Function of neutrophils and their generation (granulopoiesis). Neutrophils circulate and detect inflammatory cues. (A) Because of their short lifespan, neutrophils are continuously generated in the bone marrow of the hematopoietic system by granulopoiesis. (B) When they detect alert signals from inflamed tissue, neutrophils transmigrate into inflamed sites and initiate immune activation. (C) Sensing the size of pathogens by means of dectin-1, non-TLR pattern recognition receptor, and distinct generation of reactive oxygen species (ROS), neutrophils may surround pathogens (swarming), prey on them (phagocytosis), or project a sticky neutrophil extracellular trap (NET), while secreting context-dependent cytokines and granules (degranulation). (D, E) Self-immolation of neutrophils (D) and immune activation of other monocytes and macrophages (Mφ) increases production of IL-6, G-CSF, and GM-CSF, which in turn stimulate emergency neutrophil generation in the bone marrow (granulopoiesis) (E) and spleen (not shown). The context and signaling cues given for granulopoiesis affect the heterogeneity of newly generated neutrophils (trained granulopoiesis).