EOSINOPHIL MAJOR BASIC-PROTEIN INDUCES DEGRANULATION AND IL-8 PRODUCTION BY HUMAN EOSINOPHILS

Eosinophil granule proteins, such as major basic protein (MBP), eosino phil peroxidase (EPO), and eosinophil cationic protein (ECP), possess a wide range of biologic activities including the ability to activate other cells, such as basophils, neutrophils, and platelets. Here we ha ve analyzed the effects of these proteins on eosinophils themselves. M BP and EPO, at concentrations as low as 0.1 mu g/ml, induced eosinophi l degranulation as measured by release of eosinophil-derived neurotoxi n (EDN); in contrast, ECP, at 1 mu g/ml, was inactive. MBP (10 mu g/ml ) and EPO (0.1 mu g/ml) induced EDN release comparable with one of the strongest agonists for eosinophils, secretory IgA. Pretreatment of ce lls with dibutyryl cAMP or cytochalasin B completely abolished the EDN release induced by MBP and EPO, suggesting that the effects of MBP an d EPO are not due to cytotoxic lysis of the cells. Degranulation induc ed by MBP was only partially dependent on calcium, and no elevation of intracellular Ca2+ concentration ([Ca2+](i)) was observed in eosinoph ils stimulated with MBP. MBP stimulated the production, up to eightfol d, of IL-8 by eosinophils in a dose-dependent manner. The MBP-stimulat ed expression of IL-8 mRNA by eosinophils was confirmed by reverse tra nscription-PCR. The MBP-stimulated production of IL-8 was inhibited by actinomycin D, but not by cyclosporin A. Furthermore, MBP and calcium ionophore ionomycin synergistically induced production of leukotriene C-4 from eosinophils. Thus, MBP and EPO may act as autocrine mediator s in the pathogenesis of eosinophil-associated diseases, such as bronc hial asthma.