FIG. 5.

Principles in TLR signaling. TLR4 activates both the MyD88-dependent and MyD88-independent, TRIF-dependent pathways. The MyD88-dependent pathway is responsible for early-phase NF-κB and MAPK activation, which control the induction of proinflammatory cytokines. The MyD88-independent, TRIF-dependent pathway activates IRF3, which is required for the induction of IFN-β- and IFN-inducible genes. In addition, this pathway mediates late-phase NF-κB as well as MAPK activation, also contributing to inflammatory responses.