The c.1544+1G>A mutation was identified in Gypsy Glanzmann thrombasthenia (GT) patients. Gypsy GT patients express normal αvβ3 carrying HPA‐1b epitopes. To demonstrate HPA‐1a alloimmunization by modified antigen capture assays. Gypsy GT patients could develop anti‐HPA‐1a alloantibodies against β3 and αvβ3. Abstract BackgroundGlanzmann thrombasthenia (GT) is a rare bleeding disorder caused by the absence or the dysfunction of the platelet αIIbβ3 integrin. A founder mutation in the ITGA2B gene was previously identified in French Gypsy patients. Interestingly, this mutation was strongly linked to the human platelet antigen‐1b (HPA‐1b). The HPA‐1bb Gypsy patients are at risk of isoimmunization against αIIbβ3, as this complex is not expressed at their platelet surface. Tentatively, they would, however, not have an increased risk of developing anti‐HPA‐1a alloantibodies by exposure of αIIbβ3 on platelets from random platelet transfusions. However, the β3 chain can also associate with the αv subunit expressed at the platelet surface. Because Gypsy GT patients express normal αvβ3 carrying HPA‐1b epitopes, these patients might develop anti‐HPA‐1a alloantibodies reacting with αvβ3 and/or β3. Objectives/Patients/MethodsTo demonstrate this hypothesis, sera from HPA‐1bb (n = 5) and HPA‐1ab (n = 1) Gypsy GT patients were investigated by modified antigen capture assay using platelets or stable transfected cells. Furthermore, stable transfected cells expressing either αIIbβ3 or αvβ3 together with soluble monomeric chimeric β3 (as absorbent) were used to differentiate anti‐β3 and anti‐αvβ3 reactivity. ResultsOnly HPA‐1bb patients developed alloantibodies reacting with HPA‐1a cells. Further analysis showed that HPA‐1bb patients developed anti‐HPA‐1a alloantibodies reacting with β3 and/or αvβ3. ConclusionIn this study, we found that HPA‐1bb patients who failed to express αIIbβ3 on the platelet surface can develop alloantibodies against HPA‐1a reacting with β3 as well as αvβ3. This is of particular importance as anti‐HPA‐1a alloantibodies might cause fetal neonatal alloimmune thrombocytopenia and/or platelet transfusion refractoriness.

The frequencies of HPA genotypes in our study indicates that HPA-1a, -2a, -4a, -5a and -6a are unlikely involved in FNAIT, PTP and PTR in Burmese and Karen populations. However, HPA-1b, -2b, -3a, -3b, -4b, -5b, -6b, -15a and -15b may likely stimulate alloantibodies in these populations.

BACKGROUND Anti‐CD36s, developing after transfusion or during pregnancy, play an important role in immune‐mediated bleeding disorders among Asian populations. Currently, little is known about the clinical relevance of anti‐CD36. Here, we aimed to determine the frequency of CD36 deficiency in Thais by analyzing CD36 expression on cell surfaces and in plasma. STUDY DESIGN AND METHODS The expression and deficiency of CD36 on platelets and monocytes were determined by flow cytometry. Mutations in the CD36 gene were analyzed by nucleotide sequencing. Soluble CD36 (sCD36) in plasma was quantified with enzyme‐linked immunosorbent assay. RESULTS Fifteen of 700 blood donors (2.14%) were identified as CD36 deficient. The frequencies of Type I and II CD36 deficiency were 0.43% and 1.71%, respectively. Type I individuals exhibited c.1163A > T, c.429 + 4insG, and c.1156C > T. Type II individuals exhibited c.879 T > C, c.329‐330delAC, c.818 + 108delAACT, c.1125 + 13C > A, and c.1163A > T. CD36 on donor platelets (n = 685) showed a wide distribution of expression levels (mean fluorescence intensity, 16.71 ± 8.68). In the normal phenotype (n = 14), sCD36 concentration was 58.84 ± 11.68 ng/mL, which was significantly correlated with platelet CD36 expression (r2 = 0.8551). In Type II–deficient individuals (n = 6), a similar sCD36 concentration was detected (53.67 ± 8.17 ng/mL). However, sCD36 could not be detected in Type I individuals (n = 3). CONCLUSION CD36 Type I deficiency was found, indicating the potential for immune‐mediated platelet disorders in Thais. However, the underlying mutations differed from those reported in Japan and China. Interestingly, sCD36 could not be detected in plasma of Type I–deficient individuals. This finding may lead to the use of plasma to identify individuals at risk and to allow screening of large cohorts.

Background Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by the destruction of platelets in the fetus or newborn by maternal platelet alloantibodies, mostly against human platelet antigen (HPA)‐1a. Recent studies indicate that two anti‐HPA subtypes exist: Type I reacts with epitopes residing on the plexin‐semaphorin‐integrin (PSI) and type II with plexin‐semaphorin‐integrin/integrin epidermal growth factor 1 (I‐EGF1) domains of the β3 integrin. Here, we evaluated whether a Cys460Trp mutation in the I‐EGF1 domain found in a patient with Glanzmann thrombasthenia can alter the binding of anti‐HPA‐1a. Methods Stable HEK293 cell lines expressing wild‐type and mutant αIIbβ3 and αvβ3 were generated to prove the reactivity of different antibodies against HPA‐1a. Results Flow cytometry analysis of wild‐type (Cys460) and mutant (Trp460) expressed on HEK293 cells showed equal surface expression of αIIbβ3 and αvβ3. When tested with mutant αIIbβ3 cells, reduced binding was observed in Type II but not in Type I anti‐HPA‐1a. These results could be confirmed with platelets carrying Cys460Trp mutation. Interestingly, reduced binding of Type I antibodies was detected with mutant αvβ3 cells. Both antibody types were found in maternal sera from FNAIT cases by an antigen‐capture assay with use of HEK293 transfected cells. Conclusions These observations confirm the existence of Type I and Type II anti‐HPA‐1a. Furthermore, this study underlines different immunogenicity of HPA‐1a antigen(s) residing on either αIIbβ3 or αvβ3. Further analysis of FNAIT cases from mothers having a fetus with and without intracranial bleedings with use of such an approach may highlight the functional relevance of different anti‐HPA‐1a subtypes.