The B cell repertoire in rheumatoid arthritis. I. Frequency of EBV-inducible circulating precursors producing autoantibodies.

The frequency of B cell precursors producing antibodies against various autoantigens (Fc fragment of IgG, F(ab')2 fragment of IgG, type II collagen, cytoskeleton filaments and insulin) was determined in patients with rheumatoid arthritis (RA) using immortalization of peripheral blood B cells by the Epstein-Barr virus (EBV) and limiting dilution analysis. Equally large numbers of B cell precursors producing IgM-rheumatoid factors (RFs) were present in the peripheral blood of seronegative and seropositive RA patients and of controls. On average, 1 out of 15,000 B cells could be induced by EBV to secrete IgM-RFs, which represents 0.5-1% of the EBV-induced proliferating clones. By cloning or somatic hetero-hybridization of EBV cell lines derived from patients and controls, we obtained two types of monoclonal RFs: one polyreactive, reacting with Fc but also with the other autoantigens tested, and the other monoreactive, reacting with Fc only and that previously had only been found in the RA B cell repertoire. Moreover, patients and controls had similar numbers of circulating B cell precursors secreting IgM antibodies against other autoantigens that might be regarded as specific targets of RA (F(ab')2 fragment of IgG and type II collagen), and against cytoskeleton filaments that are targets of natural autoantibodies, increased in RA. The frequencies of EBV-induced B cells producing antibodies against all these autoantigens were of the same order of magnitude as the frequency of EBV-induced B cells producing RFs. The patients also possessed a similar number of precursors producing antibodies against insulin, an autoantigen irrelevant to the pathogenesis of the disease, taken as control. These data tend to demonstrate no abnormality in the autoantibody repertoire of B cells activable by EBV in RA, especially those secreting RFs. In vitro spontaneous RF secretion by circulating B cells was observed in seropositive RA patients but not in seronegative patients and in the controls tested. We enumerated the number of B cells spontaneously secreting RFs in seropositive RA patients and found that it correlated with the serum RF titer, but not with the number of RF-secreting B cells activated by EBV. The mean frequency values of B cells secreting RFs either spontaneously or after EBV infection were of the same order of magnitude, showing that the expanded population of in vivo-activated B cells was not (at least partially) infectable by EBV. This raised the possibility that EBV triggers a repertoire which may not reflect the status of B cells secreting autoantibodies in autoimmune diseases.