A rheumatoid factor from a normal individual encoded by VH2 and VkII gene segments

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Abstract
Objective. To gain insight into the immunoglobulin variable‐region repertoire of anti‐IgG antibodies (rheumatoid factors [RF]), we characterized the VH and Vk gene segments utilized in an IgM‐RF–secreting lymphoblastoid cell line (SSH23) isolated from a normal individual. Methods. The cell line SSH23 was established by Epstein‐Barr virus transformation of peripheral blood non–T mononuclear cells. First‐strand complementary DNA (cDNA) was generated and used for polymerase chain reaction amplification of the heavy and light chain variable domains. The amplified variable domains were sequenced and compared with an extensive database of germline and cDNA V gene segments. Results. The VH sequence was found to be identical to a previously described fetal VH2 incomplete cDNA and to differ by only 3 nucleotides from a JH proximal germline VH2 gene segment. To our knowledge, this is the first example of a VH2 rheumatoid factor. The Vk2–Jk4 light chain contains an uncommon 10–amino acid third complementarity‐determining region (CDR 3). Conclusion. Utilization of preimmune fetal VH gene segments and unusual light chain junctional diversity appear to be features shared by many physiologic and pathologic rheumatoid factors.

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