Bone Marrow Stromal Fibroblasts Secrete Interleukin-6 and Granulocyte-Macrophage Colony-Stimulating Factor in the Absence of Inflammatory Stimulation: Demonstration by Serum-Free Bioassay, Enzyme-Linked Immunosorbent Assay, and Reverse Transcriptase

Bone marrow (BM) stromal fibroblasts produce hematopoi-etic growth factors (HGFs) in response to inflammatory mediators such as tumor necrosis factor-a or interleukin-la (IL-la). In the absence of such inflammatory stimuli, produc-tion of HGFs by BM stromal cells has been problematic and controversial. In vivo, however, basal hematopoiesis main-tains blood counts within a normal homeostatic range even in the absence of inflammation, and HGFs are required for progenitor cell differentiation in vitro. To better ascertain the contribution of BM stromal fibroblasts t o basal hematopoie-sis, we therefore studied HGF production in quiescent BM stromal fibroblasts by three sensitive assays: serum-free bioassay, enzyme-linked immunosorbent assay, and reverse transcriptase polymerase chain reaction. Stromal fibroblasts EMATOPOIESIS is a dynamic, interactive process H between developing hematopoietic cells and nonhe