Similarly, the use of IL-18 to stimulate RA synovial fibroblasts in vitro induced the expression of surface vascular CAM and neutrophil chemoattractant (192); more IL-18 is then produced by synovial fibroblasts and through the action of TNF-α produced by synovial macrophages in a positive feedback mechanism. Here, IL18 is linked to rheumatoid arthritis.