Presentation Details
| Anti-GPIbα antibodies in FNAIT are associated with recurrent miscarriages Christopher J.Khoury1-3, Pingguo Chen1-4, Guangheng Zhu2, 3, Zoya Tawhidi1-3, Alan H.Lazarus1-4, 8, Yiming Wang5, Karen Chong6, David Chitayat1, 6, Heyu Ni1-4, 7, 8. 1Department of Laboratory Medicine and Pathobiology, University of Toronto., Toronto, ON, Canada.2Keenan Research Centre for Biomedical Science of St.Michael’s Hospital, Toronto, ON, Canada.3Toronto Platelet Immunology Group, Toronto, ON, Canada.4Canadian Blood Services Centre for Innovation, Toronto, ON, Canada.5Division of Clinical and Metabolic Genetics, Department of Paediatrics, The Hospital for Sick Children, University of Toronto., Toronto, ON, Canada.6The Prenatal Diagnosis and Medical Genetics Program, Department of Obstetrics and Gynecology, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.7Department of Physiology, University of Toronto, Toronto, ON, Canada.8Department of Medicine, University of Toronto, Toronto, ON, Canada |
Abstract
Background: Recurrent miscarriage is defined as the loss of 3 or more consecutive pregnancies before the 20th week of gestation, affecting 1-2% of couples. It is often difficult to determine a cause for recurrent miscarriages, as more than half of cases remain unexplained following clinical investigation. Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a suspected cause of miscarriages in humans, but clinical evidence is limited. FNAIT is classically defined by maternal antibody generation against specific human platelet antigens (HPAs) on fetal platelets, leading to thrombocytopenia, severe bleeding diatheses, and other obstetric complications. Most reported FNAIT cases (~70-90%) result from maternal alloantibodies targeting β3 integrin (HPA-1a), while cases caused by GPIbα antibodies (HPA-2b) are exceedingly rare (less than 1%). We previously described a non-classical mechanism of FNAIT in a murine model where maternal anti-GPIbα antibodies led to fetal platelet activation and thrombosis in the placenta, causing miscarriage in >83% of pregnant mice (J Clin Invest, 2011). Whether anti-GPIbα antibodies cause recurrent miscarriage in humans has not been explored. Aims: Examine sera from women experiencing unexplained recurrent miscarriages for anti-platelet antibodies and evaluate their effect on platelet function. Methods: The 3 patients recruited for this study were patients seen in the Prenatal Diagnosis and Medical Genetics Program in the Department of Obstetrics and Gynecology at Mount Sinai Hospital, Toronto. Standard workup was performed but a definitive cause for recurrent miscarriages could not be determined. We used a monoclonal antibody immobilization of platelet antigen (MAIPA) assay and flow cytometry to detect IgG against specific platelet antigens in each patient’s serum. O-sialoglycoprotein endopeptidase was used to cleave GPIbα from platelets for antibody binding assays. Gel-filtered donor platelets were incubated with patient serum or serum-purified IgG and then measured for markers of platelet activation (P-selectin and PAC-1) and desialylation (RCA-I) by flow cytometry. Results: MAIPA assays revealed high levels of anti-platelet antibodies in two of three patients. Serum from patient 1 contained anti-GPIbα IgG, patient 2 serum had IgG against both GPIbα and integrin β3, while patient 3 had no detectable anti-platelet IgG. We detected strong antibody binding to donor platelets incubated with serum from patients 1 and 2 and then found that antibody binding was attenuated to GPIbα-depleted platelets. Donor platelets incubated with serum from patients 1 and 2, but not patient 3, induced platelet activation (P-selectin expression and PAC-1 binding) and desialylation (RCA-1 binding), and purified IgG from these patients did the same, which confirmed the effect on platelets was IgG-specific. Conclusion/Discussion: We detected anti-GPIbα antibodies in 2/3 patients experiencing unexplained recurrent miscarriages, which may explain the paucity of such cases in neonates. Additionally, serum and purified IgG from both anti-platelet IgG positive patients induced activation and desialylation of donor platelets, providing a potential mechanism for how anti-platelet IgG can cause miscarriage. GPIbα antibodies could cause miscarriage by inducing fetal platelet activation, promoting pathological blood clotting, and impaired blood flow to the placenta. These initial findings provide the first evidence that anti-GPIbα antibodies in FNAIT are associated with recurrent miscarriages in humans.
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