Cytokine
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Granulocyte colony-stimulating factor (G-CSF) induces the release of mature neutrophils from storage pools and stimulates differentiation of myeloid progenitor cells. Recently, it has been shown that a standard dose of G-CSF induces immunophenotypical and functional changes of neutrophils that persist for 1 week. The authors investigated the effects of 300 micrograms of G-CSF administered subcutaneously twice, 1 week apart, to 10 healthy volunteers, on neutrophil and monocyte counts and on the plasma levels of interleukin 1 receptor antagonist (IL-1ra), tumour necrosis factor-alpha (TNF-alpha), soluble TNF receptor (sTNF-r) p55 and p75. ⋯ The increases in neutrophil counts and plasma IL-1ra levels were larger following the second injection, whereas the increase in plasma sTNF-r p75 levels was smaller. G-CSF induced increases in monocyte counts, TNF-alpha and sTNF-R p55 levels did not differ between the first and second injection. Our finding of an increased response of healthy humans to a second G-CSF challenge 1 week following a first one may be due to long-lasting increases in storage pool neutrophils.