ANTI-P57 - A NOVEL ASSOCIATION WITH NEONATAL LUPUS

IgG antibodies to a 57-kD protein (p57) present in various human and b ovine extracts were detected by immunoblotting in the serum of the mot her of a baby with congenital heart block, but not in the correspondin g cord blood, suggesting specific antibody consumption in the baby. Si nce this indicates a possible functional role for these antibodies, th e antigen target was characterized and the association of the antibodi es to heart block was further studied. A human K562 lambda gt11 cDNA l ibrary was screened and two clones were identified whose products reac ted with the prototype serum. Antibody affinity-purified by use of the cloned gene products reacted on immunoblot with the 57-kD band. Parti al sequences of both inserts were identical, but differed from DNA enc oding the Ro(SSA) and La(SSB) antigens. Antibodies to the p57 were det ected in 10% of systemic lupus erythematosus (SLE) sera, almost exclus ively in association with anti-Ro(SSA). Furthermore, they were present in 38% (8/21) mothers of babies with neonatal lupus expressing either cardiac or cutaneous manifestations. Antibodies to this 57-kD protein may be an additional risk factor for neonatal lupus in anti-Ro-positi ve women. Moreover, disappearance of antibody from cord blood suggests that they may have a role in disease manifestations.