In addition to the classical TH1 and TH2 cytokines, members of the recently identified IL-17 cytokine family play an important role in regulating cellular and humoral immune responses. At present nothing is known about the role of these cytokines in atherosclerosis. Expression of IL-17A, -E and -F was investigated in atherosclerotic tissue by rtPCR and immunohistochemistry. IL-17E and its receptor were further studied in cultured smooth muscle cells and endothelial cells, using rtPCR and western blot. rtPCR showed that IL-17A, -E and -F were expressed in the majority of plaques under investigation. IL-17A/F was expressed by mast cells in all stages of plaque development. IL-17A/F(+) neutrophils were always observed in complicated plaques, but hardly in intact lesions. IL-17A/F(+) Tcells ('TH17') were never observed. IL-17E was expressed by smooth muscle cells and endothelial cells in both normal and atherosclerotic arteries, and in advanced plaques also extensively by mature B cells. Cultured smooth muscle cells and endothelial cells were found to express both IL-17E and its functional receptor (IL-17RB). The constitutive expression of IL-17E by resident plaque cells, and the additional presence of IL-17E(+) B cells and IL-17A/F(+) neutrophils in advanced and complicated plaques indicates a complex contribution of IL-17 family cytokines in human atherosclerosis, depending on the stage and activity of the disease.