associated with low or high platelet GPIa-IIa density and consequently with slower or faster rate of platelet adhesion to type I collagen, respectively. This polymorphism could therefore present a genetic predisposition for the development of thrombotic disease and hemostasis. We investigated the relationship of the GPIa C807T dimorphism to the risk of coronary artery disease (CAD) and myocardial infarction (MI). An allele-specific polymerase chain reaction (PCR) was developed for genotyping of C807T polymorphism. DNA samples from 2237 male patients who underwent coronary angiography on account of coronary heart disease as verified illness or presumptive diagnosis were genotyped. The odds ratio was calculated as an estimate of the relative risk by multiple logistic regression. We found a strong association between the T allele and nonfatal MI among individuals younger than the mean age of 62 years (n = 1,057; odds ratio, 1.57; P = .004). The odds ratio of MI increased for T807 carriers with decreasing age. The highest odds ratio was detected within the youngest 10% of the study sample (&lt;49 years; n = 223; odds ratio, 2.61; P = .009). In contrast, no evidence of an association between C807T dimorphism with CAD was found. Our findings suggest that inherited platelet GP variations might have an important impact on acute thrombotic disease.

Association of the Platelet Glycoprotein Ia C807T Gene Polymorphism With Nonfatal Myocardial Infarction in Younger Patients

Recently, we have shown that two alleles of the glycoprotein (GP) Ia gene, designated C807 and T807, are associated with low or high platelet GPIa-IIa density and consequently with slower or faster rate of platelet adhesion to type I collagen, respectively. This polymorphism could therefore present a genetic predisposition for the development of thrombotic disease and hemostasis. We investigated the relationship of the GPIa C807T dimorphism to the risk of coronary artery disease (CAD) and myocardial infarction (MI). An allele-specific polymerase chain reaction (PCR) was developed for genotyping of C807T polymorphism. DNA samples from 2237 male patients who underwent coronary angiography on account of coronary heart disease as verified illness or presumptive diagnosis were genotyped. The odds ratio was calculated as an estimate of the relative risk by multiple logistic regression. We found a strong association between the T allele and nonfatal MI among individuals younger than the mean age of 62 years (n = 1,057; odds ratio, 1.57; P = .004). The odds ratio of MI increased for T807 carriers with decreasing age. The highest odds ratio was detected within the youngest 10% of the study sample (<49 years; n = 223; odds ratio, 2.61; P = .009). In contrast, no evidence of an association between C807T dimorphism with CAD was found. Our findings suggest that inherited platelet GP variations might have an important impact on acute thrombotic disease.