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Granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage-CSF (GM-CSF) are the principal cytokines in granulopoiesis and differentiation of granulocytic precursors. Their physiologic effects are mediated by binding to specific cell surface receptors (G-CSFr and GM-CSFr, respectively), which are widely expressed from immature bone marrow cells to mature peripheral granulocytes. The fact that concentrations of plasma G-CSF and GM-CSF and their receptors are changed in infectious diseases showing neutrophilia is known, but such changes in patients with chronic myelogenous leukemia (CML) have not been studied. Based on quantitative assays of plasma G-CSF and GM-CSF and their receptors on the peripheral granulocytes of CML patients and healthy controls, this study analyzes the differences between these groups in G-CSF and GM-CSF levels, as well as quantitative and qualitative changes in the receptors. Plasma levels of G-CSF and GM-CSF were measured in 47 patients in the chronic phase of CML and 25 healthy adults as normal controls. G-CSFr and GM-CSFr on peripheral granulocytes were analyzed by quantitative flow cytometry, and changes in G-CSF and GM-CSF receptor counts were also measured. Plasma concentrations of G-CSF and GM-CSF in CML patients were similar to normal controls (p >0.05). The quantity of G-CSFr on neutrophils was more highly expressed than on other cell types in both groups, and the amount of this receptor in patients with CML was less than in normal controls (p = 0.001). GM-CSFr was expressed in higher concentrations on monocytes than neutrophils, and there was no difference in the amount of GM-CSFr on neutrophils. After incubation with excess G-CSF, the expressed amounts of G-CSFr on neutrophils and monocytes were decreased in both groups. However, G-CSFr on the monocytes was decreased in healthy controls (p = 0.02) with no difference in patients with CML. The quantities of GM-CSFr expression on neutrophils and monocytes after incubation with excess GM-CSF were decreased in both groups. Granulocyte counts in peripheral blood of CML patients were not correlated with the plasma concentrations of G-CSF or GM-CSF, nor with the expression of G-CSFr or GM-CSFr on granulocytes. Granulopoiesis in patients with CML was not mediated by increased plasma CSF concentrations, and there was no difference in the amounts of G-CSFr or GM-CSFr expressed on the granulocytes. This suggests that a structural change may occur on monocytes of CML patients, since the binding capacity of G-CSFr to G-CSF on the monocytes is different from the normal controls.