Dental Calculus Stimulates Interleukin-1beta Secretion by Activating NLRP3 Inflammasome in Human and Mouse Phagocytes

Dental calculus is a mineralized deposit associated with periodontitis. The bacterial components contained in dental calculus can be recognized by host immune sensors, such as Toll-like receptors (TLRs), and induce transcription of proinflammatory cytokines, such as IL-1beta. Studies have shown that cellular uptake of crystalline particles may trigger NLRP3 inflammasome activation, leading to the cleavage of the IL-1beta precursor to its mature form. Phagocytosis of dental calculus in the periodontal pocket may therefore lead to the secretion of IL-1beta, promoting inflammatory responses in periodontal tissues. However, the capacity of dental calculus to induce IL-1beta secretion in human phagocytes has not been explored. To study this, we stimulated human polymorphonuclear leukocytes (PMNs) and peripheral blood mononuclear cells (PBMCs) with dental calculus collected from periodontitis patients, and measured IL-1beta secretion by ELISA. We found that calculus induced IL-1beta secretion in both human PMNs and PBMCs. Calculus also induced IL-1beta in macrophages from wild-type mice, but not in macrophages from NLRP3- and ASC-deficient mice, indicating the involvement of NLRP3 and ASC. IL-1beta induction was inhibited by polymyxin B, suggesting that LPS is one of the components of calculus that induces pro-IL-1beta transcription. To analyze the effect of the inorganic structure, we baked calculus at 250 degrees C for 1 h. This baked calculus failed to induce pro-IL-1beta transcription. However, it did induce IL-1beta secretion in lipid A-primed cells, indicating that the crystalline structure of calculus induces inflammasome activation. Furthermore, hydroxyapatite crystals, a component of dental calculus, induced IL-1beta in mouse macrophages, and baked calculus induced IL-1beta in lipid A-primed human PMNs and PBMCs. These results indicate that dental calculus stimulates IL-1beta secretion via NLRP3 inflammasome in human and mouse phagocytes, and that the crystalline structure has a partial role in the activation of NLRP3 inflammasome