Objective: The proatherogenic effect of IL-18 is shown to be dependent on IFN-gamma production. It is believed that activated T cells play a proatherogenic role through secretion of IFN-gamma. However, recent studies in vitro have shown that macrophages, NK cells, and even vascular smooth muscle cells may also secrete IFN-gamma after stimulation by cytokines like IL-18. We therefore investigated whether cells other than activated T cells can play a proatherogenic role via IFN-gamma secretion under the stimulation of IL-18 in vivo.
Methods and results: SCID/apoE knockout mice were injected intraperitoneally with either IL-18 or phosphate-buffered saline 3 times per week for 7 weeks. Our results show that administration of IL-18 leads to 3-fold larger lesions and 2-fold higher circulating IFN-gamma despite the absence of T cells. In addition, increased IFN-gamma, accompanied by elevation of the scavenger receptor/chemokine CXCL16, was observed in both lesions and spleens. Furthermore, our findings revealed that macrophages, NK cells, and vascular cells were the source of IFN-gamma under the stimulation of IL-18 in the absence of T cells in vivo.
Conclusions: The current data suggest that the proatherogenic effect of IL-18 can occur in the absence of T cells and that IFN-gamma secreted by macrophages, NK cells, and vascular cells is sufficient for the disease progression.