Eosinophil activation by eotaxin--eotaxin primes the production of reactive oxygen species from eosinophils

The CC chemokine eotaxin has been shown to possess selective chemotactic activity for eosinophils, the major effector cells in allergic inflammation. Reactive oxygen species (ROS) from eosinophils may damage cells or tissue, such as the mucosal epithelium. In this study, we examined the effect of eotaxin on ROS from eosinophils and compared its activity with RANTES and interleukin (IL)-5. Moreover, we examined the signal transduction of eotaxin and the effect of dexamethasone on ROS from eosinophils.

Eosinophils were isolated by modified CD16-negative selection. ROS in luminol-dependent or lucigenin-dependent chemiluminescence reaction were examined. Calcium ionophore A23187 was added to the mixture of eosinophils with luminol or lucigenin, and then ROS were determined.

Eotaxin primed the production of ROS in a dose-dependent manner. ROS from untreated eosinophils evoked with calcium ionophore A23187 in luminol-dependent chemiluminescence gave a maximal value of 4957+/-1035 intensity counts (IC) (mean+/-SE, n=7) and an integral value of 15.75+/-3.14 IC (x10(-4)), while eosinophils that were treated with eotaxin gave maximal values of 11 142+/-2300 IC (10 nM) and 29165+/-3718 IC (100 nM) and integral values of 41.07+5.44 IC (x10(-4)) (10 nM) and 152.90+/-22.38 IC (x10(-4))(100 nM). Moreover, eotaxin was less effective as a priming agent with lucigenin-sensitive pathways than luminol-sensitive pathways. Among several kinds of eosinophils activating cytokines and chemokines, the priming effect of eotaxin on RO5 was the most potent. Eotaxin-primed ROS were inhibited by pertussis toxin, which ADP-ribolysates G proteins; wortmannin, a phosphatidylinositol-3-kinase inhibitor; and genistein, a tyrosine kinase inhibitor, suggesting the involvement of pertussis toxin-sensitive G proteins, phosphatidylinositol-3-kinase, and tyrosine kinase in the signal transduction of eotaxin. Moreover, dexamethasone inhibited ROS from not only untreated eosinophils but also eosinophils treated with eotaxin.

Eotaxin may play an important role in the pathogenesis of allergic inflammation through eosinophil activation by priming of eosinophil oxidative metabolism, as well as by involvement in selective eosinophil chemotaxis.