TLRs and chronic inflammation.

After the discovery of Toll-like receptors (TLRs), innate immune mechanisms came back in the focus of scientific research. With more and more mechanisms of TLR biology known, it has become clear that these and also other innate immune receptors are not only of crucial importance in the immune response to invading pathogens, but also play a role in the homeostasis of commensal flora and in the response to stress and danger signals. In this respect, increasing evidence is found that inappropriate quantity or quality of TLR ligands or aberrant response to TLR activation plays a role in a variety of chronic inflammatory diseases. In this review, an overview of the currently known TLRs and their signaling pathways is given and reports about their expression and activation in chronic inflammatory diseases are recapitulated.