Toll-like receptors (TLRs) mediate cell activation by various microbial products. Here, we demonstrate that activation of dendritic cells by TLR2 or TLR4 agonists, although it led to comparable activation of NF-kappa B and mitogen-activated protein kinase (MAPK) family members, resulted in striking differences in cytokine and chemokine gene transcription, suggesting that TLR2 and TLR4 signaling is not equivalent. A TLR4 agonist specifically promoted the production of the Th1-inducing cytokine interleukin (IL) 12 p70 and the chemokine interferon-gamma inducible protein (IP)-10, which is also associated to Th1 responses. In contrast, TLR2 stimulation failed to induce IL-12 p70 and interferon-gamma inducible protein (IP)-10 but resulted in the release of the IL-12 inhibitory p40 homodimer, producing conditions that are predicted to favor Th2 development. TLR2 stimulation also resulted in preferential induction of IL-8 and p19/IL-23. Involvement of phosphatidylinositol 3-kinase and p38 MAPK in the TLR-mediated induction of several cytokine and chemokine messages was demonstrated using specific inhibitors. Thus, TLRs can translate the information regarding the nature of pathogens into differences in the cytokines and chemokines produced by dendritic cells and therefore may contribute to the polarization of the acquired immune response.
