In the aging mouse (C57BL/6) myocardium fibrosis steadily increases after 14 months of age and is accompanied by elevated numbers of myeloid derived fibroblasts. Recently, we proposed a mechanism by which inflammatory mesenchymal fibroblasts (IMF) derived from mesenchymal stem cells secrete monocyte chemoattractant protein-1 (MCP-1) necessary for myeloid fibroblast induction in the aging heart. The current study extends the characterization of this inflammatory phenotype by describing elevated interleukin-6 (IL-6) secretion and increased expression of IL-6 receptor (IL-6R) in IMF. Since IL-6R lacks an intracellular domain it requires a co-receptor gp130 (generally expressed) to induce an intracellular signal. Thus, generation of an IL-6R soluble receptor allows IL-6 signaling on cells that do not express IL-6R (or expression is low), such as endothelial cells. We investigate the function of IL-6 and IL-6R in the promotion of transendothelial migration of monocytes through cardiac endothelium and their maturation into myeloid fibroblasts in in vitro assay. Treatments with IL-6 and more extensively IL-6+IL-6R resulted in a 3-5 fold increase (above the control level) in myeloid cell migration and maturation into myeloid fibroblasts. Thus IMF can contribute both IL-6 and IL-6R to endothelial cells and facilitate myeloid cell transendothelial migration. In agreement with these data, analysis of the aged mouse heart revealed the presence of fibroblasts expressing IL-6 (procollagen type I+IL-6+ cells), M1 macrophages (CD86+ cells) and M2 macrophages (CD301+procollagen type I+ cells) that were absent in hearts from young mice. The mechanisms by which expression of these factors is upregulated in IMF are being investigated; our data suggest that MCP-1 and IL-6 expression are controlled by the farnesyltransferase (FTase)-Ras-Erk1/2 pathway. Interestingly, since atorvastatin interferes with farnesyl synthesis it also reduced MCP-1 and IL-6 expression in IMF. These data may introduce a new use of this class of drugs in the prevention of the age-related fibrosis.