ABSTRACT
Many cytokines act in a variety of tissues, and multiple cell types have been shown to produce a particular cytokine. Interleukin-6 (IL-6) falls into this category of pleiotropic molecules with significant roles in inflammation, hematopoiesis, lymphocyte activation, and differentiation. Thus, multiple transcription factors may be involved in modulating promoter activities of IL-6-responsive genes and interactions of different binding proteins and response elements will likely be found in regulating transcription in response to IL-6 in combinations with other cytokines. However, the lavage cells containing alveolar macrophages from these animals have little or no IL-6 mRNA present, whereas lung tissue homogenates containing epithelial cells and fibroblasts contain elevated levels of IL-6 mRNA. While most soluble cytokine receptors have an antagonistic activity as competitive inhibitors, the soluble IL-6 receptor is unique in that it has an agonist activity when added with ligand to cells that express the gpl30 signaling molecule.
