Signaling by mammalian TLRs in various cell type induces a diverse range of intracellular responses that together result in production of inflammatory cytokines, chemotactic factors, antimicrobial peptides, and the antiviral cytokines interferon(IFN)-α and IFN-β, the type I interferons. TLR signaling achives this by being able to activate several different signaling pathways that each activates different transcription factors. One pathway activates the NFkB transcription factors (Fig. 3.13), which are related to DIF, the factor activated by Drosophila Toll. Mammalian TLRs also activate several members of the interferon regulatory factor (IRF) transcription factor family through a second pathway, and activate members of the activator protein 1 (AP-1) family, such as c-Jun, through yet another signaling pathway involving mitogen-activated protein kinases (MAPKs). NFkB and AP-1 act primarily to induce the expression of pro-inflammatory cytokines and chemotactic