The fate of neutrophils and role of monocytes in sterile inflammation
Our immune system Is designed to protect us from harmful agents. It must initiate a rapid potent inflammatory response to eliminate invading pathogens. Although similar to the eradication of pathogens, the inflammatory response can also occur following a sterile injury and is required for tissue repair and wound healing. This includes trauma, ischaemia-reperfusion injury, autoimmunity or burn induced injury that occurs in the absence of any microorganisms. Sterile inflammation underlies the pathogenesis of many diseases and in both sterile and infectious Inflammation, neutrophils are the primary cells recruited to the sites of inflammation. They use their considerable antimicrobial arsenal to kill pathogens but also phagocytose cellular debris in order to resolve the cause of inflammation. However, these same functions can also cause collateral tissue damage and perhaps more in sterile injury where there are no pathogens to kill. Thus, it is crucial that neutrophil functions are tightly controlled during the whole process of inflammatory response. This is thought to be achieved by their innocuous clearance by other types of immune cells and in particular monocytes that enter the site of sterile injury within hours of the neutrophils. In fact, pathology text books all suggest that neutrophils are eliminated by monocytes.