The anti-inflammatory role for IkappaB kinase (IKK) beta through inhibition of ‘classical’ macrophage activation

Abstract

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 IKKMye 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 IKKMye splenocytes compared to IKKβF/F splenocytes. Furthermore, IFN production was greatly enhanced by CD4+ OTII T cells co-cultured with IKKMye macrophages. Further analysis of CD4+ OTII T cells with qRT-PCR showed increased TH1 genes including IRF1, IFN, IL-12R1 and IL-12R2 and reduced TH2 marker IL-4. In addition to the enhanced antigen-specific T cell responses, IKKMye macrophages also increased anti-tumour immunity. Injection of H-Y positive MB49 tumour cells into IKKF/F and IKKMye 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.