Various functions of mature human neutrophils are activated or potentiated by hematopoietic growth factors or proinflammatory cytokines such as granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor alpha, and interleukin 1beta. The major signaling pathways activated in human neutrophils stimulated by proinflammatory cytokines include mitogen-activated protein kinases, Janus kinase/signal transducer and activator of transcription, phosphatidylinositol 3-kinase, and nuclear factor kappaB. These signaling pathways are involved in cytokine-mediated regulation of neutrophil functions in a cytokine-specific manner.