IgG titer, subclass, and light-chain phenotype of pregnancy-induced HPA-5b antibodies that cause or do not cause neonatal alloimmune thrombocytopenia

BACKGROUND: The most common pregnancy-induced platelet-specific antibody is HPA-5b. Neonatal alloimmune thrombocytopenia that results from anti-HPA-5b may cause severe hemorrhage in only a few infants, but the sequelae for the affected children can be severe. It is therefore essential that infants at risk for neonatal alloimmune thrombocytopenia are identified. STUDY DESIGN AND METHODS: The IgG titer, subclass, and light-chain composition of pregnancy-induced anti-HPA-5b were determined by the monoclonal antibody-specific immobilization of platelet antigens assay. Sera were from 12 mothers, who among them had 16 pregnancies that resulted in an HPA-5-mismatched fetus (positive for HPA-5b). Eight mothers gave birth to an infant with a normal platelet count. Three maternal sera were obtained after delivery of a severely thrombocytopenic infant. Three alloimmunized women were followed repeatedly during the course of a subsequent pregnancy, again with an HPA-5-mismatched infant. RESULTS: There was no difference in the antibody titer or its subclass in mothers who had a thrombocytopenic child and the titer or subclass in mothers compared with those who had a child with a normal platelet count. All pregnancy-induced HPA-5b antibodies were of a predominant, lambda, light-chain type. The IgG subclass did not change during pregnancy. CONCLUSION: Neither the antibody titer nor the subclass composition predict the occurrence of thrombocytopenia in a newborn whose mother is alloimmunized against HPA-5b.     

Diagnosis and management of neonatal alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAT) is a life-threatening bleeding disorder caused by maternal platelet antibodies produced in response to fetal platelet antigens inherited from the father. Antiplatelet antibodies cross the placenta and cause destruction of fetal platelets, leading to severe thrombocytopenia, and potentially bleeding, including fatal intracerebral hemorrhage. Incompatibilities between maternal and fetal platelets for the human platelet antigen 1a (previously called PL(A1)) account for most of the patients with NAT, but other antigens are commonly implicated. Diagnostic testing for NAT involves genotyping of maternal, paternal, and sometimes fetal DNA; platelet antigen phenotyping; and maternal platelet antibody investigations using specialized platelet glycoprotein specific assays. The management of women and infants at risk for NAT remains largely empiric; and mounting evidence points to prohibitive risks of invasive procedures such as fetal blood sampling and intrauterine platelet transfusions, except in rare circumstances. Improvements in our understanding of the pathophysiology of NAT, and of clinical and laboratory predictors of severity, may help develop better treatments and improve our ability to identify mothers at risk.     

First example of familial posttransfusion purpura in two PlA1-negative sisters

Posttransfusion purpura (PTP) (platelet count 5000/microliter) was diagnosed in a female patient (never transfused, gravida IV, para IV) 1 week after transfusion for hysterectomy in 1978. She did not respond to pooled random-donor platelets but recovered following a single plasma exchange. Her platelets were PlA1 negative, and her plasma contained potent anti-PlA1. In 1986, her sister (never transfused, gravida III, para III) developed PTP (platelet counts 5-15,000/microliter) following surgery-associated transfusion. She did not respond to pooled random-donor platelets. Platelet-associated IgG was markedly elevated (5365) molecules/platelet; normal, less than 660); her plasma contained a potent platelet antibody with anti-PlA1 specificity. Her platelets were subsequently shown to be PlA1 negative. The platelet count did not rise above 30,000 per microliter, despite 3 days of high-dose methylprednisolone sodium succinate and 2 weeks of prednisone (80 mg/day). Later, her platelet count increased and remained normal after steroids were discontinued. The two sisters proved to be HLA-identical, and each possessed one haplotype carrying the DR3 marker, which has been implicated as a risk factor in neonatal alloimmune thrombocytopenia associated with anti-PlA1.     

Frequency of platelet-specific antigens among Koreans determined by a simplified immunofluorescence test

The frequencies of platelet-specific antigens among Oriental populations have not been well studied. This article reports the determination of the frequency of five major platelet-specific antigens among Korean blood donors. Both the PlA1 (Zwa) and Yukb antigens were positive in all of the 126 Koreans tested. Baka and Yuka antigens were positive in 110 (87.3%) and 2 (1.6%) of the 126 subjects, respectively. Ten (11.5%) of 87 Koreans had PlA2 (Zwb) antigens. A simplified immunofluorescence test, the adhesion slide immunofluorescence test, was devised for platelet antigen typing.     

Predictive value of sequential maternal anti-HPA-1a antibody concentrations for the severity of fetal alloimmune thrombocytopenia

BACKGROUND: Fetal/neonatal alloimmune thrombocytopenia results from maternal immunization against fetal platelet alloantigens (HPAs), and the major risk is intracranial hemorrhage. The severity of thrombocytopenia increases in subsequent pregnancies, and antenatal therapy has been developed. Until now, the fetal status can only be assessed by fetal blood sampling, which carries a risk of fetal loss or premature delivery. OBJECTIVES: To develop non-invasive methods to gain information on the fetal condition. PATIENTS/METHODS: Quantification of the maternal anti-HPA-1a alloantibody concentration was performed with a standardized monoclonal antibody-specific immobilization of platelet antigens (MAIPA) procedure for 43 mothers. A correlation between this concentration and the fetal/neonatal platelet counts was studied. RESULTS: (i) Before antenatal therapy, there was a significant correlation between maternal anti-HPA-1a concentrations > or =250 AU mL(-1) and fetal thrombocytopenia (2-66 x 10(9) L(-1)) whatever the gestational age (Fisher's exact test P = 0.0021). (ii) During subsequent pregnancies, we observed a decrease of the maternal anti-HPA-1a concentration for 14/19 women. Just before delivery, all women had anti-HPA-1a concentrations <250 AU mL(-1). In four cases, there was a therapy failure and the severely thrombocytopenic babies required postnatal therapy. CONCLUSION: The maternal anti-HPA-1a concentration could provide obstetricians with clinically useful information concerning the appropriateness and the timing of invasive monitoring procedures. However, though we observed a tendency toward a decrease in maternal antibody concentration after treatment, this finding does not allow us to draw any conclusions on the effectiveness of therapy.     

Suitability of liquid-stored donor platelets in platelet compatibility testing

Current platelet crossmatch procedures to select compatible donors for alloimmunized thrombocytopenic patients are hampered by the lack of a convenient platelet storage method. This study examined the feasibility of using washed apheresis donor platelets stored for up to 1 year in a modified Hank's buffer solution at 4 degrees C as crossmatch reagents in an indirect IgG-enzyme immunoassay. Pooled and monospecific HLA and PlA1 antisera were used to determine the antigenic reactivity of donor platelets in relation to duration of storage. There were no significant differences between mean HLA and PlA1 antigen expression in fresh and stored platelets. HLA reactivity was detected on 12 of 13 donor platelet samples stored for 3 to 9 months and on 14 of 17 platelets stored for 12 to 14 months. PlA1 reactivity was maintained at 12 to 14 months for all 12 donor platelet samples tested. In addition, incompatibility remained in 23 of 24 paired fresh and stored platelet crossmatches using individual alloimmunized patient plasmas. These data indicate that both HLA and platelet-specific PlA1 antigen reactivity can be maintained adequately in liquid storage at 4 degrees C for up to 1 year. The availability of a convenient platelet storage method should facilitate the general application of platelet crossmatching procedures for alloimmunized patients.     

Epidemiology and management of fetal and neonatal alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a disease in pregnancy characterized by maternal alloantibodies directed against the human platelet antigen (HPA). These antibodies can cause intracranial hemorrhage (ICH) or other major bleeding resulting in lifelong handicaps or death. Optimal fetal care can be provided by timely identification of pregnancies at risk. However, this can only be done by routinely antenatal screening. Whether nationwide screening is cost-effective is still being debated. HPA-1a alloantibodies are estimated to be found in 1 in 400 pregnancies resulting in severe burden and fetal ICH in 1 in 10.000 pregnancies. Antenatal treatment is focused on the prevention of fetal ICH and consists of weekly maternal IVIg administration. In high-risk FNAIT treatment should be initiated at 12–18 weeks gestational age using high dosage and in standard-risk FNAIT at 20–28 weeks gestational age using a lower dosage. Postnatal prophylactic platelet transfusions are often given in case of severe thrombocytopenia to prevent bleedings. The optimal threshold and product for postnatal transfusion is not known and international consensus is lacking. In this review practical guidelines for antenatal and postnatal management are offered to clinicians that face the challenge of reducing the risk of bleeding in fetuses and infants affected by FNAIT.     

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.     

Maternal human platelet antigen-1a antibody level correlates with the platelet count in the newborns: a retrospective study

BACKGROUND: Maternal plasma and/or serum levels of anti-HPA-1a at delivery were compared to neonatal platelet (PLT) counts. STUDY DESIGN AND METHODS: Samples from HPA-1bb women who gave birth to children with thrombocytopenia or had anamnestic information about a previous child with neonatal alloimmune thrombocytopenia (NAIT) were collected at delivery. A modified monoclonal antibody immobilization of PLT antigen method was used for quantification of anti-HPA-1a. RESULTS: The anti-HPA-1a level in women with severely thrombocytopenic children was higher than the corresponding level in mothers of children born with moderate thrombocytopenia or normal PLT counts. CONCLUSION: Our data show a significant correlation between maternal anti-HPA-1a level and the neonatal PLT count and indicate strongly that this may be a reliable predictive measure for NAIT. Suitable test systems for quantitative measurements of anti-HPA-1a must be developed and evaluated for this particular purpose.     

On the association of the platelet-specific alloantigen, Pena, with glycoprotein IIIa. Evidence for heterogeneity of glycoprotein IIIa.

Neonatal alloimmune thrombocytopenic purpura associated with a new platelet-specific alloantigen Pena has been reported. We now provide direct evidence that the Pena determinant is associated with glycoprotein (GP) IIIa, but that it is distinct from epitopes that define the PlA system. By ELISA wherein monoclonal antibodies specific for GPIIb (Tab) and specific for GPIIIa (AP3) were used to capture and hold antigens from a platelet lysate prepared under conditions that generate free GPIIb and GPIIIa, anti-Pena reacted with GPIIIa held by AP3 but not with GPIIb held by Tab. In an alternative ELISA where purified GPIIIa from both PlA1-positive and PlA1-negative platelets were used individually as antigen, anti-Pena reacted with both allelic forms of GPIIIa. By radioimmuno-precipitation, anti-Pena precipitated a single surface-labeled membrane protein with electrophoretic characteristics in sodium dodecyl sulfate-polyacrylamide gels, under nonreduced or reduced conditions, identical to those of GPIIIa. By fluorocytometry, platelets from several donors, regardless of PlA phenotype, bound an amount of anti-Pena roughly equivalent to one-half that amount of anti-PlA1 bound by PlA1 homozygous (A1/A1) platelets and roughly equal to that amount of anti-PlA1 bound by PlA1 heterozygous (A1/A2) platelets. Using platelets from donors typed homozygous for PlA1 and Pena in a quantitative indirect binding assay, 14-24,000 molecules of anti-Pena and 41-51,000 molecules of anti-PlA1 were bound per platelet at saturation. Anti-Pena completely inhibited ADP-induced aggregation of Pena-positive platelets, regardless of PlA phenotype. These results indicate that the Pena determinant is associated with GPIIIa but distinct from PlA.     

Antenatal management of fetomaternal alloimmune thrombocytopenia—report of 15 affected pregnancies

SUMMARY. The recognition that spontaneous intracranial haemorrhage (ICH) may occur in utero in fetomaternal alloimmune thrombocytopenia (FMAIT) led us to attempt to prevent this in 15 pregnancies of 11 women who had previously affected infants with FMAIT due to anti-HPA-la. The antenatal management included fetal platelet transfusions and maternal steroids and/or high-dose intravenous immunoglobulin (IVIgG). In the first pregnancy, ICH occurred between 32 and 35 weeks' gestation before any treatment had been given, emphasizing the need for earlier intervention. Five of the 14 subsequent pregnancies in this study were considered to be severely affected (severe haemorrhagic complications in a previous infant and initial fetal platelet count < 20 times 10⁹/L in this study); four were managed successfully with weekly fetal platelet transfusions started between 18 and 29 weeks and continued until delivery at 33–35 weeks, and one severely affected case who was referred at 36 weeks was managed successfully with a single platelet transfusion prior to delivery. Five pregnancies were considered to be mildly affected (previous infants were unaffected by severe bleeding and initial fetal platelet count > 50 times 10⁹/L in this study). The platelet counts were maintained in one case with steroids and in three with IVIgG without the need for repeated platelet transfusions, but in the fifth the fetal platelet count fell despite steroids and IVIgG and serial platelet transfusions were required. Four pregnancies were unsuccessful; two pregnancies were terminated after severe ICH occurred at an early stage before fetal blood sampling had been carried out, one fetus died after the mother had a severe fall despite the successful initiation of fetal platelet transfusions and one died due to a cord haematoma which occurred at the time of the initial fetal blood sampling. The optimal management of FMAIT to reduce the risk of antenatal ICH remains uncertain. Steroids and IVIgG may be effective in some mildly affected cases but serial fetal platelet transfusions are the preferred therapy for those who are severely affected.     

The human platelet alloantigens, PlA1 and PlA2, are associated with a leucine33/proline33 amino acid polymorphism in membrane glycoprotein IIIa, and are distinguishable by DNA typing.

The human platelet alloantigens, PlA1 and PlA2, comprise a diallelic antigen system located on a component of the platelet fibrinogen receptor, membrane glycoprotein (GP) IIIa. Of the known platelet alloantigens, PlA1, which is carried by 98% of the caucasian population, appears to be the alloantigen that most often provokes neonatal alloimmune thrombocytopenic purpura and posttransfusion purpura. The structural features of the GPIIIa molecule responsible for its antigenicity are as yet unknown. Using the polymerase chain reaction (PcR), we amplified the NH2-terminal region of platelet GPIIIa mRNA derived from PlA1 and PlA2 homozygous individuals. Nucleotide sequence analysis of selected amplified cDNA products revealed a C in equilibrium T polymorphism at base 196 that created a unique Nci I restriction enzyme cleavage site in the PlA2, but not the PlA1 form of GPIIIa cDNA. Subsequent restriction enzyme analysis of cDNAs generated by PcR from 10 PlA1/A1, 5 PlA2/A2, and 3 PlA1/A2 individuals showed that Nci I digestion permitted clear discrimination between the PlA1 and PlA2 alleles of GPIIIa. All PlA2/A2 individuals studied contain a C at base 196, whereas PlA1 homozygotes have a T at this position. This single base change results in a leucine/proline polymorphism at amino acid 33 from the NH2-terminus, and is likely to impart significant differences in the secondary structures of these two allelic forms of the GPIIIa molecule. The ability to perform DNA-typing analysis for PlA phenotype may have a number of useful clinical applications, including fetal testing and determination of the phenotype of severely thrombocytopenic individuals.     

Platelet alloantibodies in transfused patients

BACKGROUND: Patients receiving cellular blood components may form HLA antibodies and platelet-specific alloantibodies. STUDY DESIGN AND METHODS: Serum samples from a cohort of 252 patients with hematologic or oncologic diseases who are receiving cellular blood components were studied for platelet-reactive antibodies. Specificity of platelet alloantibodies was determined with a panel of typed platelets RESULTS: Platelet-reactive antibodies were detected in the sera of 113 patients (44.8% of 252), HLA antibodies in the sera of 108 (42.9%), and platelet-specific antibodies in the sera of 20 (8%). The following platelet-specific antibodies were identified: anti-HPA-5b (n = 10), anti-HPA-1b (n = 4), anti-HPA-5a (n = 2), anti-HPA-1a (n = 1), anti-HPA-2b (n = 1), anti-HPA-1b+5b (n = 1), and anti-HPA-1b+2b (n = 1). Fifteen sera from the 108 patients with anti-HLA (13.9%) contained additional platelet-specific alloantibodies, while in 5 sera, platelet-specific alloantibodies only were detected: anti-HPA-5b (n = 4) and anti-HPA-1a (n = 1). Of the 108 sera with HLA antibodies, 29 (26.9%) showed discordant results when studied with the lymphocytotoxicity test and the glycoprotein-specific immunoassay. Ten sera contained panreactive antibodies against platelet glycoproteins (GP) IIb/IIIa, GPIa/IIa, and/or GPIb/IX. Alloimmunization occurred in 58.3 percent of female patients with previous pregnancies, but in only 23.3 percent of those without previous pregnancies (p = 0.0049). CONCLUSION: Platelet alloantibody specificities in transfused patients (predominantly anti-HPA-5b and -1b with antigen frequencies <30% among whites) differ significantly from those observed in patients with neonatal alloimmune thrombocytopenia or posttransfusion purpura, in whom anti-HPA-1a (antigen frequency >95%) is the most prevalent specificity. HLA antibody detection yields discordant results when the lymphocytotoxicity assay and a glycoprotein-specific immunoglobulin-binding assay are used.     

血小板谱抗原的建立及其在鉴定血小板特异性抗体中的应用

目的 建立血小板谱抗原,鉴定引起血小板输注无效和新生儿血小板减少性紫癜的血小板特异性抗体,为血小板血型研究和临床治疗提供依据。方法根据中国人群人类血小板同种抗原(HPA)-1-HPA-16等位基因频率分布资料,利用聚合酶链反应-序列特异引物(PCR-SSP)技术对O型血小板供者进行HPA-1-HPA-6、HPA-15分型,筛选合适的供者,组成血小板谱抗原。通过建立的血小板谱抗原,利用简易致敏红细胞血小板血清学技术(SEPSA)鉴定同种免疫反应产生的血小板抗体的特异性。结果从O型血小板供者中筛选出11名供者,建立了血小板特异性抗体鉴定谱抗原。其可鉴定HPA-1-HPA-6,HPA-15抗体的特异性。在所筛检1 120份样本中,有3例患者检出HPA抗体,其中HPA-4b(Penb)抗体1例,HPA-15a(Govb)抗体2例。结论通过血小板谱抗原鉴定血小板抗体的特异性,对提高临床输注血小板的安全性和有效性,以及预防新生儿血小板减少性紫癜有积极的意义.     

Neonatal alloimmune thrombocytopenia due to anti-HPA-5b (Bra, Zava, Hca): the importance of third-generation platelet antibody detection techniques, a case report

Investigation of the maternal serum in a case of suspected alloimmune neonatal thrombocytopenia by conventional, second-generation platelet serological assays (platelet radioactive antiglobulin test [PRAT], platelet suspension immunofluorescence test [PSIFT] and solid-phase adherence assay (SPAA, 'Capture-P') demonstrated only the presence of HLA class-I antibodies of limited specificities: no platelet-specific antibodies were detectable. The use of a third generation, glycoprotein capture assay (monoclonal antibody-specific immobilization of platelet antigens, MAIPA) revealed the additional presence of anti-HPA-5b with a titre of 1 in 32. Despite this relatively high titre, and the fact that it was able to induce a prolonged thrombocytopenia, this antibody was not detectable by conventional assays. In view of these findings we conclude that the use of MAIPA is essential when investigating cases of suspected alloimmune neonatal thrombocytopenia.     

Asymptomatic Thrombocytopenia Developing During Pregnancy (Gestational Thrombocytopenia) - A Clinical Study

During pregnancy some women develop unexplained thrombocytopenia(gestational thrombocytopenia). Previous studies have detectedabnormal platelet antibodies, suggesting an autoimmune aetiology.To determine whether gestational thrombocytopenia is associatedwith increased maternal bleeding or adversely addressed affectsthe fetus, 31 pregnant women with asymptomatic thrombocytopeniawere compared with 12 women with thrombocytopenia associatedwith pre-eclampsia and 34 normal pregnant controls. There wasno increase in maternal bleeding in those with asymptomaticthrombocytopenia compared with the normal controls, but pre-eclampticwomen experienced more bleeding (mean difference 181 ml, 95per cent confidence limits 50-312 ml, p < 0.01). There wasno difference in the mean weights of the babies or placenta,nor in the APGAR scores between infants born to controls andthose with asymptomatic thrombocytopenia. Cord blood plateletlevels were measured in 26 women with asymptomatic thrombocytopeniaand were normal in 25 and mildly reduced in one. Thus measuresused for the treatment and delivery of pregnancies complicatedby autoimmune thrombocytopenia are not indicated in gestationalthrombocytopenia. Pregnant women should not be considered thrombocytopeniaunless the platelet count has fallen below 120 x 10⁹/l.     

Asymptomatic thrombocytopenia developing during pregnancy (gestational thrombocytopenia)--a clinical study.

During pregnancy some women develop unexplained thrombocytopenia (gestational thrombocytopenia). Previous studies have detected abnormal platelet antibodies, suggesting an autoimmune aetiology. To determine whether gestational thrombocytopenia is associated with increased maternal bleeding or adversely affects the fetus, 31 pregnant women with asymptomatic thrombocytopenia were compared with 12 women with thrombocytopenia associated with pre-eclampsia and 34 normal pregnant controls. There was no increase in maternal bleeding in those with asymptomatic thrombocytopenia compared with the normal controls, but pre-eclamptic women experienced more bleeding (mean difference 181 ml, 95 per cent confidence limits 50-312 ml, p < 0.01). There was no difference in the mean weights of the babies or placenta, nor in the APGAR scores between infants born to controls and those with asymptomatic thrombocytopenia. Cord blood platelet levels were measured in 26 women with asymptomatic thrombocytopenia and were normal in 25 and mildly reduced in one. Thus measures used for the treatment and delivery of pregnancies complicated by autoimmune thrombocytopenia are not indicated in gestational thrombocytopenia. Pregnant women should not be considered thrombocytopenic unless the platelet count has fallen below 120 x 10(9)/l.     

Neonatal alloimmune thrombocytopenia due to anti-HPA 5a in a HPA-5a homozygous neonate

The most frequently involved antigen in severe fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the human platelet antigen 1a. Cases of FNAIT caused by HPA-5a antigen are extremely rare, and usually not severe. We report a case of FNAIT caused by anti-HPA antibodies directed to the HPA-5a antigen. The thrombocytopenia was moderate with a minimal platelet count of 36 × 10⁹/L by day 3, and spontaneously resolved by day 10.The pregnancy had been obtained by in vitro fertilization using embryo donation, creating a complete genetic disparity between the HPA 5b5b mother and the HPA 5a5a homozygous neonate.The use of ART with gamete donation can increase the risk and the severity of alloimmune thrombocytopenia and must be considered in new and subsequent pregnancies.     

Prospects for risk stratification of anti-HPA-1a alloimmunized pregnant women

A diagnosis of fetal/neonatal alloimmune thrombocytopenia (FNAIT) is made if a platelet-specific antibody is detected in the mother and the fetus or newborn carries the cognate antigen. Some children will experience very low platelet counts or even intracranial hemorrhage with devastating consequences, whereas others are largely unaffected. At the moment, predictive tools to forecast the severity of FNAIT during pregnancy are not available and over- or under-treatment may put the mother or the fetus at risk. A number of potential modulators of FNAIT severity have been reported. Maternal immune responses differ in respect to the IgG subtype composition, the glycosylation pattern of the antibodies, their fine specificity, and their functional effects on platelets, the trophoblast, and endothelial cells. In addition, antibody levels are variable. The efficacy of IgG transfer and, on the fetal side, gender and inflammatory responses, were also investigated for their potential impact on FNAIT severity. These potential risk modulators are scrutinized for available experimental and clinical evidence. Antibody glycosylation and anti-endothelial activity are hot candidates which, most likely in conjunction with the antibody level, should be explored further as tools to stratify fetal risk.     

HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia

BACKGROUND: The antenatal management of fetomaternal alloimmune thrombocytopenia (FMAIT) due to HPA-1a antibodies remains controversial, and a test identifying pregnancies that do not require therapy would be of clinical value. STUDY DESIGN AND METHODS: The statistical correlation was analyzed between clinical outcome and 1) anti-HPA-1a potency in maternal serum samples determined by a monoclonal antibody immobilization of platelet (PLT) antigen assay with an international anti-HPA-1a potency standard and 2) anti-HPA-1a biological activity measured by a monocyte chemiluminescence (CL) assay. RESULTS: A total of 133 pregnancies with FMAIT due to anti-HPA-1a were analyzed. In 97 newly diagnosed cases, there was no difference in antibody potency or CL signal between cases with intracranial hemorrhage (ICH; n = 15), those with no ICH but a PLT count of less than 20 x 10(9) per L (n = 52), and those with a PLT count of at least 20 x 10(9) per L (n = 30). In 22 previously known pregnancies, the positive predictive value of maternal anti-HPA-1a of greater than 30 IU per mL for a PLT count of less than 20 x 10(9) per L was 90 percent, but the negative predictive value was only 66 percent. Antibody potency tended to stay stable throughout pregnancy (n = 16) and from one pregnancy to the next (n = 16). CONCLUSION: Neither severe thrombocytopenia nor ICH in HPA-1a-alloimmunized pregnancies can be predicted with sufficient sensitivity and specificity for clinical application from maternal anti-HPA-1a potency or bioactivity.