Interleukin-6 production by murine B cells and B cell lines

We have analyzed interleukin (IL)-6 gene transcription and IL-6 secretion by murine B cells in vitro. Mitogenic doses of lipopolysaccharide (LPS) or LPS in combination with F(ab')2 goat anti-mouse IgM antibodies (GAMmu), but not GAMmu alone, induced B cells to synthesize and release IL-6. In time course experiments, the accumulation of IL-6 mRNA was first detectable at 24-36 hr of culture and the levels were maintained through 60 hr; these kinetics correlated well with increases in supernatant IL-6 levels and were coincident with vigorous cell cycle activity. We also analyzed constitutive and LPS-induced IL-6 gene expression by the murine B cell lines: 70Z/3, 38C-13, WEHI-231, X16C, WEHI-279, and BCL1. Only the WEHI-279 and BCL1 lines produced detectable IL-6 constitutively, and the BCL1 cells could be further induced by treatment with LPS. Of the remaining cell lines, only WEHI-231 and X16C could be stimulated with LPS to produce IL-6. To evaluate whether IL-6 could influence proliferation and Ig secretion by the cell lines, low cell density cultures were established in the presence of various doses of human rIL-6 and were assessed over time for levels of [3H]thymidine uptake and supernatant Ig. Under these conditions, IL-6 had no effect on either cell function.