TNF and periodontitis: A bidirectional relationship between HDL and periodontitis has also been proposed: upregulation of proinflammatory factors caused by periodontitis can have adverse effects on serum lipid metabolism, as proposed by Fentoğlu et al.48 A significant correlation was identified between the pro-inflammatory cytokines TNF-α and IL-1b and the TC/HDL ratio in the gingival sulcus fluids and serum of hyperlipidemic patients with periodontitis.