Serum and Immunoglobulin G from the Mother of a Child with Congenital Heart Block Induce Conduction Abnormalities and Inhibit L-Type Calcium Channels in a Rat Heart Model

Abstract

Although a strong clinical association exists between congenital heart block (CHB) and an immune response to SSA/Ro and SSB/La proteins, a causative role of these antibodies in the pathogenesis is just emerging. In a preliminary report, we have demonstrated that IgG fractions isolated from the sera of mothers whose children have CHB are arrhythmogenic in the human fetal heart. To more precisely define the arrhythmogenic effect of anti-SSA/Ro-SSB/La antibodies, we used the readily available rat heart model to record: 1) ECGs from Langendorff beating hearts; 2) action potentials from atrioventricular (AV) nodal preparations; 3) L-type Ca currents, I(Ca) at the whole-cell and single channel levels; and 4) other currents such as the transient outward K+ current, I(to), the inward rectifier K+ current, I(K1), and the Na+ current, I(Na). Perfusion of hearts with purified IgG (800 microg/mL), isolated from the serum of a mother with SSA/Ro and SSB/La antibodies whose child had CHB, resulted in bradycardia associated with 2:1 AV block. Simultaneous action potentials were recorded from dissected atrial and AV nodal areas of the rat heart. Superfusion of these preparations with the same mother's IgG fraction resulted in 2:1 AV block followed by complete inhibition of AV nodal action potential. Because AV nodal electrogenesis is largely dependent on I(Ca), the effect of these antibodies on I(Ca) was subsequently determined. Superfusion of myocytes with whole serum or purified IgG (80 microg/mL) from the same mother consistently inhibited whole cell I(Ca), ensemble average Ba2+ currents (I(Ba)) and open state probability, p(o), without affecting the channel conductance. IgG had no significant effect on I(to), I(K1), or I(Na). Whole sera and IgG fractions from a healthy mother with no detectable anti-SSA/Ro or SSB/La antibodies did not inhibit I(Ca) or I(Ba). These results demonstrate that IgG containing anti-SSA/Ro and -SSB/La antibodies induces complete AV block in beating hearts and in multicellular preparations, thus implicating a preferential interaction of these autoantibodies with Ca channels and/or associated regulatory proteins. This is consistent with the observed inhibition of Ca channels that may be a critical factor contributing to the pathogenesis of CHB.

Effect of Maternal Autoantibodies on Fetal Cardiac Conduction: An Experimental Murine Model

“…Ho and colleagues (39,40) have identified sinus node hypoplasia in autopsy specimens from patients dying with complete CHB. Inhibition of L-type calcium channel currents has been demonstrated in animal models of CHB (41). L-type Ca channels are important to sinus node function and are also considered to be partially responsible for the phase-4 depolarization underlying sinus node automaticity.…”

Pacing Therapy in Infants and Children with Congenital and Acquired Complete Atrioventricular Block: Optimal Pacing Strategies, Management, and Follow-up

“…Since an association between maternal connective tissue disease and anti-SSA/Ro -SSB/La antibodies was suggested in the late 1970s (McCue et al, 1977), efforts in clinical and experimental studies have resulted in a broad understanding of the pathogenesis and clinical outcome of autoimmune-associated CCAVB (Boutjdir et al, 1998;Buyon & Clancy, 2005;Jaeggi et al, 2010). Maternal anti-SSA/Ro -SSB/La autoantibodies enter the fetal circulation between 16 and 24 weeks gestation (Buyon et al, 1995), and may induce injury to the developing cardiac conducting system and myocardial tissue in a subset of fetuses.…”

Arrhythmias Presenting in Neonatal Lupus

“…The other mechanism is the cross-reactivity of maternal antibodies with targets other than SSA ⁄ Ro and SSB ⁄ La antigens. Maternal antibodies were reported to cross-react with laminin and with human cardiac myosin heavy chain at a critical stage during foetal cardiac development [5,6], but the L-type calcium channels seem particularly important in this hypothesis [7][8][9][10].…”

“…The same group reported that the passive transfer of human anti-Ro/SSA into pregnant mice induced bradycardia and first degree AV blocks in the pups [8]. However, the penetrance was extremely low, paralleling human disease frequencies.…”

“…The other mechanism is the cross-reactivity of maternal antibodies with targets other than SSA ⁄ Ro and SSB ⁄ La antigens. Maternal antibodies were reported to cross-react with laminin and with human cardiac myosin heavy chain at a critical stage during foetal cardiac development [5,6], but the L-type calcium channels seem particularly important in this hypothesis [7][8][9][10].After preliminary reports, [11,12] Boutjdir in an outstanding paper [7] showed that IgG-enriched fractions and anti-52-kD SSA ⁄ Ro antibodies affinity-purified from the sera of mothers whose children have CHB reversibly induce complete atrioventricular (AV) block in the human foetal heart perfused by the Langendorff technique. At 33 min of perfusion, complete AV block was observed with the presence of only P waves and missing QRS complexes.…”