Posttransfusion purpura following bone marrow transplantation

BACKGROUND : Thrombocytopenia is a major cause of morbidity and hospital expense following bone marrow transplantation. Platelet transfusions in these patients are frequently complicated by the recipient's development of antibodies to HLA class I antigens. When these patients become refractory to the transfusion of HLA-matched platelets, the recipient's platelet antigen phenotype must be determined, to ensure that donor platelets will be phenotypically compatible. Cases of alloimmunization to HPA-1a and HPA-1b resulting in refractoriness to transfused platelets and the subsequent development of a posttransfusion purpura-like syndrome are reported. CASE REPORTS: In the first case, a 43-year-old woman with Stage IV infiltrating ductal breast cancer presented to the hospital for a transplant of autologous peripheral blood stem cells. After the transplant, her platelet count remained less than 10 × 10⁹ per L, despite daily platelet transfusions, including HLA-matched platelets. Fourteen days following the transplant, her serum was found to contain anti-HPA-1a. Initially, the patient was refractory to the transfusion of HPA-1a-negative platelets, but after treatment with intravenous immunoglobulin, she had transient increases in posttransfusion platelet counts. She was also treated with a staphylococcal protein A immunoadsorption column and has not had any such subsequent refractoriness. Her genotype has been found, by use of allele-specific oligonucleotide hybridization with white cell DNA, to be HPA-1b/1b. The second case involved a 32-year-old woman with chronic myelogenous leukemia who received an unrelated-donor marrow transplant. Three years later, her CML recurred, and she was treated with interferon-alpha. Four months afterward, she experienced interferon-alpha-induced thrombocytopenia and the interferon therapy was discontinued. She received 12 platelet transfusions in 20 days, but none was effective. Antibodies specific for HLA antigens and HPA-1b were detected, and three HLA-matched, HPA-1b-negative apheresis platelet components were given, but without effect. Two days after treatment with methylprednisolone (1 g intravenously) and prednisone (2 mg/kg/day orally), her platelet count was 26 × 10⁹ per L, and after 8 more days, it was 102 × 10⁹ per L, without further transfusions. She was found to be homozygous for HPA-1a (HPA-1a/1a). CONCLUSION : Anti-HPA- 1a and anti-HPA-1b can cause refractoriness to platelet transfusions in bone marrow transplant patients. Testing for platelet-specific antibodies should be considered in all patients who are refractory to HLA-matched platelets.     

Frequency of human platelet antigens among blood donors in northeastern Thailand

BACKGROUND: Platelet transfusions have been widely used in Thailand, but little is known about the phenotyping of human platelet antigens. STUDY DESIGN AND METHODS: Whole blood was collected from 483 blood donors for preparation of platelets. An improved mixed passive hemagglutination assay was used for this study. RESULTS: Frequencies demonstrated were 100 percent for HPA-1a (PlA1), 15.94 percent for HPA- 2b (Siba), 60.25 percent for HPA-3a (Baka), 98.76 percent for HPA-4a (Yukb), 1.86 percent for HPA-4b (Yuka), 5.38 percent for HPA-5b (Br(a)), and 97.72 percent for Naka. CONCLUSION: HPA-1a was found in 100 percent of Thais, which is the same frequency as in other Asian populations but somewhat different from that in whites (97.9%). Therefore, HPA-1a will not cause neonatal alloimmune thrombocytopenia or post-transfusion purpura in Thais. According to the frequencies of HPA-2b, HPA-3a, HPA-4a, HPA-4b, HPA-5b, and Naka antigens, they may induce neonatal alloimmune thrombocytopenia, posttransfusion purpura, and platelet refractoriness in Thais.     

HPA配型在免疫性血小板输注无效中的应用研究

目的探讨以HPA配型解决免疫性血小板输注无效的方案。方法 1)建立PCR-SSP方法检测HPA-1～5基因型检测方法,建立机采血小板供者库;2)采用微柱凝胶法和Capture-P法对32名血小板输血无效患者作血小板同种抗体筛查,并对2种方法比较;3)对血小板同种抗体筛查阳性患者采用已知HPA基因型的标准谱血小板作抗体鉴定并采取HPA基因型同型输注的原则寻找供者。结果 1)采用PCR-SSP方法成功检测出HPA-1～5基因型,并对1 000名血小板供者的HPA-1～5基因型定型;2)32例血小板输注无效病例中,微柱凝胶法检测血小板同种抗体阳性率为50%,Capture-P法血小板抗体阳性检出率为40%;3)32例血小板输血无效病例中2种方法同时血小板抗体阳性13例,其中2例鉴定为抗-HPA,分别为抗-HPA-5b(P=1/84)、抗-HPA-1a(P=1/55)。结论对抗-HPA引起的血小板输注无效患者采用HPA基因型相合的方法寻找供者是有效的。     

The platelet-specific alloantigen PlA1 (HPA-1a): a comparison of flow cytometric immunophenotyping and genotyping using polymerase chain reaction and restriction fragment length polymorphism in a Swedish blood donor population

BACKGROUND: There is an increasing interest in the development of rapid and reliable techniques for platelet alloantigen typing. STUDY DESIGN AND METHODS: By use of standardized flow cytometry and a specific human alloantiserum, 236 Swedish blood donors were immunophenotyped for the platelet-specific alloantigen, PlA1 (HPA-1a). RESULTS: Ten individuals (4.2%) had low fluorescence intensities and were considered PlA1- negative (HPA-1a-negative); all of them also demonstrated a PlA2/PlA2 (HPA-1b/1b) genotype in a polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) assay of the underlying DNA polymorphism. The remaining population had clear positive fluorescence and was regarded as PlA1-positive (HPA-1a-positive). The fluorescence distribution histogram among PlA1-positive (HPA-1a-positive) individuals was dome-shaped, and those individuals who were homozygous for PlA1 (HPA-1a) could not be distinguished from those who were heterozygous. This finding was further substantiated by PCR-RFLP analysis of the PlA1/PlA2 (HPA-1a/1b) genotype; a heterozygous genotype was found among those having a medium fluorescence intensity as well as among those having a strong fluorescence intensity. CONCLUSION: Flow cytometry is a valuable tool for large-scale detection of PlA1 (HPA- 1a). However, flow cytometry based on only one antiserum cannot distinguish between homozygous and heterozygous carriers of PlA1 (HPA- 1a). For zygosity testing and when platelets are difficult to obtain, the PCR-RFLP technique is the assay of choice.     

Factors that influence platelet recovery after transfusion: resolving donor quality from ABO compatibility

BACKGROUND: A system was established to examine the extent to which the apheresis donor determines platelet recovery after transfusion, to measure the impact of ABO identity, and to predict outcome by evaluating the donor. STUDY DESIGN AND METHODS: The percentage of platelet recovery was measured after prophylactic transfusion of apheresis units divided from single donors to paired recipients with uncomplicated thrombocytopenia secondary to leukemia chemotherapy. Platelet microaggregation induced by citrate was measured at the time of apheresis. RESULTS: Platelet recoveries in paired recipients correlated strongly when both transfusions were ABO- identical. When one recipient was ABO-identical and the other was ABO-nonidentical, nonidentical transfusions yielded one-third the recovery of ABO-identical transfusions. In ABO-identical transfusions, platelet recovery in donors having microaggregates in the before-apheresis ACD sample was one-third that in donors without microaggregates. This difference was observed at 1 and 24 hours. Expression of P-selectin in the apheresis units at the time of transfusion correlated well with ACD microaggregates in the before-apheresis sample. CONCLUSION: When transfusions of platelets are ABO-identical, donor quality dominates recovery in circulation. Donor quality is predicted by a rapid and simple assay of citrate-induced microaggregation performed at the time of apheresis. When donor quality is factored out, ABO identity prevails.     

Rapid detection of HPA-1 alloantibodies by platelet antigens immobilized onto microbeads

BACKGROUND: Neonatal alloimmune thrombocytopenia (NAIT) is one of the most common bleeding disorders in neonates. It occurs when alloantibodies from an immunized mother react with paternally inherited alloantigens, mostly human platelet antigen 1a (HPA-1a), on the fetal platelets (PLTs). Currently, monoclonal antibody-immobilized PLT antigen (MAIPA) assay represents the standard technique for the serologic diagnosis of NAIT. MAIPA is time-consuming, however, and limited by the availability of monoclonal antibodies (MoAbs). Here, a gel antigen-specific assay (GASA) was developed, which allows rapid detection of HPA-1 alloantibodies without the use of MoAbs. STUDY DESIGN AND METHODS: Glycoprotein (GP) IIb/IIIa was purified by affinity chromatography from outdated PLT concentrates derived from HPA-1aa or HPA-1bb donors. Purified GPs were biotinylated, immobilized onto streptavidin beads, and used for the analysis of HPA-1a alloantibodies by a microtyping system. HPA-1a serum samples derived from mothers with NAIT (n = 36) and from posttransfusion purpura patients (n = 2) as well as HPA-1b (n = 4), HPA-5b (n = 2), HPA-3a (n = 4), and HLA Class I (n = 2) alloantiserum samples from multitransfused patients were investigated in GASA and MAIPA assays. RESULTS: GASA was able to detect all HPA-1a and -1b alloantibodies recognized by MAIPA. Cross-reactivity with other PLT-reactive alloantibodies was not observed. Interestingly, 3 of 36 serum samples, which showed only moderate reactivity in MAIPA, reacted strongly in GASA. CONCLUSION: GASA has proved to be a rapid method for the detection of HPA-1a alloantibodies and maybe useful for PLT antibody screening, especially in initial assessment of suspected NAIT cases.     

Rapid phenotyping of HPA-1a using either diabody-based hemagglutination or recombinant IgG1-based assays

BACKGROUND: The HPA-1 system is carried on the beta3 integrin. HPA-1a (Zw(a), Pl(A1)) is immunogenic in an HPA-1b homozygote (HPA-1b1b). In pregnancy, 1 of 365 women forms anti-HPA-1a, which causes severe thrombocytopenia in 1 in 1100 neonates. Identification of women at risk of forming anti-HPA-1a and the screening of donors to obtain HPA-1a-negative platelets for therapy need reliable, low-cost, automated assays. STUDY DESIGN AND METHODS: A diabody with dual specificity for HPA-1a x D and an IgG1 anti-HPA-1a have been constructed by the use of the genes encoding the first anti-HPA-1a fragment. With these reagents, two complementary HPA-1a phenotyping assays have been developed. RESULTS: This diabody was used in a simple hemagglutination technique to perform HPA-1a phenotyping on soluble glycoprotein IIb/IIIa from EDTA plasma samples. Over 1000 unselected donors have been correctly HPA-1a-phenotyped by use of the diabody. The human recombinant IgG1 anti-HPA-1a was produced in a rat myeloma cell line and was fluorescein labeled for use in a whole-blood flow cytometric HPA-1a phenotyping assay. This IgG1 anti-HPA-1a shows a clear differential between HPA-1a-positive and HPA-1a-negative platelets at nM antibody concentrations. CONCLUSIONS: The two recombinant reagents described are highly suitable for screening and confirmatory HPA-1a phenotyping. They permit rapid determination of the HPA-1a phenotype and are amenable to automation.     

Developing recombinant HPA-1a-specific antibodies with abrogated Fcgamma receptor binding for the treatment of fetomaternal alloimmune thrombocytopenia

Fetomaternal alloimmune thrombocytopenia (FMAIT) is caused by maternal generation of antibodies specific for paternal platelet antigens and can lead to fetal intracranial hemorrhage. A SNP in the gene encoding integrin beta3 causes a clinically important maternal-paternal antigenic difference; Leu33 generates the human platelet antigen 1a (HPA-1a), whereas Pro33 generates HPA-1b. As a potential treatment to prevent fetal intracranial hemorrhage in HPA-1a alloimmunized pregnancies, we generated an antibody that blocks the binding of maternal HPA-1a-specific antibodies to fetal HPA-1a1b platelets by combining a high-affinity human HPA-1a-specific scFv (B2) with an IgG1 constant region modified to minimize Fcgamma receptor-dependent platelet destruction (G1Deltanab). B2G1Deltanab saturated HPA-1a+ platelets and substantially inhibited binding of clinical HPA-1a-specific sera to HPA-1a+ platelets. The response of monocytes to B2G1Deltanab-sensitized platelets was substantially less than their response to unmodified B2G1, as measured by chemiluminescence. In addition, B2G1Deltanab inhibited chemiluminescence induced by B2G1 and HPA-1a-specific sera. In a chimeric mouse model, B2G1 and polyclonal Ig preparations from clinical HPA-1a-specific sera reduced circulating HPA-1a+ platelets, concomitant with transient thrombocytopenia. As the Deltanab constant region is uninformative in mice, F(ab')2 B2G1 was used as a proof of principle blocking antibody and prevented the in vivo platelet destruction seen with B2G1 and polyclonal HPA-1a-specific antibodies. These results provide rationale for human clinical studies.     

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.     

Post-transfusion purpura in a patient with HPA-1a and GPIa/IIa antibodies

Post-transfusion purpura is a rare bleeding disorder characterized by severe and sudden thrombocytopenia within 3-12 days after blood transfusion. Typically, preformed antibodies directed against human platelet antigens, especially HPA-1a, are associated with the clinical symptoms. A 46-year-old female presenting to the hospital with acute progressive kidney insufficiency and anaemia received two units of packed red blood cells (RBC) within 2 days. On day 7, platelet count felt from 414 to 189 x 10(9) L(-1) and 1 day later dropped to 4 x 10(9) L(-1). Four platelet concentrates were applied without success. After serological confirmation of an HPA-1a antibody, the patient was treated with intravenous gamma immunoglobulin (ivIgG), and the platelet count increased to normal values on day 17. In addition to the persisting HPA-1a alloantibody, an antibody reactive with GPIa/IIa of HPA-5a- and HPA-5b-positive platelets was detected during the acute phase of thrombocytopenia. After complete remission, the patient was transfused with four units of packed RBC from HPA-1a-negative donors, and platelet counts remained normal.     

Genotyping of Eight Human Platelet Antigen Systems in Serbian Blood Donors: Foundation for Platelet Apheresis Registry

IntroductionThe aim of this study was to investigate the allele and genotype frequencies of 8 human platelet antigen (HPA) systems among blood donors from the Blood Transfusion Institute of Serbia and to compare them with published studies. These data would be useful to establish the basis for a platelet apheresis donor registry.Material and MethodsSeventy-two unrelated male platelet apheresis/blood donors from Serbia were typed for 8 HPA systems (HPA-1 to HPA-6, HPA-9, and HPA-15) via the FluoGene method, based on polymerase chain reaction-sequence-specific amplification (PCR-SSP; PCR using sequence-specific primers) with fluorometric signal detection. Allele and genotype frequencies were estimated by direct counting and compared to the expected genotype frequencies according to the Hardy-Weinberg principle. The transfusion mismatch probability was calculated for every HPA specificity.ResultsThe allele frequencies were: HPA-1a, 0.868; HPA-1b, 0.132; HPA-2a, 0.917; HPA-2b, 0.083; HPA-3a, 0.611; HPA-3b, 0.389; HPA-5a, 0.903; HPA-5b, 0.097; HPA-9a, 0.993; HPA-9b, 0.007; HPA-15a, 0.472; and HPA-15b, 0.528. For HPA-4 and HPA-6 only allele a was detected.DiscussionThe HPA allele frequencies of European populations showed no significant differences in comparison with our results. Statistically significant differences were revealed in comparison with some populations of non-European origin. In the tested donors no HPA-2 bb genotype was detected, but we found 1 donor with the rare HPA-9b allele. The biggest transfusion mismatch probability in the Serbian population is for systems HPA-15 (37.4%) and HPA-3 (36.2%), which means that more than a third of random transfusions could cause mismatch in these systems. This study was enabled by the introduction of molecular HPA typing, and it provides initial results of the HPA allele and genotype frequencies in the population of blood donors in Serbia. They will be used to provide a compatible blood supply on demand for treating patients with alloimmune thrombocytopenic disorders. The successful implementation of PCR-SSP with fluorometric signal detection could be further complemented in the future by the introduction of high-throughput methods, which will largely depend on the available financial resources.     

Frequency and specificity of platelet-specific alloantibodies in HLA-immunized haematologic–oncologic patients

The frequency and specificity of platelet-alloantibodies to human platelet antigens (HPA) -1, -3 and -5 was investigated in 59 multitransfused, HLA-immunized patients. Using the MAIPA test (monoclonal antibody specific immobilization of platelet antigens) platelet alloantibodies could be demonstrated in 10 (17%) patients.   In one patient the antibody was present prior to any transfusions and probably induced by multiple previous pregnancies. This antibody was directed to HPA-5b. The remaining nine antibodies were found in patients ( n  = 36) with HLA-antibodies reacting with over 95% of unselected lymphocytes. In these patients the target antigens were HPA-1b in six, HPA-3a in one and both antigens in two patients.   Our findings demonstrate platelet alloimmunization induced by transfusions to be restricted to patients with high HLA-immunization. 25% of these patients (9/36) show platelet-specific antibodies, primarily HPA-1b.     

Strategies for the avoidance of bacterial contamination of blood components

Gram staining and bacterial culturing methods were used to determine the incidence of bacterial contamination of cellular blood components at the time of transfusion reactions. Over a 5-year period, 2208 (4.3%) of 51,278 transfusions were complicated by reactions. Overall bacterial contamination occurred in 5 (0.03%) of 17,928 transfusions of single- donor apheresis platelets, 1 (0.14%) of 712 transfusions of pooled random-donor platelet concentrates, 1 (0.003%) of 31,385 transfusions of red cells, and 0 of 1253 transfusions of fresh-frozen plasma. Gram staining done at the time of positive cultures was positive in three of six cases. Although six of seven recipients of contaminated components suffered no clinical sequelae, contaminated transfusions may have been a contributing cause of death in one case. Attempts were made to avoid the transfusion of contaminated cellular blood components by performing routine bacterial cultures: 0 of 341 quality control cultures were positive. To avoid the transfusion of contaminated platelets by identifying bacteria, Gram staining was performed in all single-donor apheresis platelet units collected on open systems and daily in platelets stored > 48 hours: 8 (0.15%) of 5334 smears done on 3829 platelet units were interpreted as positive, and those units were not transfused, but only two of eight units were culture positive. These studies suggest that bacterial contamination can result in adverse clinical sequelae in transfusion recipients and that both culturing and Gram staining are poor methods of screening for contaminated units. More sensitive and specific methods of generalized screening for bacterial contamination are needed.     

Collection and transfusion of blood and blood components in the United States, 1994

BACKGROUND: Collections and transfusions of blood in the United States in 1994 were measured and compared with those in 1992. STUDY DESIGN AND METHODS: Completed survey questionnaires were returned by all 147 regional blood centers, 1340 American Association of Blood Banks (AABB) member hospitals, and 523 non-AABB hospitals. Statistical tests verified the representativeness of the sample. RESULTS: The United States domestic blood supply in 1994 (13,340,000 units) was 3.3 percent less than in 1992. It included allogeneic blood (11,773,000 units), autologous blood (1,013,000 units), and directed donations (334,000 units). Of these, 432,000 units were rejected on testing, 11,107,000 units were transfused to 3,398,000 patients, and 1,801,000 units were discarded or unaccounted for. Platelet transfusions amounted to 7,866,000 units. Compared with the totals for 1992, transfusions of single-donor platelets (714,000 packs or 4,284,000 units) increased by 17.6 percent, while transfusions of platelet concentrates (3,582,000 units) fell by 23.6 percent. Fresh-frozen plasma transfusions (2,621,000 units) increased by 16.2 percent over the number for 1992. CONCLUSIONS: The US blood collection rate in 1994 was 74.6 units per 1000 population of donor age, the lowest recorded level since 1971. The US RBC transfusion rate in 1994 was 42.8 units per 1000 population, about the same as 1979. Transfusions of single-donor platelets, 16.5 units per 1000 population, exceeded transfusions of platelet concentrate (13.8/1000) for the first time. Plasma transfusions were 10.1 units per 1000 population. The US blood supply in 1994 was adequate to meet patient demands.     

Gene frequencies of the HPA-1 platelet antigen alleles in the Lebanese population

The objective was to study the gene frequencies of HPA-1 in the Lebanese population for the first time. The aims of this study were to assess the prevalence of 1a and 1b HPA-1 alleles in healthy Lebanese individuals and compare with the international literature. Human platelet antigen (HPA) systems are involved in alloimmunization, organ transplantation rejection and the development of cardiovascular disease. Of several classified HPA systems, HPA-1 specifically has been considered to be the most important antigenic system implicated in the Caucasian population. This specific gene has never been investigated in our population. DNA was extracted from specimens collected from 205 healthy unrelated Lebanese individuals and tested, using a reverse hybridization polymerase chain reaction (PCR) assay, for the prevalence of 1a and 1b HPA-1 alleles. Genotypes 1a/1a, 1a/1b, and 1b/1b were assigned accordingly. We observed that the 1a/1a genotype was the most prevalent (65.85%) followed by 1a/1b (30.24%) and 1b/1b (3.91%) with allelic frequencies for 1a and 1b of 0.81 and 0.19, respectively. As compared with other ethnic groups, the Lebanese population was found to have a relatively high prevalence of the HPA-1b, which may predispose to a higher risk of alloimmunization. This report is the first to study the prevalence of the HPA-1 system in the Lebanese population and serves as a template for future clinical research involving platelet disorders and cardiovascular diseases.     

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.     

献血者血小板1-16抗原基因遗传多态性分析及已知HPA型供者数据库的建立

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

Neonatal alloimmune thrombocytopenia due to an antibody against a labile component of human platelet antigen-3b (Bak b)

We report the second case of neonatal alloimmune thrombocytopenia due to anti-human platelet antigen (HPA)-3b (Bak(b)) antibody. The infant was severely affected with intracranial haemorrhage. Most importantly, we were able to detect this antibody only by using fresh, unfixed platelets as antigen. This antibody was detectable neither by conventional mixed passive haemagglutination, platelet immunofluorescence test using fixed platelets, nor by monoclonal antigen immobilization of platelet antigen assay using solubilized platelets. We assume that this antibody reacts only with fresh platelets and that the antigen is a labile component of HPA-3b (Bak(b)).     

Fetomaternal alloimmune thrombocytopenia.

Thrombocytopenia is the second commonest haematological abnormality in the neonatal period after anaemia due to iatrogenic blood letting. One to four percent of all newborn babies have a platelet count < 150 x 10(9)/l at birth and approximately 20-40% of neonates in intensive care units are affected by neonatal thrombocytopenia. The most common cause of severe neonatal thrombocytopenia is fetomaternal platelet incompatibility and subsequent alloimmunisation. During the last decade recent advances in molecular techniques have led to rapid and efficient methods for diagnosis. Progress in fetal medicine has enabled accurate determination of fetal status, allowing improvements in fetal diagnosis and therapy. Human platelet antigen (HPA)-1a is by far the most frequently involved platelet antigen system in Caucasians accounting for 90% of cases, followed at a much lower frequency by HPA-5b (5-15%) and HPA-3a. The incidence is estimated to be 1 per 2000 to 1 per 5000 live births, but this is low in comparison to the incidence of fetomaternal platelet antigen incompatibility especially for the HPA-1 alloantigen system in the Caucasian population in whom the estimated frequency of HPA-1b1b individuals is 2%. Retrospective and prospective studies have reported that the immunogenetic background is important, and the chance of HPA-1a alloimmunisation is strongly associated with maternal HLA class II DRB3*0101 (DR52a) type. A significant association (p = 0.004) between severe thrombocytopenia and a third trimester antiHPA titre >1:32 has been observed. It is now possible to genotype the fetus or neonate and the parents, which provides confirmation as to which HPA systems are incompatible between the mother and father. Simultaneous genotyping of HPA-1, 2, 3 and 5 can be carried out using the polymerase chain reaction-sequence specific primers (PCR-SSP) protocol, which has been widely used for HLA class II determination. The platelet count may continue to fall during the first 48 h after birth and the risk of intracranial bleeding is highest during this period. The best option is transfusion of specially selected antigen negative compatible donor platelets or if unavailable, maternal washed platelets. Antenatal screening for the most common form of fetomaternal alloimmune thrombocytopenia (FMAIT), due to antiHPA-1a is under consideration, but there is no established method at present. The Scottish National Blood Transfusion Service started a study in August 1999 on 25,000 pregnancies to carry out a cost benefit analysis of routine antenatal screening. The aims of the study are to determine the frequency of HPA-1b homozygosity; monitor antibody titres during pregnancy and confirm correlation of antibody emergence with HLA-DRB3*0101, and finally to access cost effectiveness of routine screening across Scotland. Of 26,509 women screened in three Scottish regions 501 (1.9%) are HPA-1b homozygous and about 9%, of the consented women are antibody positive.     

广州地区无偿献血者HPA-1—6,15基因分型及频率调查

目的研究人类血小板基因多态性,为人类群体遗传学研究及临床输血实践提供重要数据和依据。方法通过PCR-SSP方法对广州地区706名无偿献血者的HPA1—6,15系统进行基因分型,并统计其频率。结果706份样本中HPA-3和-15基因型的杂合程度最高,其a/a、a/b、b/b的频率分别为HPA-3:0.2918、0.4830、0.2252;HPA-15:0.2691、0.5170、0.2139,不配合率较高,均达到35%以上。HPA-1、-2、-4、-5系统均以a/a纯合子为主,a基因的频率范围为0.9583—0.9993,且均未发现b/b纯合子。1b、4b的基因频率很低,分别为0.0028和0.0007。本地区的HPA-1a与中国北方、英国白人、美国黑人有统计学差异(P<0.05)。HPA-2与中国南方、北方、美国黑人和日本人有统计学差异(P<0.05);HPA-5与英国白人和美国黑人存在统计学差异(P<0.05)。HPA-6频率分别为0.9575,0.0397,0.0028。结论本研究对广州地区HPA献血员的筛查可为建立HPA供者库和对探讨由HPA引起的免疫性疾病的预防和治疗提供相关数据和研究手段。