Eosinophils are one of the major effector cells in asthma, and controlling the number and survival of eosinophils via induction of apoptosis might attenuate the severity of asthma. We have previously reported that human eosinophils express surface CD30 and that CD30 activation induces eosinophil apoptosis. In this study we investigated the effect of IL-5 and FBS on CD30 protein and mRNA expressions, as well as CD30 activation.

Eosinophils were isolated from blood collected from allergic and allergic asthmatic donors, and then incubated for 24 hrs with 15 ng/ml IL-5 and 10% FBS or only 1% FBS. Apoptosis and CD30 surface expressions were measured by flow cytometry, and mRNA expression was measured by RT-PCR. Eosinophils were also incubated with CD30 antibodies to determine its effect on eosinophil apoptosis in the presence or absence of IL-5 and FBS.

Eosinophils incubated with only 1%FBS displayed significantly higher surface CD30 expression (27.2 ± 5.2%) than in eosinophils incubated with IL-5 and FBS (14.6 ± 5.4%). Interestingly however, CD30 mRNA expression was significantly higher in eosinophils incubated with IL-5 and FBS (3-fold vs. 2-fold increase for 1%FBS as compared to fresh cells). Both CD30 surface and mRNA expressions were minimal in freshly isolated eosinophils. IL-5 and FBS failed to protect eosinophils from CD30-induced apoptosis.

Our observation indicates a possible role for IL-5 and FBS in the post-transcriptional events of CD30 expression in eosinophils. This revelation could explain a mechanism by which human eosinophils evade death and display extended survival in the airways of asthmatic individuals.