IL-5 but not interferon-gamma (IFN-gamma) inhibits eosinophil apoptosis by up-regulation of bcl-2 expression

In order to determine regulatory mechanisms of eosinophil Apoptosis, we examined the effect of recombinant IL-5 and interferon-gamma (IFN-gamma) on eosinophil Apoptosis and Bcl-2 expression. rhIL-5 (2.5 ng/ml) significantly inhibited eosinophil Apoptosis in 96 h in vitro culture compared with medium only-cultured eosinophils (89.4 +/- 3.6% versus 31.3 +/- 12.2% (mean +/- s.d.); n = 7, P < 0.05). Further, rhIL-5 significantly increased Bcl-2 protein and mRNA expression on cultured eosinophils. A phosphorothioate antisense oligonucleotide targeted at the ATG translation initiation codon of Bcl-2 (10(-5) M) could significantly block the supportive effect of rhIL-5 (0.25 ng/ml) for eosinophil survival compared with sense cDNA of Bcl-2 on 96 h culture (inhibition rate 28.01 +/- 4.56% versus 0.07 +/- 1.73%; n = 4, P < 0.05). In contrast, rhIFN-gamma (100 U/ml) significantly inhibited eosinophil Apoptosis on 96 h in vitro culture (72.7 +/- 10.5%; n = 7, P < 0.05), but did not significantly up-regulate Bcl-2 protein and mRNA. These results indicate that IL-5 has inhibitory effects on eosinophil Apoptosis by regulation of Bcl-2 expression.