In the present study, we demonstrated that peripheral blood T lymphocytes from active patients with systemic lupus erythematosus (SLE) spontaneously produced B cell stimulatory factor (BSF) after 2 days’ culture. The BSF contained B cell growth factor (BCGF) and B cell differentiation factor (BCDF) activities. These BCGF and BCDF activities spontaneously produced by T cells from active SLE patients were almost as potent as that of PHA-stimulated T cells from normal individuals and inactive SLE patients. Furthermore, B lymphocytes from active patients with SLE proliferated or secreted IgG antibody in response to BCGF or BCDF alone in the absence of anti-IgM or SAC-stimulation. Particulary, B cells from active SLE patients produced marked IgG in response to BCDF. The activity of BCGF or BCDF spontaneously secreted by T cells from active SLE patients correlated inversely with the magnitude of responsiveness of B cells in response to BCGF or BCDF. Accordingly, the mechanism for B cell activation in patients with SLE seems to be heterogeneous. Such abnormal response to BSF and/or overproduction of BSF ultimately lead to polyclonal and even autoantigen-specific B cell expansion which result in the production of autoantibodies.
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