IL1A and periodontitis: In addition, lipopolysaccharide (LPS), produced by gram-negative bacteria during periodontitis, induces periodontal inflammation characterized by high levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1, as well as of nuclear factor-κB ligand (RANKL) which, in turn, causes an excessive osteoclast formation and activation, leading to alveolar bone loss [27,28,29].