In vivo effect of human granulocyte-macrophage colony-stimulating factor (GM-CSF) on neutrophil GM-CSF receptors

The effect of in vivo administration of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on neutrophils GM-CSF receptor, was investigated in patients with neoplastic diseases and normal hematopoiesis. Patients were divided into two groups. Group A received a single dose of rhGM-CSF (5 μg/kg/day) and receptor studies were performed 90 min and 48 h after treatment. Group B received three doses, administered subcutaneously every 24 h and receptor studies were performed 90 min after first injection and 24 h after the last. Before treatment neutrophils only displayed high-affinity receptors (K(D) 85 ± 53 pM; number of receptors/cell 1318 ± 567). The first injection of rhGM-CSF produced a transient leucopenia and the internalization of GM-CSF receptor on neutrophils in both groups of patients: 90 min after s.c. administration receptors could not be detected with conventional binding studies. In group A patients, 48 h after a single dose of rhGM-CSF, receptors, albeit with a decreased affinity (K(D) = 240 ± 131 pM; number of receptors/cell 783 ± 494) were again expressed. In group B patients, 24 h after the last rhGM-CSF injection, low intermediate affinity receptors not present before treatment appeared (K(D) 720 ± 175 pM; number of receptor/cell 1222 ± 179). They were associated with a low number of high affinity receptors (K(D) = 9 ± 4 pM; number of receptors/cell 106 ± 44). These observations indicate that more than one type of GM-CSF receptor may exist on neutrophils. It may be suggested that in vivo the regulation of the GM-CSF receptor is different from that in vitro and is related to the presence of the cytokine in patient blood.