Platelet antigens and their function

Association of human platelet alloantigens encoding gene polymorphisms with the risk of Coronary artery disease in Iranian patients

Background

Coronary artery disease (CAD) is characterized by narrowing/ blockade of coronary arteries that is mainly caused by atherosclerotic plaques. Considering the involvement of platelet abnormalities, such as defective aggregation and adhesion, in the cardiovascular-related disorders, genetic variations in human platelet alloantigens (HPA) have been implicated in the CAD susceptibility. Herein, we intended to determine the association of HPA-1 to -6, -9, and -15 biallelic polymorphisms with CAD in an Iranian population.

Methods

In this retrospective case–control study, 200 CAD subjects and 100 matched healthy individuals were enrolled. DNA samples were isolated from peripheral blood samples and genotyping of HPA polymorphisms was accomplished using polymerase chain reaction-sequence-specific primers.

Results

The alleles and genotypes of studied HPA polymorphisms were equally distributed among cases and controls and therefore no statistically significant differences were detected. Univariate analysis identified no association of combined haplotypes with CAD risk. However, multivariate analysis showed a positive association of the‌ HPA1b/2a/3b haplotype with CAD after adjustment for some covariates (including BMI, TG, LDL, FBS and blood pressure) that conferred a CAD susceptibility haplotype (P = 0.015; OR = 2.792; 95% CI 1.45–8.59).

Conclusions

Although alleles, genotypes, and haplotypes of HPA polymorphisms were not associated with CAD risk, HPA1b/2a/3b haplotype was found to be a dependent disease risk haplotype in Iranian population after correcting for confounding factors.

Association of Platelet Integrin α_IIbβ₃ Polymorphisms with Atherosclerotic Coronary Heart Disease in Sudanese Patients

BACKGROUND AND OBJECTIVE

Glycoprotein IIIa and GPIIb constitutes are the fibrinogen receptor (integrin αIIbβ3). This glycoprotein has a fundamental role in atherothrombosis. This study aimed to detect the association of αIIbβ3 polymorphisms with atherosclerotic coronary heart disease in Sudanese patients and the association between the risk factors and platelet integrin αIIbβ3 polymorphisms.

MATERIALS AND METHODS

This is a case-control hospital-based study contain 50 atherosclerotic patients (>18 years) with coronary heart disease that admitted to Khartoum hospital and were compared to apparently 50 healthy Sudanese subjects at the same ages. About 5 mL of venous blood sample was collected from each patient and control. The laboratory analyses were done for HbA1c, lipid profile and for DNA genotyping.

RESULTS

LDL, HDL, HbA1c and body mass index have shown highly significant influence on patients. No significant differences were observed for triglycerides and total cholesterol levels. The risks of coronary heart disease were higher with A/B genotype in HPA3, but no association detected with coronary heart disease patients in HPA1 polymorphism.

CONCLUSION

In conclusion, HPA3 polymorphism was associated with atherosclerotic in Sudanese patients, while HPA1 polymorphism has not.

Sequence-Based Typing for Platelet alloantigens

Human platelet antigen (HPA) typing is largely performed by use of DNA-based techniques in patients that require assessing the risk of HPA alloimmunization. In this chapter, HPA typing by sequencing-based typing (SBT) techniques is described.

Role of the hemostatic system on sickle cell disease pathophysiology and potential therapeutics

Recent studies suggest that sickle cell disease (SCD) is a hypercoagulable state contributing to vaso-occlusive events in the microcirculation, resulting in acute and chronic sickle cell-related organ damage. In this article, we review the existing evidence for contribution of hemostatic system perturbation to SCD pathophysiology. We also review the data showing increased risk of thromboembolic events, particularly newer information on the incidence of venous thromboembolism. Finally, the potential role of platelet inhibitors and anticoagulants in SCD is briefly reviewed.

Human platelet antigen alleles in 998 Taiwanese blood donors determined by sequence-specific primer polymerase chain reaction

Polymorphism of human platelet antigens (HPAs) leads to alloimmunizations and immune-mediated platelet disorders including fetal-neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura (PTP), and platelet transfusion refractoriness (PTR). HPA typing and knowledge of antigen frequency in a population are important in particular for the provision of HPA-matched blood components for patients with PTR. We have performed allele genotyping for HPA-1 through -6 and -15 among 998 platelet donors from 6 blood centers in Taiwan using sequence-specific primer polymerase chain reaction. The HPA allele frequency was 99.55, and 0.45% for HPA-1a and -1b; 96.49, and 3.51% for HPA-2a and -2b; 55.81, and 44.19% for HPA-3a and -3b; 99.75, and 0.25% for HPA-4a and -4b; 98.50, and 1.50% for HPA-5a and -5b; 97.75 and 2.25% for HPA-6a and -6b; 53.71 and 46.29% for HPA-15a and -15b. HPA-15b and HPA-3a, may be considered the most important, followed by HPA-2, -6, -1, -5, and -4 systems, as a cause of FNAIT, PTP, and PTR based on allele frequency. HPA-4b and HPA-5b role cannot be excluded based on their immunogenicity. A larger-scale study will now be conducted to confirm these hypotheses and to establish an apheresis donor database for the procurement of HPA-matched apheresis platelets for patients with PTR.

Modeling and molecular dynamics of HPA-1a and -1b polymorphisms: effects on the structure of the β3 subunit of the αIIbβ3 integrin

Background

The HPA-1 alloimmune system carried by the platelet integrin αIIbβ3 is the primary cause of alloimmune thrombocytopenia in Caucasians and the HPA-1b allele might be a risk factor for thrombosis. HPA-1a and -1b alleles are defined by a leucine and a proline, respectively, at position 33 in the β3 subunit. Although the structure of αIIbβ3 is available, little is known about structural effects of the L33P substitution and its consequences on immune response and integrin functions.

Methodology/Principal Findings

A complete 3D model of the L33-β3 extracellular domain was built and a P33 model was obtained by in silico mutagenesis. We then performed molecular dynamics simulations. Analyses focused on the PSI, I-EGF-1, and I-EGF-2 domains and confirmed higher exposure of residue 33 in the L33 β3 form. These analyses also showed major structural flexibility of all three domains in both forms, but increased flexibility in the P33 β3 form. The L33P substitution does not alter the local structure (residues 33 to 35) of the PSI domain, but modifies the structural equilibrium of the three domains.

Conclusions

These results provide a better understanding of HPA-1 epitopes complexity and alloimmunization prevalence of HPA-1a. P33 gain of structure flexibility in the β3 knee may explain the increased adhesion capacity of HPA-1b platelets and the associated thrombotic risk. Our study provides important new insights into the relationship between HPA-1 variants and β3 structure that suggest possible effects on the alloimmune response and platelet function.

Prevalence of the HPA-18w to -21w alleles in the Chinese Han population

Recently, four new platelet alloantigen (HPA) systems HPA-18w to-21w were identified. However, genotyping for HPA-18w to -21w alleles was rarely reported. Here, we established a polymerase chain reaction sequence-based typing (PCR-SBT) method and investigated the distribution of HPA-18w to -21w alleles in the Chinese Han population. The specific primers of HPA-18w, -19w, -20w and -21w were designed, and the PCR products were bidirectionally sequenced. 855 randomly selected platelet donors were genotyped for HPA-18w to -21w with the PCR-SBT method. The results showed that all individuals were monomorphic for HPA-18w to HPA-20w with a/a homozygous frequency of 1.0 and absence of HPA-18bw to -20bw alleles. The frequencies of the HPA-21a/21a and HPA-21a/21b genotypes were 0.981(839/855) and 0.019(16/855), respectively. Seven mutations were confirmed on sequenced region separate from HPA polymorphisms, including ITGA2 (IVS17+48G>A and IVS17+72G>A), ITGA2B (IVS19-26C>G) and ITGB3 (IVS4+234C>T, IVS11-19 T>C, IVS11-104T>C and GT repeats from IVS11-131 to IVS11-109). These data will provide useful information for diagnosis, prevention and treatment of alloimmune thrombocytopaenia.

Human platelet antigen allele frequencies and new mutations on platelet glycoprotein genes in the Chinese Han population

BACKGROUND AND OBJECTIVES

The frequencies of human platelet antigens (HPAs) vary between different populations. In this study, we determined the HPA allele frequencies in the Chinese Han population and identified situation of incompatibility possibly leading to alloimmunisation.

METHODS

A total of 750 volunteer blood donors of the Chinese Han population were genotyped for HPA-1 to -17w systems. HPA genotyping was determined by polymerase chain reaction sequence-based typing.

RESULTS

Among the 17 HPA systems, the allele frequency is different from other populations. We noted the absence of HPA-7bw to HPA-14bw, HPA-16bw and HPA-17bw alleles in the population. The estimated incompatibility probabilities regarding platelet antigens 1 to 6w and 15 systems after transfusion of random donor platelet were from 0·004 to 0·373. Thirteen glycoprotein alleles were observed in the population. In addition, we identified 16 novel mutations on the glycoprotein genes separated from HPA polymorphisms, including GP1BA (517-525delAAC), ITGA2B (2722C>T and IVS26+85T>C), ITGA2 (1521C>T, 2474T>G and IVS20+10 G>C), ITGB3 (1476G>A, IVS10+19C>A, 1813G>A, IVS11+21G>A, IVS11+152A>G and IVS11-104T>C), GP1BB (IVS1-79G>A, IVS1-27C>T and 129G>A) and CD109 (2139A>G). Five of them could lead to amino acid deletion, substitution or premature stop codon in corresponding glycoprotein.

CONCLUSIONS

There was a high degree of polymorphism of the membrane glycoprotein genes related to human platelet alloantigen-1 to -17w systems in the Chinese Han population. These data could have some impact on the diagnosis, prevention and treatment of alloimmune thrombocytopenia.

Human platelet alloantigens HPA-1, HPA-2, and HPA-3 polymorphisms associated with extent of severe coronary artery disease

The contribution of human platelet antigen (HPA)-1 (GPIIb/IIIa), HPA-2 (GPIb/IX), and HPA-3 (GPIIb/IIIa) polymorphisms to the risk of coronary artery disease (CAD) was investigated in 341 CAD patients and 316 matched control subjects. HPA genotyping was performed by PCR-SSP. Regression analysis was employed in assessing the contribution of these variants to CAD risk. The frequency of HPA-1b (P = .009) and HPA-3b (P = .004) alleles, and HPA-1a/1b (P = .045), HPA-1b/1b (P = .007), and HPA-3b/3b (P = .008) genotypes were higher in patients than control subjects. No significant association was demonstrated between the HPA variants and 1-, 2- and 3-vessel disease. HPA-1b/2a/3b (Pc = .021) and HPA-1b/2b/3a (Pc = .002) haplotypes were positively associated with CAD, thereby conferring a disease susceptibility nature to these haplotypes. Multivariate analysis confirmed the positive association of HPA-1b/2a/3b (aOR = 3.72; 95% CI = 1.49-9.28), and in addition identified HPA-1b/2a/3a (aOR = 2.49; 95% CI = 1.06-5.86) to be positively associated with CAD, after adjusting for a number of covariates. Our results demonstrate positive association of HPA variants and specific HPA-1/HPA-2/HPA-3 haplotypes with CAD in Tunisians.

Human platelet alloantigens (HPA) 1, HPA2, HPA3, HPA4, and HPA5 polymorphisms in sickle cell anemia patients with vaso-occlusive crisis

OBJECTIVES

Vaso-occlusive crisis (VOC) is a significant cause of morbidity and mortality in sickle cell anemia (SCA) patients. Insofar as polymorphism in human platelet alloantigen (HPA) exhibit a prothrombotic nature, we hypothesized that specific HPA polymorphic variants are associated with VOC. We investigated the distribution of HPA1, HPA2, HPA3, HPA4, and HPA5 alleles genotypes among VOC and non-VOC control SCA patients.

PATIENTS/METHODS

This was a case-control study. Study subjects comprised SCA patients with (VOC group; n = 127) or without (Steady-state group; n = 130) VOC events. HPA genotyping was done by PCR-SSP.

RESULTS

Significantly higher frequencies of HPA-2b, HPA-3b, and HPA-5b alleles, and marked enrichment of HPA-3b/3b, HPA-5a/5b, and HPA-5b/5b genotypes, were seen in VOC than in control SCA patients. Taking homozygous wild-type genotypes as reference, univariate analysis identified HPA-3a/3b, HPA-3b/3b, and HPA-5b/5b to be associated with VOC. Multivariate analysis confirmed the independent association of only HPA-3a/3b and HPA-3b/3b genotypes with VOC. HPA-3 genotypes were significantly correlated with VOC frequency, type, and medication, and requirement for hospitalization. While both HPA 3a/3b (P = 0.002; OR = 2.94; 95% CI = 1.49-5.77) and 3b/3b (P = 0.006; OR = 3.16; 95% CI = 1.40-7.17) genotypes were associated with need for hospitalization, only HPA-3b/3b was associated with VOC frequency, type (localized vs. generalized), and medication (narcotics vs. NSAIDs).

CONCLUSION

This confirms the association of HPA polymorphisms with SCA VOC, of which HPA-3 appears to be independent genetic risk factors for SCA VOC.

Polymorphisms of human platelet alloantigens HPA-1 and HPA-2 associated with severe coronary artery disease

OBJECTIVES

Insofar as platelet membrane glycoprotein (GP) polymorphisms were identified as potential risk factors for coronary artery disease (CAD), we investigated the contribution of human platelet antigen (HPA)-1 (GPIIb/IIIa) and HPA-2 (GPIb/IX) alleles and haplotypes to CAD pathogenesis.

METHODS

Study subjects comprised 247 middle-age CAD patients and 316 age-, gender-, and race-matched controls; HPA genotyping was performed by polymerase chain reaction with sequence specific primers.

RESULTS

The frequencies of HPA-1b (P<.001) and HPA-2b (P<.001) alleles and HPA-1a/1b (P<.001), HPA-1b/1b (P<.001), and HPA-2a/2b (P<.001) genotypes were higher in patients than control subjects. Select HPA haplotypes comprising the HPA-1b/2a (Pc=2.2 × 10(-4)) and HPA-1b/2b (Pc=.001) haplotypes which were positively associated, and the HPA-1a/2a (Pc=3.2 × 10(-5)) which was negatively associated with CAD, confer a disease susceptibility and protective nature to these haplotypes. Multivariate analysis confirmed the positive association of HPA-1b/2a [adjusted odds ratio (aOR)=3.63; 95% CI=2.42-5.43] and HPA-1b/2b (aOR=2.92; 95% CI=1.43-5.94) haplotypes with CAD, after adjustment for a number of covariates.

CONCLUSIONS

Our results suggest that HPA-1/HPA-2 haplotypes may be considered to be a major risk factor for CAD in middle-aged Tunisians.

Inherited prothrombotic risk factors in children with stroke, transient ischemic attack, or migraine

OBJECTIVE

The aim of this study was to investigate the prevalence and possible association of inherited prothrombotic risk factors in children with stroke, transient ischemic attack, or migraine.

METHODS

We performed genotypic analysis for factor V G1691A, factor II G20210A, methylenetetrahydrofolate reductase C677T, and 4 common platelet glycoprotein polymorphisms (human platelet alloantigen-1, -2, -3, and -5) in 150 children <18 years of age with established diagnoses of stroke, transient ischemic attack, or migraine. Children were classified into 5 groups, namely, childhood arterial ischemic stroke (N = 33), perinatal arterial ischemic stroke (N = 26), hemorrhagic stroke (N = 20), transient ischemic attack (N = 36), and migraine (N = 35). The control group consisted of 112 children < or =18 years of age from the same geographical region who had no history of neurologic or thromboembolic diseases.

RESULTS

Heterozygosity for factor V G1691A was associated with approximately sevenfold increased risk for arterial ischemic stroke, perinatal arterial ischemic stroke, and transient ischemic attack. Increased risk for transient ischemic attack was found in carriers of the human platelet alloantigen-2b allele, human platelet alloantigen-5a/b genotype, and combined human platelet alloantigen-2b and human platelet alloantigen-5b genotype. The presence of the human platelet alloantigen-2b allele was associated with a 2.23-fold increased risk for migraine, whereas carriers of the human platelet alloantigen-3b allele had a lower risk for arterial ischemic stroke than did carriers of the human platelet alloantigen-3a allele.

CONCLUSIONS

Factor V G1691A has an important role in susceptibility to arterial ischemic stroke, both in the perinatal/neonatal period and in childhood, as well as transient ischemic attacks. A minor impact of human platelet alloantigen polymorphisms suggests that platelet glycoprotein polymorphisms may increase the risk of transient ischemic attacks and migraine, but this should be confirmed in larger studies.

Platelet glycoprotein IIb/IIIa (HPA-1 and HPA-3) polymorphisms in patients with hemorrhagic fever with renal syndrome

This study investigated the relationship between human platelet alloantigen (HPA) polymorphisms of glycoprotein IIb/IIIa and hemorrhagic fever with renal syndrome (HFRS). HPA-1 and HPA-3 genotyping was performed with allele-specific primer polymerase chain reaction in 104 patients with HFRS and 100 normal individuals as controls. The relationships between gene polymorphisms of HPAs and HFRS and the disease severity were analyzed. The results indicated no significant difference in HPA-1 genotype distributions (p > 0.05), but a significant difference in the distributions of genotype and allele frequencies of HPA-3 between HFRS patients and controls (p < 0.01). The distributions of HPA-3 genotype and allele frequencies differed significantly between patients with different clinical types and the HPA-3 b allele was more frequently observed in patients with more severe clinical types. These results indicate that HPA-3 polymorphism may be one of the inherited risk factors associated with the susceptibility of hantavirus infection and the disease severity of HFRS.

Polymorphisms of the human platelet alloantigens HPA-1, HPA-2, HPA-3, and HPA-4 in ischemic stroke

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), and HPA-5 (GPIa/IIa) was investigated in 329 stroke patients and 444 matched control subjects. HPA genotyping was done by PCR-SSP method. Lower HPA-1a (P < 0.001) and higher HPA-1b (P < 0.001) allele frequencies were seen in patients than control subjects, and homozygosity for HPA-1b (P < 0.001) alleles was more prevalent in stroke cases than in controls. The allele and genotype distributions of the other HPA polymorphic variants were similar between cases and controls. Select HPA combined genotypes comprising the 2121 (Pc = 0.008) and 2221 (Pc = 0.018) genotypes, which were positively associated, and the 1111 (Pc < 0.001), which was negatively associated with stroke, thereby conferred a disease susceptibility and protective nature to these genotype combinations. Multivariate analysis confirmed the negative association of the 1111 (P < 0.001) and the positive association of the 2121 (P = 0.017) combined genotypes with stroke, after adjustment for a number of covariates. This is the first evidence demonstrating differential association of the common 4 HPA gene variants and specific HPA genotype combinations with stroke.

Platelet glycoprotein Ibalpha polymorphisms and function evaluated by the platelet function analyzer PFA-100 in patients with lupus anticoagulant: the association with thromboembolic disease

Lupus anticoagulants (LA) are a surrogate marker for the risk of thromboembolic disease (TE). However, not all individuals with LA acquire TE, and it is desirable to distinguish those at risk for TE from those without. Platelets polymorphisms may contribute to the risk of TE, mainly those of glycoprotein (GP)Ibalpha: these are the variable number of tandem repeats (VNTR) and a dimorphism in the Kozak region, which affect platelet plug formation in healthy individuals under high shear stress rates. We determined polymorphisms within the GPIbalpha in individuals with persistent LA and a history of TE (LA/TE+) and in those without TE (LA/TE-). Further, we measured platelet function, as estimated by the collagen-epinephrine closure time (CEPI-CT) of the platelet function analyzer PFA-100 and compared all data with healthy controls. There was no difference of the VNTR alleles compared to healthy controls. The (-5)C allele of the Kozak dimorphism was significantly more frequent in LA patients compared to controls (p = 0.04), as a result of its increased frequency in LA/TE+ (vs controls p = 0.04), but there was no difference between LA/TE+ and LA/TE-. The increased frequency of the (-5)C allele resulted in an overrepresentation of (-5)TC genotype in the LA/TE+ group (p = 0.02) but not in a subgroup of 18 patients with arterial disease. The CEPI-CT of the PFA-100 was shorter in LA/TE+ than in LA/TE- (p = 0.044), but this difference did not persist after exclusion of patients with low platelet counts or low ristocetin cofactor activity. Unlike in healthy individuals, the CEPI-CT was not related to any Kozak dimorphism, neither in LA/TE-, nor in LA/TE+. Thus, the Kozak dimorphism may just contribute to stronger factors disposing individuals with LA towards TE without any discernible effect on their in vitro platelet function estimated by the PFA-100.

Agonists-induced platelet activation varies considerably in healthy male individuals: studies by flow cytometry

Flow cytometric evaluation of platelet function extends our understanding of platelets' role in various clinical conditions associated with either bleeding disorders, thrombosis, or monitoring of antiplatelet therapy. The use of suboptimal concentrations of various agonists may allow assessing the "activatability" of platelets. We determined platelet responsiveness to thrombin-receptor-activating peptide-6, arachidonic acid, adenosine 5c-diphosphate (ADP), epinephrine, collagen, and ristocetin at suboptimal concentrations by determination of P-selectin expression and binding of PAC-1 in 26 healthy male individuals. The response varied considerably from one individual to the next. However, within individuals, responses to all agonists except collagen correlated strongly (p<0.05), suggesting a global variability of platelet responses. Moreover, P-selectin expression and PAC-1 binding were strongly correlated (p<0.05). Interestingly, with epinephrine, PAC-1 positive events outnumbered P-selectin positive events, while this was not seen with the other agonists. Thus, epinephrine may specifically affect the conformational switch mechanism and receptor clustering. Our data indicate that the in vitro response to suboptimal concentrations of agonists varies, but individuals with selective platelet defects may still be identified based on data obtained with the various agonists.