TUMOR NECROSIS FACTOR-INDUCED INTERLEUKIN-8 EXPRESSION IN CULTURED HUMAN AIRWAY EPITHELIAL-CELLS

The effects of tumor necrosis factor-alpha (TNF-alpha) on interleukin- 8 (IL-8) expression and generation were examined in primary cultured h uman airway epithelial cells (HAEC) and a human lung epithelial cell l ine (A549). TNF-alpha increased IL-8 mRNA and protein expression in HA EC in a concentration- and time-dependent manner and these effects wer e inhibited by dexamethasone (1 mu M). There was no change in the stab ility of IL-8 mRNA, and a nuclear run-on assay confirmed that TNF-alph a increased IL-8 gene transcription. TNF-alpha-induced IL-8 mRNA expre ssion showed a biphasic response in HAEC, with an early increase at 2 h followed by a sustained increase from 8 h, which was abolished by th e addition of cycloheximide, suggesting that the synthesis of another protein was involved. A549 cells also increased IL-8 secretion and mRN A after incubation of TNF-alpha, with inhibition by dexamethasone. How ever, A549 cells showed only an early single peak. A549 cells showed a 250-fold increase in the generation of IL-8 immunoreactivity, whereas primary cultured HAEC showed only a threefold increase, suggesting th at HAEC and A549 cells may respond to TNF-alpha in different ways. The sustained increase in IL-8 secretion due to an increase in gene trans cription in response to TNF-alpha may be an important amplification st ep in inflammatory diseases of the airways.