Rheumatoid factors do not preferentially bind to ACPA-IgG or IgG with altered galactosylation

Recent reports describe interactions between the two most prominent RA-related autoantibodies, RFs and ACPAs. The main aim of the present study was to investigate whether RFs preferentially interact with ACPA-IgG over non-ACPA IgG. Additionally, interactions of RFs with IgG with altered galactose content in the Fc domain were examined, since ACPA-IgGs have been shown to have decreased Fc galactose content in RF+ patients. (Auto)antibody interactions were studied in a surface plasmon resonance imaging assay and with ELISA. Target antibodies were isolated from RA patient plasma (polyclonal ACPA- and non-ACPA-IgG) or recombinantly produced to obtain monoclonal IgG with well-defined Fc galactose content. Interacting autoantibodies were studied using autoantibody positive patient sera and two recombinantly produced IgM-RFs. The sera from 41 RF+ RA patients showed similar RF binding to ACPA- and non-ACPA-IgG and no differences in binding to IgG with normal, high or low levels of Fc galactosylation. Two monoclonal IgM-RFs, one interacting with the CH2-CH3 interface and one binding close to the C-terminal end of the CH3 domain showed no influence of the Fc glycan on IgG binding by IgM-RF. Although interactions between RF and ACPA may play a role in inflammatory processes in RA, RFs do not preferentially interact with ACPA-IgG over non-ACPA-IgG nor with agalatosylated IgG over IgG with normal or high galactosylation.