Tumour Necrosis Factor-α Regulates Human Eosinophil Apoptosis via Ligation of TNF-Receptor 1 and Balance between NF-κB and AP-1

Eosinophils play a central role in asthma. The present study was performed to investigate the effect of tumour necrosis factor-alpha (TNF-alpha) on longevity of isolated human eosinophils. In contrast to Fas, TNF-alpha inhibited eosinophil apoptosis as evidenced by a combination of flow cytometry, DNA fragmentation assay and morphological analyses. The effect of TNF-alpha on eosinophil apoptosis was reversed by a TNF-alpha neutralising antibody. The anti-alpha poptotic effect of TNF-alpha was not due to autocrine release of known survival-prolonging cytokines interleukins 3 and 5 or granulocyte-macrophage-colony-stimulating factor as their neutralisation did not affect the effect of TNF-alpha. The anti-alpha poptotic signal was mediated mainly by the TNF-receptor 1. TNF-alpha induced phosphorylation and degradation of I kappa B and an increase in NF-kappa B DNA-binding activity. The survival-prolonging effect of TNF-alpha was reversed by inhibitors of NF-kappa B pyrrolidinedithiocarbamate and gliotoxin and by an inhibitor of IkB kinase, BMS-345541. TNF-alpha induced also an increase in AP-1 DNA-binding activity and the antiapoptotic effect of TNF-alpha was potentiated by inhibitors of AP-1, SR 11302 and tanshinone IIA and by an inhibitor of c-jun-N-terminal kinase, SP600125, which is an upstream kinase activating AP-1. Our results thus suggest that TNF-alpha delays human eosinophil apoptosis via TNF-receptor 1 and the resulting changes in longevity depend on yin-yang balance between activation of NF-kappa B and AP-1.