TNF and periodontitis: Notably, our group also repeatedly demonstrated that treating these patients with HMT (i.e., non-antibiotic-dose doxycycline as a pleiotropic MMP-inhibitor) not only reduced the severity of chronic periodontitis but also decreased the biomarkers of systemic inflammation (hs-CRP, TNF-α and IL-6) and collagenolysis (MMP-8 and -9) in the circulation as well [5,6,11,12,13,14].