Promotion of Eosinophil Survival by Human Bronchial Epithelial Cells and its Modulation by Steroids

Accumulation of eosinophils in the bronchial tissue occurs in a variety of inflammatory disorders of the human airway. We asked whether airway epithelial cells released factors that could influence eosinophil survival and thus contribute to accumulation of these cells in the tissues. Using conditioned medium (CM) generated from cultured human bronchial epithelial cells (HBEC), we examined the in vitro survival of eosinophils isolated from human peripheral blood. When cultured in control medium, more than 90% of the eosinophils were dead by day 4. In contrast, culture in HBEC-CM resulted in dose-dependent survival at day 6 of 69 +/- 9.4%, 40.5 +/- 5.9%, and 25 +/- 2% viability with 2, 0.5, and 0.1% HBEC-CM, respectively (n = 4). Granulocyte/macrophage colony-stimulating factor (GM-CSF) was detected in the HBEC-CM by enzyme-linked immunosorbent assay at levels of 22 to 48 pg/ml. Furthermore, preincubation of the HBEC-CM with a neutralizing monoclonal antibody to human GM-CSF completely inhibited this increased survival of eosinophils. Because corticosteroids are potent eosinopenic agents, we also examined the effects of the synthetic steroid budesonide on this system. Budesonide inhibited both spontaneous and interleukin-1 (IL-1)-induced GM-CSF production by cultured HBEC. In addition, preincubation of eosinophils with budesonide caused marked abrogation of the survival induced subsequently with either HBEC-CM or recombinant human GM-CSF. In summary, HBEC can support eosinophil survival via the elaboration of GM-CSF and thus may contribute to the local control of inflammatory cell accumulation. Steroids may modulate this process both by inhibiting cytokine production from HBEC and by a direct effect on eosinophils, preventing their response to cytokines.