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A balance between staying and leaving
Neutrophils generated in the bone marrow are critical for inflammatory responses that fight infection. However, too many or too few neutrophils in the bloodstream are detrimental. The number of circulating neutrophils is determined by the balance between signaling mediated by the chemokines CXCL12, which retains neutrophils in the bone marrow, and CXCL2, which recruits neutrophils to tissues. Both CXCL12 and CXCL2 activate the small GTPase Rac. Campa et al. performed mathematical modeling and showed that the time it took active Rac to return to baseline determined how long neutrophils were retained in the bone marrow. Mice that were genetically deficient for a Rac inhibitor retained more neutrophils in the bone marrow and had fewer neutrophils in the blood than wild-type mice. Thus, these findings might highlight new opportunities to treat neutrophilia (too many circulating neutrophils) or neutropenia (too few circulating neutrophils).
