Monocytes in sterile inflammation: recruitment and functional consequences

Monocytes play an important role in initiating innate immune responses. Three subsets of these cells have been defined in mice including classical, nonclassical and intermediate monocytes. Each of these cell types has been extensively studied for their role in infectious diseases. However, their role in sterile injury as occurs during ischemia-reperfusion injury, atherosclerosis, and trauma has only recently been the focus of investigations. Here, we review mechanisms of monocyte recruitment to sites of sterile injury, their modes of action, and their effect on disease outcome in murine models with some references to human studies. Therapeutic strategies to target these cells must be developed with caution since each monocyte subset is capable of mediating either anti- or pro-inflammatory effects depending on the setting.