Interleukin-6 Is Not Involved in the Interleukin-1-Induced Production of Colony-Stimulating Factors by Human Bone Marrow Stromal Cells and Fibroblasts

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a role in regulation of hematopoiesis. Because IL-6 is coinduced with colony-stimulating factors (CSFs) by various cell types in response to stimulation with IL-1, we investigated whether IL-6 is involved in the IL-1– induced production of CSF by human bone marrow (BM) cells in long-term culture or human fibroblasts. We showed that IL-6 does not induce CSF production by these cells. Neither addition of exogenous IL-6 nor neutralization of endogenous production of IL-6 by an anti–IL-6 monoclonal antibody (MoAb) diminished the IL-1–induced colony-stimulating activity (CSA), indicating that IL-6 did not act synergistically with IL-1. Finally, IL-6 did not influence the kinetics of IL-1–induced CSA production by human fibroblasts. We conclude that IL-6, either alone or in combination with IL-1, does not induce CSF production by human BM stromal cells or fibroblasts.