TNF and periodontitis: Periodontitis is associated with gram-negative bacteria, including Porphyromonas gingivalis, Prevotella intermedia and Aggregatibacter actinomycetemcomitans, which trigger macrophages to produce nitric oxide (NO) and proinflammatory molecules such as interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) 5-.7