Interleukin-18 in hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is characterized by dysregulated hyperactivation of macrophages and T helper 1 (Th1) cells accompanied by excessive secretion of inflammatory cytokines. Although TNF-alpha and IFN-gamma are known to be important factors for the development of the disease, the mechanism of their overproduction has not been clarified, yet. We measured serum IL-18 levels of patients with HLH to investigate the possible significance of IL-18 in its pathophysiology, especially in IFN-gamma production. IL-18 levels were significantly increased in all patients with HLH compared with healthy controls. A significant correlation was observed between IL-18 and IFN-gamma levels. In addition to IFN-gamma and soluble Fas ligand (sFasL), IL-18 levels significantly correlated with disease activity. IL-18 may play important roles in the pathogenesis of HLH, particularly through induction of Th1 cells. In addition, IL-18 measurement may not only be useful for the diagnosis, but also for the evaluation of disease activity.