BACKGROUND: Pathologic scarring including keloid and hypertrophic scar causes aesthetic and physical problems, and there are clinical difficulties (e.g., posttreatment recurrence) in dealing with pathologic scarring. Understanding the mechanisms that underlie scar control in wound healing will help prevent and treat pathologic scarring. The authors focused on CD206+ macrophages in the wound-healing process, and hypothesized that CD206+ macrophages have antifibrotic effects on fibroblasts. METHODS: The authors established a co-culture system for CD206+ macrophages and fibroblasts (cell ratio, 1:1). The authors examined the CD206+ macrophages' antifibrotic effects on fibroblasts after a 72-hour culture, focusing on fibrosis-related genes. To identify key factor(s) in the interaction between CD206+ macrophages and fibroblasts, the authors analyzed cytokines in a conditioned medium of the co-culture system. RESULTS: Under co-culture with CD206+ macrophages, expression of the following in the fibroblasts was significantly down-regulated: type 1 (fold change, 0.38) and type 3 collagen (0.45), alpha smooth muscle actin (0.24), connective tissue growth factor (0.40), and transforming growth factor-beta (0.66); the expression of matrix metalloproteinase 1 was significantly up-regulated (1.92). Conditioned medium in the co-culture showed a high interleukin (IL)-6 concentration (419 ± 88 pg/ml). When IL-6 was added to fibroblasts, antifibrotic changes in gene expression (as observed under the co-culture) occurred in the fibroblasts. CONCLUSIONS: The authors' in vitro results revealed that CD206+ macrophages have antifibrotic effects on fibroblasts by means of a paracrine mechanism involving IL-6. Understanding these effects, especially in vivo, will help elucidate the mechanism of scar control in wound healing and contribute to the development of new scar treatments.