Despite the established role of dendritic cells (DCs) in regulating T lymphocyte activation, intracellular mechanisms responsible for controlling DC function are largely undefined. Here, we have studied DCs from mice deficient in the p50, RelA, and cRel subunits of the immunomodulatory NF-kappaB transcription factor. Although DC development and function was normal in mice lacking individual NF-kappaB subunits, development of doubly deficient p50(-/-)RelA(-/-) DCs was significantly impaired. In contrast, DCs from p50(-/-)cRel(-/-) mice developed normally, but CD40L- and TRANCE-induced survival and IL-12 production was abolished. Surprisingly, no significant impairment in MHC and costimulatory molecule expression was seen, despite significantly reduced kappaB site binding activity. These results therefore indicate essential, subunit-specific functions for NF-kappaB proteins in regulating DC development, survival, and cytokine production.

Tissue damage induced by infection or injury can result in necrosis, a mode of cell death characterized by induction of an inflammatory response. In contrast, cells dying by apoptosis do not induce inflammation. However, the reasons for underlying differences between these two modes of cell death in inducing inflammation are not known. Here we show that necrotic cells, but not apoptotic cells, activate NF-κB and induce expression of genes involved in inflammatory and tissue-repair responses, including neutrophil-specific chemokine genes KC and macrophage-inflammatory protein-2, in viable fibroblasts and macrophages. Intriguingly, NF-κB activation by necrotic cells was dependent on Toll-like receptor 2, a signaling pathway that induces inflammation in response to microbial agents. These results have identified a novel mechanism by which cell necrosis, but not apoptosis, can induce expression of genes involved in inflammation and tissue-repair responses. Furthermore, these results also demonstrate that the NF-κB/Toll-like receptor 2 pathway can be activated both by exogenous microbial agents and endogenous inflammatory stimuli.

Serum IgE concentrations and the expression of the low-affinity receptor for IgE (FceRHl/CD23) Nitric oxide (NO) generated by activated murine macrophages is cytostatic or cytotoxic for a variety of pathogens, including Leishmania major, Plasmodium falciparum, Schistosoma mansoni, Trypanosoma cruzi, and Toxoplasma gondii (1-6). NO is generated from the oxidation of the terminal guanido nitrogen atom(s) of L-arginine by an NADPH-dependent enzyme, the NO synthase (NOS) (7-9). In murine macrophages, NOS activity is induced by lipopolysaccharide (LPS) (9) IgE-IC) or by a specific monoclonal antibody (mAb) to CD23 (CD23 mAb) promotes the generation of cGMP. Simultaneous measurement of the generation of nitrite (NO-j) indicated that the enhanced production of cGMP is consequent to activation of the L-arginine:NO pathway.The low-affinity receptor for IgE (FceRII/CD23) is also expressed on normal human monocytes/macrophages after their activation in vivo (22,23). Studies in patients infected with Leishmania braziliensis or in disease-free, immunoreactive donors have shown both in situ CD23 expression and serum IgE concentrations to be increased in these conditions (23). We have, therefore, studied whether cell activation through ligation of the membrane receptor CD23 induces the L-arginine:NO pathway and results in leishmanicidal activity in human macrophages. MATERIALS AND METHODSReagents. The following reagents were used: recombinant human interleukin 4 (IL-4; a gift from J. Banchereau, Schering-Plough); IFN--y (a gift from J. M. Mencia-Huerta, Institut Beaufour, Paris); TNF-a and anti-TNF-a mAb (Genzyme); human IgE (Stallergene, Paris), and goat anti-human IgE (Nordic, Tilburg, The Netherlands). Polymyxin B, LPS (Escherichia coli 055, L-2880), NG-monomethyl-L-arginine (L-NMMA), D-NMMA, L-arginine, D-arginine, superoxide dismutase (SOD), and catalase were all obtained from Sigma.Cells. Human mononuclear cells were obtained by Ficoll gradient separation of peripheral blood leukocytes from healthy volunteers. Monocytes were separated from lymphocytes by adherence to plastic dishes coated with fetal calf serum as described (24). After this procedure, >90% of cells expressed CD14 antigen and displayed cytochemical characteristics of monocytes (24). The cells were then incubated in Dulbecco's modified Eagle's medium (DMEM) supplemented with nonessential L-amino acids, sodium pyruvate, glutamine, penicillin, streptomycin, and 10% (vol/vol) fetal calf serum (all from GIBCO). The culture medium was routinely controlled for the absence of a direct activation effect on human monocytes (CD23 expression and TNF-a production as activation Abbreviations: mAb, monoclonal antibody; CD23 mAb, anti-CD23 mAb; IgE-IC, IgE-anti-IgE immune complexes; L-NMMA, NA3-monomethyl-L-arginine; LPS, lipopolysaccharide; NOS, NO synthase; iNOS, inducible NOS; IFN-y, interferon y; IL, interleukin; TNF-a, tumor necrosis factor ai; SOD, superoxide dismutase; HPRT, hypoxanthine phosphoribosyltransferase. tTo whom reprint requests should be ad...