Alloantigen System Research Articles

Immunomodulatory effect of zidovudine (ZDV) on cytotoxic T lymphocytes previously exposed to ZDV.

In a previous study, zidovudine (ZDV) was shown to cause a concentration-dependent inhibition of antigen-specific cytotoxic T-lymphocyte (CTL) clonal expansion (S. Francke, C. G. Orosz, K. A. Hayes, and L. E. Mathes, Antimicrob. Agents Chemother. 44:1900-1905, 2000). However, this suppressive effect was lost if exposure to ZDV was delayed for 24 to 48 h during the antigen sensitization period, suggesting that antigen-primed CTL may be less susceptible than naive T lymphocytes to the suppressive effects of ZDV. The present study was undertaken to determine if naive T lymphocytes were more sensitive to the suppressive effects of ZDV than T lymphocytes previously exposed to antigen. The 50% inhibitory concentration (IC(50)) values of ZDV were determined on naive and antigen-primed T-cell responses in an alloantigen system. Lymphocyte cultures with continuous antigen exposure (double prime) were more resistant to ZDV suppression (IC(50) = 316 micro M) than were naive lymphocytes (IC(50) = 87.5 micro M). Interestingly, lymphocytes that were antigen primed but deprived of antigen during the final 7 days of culture (prime/hold) were exquisitely sensitive to ZDV suppression (IC(50) = 29.3 micro M). The addition of 80 micro M ZDV during the initial priming of the single-prime (prime/hold) and double-prime cultures did not select for a more drug-resistant cell population. The differences in ZDV sensitivities are likely a reflection of the physiological properties of the lymphocytes related to their activation state.

Genotyping for platelet‐specific antigens: techniques for the detection of single nucleotide polymorphisms

Accurate typing of patients for platelet-specific (human platelet) antigens (HPA) is required in several different clinical situations, and blood services need to maintain panels of HPA-typed apheresis platelet donors and whole-blood donors to support HPA alloimmunized patients. Six clinically relevant HPA alloantigen systems have been described and, in addition, a significant number of HPA alloantigens with a highly skewed allele frequency or of very low immunogenicity have been reported. Certain well-characterized biallelic systems such as Gov have not as yet been included in the HPA nomenclature but are included in this review. Biochemical studies have identified the platelet membrane proteins on which the HPA antigens are localized. Cloning of the genes encoding these proteins and the realization that there is adequate mRNA in fresh platelets has led to identification of the molecular basis of HPA antigens over the last decade. All but one of the biallelic platelet-specific alloantigen systems are based on a single nucleotide polymorphism in the DNA sequence, corresponding to a single amino acid substitution in the encoded primary protein sequence. The discovery of the genetic basis of the alloantigens has allowed the development of polymerase chain reaction-based techniques for HPA genotyping using genomic DNA. The genetic basis of the HPA alloantigens, the most commonly used genome typing techniques and their pitfalls, and future developments, are discussed in this review.

Cell surface antigen CD109 is a novel member of the α2 macroglobulin/C3, C4, C5 family of thioester-containing proteins

Cell surface antigen CD109 is a glycosylphosphatidylinositol (GPI)-linked glycoprotein of approximately 170 kd found on a subset of hematopoietic stem and progenitor cells and on activated platelets and T cells. Although it has been suggested that T-cell CD109 may play a role in antibody-inducing T-helper function and it is known that platelet CD109 carries the Gov alloantigen system, the role of CD109 in hematopoietic cells remains largely unknown. As a first step toward elucidating the function of CD109, we have isolated and characterized a human CD109 cDNA from KG1a and endothelial cells. The isolated cDNA comprises a 4335 bp open-reading frame encoding a 1445 amino acid (aa) protein of approximately 162 kd that contains a 21 aa N-terminal leader peptide, 17 potential N-linked glycosylation sites, and a C-terminal GPI anchor cleavage-addition site. We report that CD109 is a novel member of the alpha 2 macroglobulin (alpha 2M)/C3, C4, C5 family of thioester-containing proteins, and we demonstrate that native CD109 does indeed contain an intact thioester. Analysis of the CD109 aa sequence suggests that CD109 is likely activated by proteolytic cleavage and thereby becomes capable of thioester-mediated covalent binding to adjacent molecules or cells. In addition, the predicted chemical reactivity of the activated CD109 thioester is complement-like rather than resembling that of alpha 2M proteins. Thus, not only is CD109 potentially capable of covalent binding to carbohydrate and protein targets, but the t(1/2) of its activated thioester is likely extremely short, indicating that CD109 action is highly restricted spatially to the site of its activation.

Alloantigen system L affects the outcome of rous sarcomas.

This study was designed to examine the alloantigen system L effects on Rous sarcomas in three B complex genotypes. The parental stock was 50% Modified Wisconsin Line 3 x White Leghorn Line NIU 4 and 50% inbred Line 6.15-5. Pedigree matings of two B(2)B(5) L(1)L(2) sires to five B(2)B(5) L(1)L(2) dams per sire produced experimental chicks segregating for B and L genotypes. Chicks were inoculated with 20 pock-forming units (pfu) of Rous sarcoma virus (RSV) at 6 weeks of age. Tumors were scored six times over 10 weeks postinoculation after which the tumor scores were used to assign a tumor profile index (TPI) to each chicken. Tumor growth over time and TPI were evaluated by repeated-measures analysis of variance and analysis of variance, respectively. Six trials were conducted with a total of 151 chickens. The major histocompatibility (B) complex affected the responses as the B(2)B(2) and B(2)B(5) genotypes had significantly lower tumor growth over time and TPI than the B(5)B(5) genotype. Separate analyses revealed no significant L system effect in B(2)B(2) or B(2)B(5) backgrounds. However, L genotype significantly affected (P < 0.05) both tumor growth over time and TPI in B(5)B(5) chickens. B(5)B(5) L(1)L(2) birds had TPI significantly lower than B(5)B(5) L(1)L(1) chickens but not B(5)B(5) L(2)L(2). Mortality was lower in the B(5)B(5) L(1)L(2) birds than in B(5)B(5) L(2)L(2) chickens. The L system, or one closely linked, affects the growth and ultimate outcome of Rous sarcomas. The response may depend upon the genetic background as well as MHC type.

Overlap of direct and indirect alloreactive T-cell repertoires when MHC polymorphism is limited to the peptide binding groove

The immune response to allogeneic-MHC molecules can be divided into two pathways based on the nature of the antigen. In the direct pathway, T cells respond to intact allogeneic MHC molecules, while in the indirect pathway T cells respond to allo MHC-derived peptides presented by self-MHC. The T-cell repertoire used in the direct and indirect alloresponse have not been compared in the same alloantigen system. Here, HLA-DR transgenic mice are used to compare the repertoires of T cells that respond to the same alloantigen through either the direct or the indirect pathway. Separate direct and indirect DR1 anti-DR4 T-cell lines were generated and the T cell repertoire was analyzed by molecular methods. The same six Vβ families were involved in both direct and indirect cultures indicating a complete overlap in the Vβ gene usage. A partial overlap at the clonotype level was observed as two identical clonotypic TCRs were observed in both direct and indirect cultures. Interestingly, the T cells observed in both cultures were public as the same TCRs were identified in cultures developed from independent mice. These results raise the prospect that immune suppression of selected T cells during allo-transplantation can simultaneously modulate direct and indirect alloreactivities.

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 <150×10 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.

Alloantigen systems L and P influence phagocytic function independent of the major histocompatability complex (B) in chickens

Synthetic parent stocks were designed to produce progeny among which alleles were simultaneously segregating for nine alloantigen systems, including the MHC (B). Chicks from Ancona-derived B19B19 females crossed with White leghorn B19B21 males were blood typed, resulting in genotypic categories for the A-E, C, D, H, I, L, and P loci with the objective of determining which, if any, of the eight non-MHC alloantigen systems influence or interact with the B system genotypes for blood monocyte phagocytic activity. Leukocytes obtained from whole blood at 2 and 4 wk were separated on a Fico/Lite LymphoH,TM density gradient and were allowed to adhere to glass coverslips. The resulting adherent monocyte monolayers were incubated with viable Escherichia coli for 1 h and stained with Leukostat,TM and the phagocytic monocytes and numbers of internalized bacteria per phagocytic monocyte were scored microscopically. The combined results from two separate trials demonstrated that the genotypes of the A-E, C, D, H, and I systems did not differ in the percentage of monocytes exhibiting phagocytosis, whereas significant differences were noted relative to the B system genotype at 2 wk of age (B19B21 > B19B19; P = 0.049), L at 4 wk (L1L1 > L1L2; P = 0.009), and P at 4 wk (P4P4 > P1P1; P = 0.047). The data were further analyzed to determine any interactions of P and L alloantigen genotypes with the B system genotypes; no such interaction was observed. These studies suggest that the L and P non-MHC alloantigen systems have the potential to influence immune responses by modulating phagocytic function in chickens. Furthermore, this modulation seems to be independent of the B (MHC) system.

Detection of Gov system antibodies by MAIPA reveals an immunogenicity similar to the HPA-5 alloantigens.

The glycosylphosphatidylinositol-linked platelet protein CD109 carries the biallelic alloantigen system Gov. There is limited information on the incidence of Gov alloantibodies in neonatal alloimmune thrombocytopenia (NAITP), post-transfusion purpura (PTP) and platelet refractoriness. We adapted the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay to the detection of Gov antibodies and determined their incidence in 605 archived samples (112 with HPA antibodies) referred for the aforementioned conditions. Here, we show that CD109 expression was reduced upon platelet storage in saline or by cryopreservation, but was stable when stored as whole blood or therapeutic platelet concentrate. Fourteen of the 605 samples contained Gov alloantibodies (anti-Gova, n = 10; anti-Govb, n = 4), with the majority in platelet refractoriness (n = 9) and, of the remaining five, four in NAITP and one in PTP. In seven cases, no other HPA antibodies were detected, three being NAITP cases. The incidence of Gov antibodies was significantly lower than HPA-1 system antibodies (n = 87), but equalled the number of HPA-5 system antibodies (n = 14) and outnumbered HPA-2 and -3 system antibodies (10 altogether).

Nonmajor histocompatibility complex alloantigen effects on the fate of Rous sarcomas

Rous sarcoma virus-induced tumor outcome is controlled by the MHC (B). Additional data, using controlled segregation in families, has indicated non-MHC effects as well, but few studies have focused on blood groups other than the B complex. Segregating combinations of genes encoding erythrocyte (Ea) alloantigen systems A, C, D, E, H, I, P, and L in B2B5 and B5B5 MHC (B) backgrounds were examined for their effects on Rous sarcomas. Six-week-old chickens were inoculated in the wing-web with 30 pfu of Rous sarcoma virus (RSV). Tumors were scored six times over a 10-wk period. A tumor profile index (TPI) was assigned to each chicken based on the six tumor size scores. Response was evaluated using tumor size at each measurement period, TPI, and mortality. The genotypes of Ea systems A, C, D, E, H, I, and P had no significant effect on any parameter in either B complex population. The Ea-L system had an effect on Rous sarcomas in the B2B5 intermediate responders and B5B5 progressors. Tumor size, TPI, and mortality were all significantly lower in B2B5 L1L1 chickens than in B2B5 L1L2 chickens. Mortality was lower in the B5B5 L1L1 birds than in B5B5 L1L2 chickens. It appears that the Ea-L system, or one closely linked, is acting in a manner independent of the B complex in response to RSV challenge.

Mouse FcgammaRII is a negative regulator of FcgammaRIII in IgG immune complex-triggered inflammation but not in autoantibody-induced hemolysis.

Murine low-affinity receptors for IgG, FcgammaRII and FcgammaRIII, differ by their distinct capacities in mediating down-regulation or activation of cellular effector functions, respectively. In this study, antibodies detecting the mouse Ly-17.1 / 2 alloantigen system are demonstrated to be specific for FcgammaRII with no cross-reactivities to other FcgammaR, including FcgammaRIII. Using these FcgammaRII-specific monoclonal antibodies (mAb), the significance of FcgammaRII inhibition of FcgammaRIII was examined in two models of autoantibody [autoimmune hemolytic anemia (AIHA)]- and IgG immune complex-induced (Arthus reaction) inflammation in C57BL / 6 mice in comparison with FcgammaRII(- / -) and FcgammaRIII(- / -) mice. Our results demonstrate that both FcgammaRIII and FcgammaRII contributed to the binding of erythrocytes opsonized with the pathogenic IgG1 autoreactive anti-murine red blood cell antibody 105-2H. However, the functional blocking with anti-FcgammaRII mAb in C57BL / 6 mice and the lack of FcgammaRII expression in FcgammaRII(- / -) mice, which both lowered the threshold level of FcgammaRIII-triggered phagocytosis in vitro, did not results in enhanced disease development of 105-2H mAb-induced AIHA in vivo. This was in sharp contrast to cutaneous Arthus reaction, where FcgammaRIII-mediated activation was inhibited by FcgammaRII. Together these results show that murine AIHA is markedly different from other FcgammaR-dependent inflammatory diseases where FcgammaRIII is normally counterregulated by FcgammaRII.

Development and validation of a genotyping kit for the eight principal human platelet alloantigen systems

Thrombocytopenia in newborns is often due to maternal alloimmunization against platelet alloantigens of the foetus which have been inherited from the father and are absent in the mother. Our aim was to develop a "ready-to-use" typing kit based on polymerase chain reactions, using sequence-specific primers for rapid and simultaneous genotyping of the eight principal human platelet alloantigens. The typing technique uses two specific primer pairs for each bi-allelic system and a monomorphic primer pair as amplification control, with a single temperature cycle programme and identical PCR stringency conditions for all pairs of primers. This kit allows typing of blood samples of small volume within three hours after reception. Validation criteria are essential to check the reliability and specificity of the test, and DNA controls carrying the targeted HPA alleles must be obtained from typed individuals or created in vitro by PCR.

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

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

Developmental expression of alloantigen systems in the chicken

The different allelic forms of nine non-Mhc alloantigen systems of the chicken were examined for developmental expression on erythrocytes isolated from embryos and young chicks. Polyclonal alloantisera raised against the different antigens were used to detect these antigens on the cell surface by hemagglutination as well as by indirect immunofluorescence. The developmental stage of initial expression on erythrocytes for each of the genetic systems investigated (i.e., A, E, C, D, H, I, K, L and P) varied from day 4 to day 14 of incubation. The different antigens of each system appeared simultaneously at a particular stage of development except for those of the I system, where the I8 allelic form appeared earlier than I2.

Allele Frequencies of Human Platelet Antigen 1, 2, 3, and 5 Systems in Patients with Chronic Refractory Autoimmune Thrombocytopenia and in Normal Persons

Background and Objectives: Chronic refractory autoimmune thrombocytopenic purpura (AITP) is an autoimmune disorder due to autoantibodies against platelet glycoproteins (GP). Human platelet alloantigenic (HPA) systems are distributed to different platelet GPs. We carried out genotyping of diallelic HPA–1, –2, –3, and –5 systems to clarify potential associations between HPA alleles and the development of chronic refractory AITP. Patients and Methods: DNA was isolated from 33 unrelated German patients with chronic refractory AITP and from 80 randomly selected German blood donors to determine the phenotype and allele frequencies for the HPA–1, –2, –3, and –5 systems. Fragments carrying the polymorphic sequences corresponding to those alleles were amplified by the polymerase chain reaction and further characterized by restriction analysis. Results: Whereas HPA–1, –3, and –5 allele frequencies were identical in 33 patients with chronic refractory AITP and in controls, HPA–2 allele frequencies showed a statistically significant difference (p = 0.017). In our group of patients, the HPA–2a allele frequency was 100%, but HPA–2b was not seen. In contrast, the allele frequency of HPA–2a in the control group was 92% (n = 147), and in HPA–2b it was 8% (n = 13). Conclusion: This study suggests an association between the HPA–2a allele and chronic refractory AITP. The HPA–2a allele may be involved in the formation of an AITP–specific autoepitope.

Allele Frequencies of Human Platelet Antigen 1, 2, 3, and 5 Systems in Patients with Chronic Refractory Autoimmune Thrombocytopenia and in Normal Persons

Abstract Background and Objectives: Chronic refractory autoimmune thrombocytopenic purpura (AITP) is an autoimmune disorder due to autoantibodies against platelet glycoproteins (GP). Human platelet alloantigenic (HPA) systems are distributed to different platelet GPs. We carried out genotyping of diallelic HPA‐1, ‐2, ‐3, and ‐5 systems to clarify potential associations between HPA alleles and the development of chronic refractory AITP. Patients and Methods: DNA was isolated from 33 unrelated German patients with chronic refractory AITP and from 80 randomly selected German blood donors to determine the phenotype and allele frequencies for the HPA‐1, ‐2, ‐3, and ‐5 systems. Fragments carrying the polymorphic sequences corresponding to those alleles were amplified by the polymerase chain reaction and further characterized by restriction analysis. Results: Whereas HPA‐1, ‐3, and ‐5 allele frequencies were identical in 33 patients with chronic refractory AITP and in controls, HPA‐2 allele frequencies showed a statistically significant difference (p = 0.017). In our group of patients, the HPA‐2a allele frequency was 100%, but HPA‐2b was not seen. In contrast, the allele frequency of HPA‐2a in the control group was 92% (n = 147), and in HPA‐2b it was 8% (n = 13). Conclusion: This study suggests an association between the HPA‐2a allele and chronic refractory AITP. The HPA‐2a allele may be involved in the formation of an AITP‐specific autoepitope.

Human platelet alloantigen (HPA)-5a/b mismatch decreases disease-free survival in unrelated bone marrow transplantation.

Matching of human platelet alloantigen (HPA) systems 2-6 was retrospectively investigated in 715 unrelated bone marrow transplantations. Of the five HPA systems studied, HPA-5 mismatching was found to have a significant effect on the disease-free survival rate of recipients following transplantation in the HLA-A, -B, -C, and -DR allele-matched donor-recipient pairs. The effect of the HPA-5 mismatch was most significant in the recipient group possessing the HLA haplotype A*2402-B*5201, which is a highly frequent haplotype among the Japanese population. However, the probability of development of acute graft-versus-host disease (GVHD) was not increased significantly by the HPA-5 mismatching. These findings suggest that the HPA-5 mismatching decreases the recipient's survival by a mechanism different from that in the case of mismatching of minor antigens found often in transplant recipients developing GVHD.

Prothrombotic genetic risk factors in patients with coexisting migraine and ischemic cerebrovascular disease.

The role of hemostatic elements in stroke has been clearly defined but several prothrombotic polymorphisms of hemostatic factors, important for other thromboembolic disorders, seem not to be very significant in stroke. Recently, the high prevalence of factor V Leiden in patients with stroke and a history of migraine has suggested an association between migraine and prothrombotic genetic risk factors. Stroke being a multifactorial disease, the aim of this study was to test whether prothrombotic tendencies increase the risk of stroke in patients with migraine. We determined the prevalence of four prothrombotic genetic risk factors (factor V R/Q 506, factor II 20210 G/A, decanucleotide insertion/deletion in the factor VII promoter, and the platelet HPA-1 alloantigen system) in 17 patients with coexisting ischemic cerebrovascular disease and migraine, 107 patients with ischemic cerebrovascular disease, 106 patients with migraine, and 202 control subjects. Genotyping for all polymorphisms analyzed in our study were performed after specific genomic polymerase chain reaction, and confirmed by single-strain conformation polymorphism analysis. In the group of patients with coexisting ischemic cerebrovascular disease and migraine, the prevalence of prothrombotic genotypes (factor V Leiden, 5.8%; factor II 20210 A, 0%; factor VII A1, 70.6%; and HPA-1b, 35.3%) was similar to that obtained in all other groups. We can conclude that the studied polymorphisms do not seem to be associated with the development of ischemic cerebrovascular disease in those patients with migraine.

A novel isoform of platelet glycoprotein Ib alpha is prevalent in African Americans.

The heavy chain of platelet glycoprotein Ib (GPIb) contains two prevalent sequence polymorphisms. The first, Thr/Met145 is responsible for the human platelet alloantigen system, human platelet antigen (HPA)-2. The second is a tandem repeat polymorphism that consists of four variants, A, B, C, and D. Previous linkage studies in Caucasian and Eastern Asian populations have demonstrated that HPA-2a (Thr145) is associated with variants C and D, while HPA-2b (Met145) is associated with variants A and B. We have determined HPA-2 and variable number of tandem repeats (VNTR) genotypes in three different North American ethnic groups. The gene frequency of HPA-2b in the North American Indians was intermediate between African Americans and Caucasians, and similar to the frequency previously reported in Japanese. Furthermore, the VNTR-A allele, which previously has been reported only in Eastern Asian populations, was present in two of 101 North American Indian individuals. These data are consistent with the hypothesis that the first Native Americans migrated to North America from Eastern Asia. Analysis of HPA-2 and VNTR haplotypes demonstrated an unexpected linkage pattern in the African American population. A rare GPIb alpha isoform, HPA-2b/VNTR-C, was present in 2.2% of African American haplotypes. Furthermore, a novel GPIb alpha isoform, HPA-2a/VNTR-B, was present in 6.5% of African American haplotypes. These data suggest a more complex evolutionary pattern of GPIb alpha isoforms than previously proposed.

Three Cases of Platelet Alloimmunisation Associated with the Presence of a Novel Platelet Specific Antibody

In three cases of platelet alloimmunisation, a platelet-specific alloantibody was detected which could not be classified within the known human platelet alloantigen or HLA systems. The first case was of a family in which two siblings suffered neonatal alloimmune thrombocytopenia at birth. In the second case, the newborn was suffering from phocomelia with hypoplastic thrombocytopenia. The third case was a male who became refractory to transfusions of HLA-matched platelets after a related bone marrow transplantation. The serum samples were investigated by: enzyme-linked immunosorbent assay, platelet suspension immunofluorescence test (PSIFT), monoclonal antibody immobilisation of platelet antigens assay (MAIPA), and by the lymphocytotoxicity test. The antibody gave positive reactions with 26% of normal donor platelets. Surprisingly, no platelet-specific antibody was detected by PSIFT or by MAIPA and there was no evidence found to support classifying the antibody within the HLA system. The reactivity pattern of the antibody detected and the clinical presentation of the three cases described, strongly suggest the presence of an additional platelet-specific alloantigen system.

Three Cases of Platelet Alloimmunisation Associated with the Presence of a Novel Platelet-Specific Antibody

Background and Objectives: In three cases of platelet alloimmunisation, a platelet-specific alloantibody was detected which could not be classified within the known human platelet alloantigen or HLA systems. The first case was of a family in which two siblings suffered neonatal alloimmune thrombocytopenia at birth. In the second case, the newborn was suffering from phocomelia with hypoplastic thrombocytopenia. The third case was a male who became refractory to transfusions of HLA-matched platelets after a related bone marrow transplantation. Materials and Methods: The serum samples were investigated by: enzyme-linked immunosorbent assay, platelet suspension immunofluorescence test (PSIFT), monoclonal antibody immobilisation of platelet antigens assay (MAIPA), and by the lymphocytotoxicity test. Results: The antibody gave positive reactions with 26% of normal donor platelets. Surprisingly, no platelet-specific antibody was detected by PSIFT or by MAIPA and there was no evidence found to support classifying the antibody within the HLA system. Conclusion: The reactivity pattern of the antibody detected and the clinical presentation of the three cases described, strongly suggest the presence of an additional platelet-specific alloantigen system.