An essential role of the NF-kappa B/Toll-like receptor pathway in induction of inflammatory and tissue-repair gene expression by necrotic cells

Tissue damage induced by infection or injury can result in necrosis, a mode of cell death characterized by induction of an inflammatory response. In c ontrast, 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-kappaB and induce expression of genes inv olved in inflammatory and tissue-repair responses, including neutrophil-spe cific chemokine genes KC and macrophage-inflammatory protein-2, in viable f ibroblasts and macrophages. Intriguingly, NF-kappaB activation by necrotic cells was dependent on Toll-like receptor 2, a signaling pathway that induc es inflammation in response to microbial agents. These results have identif ied 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-kappaB/Toll-like re ceptor 2 pathway can be activated both by exogenous microbial agents and en dogenous inflammatory stimuli.