Furthermore, PBMCs of patients with periodontitis have been shown to secrete higher levels of IL-1β and IL-18 compared to healthy controls, both resting cells and cells exposed to H2S. These results have led us to hypothesize that H2S-producing microorganisms in the subgingival pocket trigger an inflammatory host response by the secretion of pro-inflammatory cytokines and that the level of this secretion may be indicative of the susceptibility of the host to periodontitis. Here, IL18 is linked to periodontitis.