TNF and bacterial infectious disease: PCT, as a 116-amino acid polypeptide, is secreted from neutrophils and parenchymal cells when bacterial infections occur and is a valuable biomarker for early diagnosis of systemic infection, especially for sepsis, and PCT can be up-regulated by bacterial endotoxins and proinflammatory mediators such as IL-6 and tumor necrosis factors and will be down-regulated when infection is controlled, and the concentrations of endotoxins and proinflammatory mediators decreas [28–31].