We evaluated the prevalence and specificity of smooth-muscle autoantibodies in 20 serum samples obtained from patients with angioimmunoblastic lymphadenopathy. Smooth-muscle antibodies in high titers were detected in 75 per cent of the samples. No such antibodies were found in 30 normal control serum samples or in 10 samples from patients with non-Hodgkin's lymphoma and 1 of 12 from patients with other types of polyclonal hypergammaglobulinemia were positive. The antibodies were polyclonal and belonged to the IgM, IgG, and IgA classes. They reacted with vimentin, the major polypeptide of the intermediate-filament cytoskeleton of mesenchymal cells. The pattern of tissue reactivity and absorption experiments both show that these antibodies recognize special antigenic determinants of the vimentin polypeptide that are shared by vimentin and other classes of intermediate-filament proteins - namely, keratin and desmin. The frequency of this unusual autoantibody activity in angioimmunoblastic lymphadenopathy suggests that, like hypergammaglobulinemia and a positive Coombs' test, it may represent a useful serologic marker for the disease.
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