Terminal differentiation of spontaneous rheumatoid factor-secreting B cells from rheumatoid arthritis patients depends on endogenous interleukin-10

Objective. The presence of serum rheumatoid factor (RF) and spontaneous RF-secreting B cells is a common feature in most patients with rheumatoid arthritis (RA), This study analyzed the cytokine(s) that controls the final maturation of B cells capable of spontaneous IgM-RF secretion in vitro. Methods. RA patients' peripheral blood mononuclear cells (PBMC), as well as adherent and nonadherent cell fractions, were cultured, and spontaneous IgM-RF and interleukin-10 (IL-10) secretion were determined by enzyme-linked immunosorbent assay. Results. The RF+ RA PBMC, but not PBMC from RF- RA patients or healthy controls, actively produced IgM-RF in a linear manner for 14 days, This activity depended on the presence of fetal calf serum and did not require cellular DNA synthesis, Spontaneous IgM-RF secretion depended on IL-10, as deduced from the following findings: 1) IL-10, but not a variety of cytokines including IL-6, restored missing IgM-RF secretion by PBMC in serum-free supplemented cultures; 2) the addition of anti-IL-10, but not anti-IL-6, blocking antibodies inhibited PBMC IgM-RF secretion, and this effect could be reversed by exogenous IL-10; and 3) RA PBMC actively produced IL-10 in vitro, The cells responsible for endogenous IL-10 production were found in the adherent cell fraction, Finally, IL-10 induced IgM-RF, but not total IgM, secretion by RA PBMC. Conclusion. In patients with RA, circulating B cells capable of spontaneous IgM-RF secretion require IL-10 production by adherent cells to reach terminal maturation.