TLR9 and periodontitis: It has been well established that in the immune system, factors such as TLR9 recognize conserved molecular structures and initiate downstream signalling pathways to control the immune response through what is called pattern recognition reception (PRR).39 Early immune pathways mediated by PRR have been linked to classical inflammation, but recent studies have demonstrated a new link between PRR and autophagy.40 Researchers have since turn to the relationship between PRR and autophagy to explain the pathological mechanisms of immune diseases, such as periodontitis and RA.