Current view of the infrapatellar fat pad (IFP) and its interaction with other joint tissues. The IFP (Hoffa) is a source of several soluble factors. Moreover, it is composed of adipocytes and stromal vascular cells, such as macrophages, T cells, and mesenchymal stem cells (MSCs). Cellular interactions have been described within the IFP, such as between adipocytes and macrophages or T cells but also between IFP and other joint tissues. The main interactions that have been described thus far and the cells/soluble mediators involved in these interactions as summarized in the present review are depicted with arrows. Red arrows indicate a pro-inflammatory/catabolic effect, green arrows indicate an anti-inflammatory/anabolic effect, and orange arrows indicate a mixture of these two, depending on the implicated cell in the target tissue. The interaction between IFP and bone remains to be investigated. FA, fatty acid; FCM, fat conditioned media; IL, interluekin; MSC, mesenchymal stem cell; PG, prostaglandin; TNF, tumor necrosis factor.