Abu-Ghazaleh, R I

Abstract Stimulation of human normodense eosinophils with immobilized secretory IgA (sIgA) or IgG, or with the soluble stimulus, FMLP, triggers the exocytotic release of the granule protein, eosinophil-derived neurotoxin (EDN). In this report, we demonstrate that these stimuli also provoke an increase in phospholipase C-mediated phosphoinositide breakdown in eosinophils. Pretreatment of eosinophils with pertussis toxin (PTX) for 2 h irreversibly abolished the increases in phospholipase C activity and EDN release induced by immobilized sIgA or FMLP. In contrast, PTX treatment only transiently inhibited eosinophil activation induced by immobilized IgG. Maximal inhibition of IgG-stimulated phosphoinositide hydrolysis and EDN release occurred after 2 h of PTX pretreatment with PTX, followed by a gradual recovery of cellular responsiveness to immobilized IgG as the duration of PTX pretreatment was extended to 16 h. Activated PTX catalyzed the in vitro ADP-ribosylation of 41- and 44-kDa proteins in eosinophil membranes. A 2-h pretreatment of intact cells with PTX markedly reduced the pools of unmodified 41- and 44-kDa substrates available for subsequent ADP-ribosylation in vitro, suggesting that both proteins were substrates for PTX in intact eosinophils. Continuous exposure of eosinophils to PTX for times ranging from 2 to 15 h resulted in the gradual reappearance of unmodified 44-kDa protein, whereas the levels of unmodified 41-kDa protein were persistently reduced in PTX-treated cells. The time course of the decline and reappearance of unmodified 44-kDa substrate in PTX-treated eosinophils closely paralleled the changes in the responsiveness of these cells to immobilized IgG. These results suggest that the receptors for sIgA, FMLP, or IgG transduce activating signals for eosinophil degranulation through differential coupling to at least two PTX-sensitive G proteins.

Abstract Eosinophil granule proteins, such as major basic protein (MBP), eosinophil 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 have analyzed the effects of these proteins on eosinophils themselves. MBP and EPO, at concentrations as low as 0.1 micrograms/ml, induced eosinophil degranulation as measured by release of eosinophil-derived neurotoxin (EDN); in contrast, ECP, at 1 micrograms/ml, was inactive. MBP (10 micrograms/ml) and EPO (0.1 micrograms/ml) induced EDN release comparable with one of the strongest agonists for eosinophils, secretory IgA. Pretreatment of cells with dibutyryl cAMP or cytochalasin B completely abolished the EDN release induced by MBP and EPO, suggesting that the effects of MBP and EPO are not due to cytotoxic lysis of the cells. Degranulation induced by MBP was only partially dependent on calcium, and no elevation of intracellular Ca2+ concentration ([Ca2+]i) was observed in eosinophils stimulated with MBP. MBP stimulated the production, up to eightfold, of IL-8 by eosinophils in a dose-dependent manner. The MBP-stimulated expression of IL-8 mRNA by eosinophils was confirmed by reverse transcription-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 C4 from eosinophils. Thus, MBP and EPO may act as autocrine mediators in the pathogenesis of eosinophil-associated diseases, such as bronchial asthma.

Abstract Eosinophils play an important role as effector cells in allergic, parasitic, and other conditions. The mechanism(s) by which eosinophils mediate their effector functions was studied by incubation of human normodense eosinophils with Sepharose beads coupled to various Ig isotypes as targets. Controls included eosinophils incubated alone or incubated with uncoated beads, human serum albumin-, or OVA-coated beads. An eosinophil granule protein, the eosinophil-derived neurotoxin (EDN), was measured as an indicator of eosinophil degranulation. Eosinophils released eosinophil-derived neurotoxin when incubated with Sepharose beads coupled to Ig of the IgG or IgA isotypes, as well as IgA-Fc fragments. Mixtures of IgG and IgA on beads did not act synergistically. Secretory IgA (sIgA) provided the most potent signal for eosinophil degranulation and was two to three times more potent than IgG. Furthermore, 2 to 17% of the normodense eosinophils bound to IgG- or IgA-coated beads, whereas 24 to 27% of the eosinophils bound to sIgA-coated beads. Thus, sIgA may be the principal Ig mediating eosinophil effector function at mucosal surfaces in helminth infections and hypersensitivity diseases, especially bronchial asthma.

Abstract Eosinophils contain four principal cationic proteins, major basic protein (MBP), eosinophil-derived neurotoxin (EDN), eosinophil cationic protein (ECP), and eosinophil peroxidase (EPO). To determine the quantities of these proteins in granulocytes and whether they are specific to eosinophils, their concentrations in ly- sates of human granulocytes were measured using specific radioimmunoassays. The effect of different methods for eosinophil lysis on the recovery of the proteins was also studied. Maximal recovery occurred at pH 2 for MBP and pH 5.6 for the other granule proteins. The proteins cosedimented with eosinophils and their concentrations (X ± SEM) in ng/106 eosinophils (and in nM/106 eosinophils) were: MBP, 8,982 ± 611 (641.6); EDN, 3,283 ± 116 (178.4); ECP, 5,269 ± 283 (250.9); and EPO, 12,174 ± 859 (171.5). Basophils from a normal person contained (in ng/106 cells) MBP, 2,374; EDN, 214; ECP, 77; and EPO, 17. Highly purified neutrophils contained (in ng/106 cells) MBP, 3 ± 0.5; EDN, 72 ± 9; and ECP, 50 ± 12. Therefore we conclude that these proteins are mainly expressed in eosinophils, but that certain ones are present in basophils and neutrophils.