Delayed eosinophil apoptosis in asthma

Background: Eosinophilic inflammation of the airways is a key characteristi c of asthma, A defect in apoptosis might contribute to the chronic tissue e osinophilia associated with asthma. Objective: Our purpose was to examine whether the rate of apoptosis differs between peripheral blood eosinophils from asthmatic patients and healthy v olunteers, Methods: Peripheral blood was obtained from volunteers with asth ma and from control volunteers. Eosinophils were isolated by CD16-negative selection to >99% purity and were cultured for 48 hours, The number of apop totic eosinophils in the culture was assessed by flow cytometric analysis o f relative DNA content in propidium iodide-stained cells. Eosinophil apopto sis is expressed as apoptosis index (number of apoptotic cells/total number of cells). Results: Eosinophils From asthmatic patients not taking steroid medication survived longer (apoptosis index 0.25) than those of healthy control subjec ts (apoptosis index 0.40, P < .05). In contrast, the rate of apoptosis in e osinophils from patients concurrently taking steroids (apoptosis index 0.46 ) is higher than that of those not using steroids (P < .01) and not differe nt from that of healthy subjects. To assess whether endogenous IL-3, IL-5, and CM-CSF production contributes to the delayed eosinophil apoptosis, the effects of the corresponding neutralizing antibodies were studied on eosino phil longevity. Neutralization of GM-CSF, but not of IL-3 or IL-5, increase d slightly but significantly (P < .01) the rate of apoptosis in eosinophils obtained from patients with asthma, To assess whether beta(2)-agonist medi cation could contribute to the observed differences, we determined the in v itro effects of albuterol, Fenoterol, and salmeterol on eosinophil apoptosi s, All beta(2)-agonists inhibited eosinophil apoptosis by 12% to 19%, A pos sibility existed that a prior in vivo exposure to IL-5, GM-CSF, or beta(2)- agonists would explain the observed difference. To study this, eosinophils were incubated with GM-CSF, IL-5, and albuterol for 2 to 3 hours, followed by washout of the added compounds, and were subsequently cultured for 48 ho urs. However, an exposure to GM-CSF (7 pmol/L) or IL-5 (10 pmol/L) for 15 t o 180 minutes was not a sufficient signal to prevent eosinophil apoptosis, In contrast, exposure to albuterol (100 nmol/L) for 120 minutes was suffici ent to induce a significant (P < .05) decrease in eosinophil apoptosis, Conclusions: The results suggest that eosinophil apoptosis is delayed in as thma, This delay may be partly explained by production of GM-CSF, The in vi tro effects of beta(2)-agonists suggest that beta(2)-agonist use might cont ribute to the prolonged eosinophil survival through inhibition of apoptosis and thus may worsen eosinophilia in asthmatic patients, Use of inhaled glu cocorticoids seems to totally reverse the delayed eosinophil apoptosis in a sthma.