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We have analysed the heavy and light chain variable region genes of two monoclonal antibodies, specific for the Sm antigen (RSP1; IgGκ) and for cardiolipin (RSP4; IgMλ), derived from a patient with active systemic lupus erythematosus (SLE). We have established that the variable region genes of the RSPI autoantibody are somatic mutants of two germ line genes from the VH4 and VκI gene families. RSP4 antibody uses gene segments closely related to a VH3 gene member and to a Vλ1 gene. The presence and distribution of the somatic mutations on both monoclonal autoantibodies are compatible with an antigen-driven immune process. These data suggest that in SLE a common antigenic stimulus may govern the autoantibody response against a wide spectrum of unrelated antigens, including native DNA, cardiolipin or Sm antigens, and provide further evidence that disease-associated autoantibodies are generated through antigen-selected somatic mutations. [ABSTRACT FROM AUTHOR]

This study explores the usage and diversity of the variable gene elements expressed by human lupus antibodies to DNA bearing the 0-81 idiotype, a marker of pathogenic anti-DNA autoantibodies. Rather than studying DNA-specific clonotypes from different patients, a panel of idiotype positive anti-DNA autoantibody-secreting clones from a single individual were analysed. By cloning and nucleotide-sequencing the heavy-chain variable gene segments, evidence was found for dominance of clonotypic patterns. Also noted was a high rate of diversification among the variable (VH), diversity (DH) and junctional (JH) gene segments utilized, with a pattern of mutations indicative of antigenic selection. These features suggest that the clones secreting the lupus pathogenic autoantibodies have been selected over multiple generations through an affinity-maturation process that is reminiscent of antigen-driven immune responses. [ABSTRACT FROM AUTHOR]