Human IgE does not bind to human FcRn

The neonatal Fc receptor (FcRn) is known to mediate placental transfer of IgG from mother to unborn. IgE is widely known for triggering immune responses to environmental antigens. Recent evidence suggests FcRn-mediated transplacental passage of IgE during pregnancy. However, direct interaction of FcRn and IgE was not investigated. Here, we compared binding of human IgE and IgG variants to recombinant soluble human FcRn with β2-microglobulin (sFcRn) in surface plasmon resonance (SPR) at pH 7.4 and pH 6.0. No interaction was found between human IgE and human sFcRn. These results imply that FcRn can only transport IgE indirectly, and thereby possibly transfer allergenic sensitivity from mother to fetus.

Evaluation of materno-fetal antibody transfer in patients with antiphospholipid syndrome

Introduction: Antiphospholipid syndrome (APS) is characterized by thrombotic events and recurrent pregnancy losses and is considered the most common acquired thrombophilia.Objective: To carry out a narrative review of the transplacental passage and antibodies in patients with APS.Methods: A narrative literature review.Results: When it is not associated with any connective tissue disease, it is said to be primary, and when in association with systemic lupus erythematosus, it is said to be secondary. Gestational morbidity is frequent, and it is crucial to evaluate the passage of these antibodies transplacentally since there are animal models of the syndrome with passive transfer of these antibodies. The transplacental passage of specific antibodies has already been determined in studies, which demonstrated low levels of these antibodies in the maternal serum, but an efficient transplacental passage for the newborn.Conclusions: There are few studies on this maternal-infant passage in patients with APS reviewed here.

Macrophage Activation Syndrome Presented in a Case of Neonatal Lupus

Macrophage activation syndrome (MAS) is a potentially life-threatening complication in many autoimmune diseases. Early recognition and intervention are essential for a favorable outcome. Neonatal lupus, an acquired autoimmune disease in neonates caused by the transplacental passage of maternal autoantibodies, is rare and usually self-limited. Herein, we report a case of MAS in a patient with neonatal lupus, which improved with intravenous immunoglobulin.

Case Report: Infantile Ischemic Stroke and Antiphospholipid Antibodies, Description of Four Cases

Antiphospholipid syndrome (APS) is a rare condition in childhood, but even more in the neonatal age. Most neonatal cases are considered a passively acquired autoimmune disease, due to a transplacental passage of maternal antiphospholipid antibodies (aPL) from mothers with primary or secondary APS or, more often, from asymptomatic aPL carriers. Exceedingly unusual is the neonatal de novo production of aPL. We present four infants with presumed perinatal stroke in presence of increased and persistent aPL levels, even after 6 months of life, opening the window on a gray zone related to the origin of these antibodies (maternal or neonatal) and on their role in the pathogenesis of stroke.

A Case Report to Assess Passive Immunity in a COVID Positive Pregnant Patient

Introduction Data regarding transplacental passage of maternal coronavirus disease 2019 (COVID-19) antibodies and potential immunity in the newborn is limited. Case Report We present a 25-year-old multigravida with known red blood cell isoimmunization, who was found to be COVID-19 positive at 27 weeks of gestation while undergoing serial periumbilical blood sampling and intrauterine transfusions. Maternal COVID-19 antibody was detected 2 weeks after positive molecular testing. Antibodies were never detected on cord blood samples from two intrauterine fetal cord blood samples as well as neonatal cord blood at the time of delivery. Conclusion This case demonstrates a lack of passive immunity of COVID-19 antibodies from a positive pregnant woman to her fetus, neither in utero nor at the time of birth. Further studies are needed to understand if passage of antibodies can occur and if that can confer passive immunity in the newborn. Key Points

Benefits and Risks of IgG Transplacental Transfer

Maternal passage of immunoglobulin G (IgG) is an important passive mechanism for protecting the infant while the neonatal immune system is still immature and ineffective. IgG is the only antibody class capable of crossing the histological layers of the placenta by attaching to the neonatal Fc receptor expressed at the level of syncytiotrophoblasts, and it offers protection against neonatal infectious pathogens. In pregnant women with autoimmune or alloimmune disorders, or in those requiring certain types of biological therapy, transplacental passage of abnormal antibodies may cause fetal or neonatal harm. In this review, we will discuss the physiological mechanisms and benefits of transplacental transfer of maternal antibodies as well as pathological maternal situations where this system is hijacked, potentially leading to adverse neonatal outcomes.