Anti-SS-A/Ro SS-B/La antibodies bind to neonatal rabbit cardiac cells and preferentially inhibit in vitro cardiac repolarization.

The neonatal lupus syndrome is the most common cause of isolated congenital heart block. There is, at present, little information about the putative role of anti-SS-A/Ro SS-B/La antibodies in the pathogenesis of congenital heart block in the neonatal lupus syndrome. Using an in vitro experimental model, the present study was designed to test the hypothesis that IgG antibodies in the sera of anti-SS-A/Ro SS-B/La-positive mothers of infants with isolated congenital heart block bind to and affect the transmembrane action potential of rabbit cardiac tissue. The results demonstrate a preferential inhibition of membrane repolarization (ADP-50 and ADP-90) and staining of cardiac cells within the neonatal, in contrast to the adult, rabbit heart by sera and IgG-enriched fractions from anti-SS-A/Ro SS-B/La-positive individuals. The results of the electrophysiologic studies demonstrate a pathophysiologic role for the IgG fraction of anti-SS-A/Ro SS-B/La-positive maternal sera in inhibiting neonatal rabbit cardiac repolarization. It is possible that antibodies to similar determinants expressed on the cell membrane of cardiac-conducting cells also may play a pathophysiologic role in the development of idiopathic congenital heart block in humans.