Role of IL-18 Signaling in Dendritic Precursor Cells
A. KOUTOULAKI, M.S. LANGLEY, D.P. AESCHLIMANN, and X.-Q. WEI, CARDIFF UNIVERSITY, Cardiff, United Kingdom | Mature dendritic cells (DC) regulate T cell responses
through cytokine production. Increased concentrations of IL-18 are correlated
with gingival sulcular depth and pathogenesis of periodontitis. The KG1 human monocytic
cell line is a DC precursor that can be differentiated into functional antigen
presenting cells by IL-18. DC activity and maturation is associated with the
induction of IFNg. IL-18 binds to IL-18Receptor a/b to secrete IFNg
in KG1 cells. Objectives: 1) to dissect the mechanism(s) by which IL-18
induces DC maturation; 2) identify the role of TNFa and TGFb1 in
regulating IL-18 signaling and IL-18R expression in KG1 cells; 3) investigate
the role of p38MAPK, ERK1/2, and Tbet; 4) determine the effect of IL-18
inhibition by soluble human (sh)IL-18RabFc. Methods: FACS and
QPCR was used to look at the effect of TNFa or TGFb1 on IL-18R expression
in KG1 cells. Cells were stimulated with rhIL-18 w/wo shIL-18RabFc to
determine p38MAPK and ERK1/2 protein phosphorylation by Western blotting. Cells
treated with p38MAPK inhibitor (SB203580) or ERK1/2 inhibitor (PD89059)
secreted IFNg measured by ELISA. Tbet expression was detected by Western
blotting in cells stimulated w/wo TNFa and/or TGFb1 followed by
IL-18. KG1 cells were primed with TNFa before stimulation with IL-18,
together with increasing doses of shIL-18RaFc, shIL-18RbFc or
shIL-18RabFc and IFNg secreted was determined by ELISA. Results:
1) IL-18Ra mRNA and protein expression was induced by TNFa. 2) IL-18
induced rapid phosphorylation of p38MAPK but not ERK1/2. 3) Blocking p38MAPK
using specific inhibitors completely abolished IFNg while inhibitors for
ERK1/2 had no significant effect. 4) IL-18 induced Tbet expression that was upregulated
by TNFa and downregulated by TGFb1. 5) shIL-18RabFc blocked
human IL-18 and reduced p38MAPK activation. Conclusions: Characterizing
the molecular events leading to IL-18 signaling is important in identifying
potential targets for blocking protein-protein interactions to manage
inflammatory processes therapeutically.
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