Feedback loop controlling normal neutrophil homeostasis in leukocyte adhesion molecule–deficient mice.

Increased granulopoiesis increases circulating neutrophils. Some of these neutrophils migrate into peripheral tissues, including the skin, gut, and mucous membranes.49 A defect in neutrophil trafficking breaks the feedback loop, which is restored by adding transmigration-competent neutrophils (this study). Cells in the tissues produce IL-17,23 which causes the release of G-CSF,23 which in turn increases granulopoiesis.16 19 Other stimuli are likely to influence neutrophil homeostasis at each step of the feedback loop (not shown).