Characteristics of nucleic acid TLR ligands

Dendritic cells (DCs) play critical roles as sentinels in host defense and can activate naïve T cells. DC activation and maturation are induced by signaling through a group of type I transmembrane proteins, Toll-like receptors (TLRs), which can discriminate various microorganism-associated molecular structures. TLR ligands include lipid, protein, and nucleic acid components, all of which function as immune adjuvants. Each TLR function is common, but nucleic acid-recognizing TLRs are distinct from other TLRs in several aspects. Here I focus on the characteristics of nucleic acid TLR ligand system and describe how nucleic acids are recognized and processed by DCs. Clarification on diversified function of TLRs should provide us with critical information for manipulating the host defense mechanism.