Porphyromonas gingivalis stimulates IL-18 secretion in monocytic THP-1 cells


Nejat Düzgüneş: 0000-0001-6159-1391


Biomedical Sciences

Document Type

Conference Presentation

Conference Title

39th Annual Meeting of the American Association for Dental Research (AADR)


Washington, DC

Conference Dates

March 3-6, 2010

Date of Presentation


Journal Title

Journal of Dental Research

Journal ISSN


Journal Volume Number

89 (Special issue A)

First Page



Objectives: Porphyromonas gingivalis (Pg) is one of the most important bacteria that contribute to the pathogenesis of chronic periodontitis. Interleukin-18 (IL-18), a potent pro-inflammatory cytokine that mediates the Th1 immune response is considered to be a key factor in the initiation and progression of periodontal disease. We examined the IL-18 levels secreted by differentiated human macrophage-like THP-1 cells after exposure to live and heat-inactivated Pg, and to lipopolysaccharide (LPS) from E. coli and Pg. Methods: THP-1 cells were differentiated with 1.6 nM phorbol 12-myristate 13-acetate (PMA) for 2 days at 37°C. Two Pg strains, the avirulent 2561 (ATCC 33277) and highly virulent W83 (ATCC BAA-308) were sub-cultivated on blood agar plates and suspended in Medium 199 (4 x 108 Pg/ml). The bacterial suspension was mixed 1:4 with RPMI/10% FBS and added to differentiated THP-1 cells, at ratios of 2-100 bacteria/cell, and incubated at 37°C for 24 h. IL-18 was determined by ELISA. LPS from E. coli and Pg were also tested at 100 ng/ml and 5 µg/ml. Results: IL-18 secretion depended on the number of bacteria/cell. For example, treatment with live Pg 2561 and W83 at 100 Pg/cell produced 388.3±2.3 and 293.0±95.5 pg IL-18/ml, respectively. IL-18 up-regulation was reduced significantly by heat-inactivation of Pg. Exposure to heat-inactivated Pg 2561 and W83 at 100 Pg/cell produced 56.4±19.4 and 122.0±21.5 pg IL-18/ml, respectively. Treatment with LPS from Pg and E. coli at 100 ng/ml resulted in the production of 32.9±5.6 and 75.9±6.2 pg IL-18/ml, respectively. Conclusion: Pg induced significant IL-18 secretion by differentiated macrophage-like THP-1 cells. The more virulent Pg W83 strain did not induce higher production of IL-18. Induction of IL-18 by heat-inactivated Pg is probably caused by LPS.