Characterization of innate immune signalings stimulated by ligands for pattern recognition receptors

The innate immunity is an essential step as the front line of host defense, and its aberrant activation particularly in response to nucleic acids is closely related to the pathogenesis of autoimmune and inflammatory diseases. Characterization of the innate immune signalings may provide a pathophysiological insight for better understanding of human diseases. Nucleic acid-mediated activation of pattern recognition receptors triggers the activation of two major intracellular signaling pathways, which are dependent on NF-κB and interferon regulatory factors, transcriptional factors. This leads to the subsequent induction of inflammatory cytokines and type I and III interferons. In this chapter, we first overview the representative families of nucleic acid sensors and their ligands and then show the fundamental techniques for extracellular or intracellular stimulation with these nucleic acid ligands and for detection of innate immune response, that is, IFN and proinflammatory cytokine induction, as assessed by luciferase assay, quantitative RT-PCR (qRT-PCR), and enzyme-linked immunosorbent assay.