Periodontitis is caused by the interaction of pathogens such as Porphyromonas gingivalis (P. gingivalis) in the plaque biofilm with host immune responses. The pathogenic mechanisms of Chronic Periodontitis and Rheumatoid Arthritis may be similar as both diseases involve chronic inflammation overall resulting in bone destruction. The Th17/IL-17 pathway has been implicated in the pathogenesis of rheumatoid arthritis, but its role in the pathogenesis of periodontitis is not fully understood. The aim of this study was to test the hypothesis that P. gingivalis promotes a Th17/IL-17 response through the activation of monocytes in vitro.
Methods:
Bulk CD4+ T-cells (0.5x106 cells) and CD14+ monocytes were isolated from PBMC of healthy donors and co-cultured at a 1:1 ratio in the presence of soluble anti-CD3 mAb with or without heat-killed P. gingivalis (hk-Pg). IL-17, IL-1β, IL-6, TNF-α production in culture supernatants were measured by ELISA. The expression of activation markers on the surface of monocytes after stimulation with hk-Pg was detected by flow cytometry.
Results:
Hk-Pg-stimulation of monocytes resulted in a statistically significant increase in both the expression of activation markers CD40, CD54 and HLA–DR and the production of TNF-α, IL-1β and IL-6 when compared to stimulation with culture medium. For example, the CD54 mean fluorescence intensity was 2,771 ± 228 vs. 8,786 ± 384 (P < 0.05, n =6) and TNF-α production was 78 vs. 2,997 ± 1,132 pg/ml (P < 0.05, n=6) for control vs. hk-Pg, respectively. In monocyte/CD4+ T-cell co-cultures, hk-Pg induced IL-17 production in a dose- and time-dependent manner. E.g. at day 3, we detected 521 ± 138 vs. 1,548 ± 504 pg/ml IL-17 (P < 0.05, n =6) in the absence vs. presence of hk-Pg, respectively.
Conclusions:
These results demonstrate that heat-killed P. gingivalis can activate monocytes and induce IL-17 production in CD4+ T-cell/monocyte co-cultures in vitro.