S100A8 is a calcium binding protein belonging to the S100 family that is secreted by neutrophils and monocytes during active infection. After bacterial infection, neutrophils, macrophages, and monocytes express and secrete S100A8/A9 in order to modulate inflammatory processes with the induction of inflammatory cytokines, reactive oxygen species (ROS), and nitric oxide (NO). S100A8 can form a stable homodimer or heterodimer with S100A9, and both are released upon infection to mediate the inflammatory response. In addition to being secreted in response to infection, S100A8/A9 is secreted in metabolic inflammatory diseases such as gout, diabetes, obesity, and patients with autoimmune diseases.