Human platelet Ag (HPA)-1a, located on integrin β3, is the main target for alloantibodies responsible for fetal and neonatal alloimmune thrombocytopenia (FNAIT) in the white population. There are ongoing efforts to develop an Ab prophylaxis and therapy to prevent or treat FNAIT. In this study, an mAb specific for HPA-1a, named 26.4, was derived from an immortalized B cell from an alloimmunized woman who had an infant affected by FNAIT. It is the only HPA-1a–specific human mAb with naturally paired H and L chains. Specific binding of mAb 26.4, both native and recombinant forms, to platelets and to purified integrins αIIbβ3 (from platelets) and αVβ3 (from trophoblasts) from HPA-1a+ donors was demonstrated by flow cytometry and surface plasmon resonance technology, respectively. No binding to HPA-1a− platelets or integrins was detected. Moreover, the Ab binds with higher affinity to integrin αVβ3 compared with a second HPA-1a–specific human mAb, B2G1. Further in vitro experimentation demonstrated that mAb 26.4 can opsonize HPA-1a+ platelets for enhanced phagocytosis by monocytes, inhibit binding of maternal polyclonal anti–HPA-1a Abs, and weakly inhibit aggregation of HPA-1a–heterozygous platelets, the latter with no predicted clinical relevance. Thus, mAb 26.4 is highly specific for HPA-1a and could potentially be explored for use as a prophylactic or therapeutic reagent for FNAIT intervention and as a phenotyping reagent to identify women at risk for immunization.

BackgroundFetal and neonatal alloimmune thrombocytopenia (FNAIT) is a bleeding disorder caused by maternal antibodies against paternal human platelet antigens (HPAs) on fetal platelets. Antibodies against HPA-1a are accountable for the majority of FNAIT cases. We have previously shown that high levels of maternal anti-HPA-1a antibodies are associated with clinically significant reduced birth weight in newborn boys. Chronic inflammatory placental lesions are associated with increased risk of reduced birth weight and have previously been reported in connection with FNAIT pregnancies. The HPA-1a epitope is located on integrin β3 that is associated with integrin αIIb (the fibrinogen receptor) on platelets and megakaryocytes. Integrin β3 is also associated with integrin αV forming the αVβ3 integrin heterodimer, the vitronectin receptor, which is expressed on various cell types, including trophoblast cells. It is therefore thinkable that maternal anti-HPA-1a antibodies present during early pregnancy may affect placenta function through binding to the HPA-1a antigen epitope on invasive throphoblasts. The aim of the study was to examine whether interaction of a human anti-HPA-1a monoclonal antibody (mAb) with HPA-1a on trophoblast cells affect adhesion, migration and invasion of extravillous trophoblast cells.MethodsAn in vitro model with human anti-HPA-1a mAb, clone 26.4, and the first trimester extravillous trophoblast cell line HTR8/SVneo was employed. The xCELLigence system was utilized to assess the possible effect of anti-HPA-1a mAb on adhesion and migration of HTR8/SVneo cells. Specially designed chambers precoated with Matrigel were used to assess the effect on the invasive capacity of cells.ResultsWe found that human anti-HPA-1a mAb 26.4 partially inhibits adhesion and migratory capacity of HTR8/SVneo cells.ConclusionsOur findings suggest that anti-HPA-1a antibodies may affect trophoblast functions crucial for normal placental development. Future studies including primary throphoblast cells and polyclonal anti-HPA-1a antibodies are needed to confirm these results.

Paraneoplastic neurological syndromes in patients with Hodgkin's disease are rare findings. Subacute, paraneoplastic cerebellar degeneration or autonomic dysfunctions were described before. In some of these cases, autoantibodies against central or peripheral nervous system structures were found in serum and CSF. We present a 30-year-old white male who developed a progredient, clinical and electrophysiological distal sensomotoric neuropathy. Six months after the beginning of the neurological disturbances, Hodgkin's disease (Stadium III BE) was diagnosed. Other reasons for neuropathy, such as direct impairment of the peripheral nervous system by tumor masses or drug-induced neuropathy, were excluded. Cerebrospinal fluid (CSF) analysis showed a mild pleocytosis, elevated total protein (9.8 g/l) and identical oligoclonal bands in serum and CSF. Blood-CSF barrier damage was detected by Reiber formula. Indirect immunofluorescence and western blot analysis demonstrated an autoantibody against peripheral and central nervous system structures in serum and CSF. Although the autoantibody responded to a 38-40 kDa-protein in western blot and showed nuclear staining of myenteric plexus and Purkinje cell nuclei in the immunofluorescence test, this antibody was shown to be not identical to anti-Hu. An intrathecal synthesis of the antineuronal antibody was detected by antibody specificity index. Tumor therapy, plasmapheresis and treatment with intravenous immunoglobulins did not improve the neuropathy. According to our knowledge this is the first case of antineuronal antibody-associated sensomotoric neuropathy in Hodgkin's disease.

Alloimmunization against human platelet antigen (HPA)‐1a during pregnancy can cause foetal/neonatal alloimmune thrombocytopenia (FNAIT) and severe bleeding in the foetus or newborn and likely depends on several factors. HPA‐1a alloimmunization is associated with DRB3*01:01, which is associated with several DR‐DQ haplotypes. However, it is not known to what extent these haplotypes contribute to the prevalence of HPA‐1a alloimmunization. HPA‐1a–alloimmunized women, identified in a prospective study, and random donors were typed for selected DRB3, DRB4, DRB1, DQA1 and DQB1 alleles to determine allele and DR‐DQ haplotype frequencies. DRB3*01:01 was carried by 94% HPA‐1a–immunized women compared to 27% in the general population. In the first population, the DR3‐DQ2 haplotype was overrepresented (P < .003). The prevalence of HPA‐1a alloimmunization was estimated to be about twice as frequent with DR3‐DQ2 compared to DR13‐DQ6, together accounting for about 90% of DRB3*01:01–positive individuals. Further, we examined DQB1*02 and DRB4*01:01 alleles for their reported association with HPA‐1a alloimmunization, in the context of DR‐DQ haplotypes. Since ~ 80% of DQB1*02 alleles are linked to the DR3‐DQ2 haplotype, the association might be coincidental. However, the DQB1*02:02–associated DR7‐DQ2 haplotype was also overrepresented in alloimmunized women, suggesting a role for this allele or haplotype in HPA‐1a alloimmunization. As DRB4*01:01 is predominantly associated with the DR7‐DQ2 haplotype in HPA‐1a–alloimmunized individuals, the reported association with FNAIT may be coincidental. Typing for DR‐DQ haplotypes revealed important genetic associations with HPA‐1a alloimmunization not evident from typing individual alleles, and the presence of different DRB3‐associated DR‐DQ haplotypes showed different prevalence of HPA‐1a alloimmunization.

No abstract