Briefly, a heterodimer consisting of a cytokine-like α subunit (IL-12 p35, IL-23 p19 and IL-27 p28) and a receptor-like β subunit (IL-12 p40 for both IL-12 and IL-23, Epstein-Barr virus-induced gene 3 for IL-27) binds to a group of receptors (similar to the binding of IL-6 and gp130), which activates the downstream JAK-STAT signalling pathway.131–133 Among these cytokines, IL-23 is closely associated with Th17 cells, and IL-27 exerted a potential protective effect in the immune response to periodontitis, which is discussed later. This evidence concerns the gene IL6 and periodontitis.