Background Congenital heart block (CHB) may develop in fetuses of women with anti-Ro/La autoantibodies following placental transfer of maternal autoantibodies and disruption of the fetal atrioventricular (AV) conduction system. Animal models of CHB currently rely on immunisation or transfer of anti-Ro/La antibodies purified from mothers of children with CHB, which does not allow precise identification of the disease-inducing antibody specificity.

Objective To determine the ability of different anti-Ro52 monoclonal antibodies to induce cardiac electrophysiological abnormalities in vivo and affect the calcium homoeostasis of cardiomyocytes in vitro.

Methods Monoclonal antibodies recognising different domains of Ro52 were generated and injected into pregnant rats, and ECG was recorded on newborn pups. Cultures of rat neonatal cardiomyocytes were established to assess the effect of the different anti-Ro52 monoclonal antibodies on calcium homoeostasis.

Results First-degree AV block and bradycardia developed after maternal transfer of antibodies specific for amino acids 200–239 of Ro52 (p200), while pups exposed to antibodies targeting N- or C-terminal epitopes of Ro52 did not show any electrocardiogram abnormalities. Addition of an anti-p200 antibody to cultured cardiomyocytes induced calcium dyshomoeostasis in a time- and dose-dependent manner, while addition of other Ro52 antibodies had no effect.

Conclusion These data for the first time show unambiguously that antibodies specific for amino acids 200–239 of Ro52 can induce cardiac conduction defects in the absence of other autoantibodies, and may therefore be the main initiators of cardiac pathology in the pool of anti-Ro52 antibodies in mothers of children with CHB.