[Immunoresponse to SS-A 52-kDa and 60-kDa proteins in mothers of infants with neonatal lupus erythematosus]

Abstract

Background: Neonatal lupus erythematosus (NLE) is a rare disorder caused by the transplacental passage of maternal autoantibodies and manifests with characteristic skin eruption and/or congenital heart block. Anti-SS-A 52-kDa and 60-kDa antibodies are important serology markers for the diagnosis of NLE. However, women who have these antibodies do not always give birth to children with NLE. Therefore, we investigated the avidity (quality of the antibody) using urea derivative.

Methods: The sera of 54 women and 19 umbilical cord blood specimens were measured using a commercial ELISA kit (MESACUP 52K SS-A/Ro and 60K SS-A/Ro, MBL). Avidity index (AI) was obtained using a reagent prepared according to the method described in the European patent EP 0875761 as well as in the Japanese patent application No. 10-121896.

Results: Mothers with infants demonstrating atrioventricular block (AB) showed higher antibody indices for 52-kDa protein than mothers of infants without AB (p=0.0145). Mothers with cutaneous NLE had higher antibody indices for 60-kDa protein than mothers without cutaneous NLE (p=0.0058). Mothers had higher antibody indices and AIs than fetuses. There was a positive correlation between the antibody index and AI. The level of AI was increased in patients demonstrating low platelet counts in umbilical cord blood, but high antibody indices did not always increase in relation to the low platelet counts in umbilical cord blood.

Conclusions: Mothers with high antibody indices do not always give birth to children with NLE, even if the AIs of the mother are high. The fetus side, that is, the factor on the antigen side would be more important. However, we conjecture that anti-60-kDa antibody influences the development of cutaneous NLE, and that anti-52-kDa antibody influences the development of NLE with AB. The high AI may be related to more severe symptoms of NLE.