Generation of oxygen free radicals from blood eosinophils from asthma patients after stimulation with PAF or phorbol ester

Abstract

Eosinophils (EOS) may play an important role in the pathophysiology of bronchial asthma because they can release oxygen free radicals and several basic proteins which are cytotoxic to bronchial epithelium. We have studied the response of EOS isolated from the blood of atopic subjects with symptoms of asthma (AS, n = 7) or rhinitis (AR, n = 4) or without symptoms (AA, n = 5) and of subjects with the hypereosinophilic syndrome (HES, n = 5). EOS were separated using metrizamide density gradients and activated in vitro with platelet-activating factor (PAF, 100 nM) or phorbol 12-myristate-13-acetate (PMA, 100 nM). Oxygen free radical generation was assessed by a lucigenin-enhanced chemiluminescence (CL) assay. EOS purity was 83 ± 17% (mean ± SEM) with greater than 95% viability. Background CL responses of EOS from HES were significantly higher than those from AA (p < 0.01) and AR (p < 0.05). Normodense EOS from AS (PAF-induced CL = 90 ± 27 mV) were more responsive to PAF than were those from AR (17 ± 13 mV, p < 0.01) and from AA (23 ± 14 mV, p < 0.01). Similar results were obtained with PMA. Hypodense EOS from HES subjects were as responsive as normodense EOS from AS to PMA and PAF. Thus, EOS from AS have an enhanced potential for activation, particularly by PAF; this may represent an important mechanism for the perpetuation of the inflammatory response in asthma, since EOS can also release PAF.