Elevated serum granulocyte colony-stimulating factor levels in patients with active phase of sweet syndrome and patients with active Behcet disease - Implication in neutrophil apoptosis dysfunction

Background: Sweet syndrome (SS), an acute inflammatory disease, has clinical and laboratory features similar to those of Behcet disease (BD). Serum levels of granulocyte colony-stimulating factor (G-CSF) are elevated in patients with SS, and exogenous administration of G-CSF has repeatedly been implicated in the causation of SS. Granulocyte colony-stimulating factor is a hematopoietic growth factor that regulates the production and differentiation of neutrophils. Objectives: To clarify the role of elevated serum G-CSF levels in patients with active SS and active BD compared with those with inactive SS or BD and healthy controls. To then analyze neutrophil apoptosis in the active state of SS and BD; and to also investigate the influence of autologous serum on neutrophil apoptosis. Methods: Serum G-CSF was examined in 5 patients with active SS, 7 with inactive SS, 7 with active BD, 9 with inactive BD, and 5 healthy controls by means of an enzyme immunoassay kit. We measured apoptotic cells in the neutrophil fraction of peripheral blood collections in patients with active diseases and controls by means of flow cytometry. Results: Serum G-CSF level was significantly higher in patients with active SS than in those with inactive SS. The difference in serum G-CSF levels among patients with active and inactive BD was also significant. Serum G-CSF level was significantly higher in patients with active SS than in those with active BD. Neutrophil apoptosis was significantly higher in patients with active SS than healthy controls. This increased apoptosis rate was also seen in patients with active BD. The increased rate of neutrophil apoptosis was significantly suppressed when the neutrophils were cultured for 18 hours in the presence of autologous active SS serum. Similarly, neutrophil apoptosis was suppressed in the presence of autologous serum in patients with active BD, but not significantly so. Conclusions: These findings indicate that increased production of G-CSF in patients with SS and BD may play an important role in the manifestation of these disorders. Given the suppression of neutrophil apoptosis in the active state in the presence of the influence of autologous serum, which includes elevated G-CSF level, we propose that serum G-CSF plays a significant role in the suppression of neutrophil apoptosis. Furthermore, G-CSF-induced suppression of neutrophil apoptosis appears to be deeply involved in the pathogenesis of SS and BD.