Inhibition of IL-2 Expression by P. gingivalis Figure 2. P. gingivalis is able to attach and induce ROS production in Jurkat T-cells. A- Jurkat T-cells cells were stimulated with FITC-labeled P. gingivalis (108 CFU/ml, MOI:100) for 24 h and analyzed by confocal microscopy. Magnification is 663, with a 26digital zoom. B- ROS production in Jurkat T-cells was detected by luminol-amplified chemiluminescence following treatment with 108 CFU/ml of viable P. gingivalis (MOI:100) for 30 min. Shown is a representative graph of five independent experiments. doi:10.1371/journal.pone.0045192.g002 regulatory T-cells [3]. Intracellular free Ca2+ is an important signaling molecule that is required for the activation of T-cells upon recognition of a foreign antigen [21]. Activation of the transcription factors AP-1, NFAT and NF-kB, and subsequent gene-expression and cytokine release requires a sustained Ca2+ influx [22]. These transcription factors are activated through Figure 3. P. gingivalis suppressed AP-1 and NF-kB activity. Jurkat T-cells (106 cells/ml) were transfected with either AP-1 (A) or NF-kB (B) luciferase reporter plasmids. The cells were treated with viable or heat-killed P. gingivalis (108 CFU/ml, MOI:100) for 24 h. AP-1 and NF-kB activation were determined by measuring luciferase activity, which was normalized against the internal control Renilla. *-p,0.05; **-p,0.01 (Student’s t-test). doi:10.1371/journal.pone.0045192.g003 PLOS ONE | www.plosone.org 5 September 2012 | Volume 7 | Issue 9 | e45192