Estimation of amounts of anti-La(SS-B) antibody directed against immunodominant epitopes of the La(SS-B) autoantigen

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Abstract
The contribution of circulating anti-La(SS-B) antibody to the hypergammaglobulinaemia seen in primary Sjögren's syndrome is unknown. In this study levels of anti-La(SS-B) antibody directed against three immunodominant epitopes of the anti-La(SS-B) autoantigen were measured by ELISA in 84 anti-La(SS-B)+ sera using purified recombinant protein and antibody affinity-purified against the three anti-La(SS-B) fusion proteins. There was marked variation in the amounts of IgG anti-La(SS-B) antibody detected, with levels ranging from 0.02 mg/ml to 11 mg/ml. The anti-La(SS-B) levels were greater than 1 mg/ml in 61% of patients; in 18% of sera the anti-La(SS-B) level constituted 10% or more of the total serum IgG. However, other patients were seen with marked hypergammaglobulinaemia and low anti-La(SS-B) concentrations. These results support an antigen-driven mechanism for the anti-La(SS-B) response and suggest that anti-La(SS-B) antibody production is regulated independently of other immunoglobulins.