B Cell Tolerance and Obstetric Antiphospholipid Syndrome

Obstetric antiphospholipid syndrome (OAPS) is an autoimmune disorder characterized by antiphospholipid antibody-mediated inflammatory environment at the maternal-fetal interface. It leads to significant complications, including pre-fetal or fetal demise, preeclampsia, and placental insufficiency. Pregnancy leads to significant changes in the immune profile that facilitate fetal tolerance while ensuring protection from infections. A controlled inflammation at the maternal-fetal interface is essential during implantation as trophoblasts need to invade the endometrial lining. However, excessive inflammation can disrupt this balance and contribute to pregnancy-related complications. Consequently, the increased activation of the innate immune system is counteracted by the tolerogenic responses of the adaptive immune system. There is a shift from T helper (Th) 1 to Th2 responses from the first to the third trimester of pregnancy. This is associated with a decrease in lymphopoiesis, together with a prolonged B cell lifespan. Thus, during pregnancy, antibody-producing B cells are prone to activation, potentially leading to a loss of tolerance. Changes in B cell function, antigen presentation, and antibody affinity are seen in women with antiphospholipid syndrome. It is essential to understand the defects in B cell regulation in OAPS as they are likely to induce a breach in immune homeostasis. Herein, we will review the role of B cell tolerance in OAPS, including a discussion of potential novel therapeutic effects to improve maternal and fetal health.