[Progress in functions and mechanisms of immunosuppressive neutrophil subsets: An update]

Neutrophils are the most abundant circulating leukocytes in healthy adults, serving as the first-line defense against infections. In the last few years, scientists have reported neutrophils of immune suppressive properties, such as tumor-associated neutrophils (TAN) and low-density neutrophils (LDN). These neutrophils are found to be involved in many physiological and pathological conditions owing to their ability of regulating T cell functions and promoting angiogenesis and tumor growth through a number of mechanisms, including PD-1/PD-L1, antigen presentation, reactive oxygen species (ROS), arginase-1 (Arg1), inducible nitric oxide synthase (iNOS), etc. This review summarizes the recent advances in investigating the function and mechanism of immune suppressive neutrophils.