IL-5 priming of the PMA-induced oxidative metabolism of human eosinophils from allergic and normal subjects during a pollen season

Aim To study the effect of IL‐5 priming on the PMA‐induced oxidative metabolism of blood eosinophils from allergic patients and healthy controls, during pollen exposure. Methods Twenty birch pollen allergic patients with seasonal symptoms of rhinitis or rhinitis plus asthma were studied during the birch pollen season of Sweden. Eosinophils were purified to > 95% by Percoll gradients followed by the MACS system. Oxidative metabolism was measured by a lucigenin enhanced chemiluminescence (CL) assay. Eosinophils were primed with IL‐5 and subsequently stimulated with PMA. The signal transduction mechanisms of IL‐5 priming were studied using the MEK inhibitor PD 98059, the PkC inhibitors Staurosporine, Ro 318220, Gö 6983 and the PI₃kinase inhibitor Wortmannin. Results During the season, the eosinophils from the allergic patients showed a reduced t_½rise compared to the non‐allergic controls (P = 0.019) after stimulation. IL‐5 reduced the total PMA CL response both in control and patients’ cells (P = 0.012 and 0.0054 resp.), whereas it primed it in terms of the t_½rise of the curves, in both groups (P = 0.012 and 0.0015 resp.). The PMA‐induced CL reactions were inhibited by PD 98059, all PkC‐inhibitors and Wortmannin. IL‐5 priming counteracted only the MEK inhibition significantly. Conclusions Blood eosinophils from allergic patients are primed in vivo, as compared to eosinophils from non‐allergic controls, during a pollen season. Interleukin‐5 primes equally the PMA‐induced oxidative metabolism of human eosinophils from healthy or allergic subjects. The mechanism of IL‐5 priming after PMA stimulation of oxygen radical production is MEK independent.