AB0066 Combination of il-10 and il-18 but not il-6 and il-18 induces ifn-gamma production and surface expression of trail on nk cells

Background Adult-onset Still’s disease (AOSD) is a systemic inflammatory disease, the cause of which is largely unknown. AOSD has been recently classified as one of the autoinflammatory diseases, in which innate rather than acquired immunity plays an important role. Serum IL-18 has been shown to be significantly high in AOSD patients. Objectives The aim of this study was to quantify the levels of multiple cytokines in the serum of AOSD patients, and compare the serum cytokine profile with that of healthy controls. We also attempted to evaluate the effects of the cytokines that were upregulated in the AOSD serum on natural killer (NK) cells, since NK cells are cells of innate immunity and IL-18 has been shown to enhance their cytotoxicity.1 Methods We quantified the serum levels of 10 cytokines (IFN-α, IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12p70, IL-17A and TNF-α) in patients with AOSD and healthy controls using multiplex bead array assays and IL-18 using ELISA. We next sorted NK cells from peripheral blood mononuclear cells (PBMCs) of healthy controls, stimulated them in vitro, and quantified the level of IFN-γ in the culture supernatant by ELISA and also assessed the surface expression level of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) on the cells. Results Compared to samples from healthy controls, the mean serum levels of IL-6 and IL-18 from AOSD patients were significantly higher. IL-10 was detectable in some of the patients. Originally, IL-18 was identified as a stimulator of IFN-γ production2, however, serum IFN-γ was below the detection limit. When NK cells were stimulated in vitro with IL-18 alone, the protein level of IFN-γ in the culture supernatant was still below the detection limit. When we further added IL-6 and/or IL-10 to the culture, the combination of IL-10 and IL-18, but not IL-6 and IL-18, induced IFN-γ. As IL-6 is a classic pro-inflammatory cytokine and IL-10 is considered to be an anti-inflammatory cytokine, this result was rather unexpected. Thus, we evaluated the expression of IL-6 and IL-10 receptors on NK cells and found that IL-10 receptors (IL-10R and IL-10Rβ) were present, but IL-6 receptors (IL-6R and gp130) were absent. We also assessed TRAIL expression on NK cells. Here, too, the combination of IL-10 and IL-18 induced TRAIL expression the most potently. Although a previous research showed that the combination of TLR3 and IL-18 signalling synergistically induced TRAIL on NK cells in an IFN-γ dependent manner3, the addition of an anti-IFN-γ antibody did not diminish the TRAIL expression. Conclusions A combination IL-10 and IL-18, not IL-6 and IL-18, induced the production of IFN-γ and surface expression of TRAIL in NK cells. This TRAIL expression did not evidently depend on IFN-γ. TRAIL was expected to be useful for the treatment of malignancy, but it turned out to be toxic to hepatocytes4. Since NK cells are rich in the liver and the abnormality of liver function is among the major symptoms in AOSD, we suggest that the combination of IL-10 and IL-18 may cause liver dysfunction by inducing TRAIL on NK cells in the liver. References [1] Akira S. Curr Opin Immunol. 2000;12:59–63. [2] Okamura H, et al. Nature1995;378:88–91. [3] Tu Z, et al. Cell Immunol2011;271:286–91. [4] Jo M, et al. Nat Med. 2000;6:564–7. Disclosure of Interest None declared