Rheumatoid factor: structural and genetic studies indicating novel binding sites may confer the specificity for IgG...

Comparison of sequences of mouse rheumatoid factor light chains has previously suggested that the sites for rheumatoid factor activity lie outside the conventional hypervariable regions which normally bind antigen and, instead, may be related to the light chain variable region framework sequences. Comparison with amino acid sequences of human rheumatoid factors reveals that similar sequences are present in the variable region frameworks of these antibodies as well. It is therefore proposed that novel binding sites may be present in these framework regions which confer a structural specificity for binding IgG Fc.