Analysis of Monoclonal Rheumatoid Factors obtained from the B‐Cell Repertoire in Rheumatoid Arthritis

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Abstract
We have sought to determine whether rheumatoid factors (RF) produced in rheumatoid arthritis (RA) were different from physiological RF produced in normal, healthy adults. RF‐secreting clones were established following Epstein Barr virus (EBV) stimulation of peripheral blood lymphocytes. Ten RF‐secreting clones were established from seven RA patients and 16 from six healthy controls. All monoclonal RF (MRF), except two in each group, were monoreactive and ten of these were shown to have low to medium affinity for IgG, Fc, irrespective of their origin. A majority (74%) of the MRF bound to protein A, indicating that genes of the VHIII family were preferentially used for synthesizing these autoantibodies. The expression of cross‐reactive idiotypes (CRI) by the MRF did not allow distinction between those derived from RA patients and controls. The VHI‐associated CRI G8 and VHIII‐associated CR1 D12 were expressed at low frequency in both panels of RF. These CRI have been shown to be expressed at high frequency in RF paraproteins. However, the idRQ idiotype was expressed within both panels of RF. A possible distinction between polyreactive and monoreactive MRF appeared to be light chain usage since all (four) polyreactive RF used λ chains while the normal κ/λ ratio was observed for monoreactive RF. The frequency of EBV‐activated cells secreting IgM bearing CRI or secreting RF was determined and showed that CRI expression occurred with a higher frequency than did RF, suggesting a dissociation between CRI expression and RF activity.

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