The majority of human monoclonal IgM rheumatoid factors express a "primary structure-dependent" cross-reactive idiotype.
Genetic studies of human immunoglobulin variable regions have been hampered by the lack of anti-idiotypic antibodies that recognize specific heavy and light chain variable region sequences. Sixty percent of human monoclonal IgM anti-IgG autoantibodies (rheumatoid factors [RF]) from unrelated individuals share a cross-reactive idiotype (CRI) termed Wa. In previous experiments in which we used an enzyme-linked immunosorbent assay, we reported that a synthetic peptide (PSL2), corresponding to the second hypervariable region in the kappa light chain of a monoclonal IgM-RF (Sie), induced rabbit antibodies reactive with several RF paraproteins. In the present experiments, to avoid interference due to the human IgM-RF binding toward rabbit IgG, the reactivity of the anti-PSL2 antibody to the separated heavy and light chains of multiple IgM proteins and Bence-Jones proteins was assessed by the Western blot technique. The PSL2-induced anti-CRI reacted well with the separated kappa chains from 10 out of 12 IgM-RF, zero out of four light chains from IgM proteins lacking anti-IgG activity, and one out of six kappa Bence-Jones proteins. The results show that the PSL2-CRI is associated with RF and is not a kappa subgroup marker. Furthermore, a comparison of the reported light chain sequences of the PSL2-CRI-positive IgM-RF suggests that the majority of human IgM-RF light chains derive from a single germ-line VK gene or from a family of closely related VK genes that is highly conserved in the human population. Synthetic peptide-induced anti-CRI provide a potent tool for analyzing the genetic basis of CRI and abnormal autoantibody production in humans.
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000032:analysis*; D001536:Bence Jones Protein / Q000302:isolation & purification; D003429:Cross Reactions; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000302:isolation & purification; D007130:Immunoglobulin Idiotypes / Q000032:analysis*; D007147:Immunoglobulin Light Chains / Q000302:isolation & purification; D007075:Immunoglobulin M / Q000032:analysis*; D007135:Immunoglobulin Variable Region / Q000302:isolation & purification; D010446:Peptide Fragments / Q000276:immunology; D012217:Rheumatoid Factor / Q000032:analysis*
D000911:Antibodies, Monoclonal; D007143:Immunoglobulin Heavy Chains; D007130:Immunoglobulin Idiotypes; D007147:Immunoglobulin Light Chains; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region; D010446:Peptide Fragments; D001536:Bence Jones Protein; D012217:Rheumatoid Factor