S100A9 and infection: This subgroup is characterized by the expression of the calprotectin subunits encoded by S100A8 and S100A9. It is known that S100A8/A9 heterodimer secretion is increased in infection-induced inflammation and has some antibacterial effects mediated by secretion of proinflammatory cytokines, release of reactive oxygen species and recruitment of other inflammatory cells, as well as chelation of Zn2+ necessary for bacterial enzymatic activity24.