Production of B cell-stimulating factors by B cells in patients with systemic lupus erythematosus

Abstract

The production of B cell-stimulating factors (BSF) by B cells in patients with systemic lupus erythematosus (SLE) was studied in vitro. B cells from SLE patients markedly proliferated and differentiated into Ig-producing cells by in vitro culture without any stimulation. The culture supernatant of these B cells contained BSF activity that stimulated Staphylococcus aureus Cowan I-treated normal B cells to proliferate and differentiate into Ig-producing cells. By a Percoll gradient density centrifugation, BSF-producing cells were enriched in the higher density fraction, but were reduced in the lower density fraction. The BSF also stimulated the proliferation and the differentiation of SLE B cells. By a Percoll gradient density centrifugation, SLE B cells responsive to the BSF were enriched in the higher density fraction, but were reduced in the lower density fraction. The Mr of the BSF was estimated as about 18,000 Da by Sephacryl S-200 column chromatography. The BSF fraction did not possess IL-2 and IFN activity, but possessed IL-1 activity, which stimulated murine thymocyte proliferative responses. The BSF activity was partially, but not completely, absorbed by an anti-IL-1 alpha antibody. Furthermore, the BSF possessed IL-4 activity, which induced not only the proliferative responses of normal B cells stimulated with B cell mitogens, but also the expression of low affinity Fc epsilon R/CD23 on normal B cells. The BSF also possessed IL-6 activity, which induced the proliferative responses of IL-6-dependent hybridoma cells, MH-60 BSF2. Moreover, human rIL-1, rIL-4, and rIL-6 stimulated SLE B cells. These results suggest that SLE B cells spontaneously produce the BSF such as IL-1 alpha, IL-4, and IL-6 and express their receptors on their surface, and the interaction between the BSF and their receptors stimulates SLE B cells to spontaneously proliferate and differentiate into Ig-producing cells as an autocrine mechanism.