The anti-inflammatory role for IkappaB kinase (IKK) beta through inhibition of ‘classical’ macrophage activation
Recent research has revealed a role of NF-B in the resolution of inflammation. Using Cre-lox mediated gene targeting, IKK was selectively deleted in macrophages (IKKβ∆Mye). From in vitro studies, LPS stimulated IKKMye macrophages increased STAT1 phosphorylation, iNOS, MHC II and IL-12 production, suggesting negative cross talk between NF-B and STAT1 signalling pathways. Since IKK is required for TNF gene expression and TNF signalling, I investigated the hypothesis that TNF inhibits ‘classical’ macrophage activation through IKK activation. Macrophages from p55-/- and mice treated with anti-TNF antibody show increased STAT1 activation and IL-12 expression after LPS and IFN stimulation. BMDM infected with adenovirus expressing IKKβ dominant negative rescued the inhibitory effect of TNFα on IL-12p40 production, indicating TNFα inhibits IL-12p40 via IKKβ activation. Macrophages are antigen presenting cells while IL-12 and MHC II are critical factors for TH1 cell development. I thus investigate the inhibitory effects of IKKβ∆Mye macrophages in TH1 responses. FACS analysis showed higher MHC II, costimulatory molecules expression on IKKβ∆Mye macrophages after LPS stimulation. In a DTH model, recall assay has shown increased antigen-specific IFN production from IKKMye splenocytes compared to IKKβF/F splenocytes. Furthermore, IFN production was greatly enhanced by CD4+ OTII T cells co-cultured with IKKMye macrophages. Further analysis of CD4+ OTII T cells with qRT-PCR showed increased TH1 genes including IRF1, IFN, IL-12R1 and IL-12R2 and reduced TH2 marker IL-4. In addition to the enhanced antigen-specific T cell responses, IKKMye macrophages also increased anti-tumour immunity. Injection of H-Y positive MB49 tumour cells into IKKF/F and IKKMye female mice has shown tumour rejection, but no tumours were rejected after CD8+ T cells depletion, suggesting tumour rejection is associated with enhanced CTL activity. Taken together, these studies demonstrated the negative regulatory roles of IKK in macrophage activation and their impact to the innate and adaptive immunity.
AuthorsFong, Carol Ho Yan
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