Passively acquired autoimmunity and the maternal fetal dyad in systemic lupus erythematosus

Abstract

Neonatal lupus syndromes consist of transient cutaneous and hematologic abnormalities and permanent cardiac disorders all of which result from a common pathogenetic mechanism, the passive transfer of maternal autoantibodies. Detrimental antibodies such as SSA/Ro and SSB/La gain access to the fetal circulation via the normal active transport system of the trophoblast tissue which is operative after 20 weeks gestation. Despite functional maturation of the cardiac conduction system by 16 weeks gestation, fetal bradycardias are most often encountered after this time. Several lines of evidence are advanced in this review to support the role of myocarditis as the initial consequence of autoantibody attack on the fetal heart. The end result of this inflammatory insult is permanent fibrosis manifest as complete congenital heart block (CCHB). Despite the clearly demonstrated presence of SSA/Ro and SSB/La in fetal tissues as well as their fluctuation in quantity during the cell cycle, the precise accessibility of these antigens to their respective autoantibodies in unknown at the present time. However, ultraviolet light is reported to induce cell surface expression of SSA/Ro on cultured keratinocytes. The recognition of CCHB by fetal echocardiogram is presented. The rationale for the use of dexamethasone which crosses the placenta in an active form to treat fetal immune effector functions is discussed. Intense maternal plasmapheresis in an attempt to rapidly decrease maternal autoantibodies may provide another approach to the management of CCHB. Through increasing knowledge of this model of "passively acquired pure" systemic lupus erythematosus, insights into mechanisms of tissue injury and strategies for treatment will emerge.