Toll-like receptors and acquired immunity.

Toll-like receptors are a family of pattern recognition receptors (PRRs) that evolved to detect microbial infection. These receptors recognize conserved molecular products derived from different classes of microorganisms, including Gram-positive and -negative bacteria, fungi, protozoa and viruses. Following recognition of ligands TLRs initiate signaling events that result in acute innate responses. In addition, TLRs are responsible for initiation of adaptive immune responses against pathogen-derived antigens primarily through triggering dendritic cell activation. Control of adaptive immunity by TLRs is a complex phenomenon and much needs to be understood about how different TLRs tailor the outcome of adaptive immune responses to the advantage of the host. Although TLRs have evolved to induce protective immune responses, under some circumstances, activation of these receptors may lead to autoimmune diseases.