Delayed detectability of anti-HPA-3a by the MAIPA assay in a severe neonatal alloimmune thrombocytopenia, but successful transfusion of incompatible donor platelets: a case report

PLT antigen discrepancy pattern among couples with recurrent abortion

Background

Recurrent abortion refers to a condition of two or more consecutive pregnancies without known etiology affected by miscarriage before the completion of the 20th week of gestational age. However, several hypotheses have been proposed, but not much data are available concerning the relationship between human platelet antigens (HPAs) polymorphisms and recurrent abortion. This study was conducted to evaluate the genetic differences between HPA-1, -2, -3, -5, and - 15 in Iranian couples with a history of recurrent abortion.

Methods

In this cross-sectional study, a total of 74 couples with at least 2 recurrent abortions without any known specified reasons enrolled in the study. HPA polymorphisms genotyping was performed by single-specific primer PCR. Genotype frequency was calculated using the Hardy-Weinberg equation.

Results

A total of 39 couples (52.7%) had HPA genotyping partial mismatches. The most common partial mismatch pairs were found concomitantly on both HPA-15a and HPA-15b in three couples (4%), followed by two (2.7%) on HPA-3a and one (1.3%) in each HPA-2b and HPA-5b. There was a deviation from the Hardy-Weinberg equilibrium in the HPA-2 and -5 systems.

Conclusion

The present study declared that partial mismatches of HPA-3 and -15 genotypes were common among Iranian couples due to the history of recurrent abortion and approximately half of the couples carried at least one HPA gene that was absent in their partners. Further studies might be helpful to clarify the association between HPA polymorphisms and recurrent abortion, such as an investigation into the alloantibodies against HPAs.

Fetale und neonatale Alloimmunthrombozytopenie, Teil 1

Die fetale und neonatale Alloimmunthrombozytopenie (FNAIT) wird durch mütterliche Antikörper hervorgerufen, die gegen ein vom Vater ererbtes Blutgruppenmerkmal an fetalen Thrombozyten gerichtet sind. Teil 1 des Beitrags stellt die Ätiologie, die Pathogenese und die Diagnostik der FNAIT dar, während Teil 2 die Risikostratifizierung und Behandlung der FNAIT thematisiert 1.

Application of lyophilised human platelets for antibody detection in solid phase red cell adherence assay

Antibodies against human platelets cause a variety of thrombocytopenic disorders, which lead to potentially fatal haemorrhage. Therefore, their prompt detection is mandatory for successful patient treatment. Solid phase red cell adherence (SPRCA) assay allows for platelet antibody detection widely. However, preparation of fresh platelets with HLA-I and human platelet antigens (HPA)1-5,15 genotyped as target cells is inconvenient and fresh platelets have a short shelf life. In this study, the lyophilised human platelets for antibody detection in SPRCA were prepared. Firstly, platelets were resuspended in lyophilisation buffer and freeze-dried. Then the characteristics of lyophilised platelet were analysed. Rehydrated platelets were recovered with a mean rate of 80.91% ± 2.87%, and still retained spherical morphology. Indirect flow cytometry showed that glycoproteins IIb/IIIa, Ia/IIa, Ib/IX, IV, CD109, and HLA class I were present on the surface of the lyophilised platelets at a comparable level to that of fresh platelets. The consistent results obtained with WHO reference reagents containing anti-HPA-1a, anti-HPA-3a, and anti-HPA-5b, as well as clinical samples from the same donors containing anti-HLA antibodies when reacting with lyophilised versus fresh platelets confirmed good antigenicity preservation of platelets after freeze-drying. Further investigation showed that the lyophilised platelets could be stored at 2-8 °C for up to 14 months and the reconstituted suspension was stable for 48 h. Therefore, lyophilised platelets can be a convenient alternative to fresh platelets to use for anti-platelet antibody detection in SPRCA tests.

Platelet antibody analysis by three different tests

BACKGROUND

Platelet-reactive antibodies lead to thrombocytopenia and bleeding disorders, and diverse assays are used for their detection. In this retrospective analysis, the applicability of three different test systems was compared and antibody specificities were assessed.

METHODS

Sera of 1,234 patients were tested with an enzyme-linked immunosorbent assay (ELISA; Lifecodes PAKPLUS(®) or PAK 12(®), Gen-Probe) and a solid-phase assay (Capture-P Ready Screen(®), Immucor Inc.). In cases of suspected anti-HLA class I antibodies, a specific lymphocytotoxicity test (LCT, Bio-Rad(®)) was performed.

RESULTS

Platelet antibodies were detected in 366 of 1,234 samples (29.7%). In 70.3% concordant negative but only in 8.4% concordant positive results were obtained with both the methods; 185 of 1,053 in the solid-phase assay negative samples were positive in the ELISA (15.0%). In samples positive in both methods, most antibodies reacted against HLA class I antigens. Glycoprotein (GP) specific platelet antibodies, mainly against GPIIb/IIIa and GPIa/IIa, were more frequently detectable in the ELISA than in the solid-phase assay, whereas weakly positive results have to be interpreted cautiously.

CONCLUSION

ELISA, solid-phase assay, and LCT showed highly divergent results. Due to several limitations, the additional analysis by the "monoclonal antibody-specific immobilization of platelet antigen" (MAIPA)-assay is highly recommended.

Simultaneous occurrence of foetal and neonatal alloimmune thrombocytopenia and neonatal neutropenia due to maternal neutrophilic autoantibodies: a case study and review of the literature

Foetal and neonatal alloimmune thrombocytopenia (FNAIT) and neonatal neutropenia caused by maternal autoantibodies against neutrophils are rare disorders. We describe a newborn with severe thrombocytopenia and intracerebral bleeding caused by maternal anti-HPA-3a alloantibodies and mild neutropenia caused by maternal autoantibodies against HNA-1b. This appears to be the first case of simultaneous occurrence of these two conditions.

CONCLUSION

This case report and review of the literature demonstrate that anti-HPA-3a antibodies can be overlooked by standard assays.

The αIIb p.Leu841Met (Cab3(a+) ) polymorphism results in a new human platelet alloantigen involved in neonatal alloimmune thrombocytopenia

BACKGROUND

Fetal-neonatal alloimmune thrombocytopenia (FNAIT) diagnosis relies on maternofetal incompatibility and alloantibody identification. Genotyping for rare platelet (PLT) polymorphisms allowed the identification of three families with suspected or confirmed maternofetal incompatibility for the αIIb-c.2614C>A mutation (Halle et al., Transfusion 2008;48:14-15).

STUDY DESIGN AND METHODS

A polymerase chain reaction-sequence-specific primers amplification assay was designed to genotype the αIIb-c.2614C>A mutation. HEK293 cells expressing αIIb-Leu841 or αIIb-Met841 αIIbβ3 forms were used to probe the reactivity of maternal sera from these families and to study the effects of the substitution on αIIbβ3 expression and functions.

RESULTS

Tested by flow cytometry (FCM), one serum sample specifically reacted with αIIb-Met841 but not with αIIb-Leu841 αIIbβ3. This specificity revealed the αIIb-Leu841 polymorphism as a new alloantigen named Cab3(a+) . Cross-match testing using FCM also showed the Cab3(a+) antigen to be expressed at the PLT surface. As for anti-human PLT alloantigen (HPA)-3a (or -3b) and anti-HPA-9bw, detection of anti-Cab3(a+) alloantibodies appeared difficult and required whole PLT assays when classical monoclonal antibody-specific immobilization of PLT antigen test failed. In our FNAIT set, the immune response to Cab3(a+) maternofetal incompatibility could induce severe thrombocytopenias and life-threatening hemorrhages. The p.Leu841Met substitution has limited effects, if any, on local αIIb structure, preserving both αIIbβ3 expression and functions.

CONCLUSION

The Cab3(a+) polymorphism is a new rare alloantigen (allelic frequency <1%) carried by αIIb that might result in severe life-threatening thrombocytopenias. In Sub-Saharan African populations, higher Cab3(a+) gene frequencies (up to 8.2%; Halle et al., Transfusion 2008;48:14-15) and homozygous people are observed.

Human platelet antigen 1a epitopes are dependent on the cation-regulated conformation of integrin α(IIb)β(3) (GPIIb/IIIa)

BACKGROUND

The HPA-1a (Leu(33)) polymorphism of platelet integrin αIIbβ3 is the target of alloantibodies in 70-80% cases of neonatal alloimmune thrombocytopenia (NAIT) in Caucasians and reliable detection of these antibodies is essential for appropriate clinical management. However, the ability to detect such antibodies is highly variable between laboratories and, in a number of clinical cases where there is a HPA-1 genotype mismatch between mother and neonate, HPA-1a antibodies are undetectable. Furthermore, some studies have not shown a consistent relationship between maternal anti-HPA-1a level and neonatal platelet count. Since the integrity and conformation of the αIIbβ3 complex are dependent on divalent cations, we investigated whether HPA-1a epitope integrity and/or conformation might be affected by the presence of the cation chelator EDTA in patient samples or in assay buffers, thus providing a possible explanation for the variable sensitivity of current assays.

PRINCIPLE FINDINGS

Exposure of the αIIbβ3 complex to EDTA resulted in reduced reactivity of three anti-HPA-1a mAbs (B2, 19-7 and 23-15). More significantly, cation chelation adversely affected detection of polyclonal anti-HPA-1a, not only in the platelet immunofluorescence assay, where alloantibody binding was reduced compared to control platelets (mean MFI reduction 44.5%, range 17.3-69.7%, n=4), but also in the commonly used monoclonal antibody specific immobilisation of platelet antigens assay (MAIPA) where both alloantibody and monoclonal capture antibody binding were reduced (mean OD reduction 82.8%, range 68.3-96.6%, n=9).

CONCLUSIONS

These data show that HPA-1a antibodies recognise epitopes on αIIbβ3 that are sensitive to EDTA treatment and that cation chelation grossly reduces the sensitivity of the MAIPA assay by diminishing not only HPA-1a alloantibody binding but also 'capture' monoclonal antibody binding. These findings may, in part, explain the current variability in antibody measurement and will guide the development of more sensitive tests for anti-integrin antibodies in NAIT and other conditions.

Release of immune modulation factors from platelet concentrates during storage after photochemical pathogen inactivation treatment

BACKGROUND

Blood platelets (PLTs) are critical for hemostasis, and they contain biologically active constituents with the potential to modulate inflammatory responses. This study examined the effects of photochemical pathogen inactivation treatment (PCT) on the release of cytokines and/or chemokines from PLT components.

STUDY DESIGN AND METHODS

Double-dose apheresis PLT components were suspended in plasma-PLT additive solution mixtures and divided into paired therapeutic units. One unit served as an untreated control and the other unit was treated with PCT. PLT concentrations, pH, and levels of cytokines and/or chemokines (CD62p, platelet-derived growth factor-AB, interleukin [IL]-8, soluble CD40 ligand [sCD40L], IL-1beta, and tumor necrosis factor alpha) were measured during 7 days of storage in PLT component supernatants and PLT lysates.

RESULTS

PLT content, pH, and cytokine and/or chemokine content and release from PLT component prepared with PCT were not different (p > 0.05) from paired control components during storage. Levels of sCD40L, however, increased significantly during storage while decreasing in parallel within PLT lysates, although no differences were detected between paired PCT and control PLT component.

CONCLUSION

PCT did not increase the release or secretion of PLT chemokines and/or cytokines over a 7-day period compared to conventional PLT component.

The importance of using multiple techniques for detection of platelet antibodies

In red cell immunology, it has long been known that no one technique will detect all clinically significant antibodies. The same appears to be true for platelet immunology, and we highlight this fact by showing four examples of anti-human platelet antigen-1a that were not detected by the monoclonal antibody-specific immobilization of platelet antigen test, the most commonly used technique. Each antibody was found in a case of fetomaternal alloimmune thrombocytopenia in which the fetus or neonate was severely affected.

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

BACKGROUND AND OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Blood product replacement in the perinatal period

OBJECTIVE

In this article, we will describe some of the special compatibility testing procedures and blood component preparation and modification techniques used in intrauterine and neonatal transfusion medicine. We also will review the transfusion therapy used in hemolytic disease of the fetus and newborn (HDFN) and fetal and neonatal alloimmune thrombocytopenia (FNAIT).

FINDING

Transfusion therapy in the fetus and neonate requires blood typing and compatibility testing techniques not routinely used for adults. These include: cord blood testing, special attention to the volume and speed of infusion, cytomegalovirus risk reduction, and routine irradiation of cellular blood components. The treatment of HDFN and FNAIT involves phenotyping and/or genotyping of fetal and paternal red blood cells and platelets. In FNAIT, platelet products are chosen based on the absence of platelet-specific antigens.

CONCLUSION

Fetal and neonatal transfusion medicine require special attention to the unique anatomic and physiologic features of early human development.