Citations

Abstract Basophils infiltrate the skin and other tissues as part of T lymphocyte and/or antibody-mediated immune responses to certain protein antigens, viruses, tumors, and parasites. Although basophils may comprise a significant fraction of leukocytes in these reactions, their precise role has been poorly understood. Guinea pigs expressing acquired immunity to the tick Amblyomma americanum develop basophil- and eosinophil-rich cutaneous inflammatory responses at tick feeding sites, and tick rejection is associated with extensive local basophil degranulation. We report that a specific anti-basophil serum (ABS) eliminate basophils at tick feeding sites and abolished immunity to A. americanum. ABS does not react with eosinophils and did not reduce blood or bone marrow eosinophils; however, ABS-treated animals had diminished eosinophils at tick feeding sites, perhaps because these sites were deficient in basophil-derived eosinophil-chemotactic factors. AES treatment markedly reduced feeding site eosinophils, did not affect basophil levels, and partially impaired tick resistance. Taken together, our experiments suggest cooperation between basophils and eosinophils in the expression of immunity to ticks in guinea pigs.

Abstract Human eosinophils have been reported to express both the mRNA and protein for the high affinity IgE receptor (FcεRI); it is speculated that this receptor plays a role in eosinophil mediator release in allergic diseases. However, questions still remain. How much of the FcεRI protein is actually expressed on the cell surface of the eosinophil? If they are present, are these IgE receptors associated with effector functions of eosinophils? To address these issues, we studied blood eosinophils from patients with ragweed hay fever. A high level of low affinity IgG receptor (FcγRII, CD32), but no expression of FcεRI, was detectable on the eosinophil surface by standard FACS analysis. However, after in vitro sensitization with biotinylated chimeric IgE (cIgE), cell-bound cIgE was detected by PE-conjugated streptavidin. This cIgE binding was partially inhibited by anti-FcεRI mAb, suggesting that eosinophils do express minimal amounts of FcεRI detectable only by a sensitive method. Indeed, FACS analysis of whole blood showed that eosinophils express ∼0.5% of the FcεRI that basophils express. When stimulated with human IgE or anti-human IgE, these eosinophils did not exert effector functions; there was neither production of leukotriene C4 or superoxide anion nor any detectable degranulation response. In contrast, eosinophils possessed membrane-bound human IgG and showed functional responses when stimulated with human IgG or anti-human IgG. Thus, IgG and/or cytokines, such as IL-5, appear to be more important for eosinophil activation in allergic diseases than IgE.

Abstract Eosinophils isolated from normal individuals were cultured in the presence of human rIL-5 (hrIL-5) for up to 14 days, and the effects of this exposure were determined. First, the hrIL-5-cultured eosinophils were activated and degranulated more readily than freshly isolated eosinophils. For example, eosinophils cultured for 7 days with hrIL-5 released 30 and 10% of granule eosinophil-derived neurotoxin (EDN) when exposed to Sepharose 4B beads coupled to secretory IgA and IgG, respectively, whereas freshly isolated eosinophils released only 19 and 4%, respectively, of their EDN in response to the same stimuli. Degranulation of hrIL-5-cultured eosinophils was not augmented by further exposure to hrIL-5, whereas degranulation of freshly isolated cells to secretory IgA and IgG beads was increased by exposure to hrIL-5. Second, eosinophils cultured with hrIL-5 had prolonged viability in vitro. For example, after four days of culture with 50 U/ml of hrIL-5, 86% of eosinophils were viable compared to 12% in medium alone. Third, hrIL-5-cultured eosinophils became hypodense, and electron microscopy showed that they contained granules with core and matrix lucency and with evidence of granule fusion. Fourth, hrIL-5-cultured eosinophils spontaneously lost 30 to 60% of their EDN, eosinophil cationic protein, and eosinophil peroxidase and about 50% of their eosinophil granule major basic protein content compared to freshly isolated eosinophils, and all four of the granule proteins were released into the culture medium. Fifth, detailed studies of eosinophils cultured in hrIL-5 showed that 89 +/- 10% of the starting quantity of EDN could be recovered at 7 days. Whereas 99 +/- 1% of the EDN at day 0 was cell associated, by 7 days 60 +/- 9% was in the cell supernatants. Thus, hrIL-5 activates eosinophils, increases their viability, decreases their density, and their content of granule proteins and causes release of the granule proteins into culture fluids. The striking loss of granule proteins during culture with hrIL-5 may be an important mechanism for deposition of these cationic toxins in various diseases where IL-5 plays a role.

Abstract The human eosinophil granule contains a number of cationic proteins that have been identified and purified to homogeneity, including the major basic protein (MBP), the eosinophil cationic protein (ECP), and the eosinophil-derived neurotoxin (EDN). Because of confusion in the literature regarding the distinctiveness of MBP and ECP, we investigated the immunochemical and physicochemical properties of these purified proteins by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE), by specific double antibody radioimmunoassays (RIA) for MBP and ECP, and by fractionation of acid-solubilized eosinophil granules on Sephadex G-50 columns. Analysis of a mixture of the three purified proteins by SDS-PAGE showed that they migrated as three distinct bands with differing m.w. Comparison by specific RIA for MBP and ECP did not demonstrate any appreciable immunochemical cross-reactivities among the three proteins. Sephadex G-50 column fractions of acid-solubilized eosinophil granules were analyzed by RIA and by SDS-PAGE analysis of individual column fractions. MBP, ECP, and EDN eluted at different volumes from Sephadex G-50 columns as determined by RIA and SDS-PAGE. Soluble extracts of eosinophil granules from patients with the hypereosinophilic syndrome contained between six and 64 times more MBP than ECP on a weight basis. These observations demonstrate that MBP, ECP, and EDN are distinctive cationic proteins of the human eosinophil granule and that eosinophil granules from patients with eosinophilia contain considerably greater quantities of MBP than ECP.

Abstract Eosinophils play a key role in the pathogenesis of asthma and other allergic inflammatory diseases. We have previously shown that treatment of eosinophils with lidocaine preferentially inhibits IL-5-induced survival. This inhibition cannot be overcome by increasing concentrations of IL-5 and is not due to the blocking of Na+ channels by lidocaine. Here we report that one class of K+ channel blockers, the sulfonylureas, inhibits eosinophil survival in a manner similar to lidocaine. The sulfonylurea glyburide inhibits eosinophil survival even at high concentrations of IL-5. In contrast, increasing concentrations of IL-3 or granulocyte-macrophage CSF overcome glyburide inhibition. Glyburide also blocks cytokine-induced eosinophil superoxide production. Similar results were seen with the sulfonylureas tolbutamide and glipizide. Interestingly, the effects of glyburide are not antagonized by the ATP-sensitive K+ channel openers cromakalim, pinacidil, or diazoxide. Although Scatchard analysis of [3H]glyburide binding to eosinophil membranes indicated that the high affinity sulfonylurea receptor (SUR1) is not present on eosinophils, human eosinophils do express mRNA homologous to the sulfonylurea receptor family, in keeping with the presence of a sulfonylurea receptor. Finally, coculture of eosinophils with combinations of glyburide, lidocaine, and dexamethasone resulted in synergistic inhibition of cytokine-mediated eosinophil survival and superoxide production. These results have intriguing clinical implications for the treatment of eosinophil-associated diseases.

Abstract Eosinophils and cytokines active on eosinophils, especially IL-5, are believed to be critically involved in chronic allergic diseases. IL-5 activates eosinophils and enhances their survival in vitro by delaying apoptosis. In this study, we found that lidocaine and six analogues blunt responses of eosinophils to IL-5. Lidocaine and its derivatives inhibit IL-5-mediated eosinophil survival in a concentration-dependent manner (IC50 = 110 μM for 30 pg/ml IL-5). At suboptimal lidocaine concentrations, the eosinophil survival response to IL-5 shifts and more IL-5 is required to maintain survival. The inhibitory effect requires at least 24-h exposure of eosinophils to lidocaine, and the protein kinase C activator, PMA, completely reverses the inhibition. A multiparameter flow-cytometric analysis shows that lidocaine hastens the apoptosis of eosinophils normally delayed by IL-5. Lidocaine does not affect IL-5R expression or IL-5-induced protein tyrosine phosphorylation. Lidocaine also inhibits eosinophil survival mediated by IL-3 or granulocyte-macrophage CSF, although less potently than that mediated by IL-5. Furthermore, lidocaine inhibits eosinophil superoxide production stimulated by IL-5, granulocyte-macrophage CSF, or IL-3, but not that stimulated by platelet-activating factor, immobilized IgG, or PMA. Lidocaine and its derivatives show novel immunomodulatory properties and are able to blunt eosinophil responses to cytokines in addition to their local anesthetic or antiarrhythmic properties. Thus, lidocaine and its derivatives may represent a new class of therapeutic agents to treat patients with allergic diseases.

Abstract Eosinophil activation and subsequent release of inflammatory mediators are implicated in the pathophysiology of allergic diseases. Eosinophils are activated by various classes of secretagogues, such as cytokines (e.g., IL-5), lipid mediators (e.g., platelet-activating factor (PAF)), and Ig (e.g., immobilized IgG). However, do these agonists act directly on eosinophils or indirectly through the generation of intermediate active metabolites? We now report that endogenous PAF produced by activated eosinophils plays a critical role in eosinophil functions. Human eosinophils produced superoxide when stimulated with immobilized IgG, soluble IL-5, or PAF. Pretreating eosinophils with pertussis toxin abolished their responses to these stimuli, suggesting involvement of a metabolite(s) that acts on G proteins. Indeed, PAF was detected in supernatants from eosinophils stimulated with IgG or IL-5. Furthermore, structurally distinct PAF antagonists, including CV6209, hexanolamine PAF, and Y-24180 (israpafant), inhibited IgG- or IL-5-induced superoxide production and degranulation. Previous reports indicated that exogenous PAF stimulates eosinophil eicosanoid production through formation of lipid bodies. We found in this study that IgG or IL-5 also induces lipid body formation and subsequent leukotriene C4 production mediated by endogenous PAF. Finally, inhibition of cytosolic phospholipase A2, one of the key enzymes involved in PAF synthesis, attenuated both PAF production and effector functions of eosinophils. These findings suggest that endogenous PAF plays important roles in eosinophil functional responses to various exogenous stimuli, such as cytokines and Igs. Therefore, inhibition of PAF synthesis or action may be beneficial for the treatment of eosinophilic inflammation.

Abstract An IgG-coated surface, such as found on parasites, is one of the most effective physiologic stimuli for eosinophil activation. Recent evidence suggests that cellular adhesion, especially that through the β 2 integrin, is an important step in cellular activation and accumulation. Therefore, we investigated the role of adhesion molecules in IgG-stimulated eosinophil functions. Cross-linking of eosinophil cytophilic IgG by anti-IgG immobilized to tissue culture plates induced degranulation, whereas soluble anti-IgG did not. Similarly, eosinophils exposed to human IgG immobilized to plates adhered and degranulated; in addition, adherence and subsequent degranulation were inhibited by mAbs to CD18 and CD11b, but not by mAb to CD29, suggesting an important role of β 2 integrin for these responses. Eosinophil degranulation induced by IgG covalently coupled to Sepharose 4B beads was also inhibited by mAb to CD18. Furthermore, fibrinogen, a ligand for CD11b/18, showed synergistic enhancement of IgG-induced degranulation when it was co-immobilized with IgG to plates. A morphologic study showed that eosinophils, stimulated by immobilized IgG, protrude numerous pseudopods; this morphologic change was inhibited by mAb to CD18. This cellular adhesion seems to affect the early signaling events in eosinophils because the production of inositol phosphates was abolished by mAb to CD18. Interestingly, although superoxide production by eosinophils triggered by immobilized IgG was inhibited by mAb to CD18, superoxide production and morphologic change of neutrophils were not. These results suggest that cell adhesion through CD11b/18 is a crucial step for the activation, signaling, and effector function of eosinophils stimulated by IgG.

Abstract Cellular adhesion plays an important role in the recruitment and activation of eosinophils. Here, we investigated whether extracellular matrix (ECM) proteins modify effector functions of activated human eosinophils. We coated 96-well plates with laminin or fibronectin and blocked nonspecific protein-binding sites with human serum albumin (HSA). When eosinophils were stimulated with platelet-activating factor (PAF) and incubated in these ECM-coated wells, the eosinophils adhered using both β 1- and β 2-integrins. Degranulation of eosinophils adherent to laminin- and fibronectin-coated wells was reduced about 50% compared with cells adherent to uncoated, HSA-blocked wells. Furthermore, these inhibitory effects of laminin and fibronectin were concentration-dependent and secretagogue-specific, that is, degranulation induced by C5a and IL-5 was inhibited while degranulation induced by secretory IgA and PMA was not inhibited. Plasma fibronectin, type I collagen and type IV collagen also inhibited PAF- and C5a-induced eosinophil degranulation, whereas fibrinogen did not. By microscopy, PAF-stimulated eosinophils, adhering to uncoated HSA-blocked wells, appeared elongated with many pseudopods. In contrast, eosinophils adhering to laminin-coated wells appeared oval with few pseudopods. Furthermore, when cells were incubated in laminin-coated wells, PAF-stimulated production of a second messenger, inositol phosphate, was markedly reduced. These findings suggest that ECM protein, such as laminin and fibronectin, attenuate both activation and degranulation of eosinophils and also influence their morphology after stimulation by physiologic secretagogues. Thus, ECM proteins may regulate activation of eosinophils, as they traverse between the peripheral blood and their targets.

Abstract To study the capacity and regulation of cytokine production by normal peripheral blood eosinophils, we isolated eosinophils from healthy individuals and stimulated them with immobilized Ig or TNF-α, with or without exogenous IL-5. By reverse transcription-PCR, uncultured, freshly isolated eosinophils constitutively expressed mRNA for IL-4, IL-10, and TGF-β1. Eosinophils stimulated by immobilized secretory IgA, immobilized IgA, immobilized IgG, or TNF-α for 3 h expressed mRNA encoding IL-3, IL-4, IL-8, IL-10, granulocyte-macrophage CSF, TNF-α, TGF-β, and RANTES. The mRNA for IL-2, IL-5, or IFN-γ was not detected. IL-4 and IL-10 protein, but not IL-8, were measurable in lysates of fresh eosinophils or eosinophils cultured with medium alone for 24 h. Eosinophils incubated with immobilized Ig or TNF-α released IL-8 protein into the supernatants. In contrast, IL-4 and IL-10 proteins were not detectable. Soluble secretory IgA immune complexes also induced degranulation, as measured by eosinophil-derived neurotoxin, and IL-8 release, but not IL-4 or IL-10 release, from eosinophils. Release of IL-8 protein and storage of IL-4 and IL-10 proteins were enhanced by exogenous IL-5 and inhibited by a transcription inhibitor, actinomycin D. Degranulation of stored granule proteins was not affected by actinomycin D. Therefore, normal peripheral blood eosinophils can transcribe and synthesize several cytokines, including IL-4, IL-8, and IL-10; some are stored, and some are released. These cytokines may play important roles in modulating immune responses in diseases associated with eosinophils.