Fig. (1) TLR signal transduction pathway. TLR2 can form a homodimer or a heterodimer with TLR1 and TLR6. TLR3, TLR7, TLR8 and TLR9 localize in endosomal compartments. LPS activates TLR4. Each TLR mediates distinctive responses in association with TIR domain-containing adapters (MyD88, TIRAP/MAL, TRIF and TRAM). IRAK and TRAF6 activate NF-κB and induce inflammatory cytokine secre-tion activating the IFN pathway.