The mechanisms of serum-treated zymosan (STZ)-induced oxidative metabolismby human eosinophils and the effects of IL-5 priming

Background: The aim of this work was to study the mechanisms of action of I L-5 on the subsequent stimulation of the oxidative metabolism of blood eosi nophils by serum-treated zymosan (STZ), in terms of signal transduction cha racteristics, and by comparing the response of cells from healthy and aller gic subjects during environmental exposure to birch pollen. Methods: Eosinophils from healthy controls and allergic patients were purif ied to over 95% by Percoll gradients and the MACS system. Oxidative metabol ism was measured by a lucigenin-enhanced chemiluminescence (CL) assay. Eosi nophils were primed with IL-5 and subsequently stimulated with STZ. The sig nal transduction mechanisms of IL-5 priming were studied with the MEK inhib itor PD 98059,the PkC inhibitors staurosporine and Ro 318220, and the PI3 k inase inhibitor wortmannin. Results: IL-5 increased the maximum radical production (P=0.0079) and reduc ed the t(1/2) rise (0.000018) of the CL reactions. The t(1/2) rise was PkC dependent and MEK independent, while the maximum radical production was PkC , MEK, and PI3 kinase dependent. During the pollen season, IL-5 reduced the total STZ-induced CL response in the patients' cells (P=0.016), but not in the control cells, whereas it primed the response to STZ of both cell popu lations in terms of the t(1/2) rise (P=0.012 and 0.00066, respectively). Conclusions: STZ-induced oxidative metabolism consists of different stages. The initial stage (t(1/2) rises of the curves) is PkC dependent and MEK in dependent, while the end stage (maximum radical production) is PkC, MEK, an d PI3 kinase dependent. IL-5 shortened the initial stage, and increased the end stage. During allergen exposure, however, the end stage was reduced by IL-5. This could be due to increased amounts of hypodense eosinophils and/ or some abnormality in cell responses.