title: Human rheumatoid factors bear the internal image of the Fc binding region of staphylococcal protein A.
abstract: The binding specificity of rheumatoid factors (RFs) to human Fc resembles that of some microbial Fc-binding proteins, suggesting conformational similarities in their Fc-binding regions. Using polyclonal chicken antibodies against SPA, we have detected a crossreactive determinant shared by human RFs from different individuals, but not by non-RF IgM and IgG. Chicken anti-SPA was shown to bind to 18 of 19 IgM RFs and 2 of 2 IgG RFs isolated from different individuals. This binding was inhibitable with SPA, fragment D of SPA, human IgG, and Fc fragment of IgG. The binding site for RF was located on the Fab' fragment of chicken anti-SPA. The antigenic mimicry of RFs by a protein of microbial origin suggests that the immune response to infectious agents could induce or modulate RF production through an internal image autoantiidiotype mechanism.
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001666:Binding Sites, Antibody; D002645:Chickens; D000939:Epitopes / Q000276:immunology; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology; D012217:Rheumatoid Factor / Q000276:immunology*; D013205:Staphylococcal Protein A / Q000276:immunology*
chemical_list: D000906:Antibodies; D000939:Epitopes; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D010446:Peptide Fragments; D013205:Staphylococcal Protein A; D012217:Rheumatoid Factor