Subclass distribution of maternal and neonatal Anti-Ro(SSA) and La(SSB) antibodies in congenital heart block

Objective. To compare the subclass distribution of anti-48 kDa La(SSB) and anti-52 and 60 kDa Ro(SSA) antibodies in the maternal and neonatal circulation, in pregnancies affected and unaffected by the development of congenital heart block (CHB). Methods. Sera were obtained from 32 mothers (during 34 pregnancies, 23 complicated by CHB and 11 healthy) demonstrated to have anti-Ro(SSA) and/or La(SSB). Maternal and neonatal autoantibodies were evaluated for subclass distribution by ELISA. Results. All 4 subclasses of anti-Ro(SSA) and La(SSB) antibodies cross the placenta and are detectable in sera obtained from the umbilical cord. IgG1 and IgG3 were the major subclasses represented in the 48 kDa La(SSB) and 52 kDa Ro(SSA) responses. All subclasses, including IgG2 and IgG4, were observed in about one-third of the anti-52 kDa Ro(SSA) and 48 kDaLa(SSB) responses. In contrast, anti-60 kDa antibodies were, with rare exception, confined to IgG1. Except for anti-48 kDa La(SSB) IgG3 antibodies, no significant differences were observed between affected and unaffected pregnancies in the ratio of maternal to neonatal levels of any of the antibody subclasses. Overall, there were no significant differences in the subclass profiles between mothers whose children had heart block and those who did not. Conclusion. The IgG subclasses of anti-48 kDa La(SSB) and anti-52 and 60 kDa Ro(SSA) do not account for the susceptibility of one fetus versus another for the development of CHB. Anti-60 kDa Ro(SSA) antibodies are more restricted in subclass distribution than anti-52 kDa Ro(SSA) or 48 kDa La(SSB) responses.