Figure 2.

Signaling pathways initiated by TLR-2 and TLR-4 activation. Upon ligation of the TLR-4 receptor complex by exogenous (eg, LPS) or endogenous (eg, hyaluronic acid and β-defensin 2) ligands, MyD88-dependent and MyD88-independent signaling pathways are initiated leading to activation of the transcription factors NF-κB and IRF3. TLR-2 heterodimerises with either TLR-1 or -6 in order to recognise distinct groups of exogenous ligands and signal through a MyD88-dependent pathway. TLR-1/2 recognizes triacyalted (TriAc) lipoproteins and lipoarabinomannan whereas TLR-2/6 recognizes diacylated (DiAc) lipoproteins, lipoteichoic acid and zymosan. TLR-2 may also initiate responses to endogenous products released by necrotic cells.