Emerging Th17 Responses for Development of Atherosclerosis Infected by P. gingivalis

Objectives: Porphyromonas gingivalis has shown to be an important risk factor for atherosclerosis. It can accelerate the development of atherosclerotic lesion in murine models correlating with inflammatory cytokines secreted by T cells. Th17 cells have been implicated to play a critical role in chronic inflammatory diseases and promote the development of atherosclerotic lesion. Therefore, the purpose of this study was to investigate Th17 cells and Th17-related molecules in P. gingivalis-induced atherosclerosis over the time course.
Methods: Eight-week-old male Apolipoprotein E-deficient mice were intravenously injected with P. gingivalis three times per week for total ten times. Serum, spleen and aortic tissue samples were collected 1, 3, 5 weeks after the last infection. The proximal aorta lesion areas were examined by Oil Red-O staining, flow cytometry analyzed the Th17 responses in splenic cultures, and the expressions of Th17-related molecules in spleen and aortic tissues were examined by ELISA and Real-time PCR.
Results: P. gingivalis inoculation accelerated atherosclerotic plague accumulation in the aortic sinus of ApoE-/- mice. Flow cytometry analysis of CD4⁺ T cells showed that P. gingivalis challenge enhanced the proportion of Th17 cells after 1 week, but reduced from 3 week. Moreover, the production of IL-17 was increased by anti-CD3 antibody stimulation, and was decreased after 3 weeks. The expression of IL-10 was apparently increased from 1 week to 5 week. However, IFN-γ level was higher in 3 week. Real-time PCR analysis showed that Th17-related molecules: IL-6 and RORγt levels were increased after P. gingivalis injection, but the expressions of TGF-β, STAT3, IL-23 and IL-21 were higher after injection 1 week, then dropped down.
Conclusions: Although the level of IL-17 was decreased over time, these results still indicated that P. gingivalis infection enhances Th17 responses to accelerate the development of atherosclerosis.