Structural Basis of a Conventional Recognition Mode of IGHV1-69 Rheumatoid Factors

Rheumatoid factors (RFs) are autoantibodies that recognize the fragment crystallizable (Fc) region of immunoglobulin G (IgG). Genetically diverse RFs are produced in rheumatoid arthritis patients; however, in hematologic diseases, such as cryoglobulinemia and B cell lymphoma, RFs from a limited combination of heavy chain V-region genes and J-region genes are produced in large quantities and forms immune complexes with IgG. These genetically limited RFs have historically been used for the immunochemical characterization of RFs. Among them, RFs derived from the heavy-chain germline gene IGHV1-69 are the most common. Recently, the crystal structure of an IGHV1-69-derived RF named YES8c was elucidated in complex with human IgG1-Fc. Based on the structure and mutant analyses, a recognition mechanism for the autoantigen (IgG-Fc) common to IGHV1-69-derived RFs was proposed. This review summarizes the immunochemical character of the IGHV1-69-derived RFs, and then focuses on the recognition mechanism of the IGHV1-69-derived RFs, referring the structural features of the IGHV1-69-derived neutralizing antibodies.