Bronchial Epithelial Cell-derived Cytokines (G-CSF and GM-CSF Promote the Survical of Peripheral Blood Neutrophils In Vitro

Abstract

Neutrophil accumulation in the respiratory tract occurs in a variety of inflammatory disorders, particularly those associated with cigarette smoking. We examined whether bronchial epithelial cells could contribute to this accumulation through the production of factors that increased the survival of neutrophils. Pure primary cultures of human bronchial epithelial cells (HBEC) were used to generate conditioned medium (CM), and the effect of this CM on the survival of neutrophils in vitro was examined. When neutrophils were cultured in control medium, survival was 8.7 ± 1.7% at 72 h. In contrast, culture of neutrophils in CM resulted in a dose-dependent increase in survival: 22.6 ± 5.5, 43.6 ± 4.2, and 64 ± 3.8% in 1, 10, and 50% CM respectively (mean ± SEM; P < 0.05). As evidenced by the examination of neutrophil DNA, this prolongation of survival was associated with suppression of apoptosis. Cytokines with known actions on neutrophil biology identified in the CM included granulocyte colony-stimulating factor (G-CSF), granulocyte/macrophage colony-stimulating factor (GM-CSF), and interleukin-8. Through the use of specific neutralizing antibodies, G-CSF and GM-CSF were identified as promoting neutrophil survival. Neutrophil survival was prolonged in the presence of either recombinant human (rh) G-CSF or rhGM-CSF alone in a dose-dependent fashion. In contrast to the response of eosinophils to HBEC-CM, steroid treatment did not prevent the increase in neutrophil survival induced by HBEC-CM. In summary, we show that bronchial epithelial cells markedly increase the survival of human neutrophils in vitro via the release of G-CSF and GM-CSF. In this way, HBEC cells might contribute to the accumulation of neutrophils during chronic inflammation in vivo.