Genotype frequencies of the human platelet antigen, Ca/Tu, in Japanese, determined by a PCR-RFLP method

Low-frequency human platelet antigens as triggers for neonatal alloimmune thrombocytopenia

BACKGROUND

Twenty-four low-frequency human platelet antigens (LFHPAs) have been implicated as immunogens in neonatal alloimmune thrombocytopenia (NAIT). We performed studies to define more fully how often these antigens trigger maternal immunization leading to NAIT.

STUDY DESIGN AND METHODS

In a Phase 1 study, fathers of selected NAIT cases not resolved by serologic testing but thought to have a high likelihood of NAIT on clinical and serologic grounds were typed for LFHPAs by DNA sequencing. In a Phase 2 study, high-throughput methods were used to type fathers of 1067 consecutive unresolved NAIT cases for LFHPAs. Mothers of 1338 unresolved cases were also typed to assess the prevalence of LFHPAs in a population racially/ethnically similar to the fathers.

RESULTS

In Phase 1, LFHPAs were identified in 16 of 244 fathers (6.55%). In Phase 2, LFPAs were found in only 28 of 1067 fathers (2.62%). LFHPAs were identified in 27 of 1338 maternal samples (2.01%). HPA-9bw was by far the most common LFHPA identified in the populations studied and was the only LFHPA that was significantly more common in fathers than in mothers of affected infants (p = 0.02).

CONCLUSIONS

Maternal immunization against recognized LFHPAs accounts for only a small fraction of the cases of apparent NAIT not resolved by standard serologic testing. Typing of the fathers of such cases for LFHPAs is likely to be rewarding only when a maternal antibody specific for a paternal platelet glycoprotein is demonstrated and/or there is compelling clinical evidence for NAIT.

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.

Human platelet antigens frequencies in Maori and Polynesian populations

BACKGROUND

Allele frequencies of human platelet antigens (HPA) reflect population history and possibility of platelet-specific alloimmunization. Here, we report on screening of variants at HPA loci for Polynesian and Maori subjects.

OBJECTIVES

Our aims are to evaluate new HPA genotyping methods, compile and analyse new HPA datasets for these subjects, use HPA data for tracing ancestry, migration patterns, genetic admixture and its potential influence on health.

MATERIALS AND METHODS

A total of 75 Maori and 25 Polynesian DNA samples were genotyped using commercial BAGene HPA-TYPE DNA-SSP kits, BLOODchip hybridization SNP assays and DNA sequence based typing.

RESULTS

Genotyping was successful and cross validation of PCR-SSP and BLOODchip gave 100% agreement. Among the HPA loci tested, only six are dimorphic (HPA-1 to -3, -5, -6 and -15) and all others are monomorphic. The Polynesians and Maori have the 'a' allele form as the most common for all loci except HPA-15.

CONCLUSIONS

The newly observed HPA data as well as principal coordinate analysis clearly indicate genetic contributions from both, Asia and Australasia in Maori and Polynesian populations together with recent admixture with Europeans. In addition, different prevalences of HPA alleles among Polynesian, Maori and European populations contribute towards different risk profiles for platelet-specific alloimmunization. This is the first report for these populations and our findings are of direct practical relevance for blood transfusion centres, the management of pregnancies, assessment of neonatal alloimmune thrombocytopenia and management of multi-transfused patients.

Neonatal alloimmune thrombocytopenia: pathogenesis, diagnosis and management

Neonatal alloimmune thrombocytopenia, (NAIT) is caused by maternal antibodies raised against alloantigens carried on fetal platelets. Although many cases are mild, NAIT is a significant cause of morbidity and mortality in newborns and is the most common cause of intracranial haemorrhage in full-term infants. In this report, we review the pathogenesis, clinical presentation, laboratory diagnosis and prenatal and post-natal management of NAIT and highlight areas of controversy that deserve the attention of clinical and laboratory investigators.

A new Ser472Asn (Cab2(a+)) polymorphism localized within the αIIb "thigh" domain is involved in neonatal thrombocytopenia

BACKGROUND

A new platelet antigen, Cab2(a+), was identified in a case of severe neonatal alloimmune thrombocytopenia (<8 × 10(9)/L) in twins.

STUDY DESIGN AND METHODS

Coding sequences of αIIb and β3 genes from parents were amplified and sequenced. CHO cell lines expressing wild-type or mutated forms of the complex were established to study the role of the mutation in alloimmunization and in αIIbβ3 functions.

RESULTS

The father and twins were heterozygous for a single αIIb c.1508G>A mutation leading to a Ser472Asn substitution. Immunologic assays with transfected CHO cells revealed the Asn472 form of αIIbβ3 responsible for the Cab2(a+) epitope but not an Ala472 form. Using these cells lines we demonstrated that both Ser472Asn and Ser472Ala substitutions produced limited structural alteration as revealed by the reactivity of a panel of anti-αIIbβ3 monoclonal antibodies (MoAbs). Activated Asn472 and Ala472 forms of αIIbβ3 supported 1) binding of soluble fibrinogen and of the ligand mimetic MoAb PAC-1, 2) ligand-induced binding site epitopes exposure (MoAbs AP-5 and D3GP3), and 3) cell aggregation. Adhesion onto adsorbed fibrinogen was conserved and was specifically inhibited by MoAb AP-2 or peptide RGDS. Finally outside-in signaling was not affected.

CONCLUSION

We have characterized a new low-frequency alloantigen (<1%) resulting from the Ser472Asn substitution in αIIb and shown this polymorphism to have a limited effect, if any, on the αIIbβ3 complex functions.

Neonatal alloimmune thrombocytopenia caused by an antibody specific for a newly identified allele of human platelet antigen-7

BACKGROUND

Neonatal alloimmune thrombocytopenia (NAIT) is a neonatal disorder characterized by maternal alloimmunization against fetal platelet (PLT) antigens inherited from the father. A healthy 30-year-old Japanese woman (Hit) gave birth to her second child after an uneventful pregnancy. Nine hours after birth, the infant presented with severe petechiae and a PLT count of 6 x 10(9)/L.

STUDY DESIGN AND METHODS

To elucidate the maternal cause of NAIT in the infant, serologic and genetic studies, including PLT genotyping and sequence-based analysis, were conducted. Additionally, serologic screening for the new PLT antigen was performed.

RESULTS

Serum from the NAIT infant's mother contained antibodies directed against a human PLT antigen (HPA) of the newborn. Using five-cell-lineage flow cytometry, we localized the antigen to a PLT glycoprotein (GP). Subsequent monoclonal antibody immobilization of PLT antigen assay and PLT immunofluorescence inhibition experiments localized the antigen to the GPIIIa subunit of the GPIIb/IIIa complex. GPIIIa localization was confirmed by sequence-based typing studies, which identified a 1297C>T (407proline>serine substitution) mutation on the ninth exon of the GPIIIa gene. This mutation identified the third allele of HPA-7. Anti-Hit(a) reacted with mutated GPIIIa-transfected cells but not with stable transfectants expressing wild-type GPIIIa. Serologic screening for Hit(a) in the Japanese population revealed a phenotypic frequency of approximately 0.0015.

CONCLUSIONS

We identified a new third allele of HPA-7, which is characterized by a 1297C>T mutation in the GPIIIa gene. This 1297C>T allele was found in 0.15% of the Japanese population. An antibody against this antigen could be the cause of severe NAIT.

HPA polymorphism in sub-Saharan African populations: Beninese, Cameroonians, Congolese, and Pygmies

The frequency of human platelet antigen-1 (HPA-1) to HPA-11w (excluding HPA-8w) and HPA-15 systems was studied in four sub-Saharan populations: Beninese, Congolese (Democratic Republic of Congo Kinshasa), Cameroonians, and Aka pygmies (Central African Republic). No report of HPA prevalence has previously been published concerning these populations which are characterized by the highest HPA-2b gene frequencies of any reported to date (Aka 0.393, Benin 0.292, Cameroon 0.237, and Congo 0.224) and at lesser degree HPA-5b (Aka 0.405, Congo 0.268, Cameroon 0.254, and Benin 0.182). This study is of great importance (i) particularly in the context of the diversity caused by the population migrations, we may observe today in our hospitals (ii) to confirm that the Pygmy population with distinctive frequencies (absence of the HPA-1b, HPA-2b, and HPA-5b highest frequencies) is an isolated population.

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.

Report on the Tenth International Platelet Genotyping and Serology Workshop on behalf of the International Society of Blood Transfusion

BACKGROUND AND OBJECTIVES

The aims of the 10th International Platelet Serology and Genotyping Workshop were to evaluate the proficiency of platelet immunology determinations.

MATERIALS AND METHODS

There were 40 participants from 25 countries of four continents. Thirty-eight institutions reported results for genotyping, and 38 institutions reported their serological results. For genotyping, EDTA-anticoagulated whole-blood samples were provided (to allow the inclusion of DNA-separation methodology in the analysis) as well as separated DNA of a and b alleles for human platelet antigen (HPA)-1 to -6. For serological evaluations, sera contained allo- and autoantibodies, and for sensitivity testing a standard freeze-dried sample of HPA-5 antibody.

RESULTS

All participants reported HPA-1, -2, -3 and -5 genotyping results; HPA-4 was determined in 29 laboratories and HPA-6 in 21. Results from 16 laboratories were concordant with the majority vote for all allotypes, eight institutions reported one deviation, five laboratories two, and nine laboratories three or more deviations. Twelve institutions had no deviation from the majority vote for HPA antibodies, nine had one, three had two, and 14 had three or more deviations. Most laboratories reported a reactivity of the standard anti-HPA-5b sample with HPA-5b platelets at a dilution of 1:4-1:8. Four laboratories detected anti-Gova in one sample. Seventeen laboratories reported no deviation from the majority vote for pan-reactive platelet antibodies, 12 had one deviation, two had two, and seven had three or more deviations. In addition, seven participants reported antibodies against glycoprotein IV (GPIV), three against glycoprotein V (GPV) and three against CD 109. These results were discussed at a meeting organized jointly with the International Society of Blood Transfusion (ISBT) 2000 Congress.

CONCLUSION

The results for pan-reactive antibodies were heterogeneous with most discrepancies from the majority vote. The provision of sufficient samples for many participants is difficult. Based on the results and discussion it is clear that frequent workshops are needed in the future. Therefore, workshops shall be organized regionally, and each region shall participate with one institution in international workshops. The latter are needed to assure international exchange of experience and quality.

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.

Clinical aspects and typing of platelet alloantigens

Platelet alloantigens can induce the formation of corresponding alloantibodies when exposed to phenotypically negative individuals. These antibodies are responsible for fetal and neonatal alloimmune thrombocytopenia, posttransfusion purpura, passive alloimmune thrombocytopenia and transplantation-associated thrombocytopenia and may contribute to platelet transfusion refractoriness together with HLA antibodies. Besides antibody detection laboratory diagnosis of the clinical syndromes requires alloantigen typing. Furthermore, typed platelet donors are a prerequisite for effective platelet transfusion therapy. Different techniques for phenotyping are well established and easy to perform but they rely on the availability of antisera. Since the molecular genetic background of the clinically most relevant alloantigens has been elucidated during the last years various genotyping methods have been applied to the platelet membrane polymorphisms and thus facilitated widespread platelet alloantigen typing. Generation of antibodies from phage display libraries and of lymphoblastoid cell lines from donors with all genetic variants will allow further developments.

Distribution of human platelet antigens in a Chinese population

We report the distribution of the human platelet antigens HPA-1, -2, -3, -4 and -5 as determined using the polymerase chain reaction with sequence-specific primers in 100 random, healthy Chinese in Hong Kong. The HPA-1a, -2a, -4a and -5a genes were present in every sample tested, HPA-1b, -2b and -5b were rare, and the sample was monomorphic for HPA-4a. HPA-3a and -3b genes showed frequencies of 0.525 and 0.475 respectively. There was no departure from Hardy-Weinberg equilibrium in any of the five HPA systems studied.

Maternal DRB1*1501, DQA1*0102, DQB1*0602 haplotype in fetomaternal alloimmunization against human platelet alloantigen HPA-6b (GPIIIa-Gln489)

Fetomaternal incompatibility of platelet alloantigens may lead to alloimmunization and neonatal alloimmune thrombocytopenia (NAIT). Human platelet alloantigen (HPA) 6b, which associates with residue Gln 489 of platelet membrane glycoprotein IIIa, has been described as a cause of NAIT. We have studied the MHC genes of all available family members in the six thus far reported families with a thrombocytopenic newborn and fetomaternal HPA-6b incompatibility. Maternal HPA-6b antibodies could be detected in five mothers to the altogether seven thrombocytopenic male infants. The MHC genes HLA-DRB, -DQA1, -DQB1, -DPB1, TAP1,2 and HSP70-Hom were studied by using polymerase chain reaction (PCR)-based DNA analysis methods. All five mothers with detectable circulating HPA-6b antibodies at the time of delivery shared an identical DRB1*1501, DQA1*0102, DQB1*0602 haplotype. The sixth, HPA antibody negative mother and a HPA-6b-negative mother to a healthy HPA-6b+ child were negative for this haplotype. The frequency of DRB1*15-positive haplotype was increased in immunized mothers (100%) as compared with the general Finnish population (27%), but the association was not statistically significant after correction. We conclude that there is a potential association between the MHC haplotype DRB1*1501, DQA1*0102, DQB1*0602 and alloimmunization to the HPA-6b antigen and that this alloimmunization probably involves different HLA class II molecules from immunization to HPA-1a.

Gene frequencies of human platelet antigens on glycoprotein IIIa in Japanese

BACKGROUND

Polymorphism of glycoprotein IIIa on human platelets is one of the factors in alloimmunization that causes neonatal alloimmune thrombocytopenia and refractoriness to platelet transfusion.

STUDY DESIGN AND METHODS

DNA typing methods were originally developed to determine the genotypes of five human platelet antigen (HPA) systems located on glycoprotein IIIa: HPA-1, HPA-4, HPA-6W, HPA-7W and HPA-8W. The gene frequencies of these platelet antigens were determined by DNA typing of 331 unrelated Japanese donors.

RESULTS

The gene frequencies of the low-frequency antigens were 0.002, 0.011, and 0.027 for HPA-1b, HPA-4b, and HPA-6W(b), respectively. All 331 Japanese donors tested were HPA-7W(a/a) and HPA-8W(a/a). Moreover, in the present study, none of the donors tested had two or more of these low-frequency antigens.

CONCLUSION

The risk of neonatal alloimmune thrombocytopenia and refractoriness to platelet transfusion induced by the antigens of the HPA-1, HPA-7W, and HPA-8W systems was extremely rare in Japanese. However, attention must be paid to the involvement of the HPA-4 and HPA-6W systems in these clinical disorders.