Aspirin activation of eosinophils and mast cells: implications in the pathogenesis of aspirin-exacerbated respiratory disease.

Reactions to aspirin and nonsteroidal anti-inflammatory drugs in patients with aspirin-exacerbated respiratory disease (AERD) are triggered when constraints upon activated eosinophils, normally supplied by PGE2, are removed secondary to cyclooxygenase-1 inhibition. However, the mechanism driving the concomitant cellular activation is unknown. We investigated the capacity of aspirin itself to provide this activation signal. Eosinophils were enriched from peripheral blood samples and activated with lysine ASA (LysASA). Parallel samples were stimulated with related nonsteroidal anti-inflammatory drugs. Activation was evaluated as Ca2+ flux, secretion of cysteinyl leukotrienes (CysLT), and eosinophil-derived neurotoxin (EDN) release. CD34+ progenitor-derived mast cells were also used to test the influence of aspirin on human mast cells with measurements of Ca2+ flux and PGD2 release. LysASA induced Ca2+ fluxes and EDN release, but not CysLT secretion from circulating eosinophils. There was no difference in the sensitivity or extent of activation between AERD and control subjects, and sodium salicylate was without effect. Like eosinophils, aspirin was able to activate human mast cells directly through Ca2+ flux and PGD2 release. AERD is associated with eosinophils maturing locally in a high IFN-γ milieu. As such, in additional studies, eosinophil progenitors were differentiated in the presence of IFN-γ prior to activation with aspirin. Eosinophils matured in the presence of IFN-γ displayed robust secretion of both EDN and CysLTs. These studies identify aspirin as the trigger of eosinophil and mast cell activation in AERD, acting in synergy with its ability to release cells from the anti-inflammatory constraints of PGE2.

Human airway eosinophils respond to chemoattractants with greater eosinophil-derived neurotoxin release, adherence to fibronectin, and activation of the Ras-ERK pathway when compared with blood eosinophils.

Human blood eosinophils exposed ex vivo to hematopoietic cytokines (e.g., IL-5 or GM-CSF) subsequently display enhanced responsiveness to numerous chemoattractants, such as chemokines, platelet-activating factor, or FMLP, through a process known as priming. Airway eosinophils, obtained by bronchoalveolar lavage after segmental Ag challenge, also exhibit enhanced responsiveness to selected chemoattractants, suggesting that they are primed during cell trafficking from the blood to the airway. Earlier work has shown that chemoattractants stimulate greater activation of ERK1 and ERK2 following IL-5 priming in vitro, thus revealing that ERK1/ERK2 activity can be a molecular readout of priming under these circumstances. Because few studies have examined the intracellular mechanisms regulating priming as it relates to human airway eosinophils, we evaluated the responsiveness of blood and airway eosinophils to chemoattractants (FMLP, platelet-activating factor, CCL11, CCL5, CXCL8) with respect to degranulation, adherence to fibronectin, or Ras-ERK signaling cascade activation. When compared with blood eosinophils, airway eosinophils exhibited greater FMLP-stimulated eosinophil-derived neurotoxin release as well as augmented FMLP- and CCL11-stimulated adherence to fibronectin. In airway eosinophils, FMLP, CCL11, and CCL5 stimulated greater activation of Ras or ERK1/ERK2 when compared with baseline. Ras activation by FMLP in blood eosinophils was also enhanced following IL-5 priming. These studies are consistent with a model of in vivo priming of eosinophils by IL-5 or related cytokines following allergen challenge, and further demonstrate the key role of priming in the chemoattractant-stimulated responses of eosinophils. These data also demonstrate the importance of the Ras-ERK signaling pathway in the regulation of eosinophil responses to chemoattractants in the airway. Human airway eosinophils respond to several chemoattractants with increased activation of the Ras-ERK cascade, eosinophil-derived neurotoxin release, and adherence to fibronectin relative to blood eosinophils.

IL-5 receptor α levels in patients with marked eosinophilia or mastocytosis.

BACKGROUND: IL-5 plays a central role in the development and maintenance of eosinophilia (EO) and eosinophil activation in a wide variety of eosinophilic disorders. Although IL-5, IL-3, and GM-CSF can modulate the expression of IL-5 receptor α (IL-5Rα) on eosinophils in vitro, little is known about soluble and surface IL-5Rα levels in vivo. OBJECTIVE: To assess soluble and surface IL-5Rα levels in patients with EO and/or mastocytosis. METHODS: Surface IL-5Rα expression was assessed by flow cytometry in blood and/or bone marrow from subjects with EO (n = 39) and systemic mastocytosis (n = 8) and from normal volunteers (n = 28). Soluble IL-5Rα (sIL-5Rα) level was measured in a cohort of 177 untreated subjects and correlated with EO, eosinophil activation, and serum tryptase and cytokine levels. RESULTS: IL-5Rα expression on eosinophils inversely correlated with EO (r = -0.48; P < .0001), whereas serum levels of sIL-5Rα increased with the eosinophil count (r = 0.56; P < .0001) and serum IL-5 (r = 0.40; P < .0001) and IL-13 (r = 0.29; P = .004) levels. Of interest, sIL-5Rα level was significantly elevated in patients with systemic mastocytosis without EO. Although sIL-5Rα levels correlated with serum tryptase levels in these patients, eosinophil activation, assessed by CD69 expression on eosinophils and serum eosinophil-derived neurotoxin levels, was increased compared with that in normal subjects. CONCLUSIONS: These data are consistent with an in vivo IL-5Rα regulatory pathway in human eosinophils similar to that described in vitro and involving a balance between soluble and surface receptor levels. This may have implications with respect to the use of novel therapeutic agents targeting IL-5 and its receptor in patients with EO and/or mastocytosis.

Antigen-specific IgG and IgA, but not IgE, activate the effector functions of eosinophils in the presence of antigen.

BACKGROUND: Activated eosinophils are thought to play an important role in allergic inflammation. Prior reports suggest that eosinophils have receptors recognizing IgA, IgG and IgE; however, little is known regarding the direct effects of antigens and antigen-specific immunoglobulins on the functions of eosinophils. METHODS: To investigate eosinophil activation by antigens mediated by the various antigen-specific immunoglobulins, we used dansyl-conjugated bovine serum albumin (DNS-BSA) and recombinant dansyl-specific antibodies (human IgG 1-4, IgA and IgE). Eosinophils from healthy donors were incubated in the wells coated with dansyl-specific immunoglobulins with or without DNS-BSA. Eosinophil activation was monitored by superoxide production and eosinophil-derived neurotoxin (EDN) release. RESULTS: Superoxide production and EDN release by eosinophils were induced by the dansyl-specific reaction via all IgG subclasses (IgG 1-4) and IgA in the presence of DNS-BSA; the responses were not observed in the absence of antigen, DNS-BSA. The immune complexes (ICs) of DNS-BSA and dansyl-specific IgE did not induce these responses. Furthermore, IgE ICs did not enhance eosinophil activation stimulated with various immunoglobulins, IL-5 or platelet-activating factor. CONCLUSION: These data suggest that ICs of antigens and antigen-specific IgGs and IgA, but not IgE, in inflamed tissues may activate eosinophils and play an important role in allergic inflammation.

Biology of the eosinophil.

In this review, we aim to put in perspective the biology of a multifunctional leukocyte, the eosinophil, by placing it in the context of innate and adaptive immune responses. Eosinophils have a unique contribution in initiating inflammatory and adaptive responses, due to their bidirectional interactions with dendritic cells and T cells, as well as their large panel of secreted cytokines and soluble mediators. The mechanisms and consequences of eosinophil responses in experimental inflammatory models and human diseases are discussed.

Recognition of fungal protease activities induces cellular activation and eosinophil-derived neurotoxin release in human eosinophils.

Eosinophils are multifunctional leukocytes implicated in the pathogenesis of asthma and in immunity to certain organisms. Associations between exposure to an environmental fungus, such as Alternaria, and asthma have been recognized clinically. Protease-activated receptors (PARs) are G protein-coupled receptors that are cleaved and activated by serine proteases, but their roles in innate immunity remain unknown. We previously found that human eosinophils respond vigorously to Alternaria organisms and to the secretory product(s) of Alternaria with eosinophils releasing their proinflammatory mediators. In this study, we investigated the roles of protease(s) produced by Alternaria and of PARs expressed on eosinophils in their immune responses against fungal organisms. We found that Alternaria alternata produces aspartate protease(s) and that human peripheral blood eosinophils degranulate in response to the cell-free extract of A. alternata. Eosinophils showed an increased intracellular calcium concentration in response to Alternaria that was desensitized by peptide and protease ligands for PAR-2 and inhibited by a PAR-2 antagonistic peptide. Alternaria-derived aspartate protease(s) cleaved PAR-2 to expose neo-ligands; these neo-ligands activated eosinophil degranulation in the absence of proteases. Finally, treatment of Alternaria extract with aspartate protease inhibitors, which are conventionally used for HIV-1 and other microbes, attenuated the eosinophils' responses to Alternaria. Thus, fungal aspartate protease and eosinophil PAR-2 appear critical for the eosinophils' innate immune response to certain fungi, suggesting a novel mechanism for pathologic inflammation in asthma and for host-pathogen interaction.

Eosinophil-derived neurotoxin: A biologically and analytically attractive asthma biomarker.

There is a growing body of evidence for the utility of eosinophil-derived neurotoxin (EDN) as a biomarker in asthma, including association with eosinophilic airway inflammation, assessment of disease severity and potential for predicting pathogenic risks, including exacerbations. However, to interpret any biomarker data with confidence, it is first important to understand the preanalytical factors and biological variation that may affect its reliable measurement and results interpretation. In this study we defined the healthy serum EDN reference range for men and women as 1.98 to 26.10 ng/mL, with no significant gender differences. Smoking did not impact the mean EDN levels and no circadian rhythm was identified for EDN, unlike blood eosinophils (EOS) where levels peaked at 00:00h. EDN expression in different cell types was investigated and shown to occur primarily in eosinophils, indicating they are likely to be the main cellular repository for EDN. We also confirm that the quantification of serum EDN is not influenced by the type of storage tube used, and it is stable at ambient temperature or when refrigerated for at least 7 days and for up to one year when frozen at -20°C or -80°C. In summary, EDN is a stable biomarker that may prove useful in precision medicine approaches by enabling the identification of a subpopulation of asthma patients with activated eosinophils and a more severe form of the disease.

Clinical relevance of IgG antibodies against food antigens in Crohn's disease: a double-blind cross-over diet intervention study.

BACKGROUND: Environmental factors are thought to play an important role in the development of Crohn's disease (CD). Immune responses against auto-antigens or food antigens may be a reason for the perpetuation of inflammation. METHODS: In a pilot study, 79 CD patients and 20 healthy controls were examined for food immunoglobulin G (IgG). Thereafter, the clinical relevance of these food IgG antibodies was assessed in a double-blind cross-over study with 40 patients. Based on the IgG antibodies, a nutritional intervention was planned. The interferon (IFN)gamma secretion of T cells was measured. Eosinophil-derived neurotoxin was quantified in stool. RESULTS: The pilot study resulted in a significant difference of IgG antibodies in serum between CD patients and healthy controls. In 84 and 83% of the patients, respectively, IgG antibodies against processed cheese and yeast were detected. The daily stool frequency significantly decreased by 11% during a specific diet compared with a sham diet. Abdominal pain reduced and general well-being improved. IFNgamma secretion of T cells increased. No difference for eosinophil-derived neurotoxin in stool was detected. CONCLUSION: A nutritional intervention based on circulating IgG antibodies against food antigens showed effects with respect to stool frequency. The mechanisms by which IgG antibodies might contribute to disease activity remain to be elucidated.

Pimecrolimus reduces eosinophil activation associated with calcium mobilization.

BACKGROUND: Pimecrolimus is a calcineurin inhibitor that inhibits T cell and mast cell activation and effectively treats atopic dermatitis. However, its effects on eosinophils, a cell type implicated in allergic disease pathology, are unknown. Therefore, we examined the effects of pimecrolimus on eosinophil superoxide anion production, degranulation and survival. METHODS: Purified eosinophils from normal or atopic donors were incubated with serial dilutions of pimecrolimus (microM to nM) and then stimulated with platelet activating factor (PAF), interleukin 5 (IL5), secretory immunoglobulin A (sIgA) or Alternaria alternata (Alt) fungus extract. Eosinophil activation was monitored by cytochrome c reduction resulting from superoxide anion production and by a 2-site immunoassay for eosinophil-derived neurotoxin (EDN) in cellular supernatants, as a marker of degranulation. Eosinophil survival was measured by propidium iodide exclusion using flow cytometry after 4 days in culture. RESULTS: Normal and atopic eosinophil superoxide anion production induced by PAF, and associated with increased intracellular calcium, was inhibited up to 37% with 1 microM pimecrolimus. However, superoxide anion production induced by IL5 and sIgA was not consistently inhibited. EDN release, which ultimately depends on calcium, was inhibited about 30% with PAF, IL5 and sIgA stimulation for normal and atopic donor eosinophils. Furthermore, calcium-dependent Alt-induced EDN release was inhibited up to 49% with nanomolar pimecrolimus. Finally, increased eosinophil survival promoted by IL5 and sIgA was not influenced by pimecrolimus. CONCLUSION: Pimecrolimus moderately inhibits eosinophil superoxide anion production and EDN release associated with calcium mobilization, which may contribute to its efficacy in treating atopic dermatitis.

Host antimicrobial proteins as endogenous immunomodulators.

Host defense mechanisms are multilayered and involve physical as well as chemical barriers, antimicrobial factors as well as a broad set of immunocompetent cells. The mode of action of antimicrobial factors is variable, ranging from opsonisation and agglutination to direct killing of pathogens. In the last years it has become increasingly clear that some of these factors act as endogenous ligands that bind to distinct host receptors, as for example pathogen recognition receptors (PRRs), thereby influencing distinct immunological processes like chemotaxis, modulation of phagocytosis, dendritic cell maturation or the production of cytokines. By that way, these factors are implicated to protect the host by preventing and clearing of microbial infections.

Eosinophil Cationic Protein (ECP), a predictive marker of bullous pemphigoid severity and outcome.

Bullous Pemphigoid (BP) is an inflammatory rare autoimmune bullous dermatosis, which outcome cannot be predicted through clinical investigations. Eosinophils are the main immune infiltrated cells in BP. However, the release of Major Basic Protein (MBP), Eosinophil Derived Neurotoxin (EDN), and Eosinophil Cationic Protein (ECP) upon eosinophil activation has still not been evaluated with respect to BP development. MBP, EDN and ECP were measured by ELISA in serum (n = 61) and blister fluid (n = 20) of patients with BP at baseline, and in serum after 2 months of treatment (n = 41). Eosinophil activation in BP patients was illustrated at baseline by significantly higher MBP, EDN and ECP serum concentrations as compared with control subjects (n = 20), but without distinction according to disease severity or outcome. EDN and ECP values were even higher in the blister fluids (P < 0.01 and P < 0.05, respectively), whereas MBP values were lower (P < 0.001). ECP serum concentration decreased after 60 days of treatment in BP patients with ongoing remission but not in patients who later relapsed (P < 0.05). A reduction of at least 12.8 ng/mL in ECP concentrations provided a positive predictive value for remission of 81%, showing that ECP serum variation could be a useful biomarker stratifying BP patients at risk of relapse.

The production of the eosinophil proteins ECP and EPX/EDN are regulated in a reciprocal manner.

Previous studies showed that the biological activity and the eosinophil content of eosinophil cationic protein (ECP, RNase 3) are determined by single-nucleotide polymorphisms (SNPs) in the ECP (RNase3) gene. In this study, we report the prevalence of a common SNP in the eosinophil protein x/eosinophil-derived neurotoxin (EPX/EDN, RNase2) and the association with the cellular contents of EPX/EDN and ECP. The genes were sequenced and the EPX/EDN405(G>C) rs2013109 SNPs were also determined by TaqMan 5'nuclease allelic discrimination assay. ECP and EPX/EDN in purified eosinophils or in whole blood extracts were analysed by sensitive immunoassays. The study included 379 non-allergic and allergic subjects. The genotype prevalence of the EPX/EDN405(G>C) polymorphism was GG 59%, GC 36% and CC 6%. The cellular contents of ECP and EPX/EDN were related in a reciprocal fashion with the sums of the protein contents being constant. The contents were associated with the ECP562(G>C) rs2233860 and EPX/EDN405(G>C) gene polymorphisms. The cellular content of eosinophil peroxidase (EPO) was not associated with the ECP and EPX/EDN genotypes. The prevalence of the EPX/EDN405(G>C) genotypes and the contents of the proteins were similar in non-allergic and allergic subjects.The production and storage of the two ancestral proteins, ECP and EPX/EDN likely share common regulatory mechanisms, which result in opposing productions of the two proteins.

Leukotriene B4 induces release of antimicrobial peptides in lungs of virally infected mice.

Leukotriene B(4) (LTB(4)) is a lipid mediator of inflammation that was recently shown to exert antiviral activities. In this study, we demonstrate that the release of antimicrobial proteins by neutrophils contribute to an early host defense against influenza virus infection in vitro as well as in vivo. Daily i.v. treatments with LTB(4) lead to a significant decrease in lung viral loads at day 5 postinfection in mice infected with influenza A virus compared with the placebo-treated group. This reduction in viral load was not present in mice deficient in the high-affinity LTB(4) receptor. Viral clearance in lungs was associated with up-regulated presence of antimicrobial peptides such as beta-defensin-3, members of the mouse eosinophil-related RNase family, and the mouse cathelicidin-related antimicrobial peptide. Our results also indicate that neutrophils are important in the antiviral effect of LTB(4). Viral loads in neutrophil-depleted mice were not diminished by LTB(4) administration, and a substantial reduction in the presence of murine cathelicidin-related antimicrobial peptide and the murine eosinophil-related RNase family in lung tissue was observed. Moreover, in vitro treatment of human neutrophil cultures with LTB(4) led rapidly to the secretion of the human cathelicidin LL-37 and eosinophil-derived neurotoxin, known as antiviral peptides. Pretreatment of cell cultures with specific LTB(4) receptor antagonists clearly demonstrate the implication of the high-affinity LTB(4) receptor in the LTB(4)-mediated activity. Together, these results demonstrate the importance of neutrophils and the secretion of antimicrobial peptides during the early immune response mediated by LTB(4) against a viral pathogen.

Eosinophils contribute to innate antiviral immunity and promote clearance of respiratory syncytial virus.

Eosinophils are recruited to the lungs in response to respiratory syncytial virus (RSV) infection; however, their role in promoting antiviral host defense remains unclear. Here, we demonstrate that eosinophils express TLRs that recognize viral nucleic acids, are activated and degranulate after single-stranded RNA (ssRNA) stimulation of the TLR-7-MyD88 pathway, and provide host defense against RSV that is MyD88 dependent. In contrast to wild-type mice, virus clearance from lung tissue was more rapid in hypereosinophilic (interleukin-5 transgenic) mice. Transfer of wild-type but not MyD88-deficient eosinophils to the lungs of RSV-infected wild-type mice accelerated virus clearance and inhibited the development of airways hyperreactivity. Similar responses were observed when infected recipient mice were MyD88 deficient. Eosinophils isolated from infected hypereosinophilic MyD88-sufficient but not MyD88-deficient mice expressed greater amounts of IFN regulatory factor (IRF)-7 and eosinophil-associated ribonucleases EAR-1 and EAR-2. Hypereosinophilia in the airways of infected mice also correlated with increased expression of IRF-7, IFN-beta, and NOS-2, and inhibition of NO production with the NOS-2 inhibitor L-NMA partially reversed the accelerated virus clearance promoted by eosinophils. Collectively, our results demonstrate that eosinophils can protect against RSV in vivo, as they promote virus clearance and may thus limit virus-induced lung dysfunction.