Differential response of peripheral blood dendritic cells to periodontal pathogens

Objectives: The aim of this investigation was to determine the antigenic potential of P. gingivalis and A. actinomycetemcomitans by assessing the pattern of cytokine synthesis of dendritic cells activated in vitro. Methods: Peripheral blood mononuclear cells were isolated over a Ficoll gradient and monocytes (CD14⁺ cells) were purified using magnetic columns. Cell purity was evaluated by flow cytometry. Monocytes were differentiated to dendritic cells (DCs) using a standard differentiation protocol and immature DCs were then stimulated with 10¹ to 10⁹ bacteria/mL of P. gingivalis ATCC 33277 or A. actinomycetemcomitans ATCC 33384. DCs activation was evaluated by flow cytometry, cytoplasmic RNA was isolated with the NP-40 method and cytokine expression was assessed by quantitative real-time PCR. Results: More than 97% of monocytes differentiated to DCs in all cases. Different DC activation levels were observed when exposed to the assayed bacteria, demonstrating Aa comparable levels of DCs activation than Pg but with lower bacterial number. Different patterns of cytokine expression in a dose-dependant manner were observed. Higher levels of IL6, IL10 and TNFa were observed in Aa-stimulated DCs and IFNg, IL1b and IL12 in Pg-simulated DCs. Aa showed a lower threshold of cytokine expression in stimulated DCs than Pg did. Conclusion: These data show a differential antigenic potential of Aa versus Pg. This variability between both periodontal pathogens might explain the variable host response and local disease activity depending on the local microbial ecology during periodontal diseases.