TNF and infection: Infection of MG6 cells with P. gingivalis significantly increased the mRNA expression levels of proinflammatory mediators, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) (Fig. 6a), without affecting the mRNA expression of anti-inflammatory mediators, including IL-10, arginase-1 and IL-4 (Supplementary Fig. S3).