Coexistence of Protein AA and Immunoglobulin Light‐Chain Fragments in Amyloid Fibrils

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Abstract
Coexistence of amyloid fibril protein AA and homogeneous immunoglobulin light-chain fragments was found in the isolated amyloid fibrils of 2 patients with amyloidosis secondary to rheumatoid arthritis. The light-chain amyloid fibril protein showed antigenic identity with a light-chain amyloid from a patient with primary amyloidosis, which was identified as the V.lambda.IV subgroup by amino acid sequence analysis. In amyloid fibrils isolated from another patient with primary amyloidosis, there was a mixture of V.lambda.IV and V.lambda.V homogeneous immunoglobulin light chains. A mixture of protein AA and .lambda. light chains or 2 different types of homogeneous light chains may be found in the amyloid fibrils of some patients.