Characterization of B cell growth in systemic lupus erythematosus. Effects of recombinant 12‐kDa B cell growth factor, interleukin 4 and transforming growth factor‐β

B cells from systemic lupus erythematosus (SLE) patients have been shown to be hyperactive as measured by proliferation and immunoglobulin production. We find that B cells from 6 of 13 SLE patients, in the absence of prior activation, respond two to three times better to recombinant 12‐kDa B cell growth factor (BCGF) than do normal or rheumatoid arthritis B cells (p < 0.005). B cells from normally responsive SLE patients require an anti−μ antibody activation step to generate similar proliferative signal in response to r12‐kDa‐BCGF. There are no clinical or serological parameters that distinguish these hyperresponsive SLE patients from the normally responsive SLE patients. The combination of r12‐kDa‐BCGF and interleukin 4 (IL 4) gives an enhanced response with both normal and SLE B cells. Transforming growth factor type β (TGF‐β) suppresses the response to r12‐kDa‐BCGF in a dose‐dependent fashion using B cells from both healthy donors and SLE patients. We conclude that peripheral blood B cells are in an activated state (as detected by response to 12‐kDa‐BCGF) in approximately 50% of SLE patients. These B cells respond normally to regulation by IL 4 and TGF‐β. A therapeutic approach aimed at reducing the B cell hyperactivity in SLE would involve suppressing the effects of 12‐kDa‐BCGF and IL 4 while at the same time enhancing the effects of TGF‐β.