IL-5 increases expression of 5-lipoxygenase-activating protein and translocates 5-lipoxygenase to the nucleus in human blood eosinophils

Cysteinyl-leukotrienes are potent bronchoconstrictor mediators synthesized by the 5-lipoxygenase (5-LO) pathway. Eosinophilopoietic cytokines such as IL-5 enhance cysteinyl-leukotriene synthesis in eosinophils in vitro, mimic king changes in eosinophils from asthmatic patients, but the mechanism is u nknown. We hypothesized that IL-5 induces the expression of 5-LO and/or its activating protein FLAP in eosinophils, and that this might be modulated b y anti-inflammatory corticosteroids. Compared with control cultures, IL-5 i ncreased the proportion of normal blood eosinophils immunostaining for FLAP (65 +/- 4 vs 34 +/- 4%; p < 0.0001), enhanced immunoblot levels of FLAP by 51 +/- 14% (p = 0.03), and quadrupled iouophore-stimulated leukotriene C-4 synthesis from 5.7 to 20.8 ng/10(6) cells (p < 0.02), IL-5 effects persist ed for 24 h and were abolished by cycloheximide and actinomycin D, The prop ortion of FLAP(+) eosinophils was also increased by dexamethasone (p < 0.00 01), Neither IL-5 nor dexamethasone altered 5-LO expression, but IL-5 signi ficantly increased 5-LO immunofluorescence localizing to eosinophil nuclei. Compared with normal subjects, allergic asthmatic patients had a greater p roportion of circulating FLAP(+) eosinophils (46 +/- 6 vs 27 +/- 3%;p < 0.0 3) and a smaller IL-5-induced increase in FLAP immunoreactivity (p < 0.05), Thus, IL-5 increases FLAP expression and translocates 5-LO to the nucleus in normal blood eosinophils in vitro. This is associated with an enhanced c apacity for cysteinyl-leukotriene synthesis and mimics in vivo increases in FLAP expression in eosinophils from allergic asthmatics.