Strain-specific requirement for eosinophils in the recruitment of T cells to the lung during the development of allergic asthma

Immunosuppressive Ability of Trichinella spiralis Adults Can Ameliorate Type 2 Inflammation in a Murine Allergy Model

BACKGROUND

There is an increase in the global incidence of allergies. The hygiene hypothesis and the old friend hypothesis reveal that helminths are associated with the prevalence of allergic diseases. The therapeutic potential of Trichinella spiralis is recognized; however, the stage at which it exerts its immunomodulatory effect is unclear.

METHODS

We evaluated the differentiation of bone marrow-derived macrophages stimulated with T spiralis excretory-secretory products. Based on an ovalbumin-induced murine model, T spiralis was introduced during 3 allergy phases. Cytokine levels and immune cell subsets in the lung, spleen, and peritoneal cavity were assessed.

RESULTS

We found that T spiralis infection reduced lung inflammation, increased anti-inflammatory cytokines, and decreased Th2 cytokines and alarms. Recruitment of eosinophils, CD11b+ dendritic cells, and interstitial macrophages to the lung was significantly suppressed, whereas Treg cells and alternatively activated macrophages increased in T spiralis infection groups vs the ovalbumin group. Notably, when T spiralis was infected prior to ovalbumin challenge, intestinal adults promoted proportions of CD103+ dendritic cells and alveolar macrophages.

CONCLUSIONS

T spiralis strongly suppressed type 2 inflammation, and adults maintained lung immune homeostasis.

MHCII+CD80+ thymic eosinophils increase in abundance during neonatal development in mice and their accumulation is microbiota dependent

Eosinophils are present in the thymus of mammals, yet their function at this site during homeostatic development is unknown. We used flow cytometry to determine the abundance and phenotype of eosinophils (here defined as SSchigh SiglecF+ CD11b+ CD45+ cells) in the thymus of mice during the neonatal period, the later postnatal period, and into adulthood. We show that both the total number of thymic eosinophils and their frequency among leukocytes increase over the first 2 wk of life and that their accumulation in the thymus is dependent on the presence of an intact bacterial microbiota. We report that thymic eosinophils express the interleukin-5 receptor (CD125), CD80, and IDO, and that subsets of thymic eosinophils express CD11c and major histocompatibility complex II (MHCII). We found that the frequency of MHCII-expressing thymic eosinophils increases over the first 2 wk of life, and that during this early-life period the highest frequency of MHCII-expressing thymic eosinophils is located in the inner medullary region. These data suggest a temporal and microbiota-dependent regulation of eosinophil abundance and functional capabilities in the thymus.

Eosinophils protect pressure overload- and β-adrenoreceptor agonist-induced cardiac hypertrophy

AIMS

Blood eosinophil (EOS) counts and EOS cationic protein (ECP) levels associate positively with major cardiovascular disease (CVD) risk factors and prevalence. This study investigates the role of EOS in cardiac hypertrophy.

METHODS AND RESULTS

A retrospective cross-section study of 644 consecutive inpatients with hypertension examined the association between blood EOS counts and cardiac hypertrophy. Pressure overload- and β-adrenoreceptor agonist isoproterenol-induced cardiac hypertrophy was produced in EOS-deficient ΔdblGATA mice. This study revealed positive correlations between blood EOS counts and left ventricular (LV) mass and mass index in humans. ΔdblGATA mice showed exacerbated cardiac hypertrophy and dysfunction, with increased LV wall thickness, reduced LV internal diameter, and increased myocardial cell size, death, and fibrosis. Repopulation of EOS from wild-type (WT) mice, but not those from IL4-deficient mice ameliorated cardiac hypertrophy and cardiac dysfunctions. In ΔdblGATA and WT mice, administration of ECP mEar1 improved cardiac hypertrophy and function. Mechanistic studies demonstrated that EOS expression of IL4, IL13, and mEar1 was essential to control mouse cardiomyocyte hypertrophy and death and cardiac fibroblast TGF-β signalling and fibrotic protein synthesis. The use of human cardiac cells yielded the same results. Human ECP, EOS-derived neurotoxin, human EOS, or murine recombinant mEar1 reduced human cardiomyocyte death and hypertrophy and human cardiac fibroblast TGF-β signalling.

CONCLUSION

Although blood EOS counts correlated positively with LV mass or LV mass index in humans, this study established a cardioprotective role for EOS IL4 and cationic proteins in cardiac hypertrophy and tested a therapeutic possibility of ECPs in this human CVD.

Multiple Orientia clusters and Th1-skewed chemokine profile: a cross-sectional study in patients with scrub typhus from Nepal

OBJECTIVES

Scrub typhus is an emerging infectious disease in Asia caused by Orientia tsutsugamushi (Ot). From Nepal, only scant data on the genetic epidemiology of this agent is available, and determinants of immunoregulation are poorly understood.

METHODS

Patients (n = 238) referred to the National Public Health Laboratory (Kathmandu, Nepal) from all over Nepal for suspected scrub typhus were enrolled upon positive immunoglobulin (Ig)M testing between July and October 2015. From Ot 16S and 47 kD polymerase chain reaction (PCR)-positive samples, the variable domain I of the 56 kD gene was sequenced and phylogenetically analyzed. T helper (Th) cell-associated cytokines (n = 13) and chemokines (n = 12) were quantified by multiplex bead arrays.

RESULTS

In 93/238 (39.1%) IgM-positive samples, Ot DNA was detected by quantitative PCR. Phylogenetic analysis of 56 kD sequences revealed seven distinct clusters, six of them with high homologies to strains detected in other countries. The Th1-related cytokines interferon-γ and C-X-C motif chemokine ligand 10 were strongly upregulated and correlated with bacteremia, while levels of Th2-associated chemokines were reduced. Bacteremia also correlated with concentrations of interleukin (IL)-6 and IL-10 but not tumor necrosis factor-α.

CONCLUSION

We identified a considerable genetic heterogeneity of human-pathogenic Ot strains circulating in Nepal. Acute Nepalese scrub typhus patients showed strong Th1 but impaired Th2 responses, especially on the chemokine level.

C5aR1 activation in mice controls inflammatory eosinophil recruitment and functions in allergic asthma

BACKGROUND

Pulmonary eosinophils comprise at least two distinct populations of resident eosinophils (rEOS) and inflammatory eosinophils (iEOS), the latter recruited in response to pulmonary inflammation. Here, we determined the impact of complement activation on rEOS and iEOS trafficking and function in two models of pulmonary inflammation.

METHODS

BALB/c wild-type and C5ar1^-/- mice were exposed to different allergens or IL-33. Eosinophil populations in the airways, lung, or mediastinal lymph nodes (mLN) were characterized by FACS or immunohistochemistry. rEOS and iEOS functions were determined in vivo and in vitro.

RESULTS

HDM and IL-33 exposure induced a strong accumulation of iEOS but not rEOS in the airways, lungs, and mLNs. rEOS and iEOS expressed C3/C5 and C5aR1, which were significantly higher in iEOS. Initial pulmonary trafficking of iEOS was markedly reduced in C5ar1^-/- mice and associated with less IL-5 production from ILC2 cells. Functionally, adoptively transferred pulmonary iEOS from WT but not from C5ar1^-/- mice-induced airway hyperresponsiveness (AHR), which was associated with significantly reduced C5ar1^-/- iEOS degranulation. Pulmonary iEOS but not rEOS were frequently associated with T cells in lung tissue. After HDM or IL-33 exposure, iEOS but not rEOS were found in mLNs, which were significantly reduced in C5ar1^-/- mice. C5ar1^-/- iEOS expressed less costimulatory molecules, associated with a decreased potency to drive antigen-specific T cell proliferation and differentiation into memory T cells.

CONCLUSIONS

We uncovered novel roles for C5aR1 in iEOS trafficking and activation, which affects key aspects of allergic inflammation such as AHR, ILC2, and T cell activation.

Eosinophils Recruited during Pulmonary Vaccination Regulate Mucosal Antibody Production

Eosinophils have been previously shown to be able to regulate early humoral responses during systemic vaccination. Here we investigated the role of eosinophils during pulmonary vaccination, comparing vaccine-induced responses in eosinophil-deficient (ΔdblGATA) and wild-type mice using a Th2 adjuvant. We observed that eosinophils were needed to induce a complete vaccine response, thereby eliciting specific antibody-secreting plasma cells in the regional lymph nodes and antibody secretion in the BAL at the early stage of the immune response. Reintroduction of eosinophils in the lungs of ΔdblGATA mice during the priming stage enhanced both specific IgM and IgG plasma cells but not specific IgA plasma cells. Upon vaccination, eosinophils migrated to the lungs and secreted cytokines involved in B-cell activation, which might promote antibody production. Importantly, however, the absence of eosinophils did not impair late immune responses in a prime/boost protocol because, in that setup, we uncovered a compensating mechanism involving a Th17 pathway. In conclusion, our data demonstrate for the first time a new role for eosinophils during lung mucosal vaccination, whereby they accelerate early immune responses (IgM and IgG) while regulating IgA production at the late stages.

Living without eosinophils: evidence from mouse and man

The enduring view of eosinophils, as immune effector cells whose primary function is host defence against infection by helminths and other microbial pathogens, sets the stage for a fundamental question regarding the safety of therapeutic eosinophil depletion. If eosinophils are significantly reduced or altogether depleted in an effort to alleviate the negative effects of tissue eosinophilia and eosinophilic inflammation in conditions such as asthma, COPD, chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome, would these patients become susceptible to infection or another illness? Development of mouse models in which the eosinophil lineage has been ablated, observations in patients naturally lacking eosinophils and data from studies of eosinophil-depleting medical therapies indicate that the absence of eosinophils is not detrimental to health. The evidence available to date, as presented in this review, supports the conclusion that even if certain homeostatic roles for the eosinophil may be demonstrable in controlled animal models and human in vitro settings, the evolution of the human species appears to have provided sufficient immune redundancy such that one may be hale and hearty without eosinophils.

Eotaxin-2 and eotaxin-3 in malaria exposure and pregnancy

Background

Eotaxin-1 concentrations in plasma have been inversely associated with malaria exposure, malaria infection and pregnancy, but the effect of these conditions on the levels of the related chemokines eotaxin-2 and eotaxin-3 remains unknown.

Methods

Eotaxin-2 and -3 concentrations were measured in 310 peripheral or placental plasma samples from pregnant and non-pregnant individuals from Papua New Guinea (malaria-endemic country) and Spain (malaria-naïve individuals) with previous data on eotaxin-1 concentrations. Correlations between eotaxin concentrations were examined with the Spearman’s test. Differences in eotaxin concentrations among groups were evaluated with the Kruskal–Wallis or Mann Whitney tests. The pairwise Wilcoxon test was performed to compare eotaxin-2 concentration between peripheral and placental matched plasmas. Univariable and multivariable linear regression models were estimated to assess the association between eotaxins and Plasmodium infection or gestational age.

Results

Eotaxin-2 concentrations in plasma showed a weak positive correlation with eotaxin-3 (rho = 0.35, p < 0.05) concentrations. Eotaxin-2 concentrations in the malaria-exposed non-pregnant group were significantly lower than the in the malaria-naive non-pregnant and the malaria-exposed pregnant groups. Eotaxin-3 plasma concentrations were lower in malaria-exposed than in non-exposed groups (p < 0.05), but no differences were found associated to pregnancy. Eotaxin-2 and eotaxin-3 plasma concentrations were negatively correlated with anti-Plasmodium IgG levels: PfDBL5ε-IgG (rhoEo2 = − 0.35, p = 0.005; rhoEo3 =− 0.37, p = 0.011), and eotaxin-3 was negatively correlated with PfDBL3x-IgG levels (rhoEo3 =− 0.36; p = 0.011). Negative correlations of eotaxin-2 and 3 in plasma were also observed with atypical memory B cells (rhoEo2 = − 0.37, p < 0.001; rhoEo3= − 0.28, p = 0.006), a B cell subset expanded in malaria-exposed individuals. In addition, a borderline negative association was observed between eotaxin-3 concentrations and Plasmodium infection (adjusted effect estimate, β = − 0.279, 95% CI − 0.605; 0.047, p = 0.091). Moreover, eotaxin-2 placental concentrations were significantly increased compared to peripheral concentrations in the malaria-exposed pregnant group whereas the contrary was observed in the non-exposed pregnant group (p < 0.005).

Conclusion

Although a clear epidemiological negative association is observed between eotaxins concentrations and malaria exposure and/or infection, pregnancy may alter this association for eotaxin-2. Further research is required to understand the role of these chemokines in this disease and in combination with pregnancy.

“Just one word, plastic!”: Controversies and caveats in innate lymphoid cell plasticity

Innate lymphoid cells (ILCs) are frontline immune effectors involved in the early stages of host defense and maintenance of tissue homeostasis, particularly at mucosal surfaces such as the intestine, lung, and skin. Canonical ILCs are described as tissue-resident cells that populate peripheral tissues early in life and respond appropriately based on environmental exposure and their anatomical niche and tissue microenvironment. Intriguingly, there are accumulating reports of ILC “plasticity” that note the existence of non-canonical ILCs that exhibit distinct patterns of master transcription factor expression and cytokine production profiles in response to tissue inflammation. Yet this concept of ILC-plasticity is controversial due to several confounding caveats that include, among others, the independent large-scale recruitment of new ILC subsets from distal sites and the local, in situ, differentiation of uncommitted resident precursors. Nevertheless, the ability of ILCs to acquire unique characteristics and adapt to local environmental cues is an attractive paradigm because it would enable the rapid adaptation of innate responses to a wider array of pathogens even in the absence of pre-existing ‘prototypical’ ILC responder subsets. Despite the impressive recent progress in understanding ILC biology, the true contribution of ILC plasticity to tissue homeostasis and disease and how it is regulated remains obscure. Here, we detail current methodologies used to study ILC plasticity in mice and review the mechanisms that drive and regulate functional ILC plasticity in response to polarizing signals in their microenvironment and different cytokine milieus. Finally, we discuss the physiological relevance of ILC plasticity and its implications for potential therapeutics and treatments.

Endoplasmic reticulum stress in airway hyperresponsiveness

Airway hyperresponsiveness(AHR) is a major clinical phenomenon in lung diseases (asthma, COPD and pulmonary fibrosis) and not only a high-risk factor for perioperative airway spasm leading to hypoxaemia, haemodynamic instability and even "silent lung", but also a potential risk for increased mortality from underlying diseases (e.g. asthma, COPD). Airway reactivity is closely linked to airway inflammation, remodelling and increased mucus secretion, and endoplasmic reticulum stress is an important mechanism for the development of these pathologies. This review, therefore, focuses on the effects of endoplasmic reticulum stress on the immune cells involved in airway hyperreactivity (epithelial cells, dendritic cells, eosinophils and neutrophils) in inflammation and mucus & sputum secretion; and on the differentiation and remodelling of airway smooth muscle cells and epithelial cells. The aim is to clarify the mechanisms associated with endoplasmic reticulum stress in airway hyperresponsiveness and to find new ideas and methods for the prevention of airway hyperresponsiveness in the perioperative period.

Therapeutic Potential for Intractable Asthma by Targeting L-Type Amino Acid Transporter 1

Bronchial asthma is a chronic disease characterized by airway inflammation, obstruction, and hyperresponsiveness. CD4⁺ T cells, particularly T helper (Th) 2 cells, and their specific cytokines are important mediators in asthma pathogenesis. However, it has been established that Th subsets, other than Th2, as well as various cell types, including innate lymphoid cells (ILCs), significantly contribute to the development of allergic inflammation. These cells require facilitated amino acid uptake to ensure their full function upon activation. Emerging studies have suggested the potential of pharmacological inhibition of amino acid transporters to inhibit T cell activation and the application of this strategy for treating immunological and inflammatory disorders. In the present review, we explore the possibility of targeting L-type amino acid transporter (LAT) as a novel therapeutic approach for bronchial asthma, including its steroid-resistant endotypes.

NLRC4 Inflammasome-Mediated Regulation of Eosinophilic Functions

Eosinophils play critical roles in the maintenance of homeostasis in innate and adaptive immunity. Although primarily known for their roles in parasitic infections and the development of Th2 cell responses, eosinophils also play complex roles in other immune responses ranging from anti-inflammation to defense against viral and bacterial infections. However, the contributions of pattern recognition receptors in general, and NOD-like receptors (NLRs) in particular, to eosinophil involvement in these immune responses remain relatively underappreciated. Our in vivo studies demonstrated that NLRC4 deficient mice had a decreased number of eosinophils and impaired Th2 responses after induction of an allergic airway disease model. Our in vitro data, utilizing human eosinophilic EoL-1 cells, suggested that TLR2 induction markedly induced pro-inflammatory responses and inflammasome forming NLRC4 and NLRP3. Moreover, activation by their specific ligands resulted in caspase-1 cleavage and mature IL-1β secretion. Interestingly, Th2 responses such as secretion of IL-5 and IL-13 decreased after transfection of EoL-1 cells with short interfering RNAs targeting human NLRC4. Specific induction of NLRC4 with PAM3CSK4 and flagellin upregulated the expression of IL-5 receptor and expression of Fc epsilon receptors (FcεR1α, FcεR2). Strikingly, activation of the NLRC4 inflammasome also promoted expression of the costimulatory receptor CD80 as well as expression of immunoregulatory receptors PD-L1 and Siglec-8. Concomitant with NLRC4 upregulation, we found an increase in expression and activation of matrix metalloproteinase (MMP)-9, but not MMP-2. Collectively, our results present new potential roles of NLRC4 in mediating a variety of eosinopilic functions.

Pulmonary Eosinophils at the Center of the Allergic Space-Time Continuum

Eosinophils are typically a minority population of circulating granulocytes being released from the bone-marrow as terminally differentiated cells. Besides their function in the defense against parasites and in promoting allergic airway inflammation, regulatory functions have now been attributed to eosinophils in various organs. Although eosinophils are involved in the inflammatory response to allergens, it remains unclear whether they are drivers of the asthma pathology or merely recruited effector cells. Recent findings highlight the homeostatic and pro-resolving capacity of eosinophils and raise the question at what point in time their function is regulated. Similarly, eosinophils from different physical locations display phenotypic and functional diversity. However, it remains unclear whether eosinophil plasticity remains as they develop and travel from the bone marrow to the tissue, in homeostasis or during inflammation. In the tissue, eosinophils of different ages and origin along the inflammatory trajectory may exhibit functional diversity as circumstances change. Herein, we outline the inflammatory time line of allergic airway inflammation from acute, late, adaptive to chronic processes. We summarize the function of the eosinophils in regards to their resident localization and time of recruitment to the lung, in all stages of the inflammatory response. In all, we argue that immunological differences in eosinophils are a function of time and space as the allergic inflammatory response is initiated and resolved.

Eosinophils participate in modulation of liver immune response and tissue damage induced by Schistosoma mansoni infection in mice

The severity of chronic schistosomiasis has been mainly associated with the intensity and extension of the inflammatory response induced by egg-secreted antigens in the host tissue, especially in the liver and intestine. During acute schistosomiasis, eosinophils account for approximately 50% of the cells that compose the liver granulomas; however, the role of this cell-type in the pathology of schistosomiasis remains controversial. In the current study, we compared the parasite burden and liver immunopathological changes during experimental schistosomiasis in wild-type (WT) BALB/c mice and BALB/c mice selectively deficient for the differentiation of eosinophils (ΔdblGATA). Our data demonstrated that the absence of eosinophil differentiation did not alter the S. mansoni load or the liver retention of parasite eggs; however, there were significant changes in the liver immune response profile and tissue damage. S. mansoni infection in ΔdblGATA mice resulted in significantly lower liver concentrations of IL-5, IL-13, IL-33, IL-17, IL-10, and TGF-β and higher concentrations of IFN-γ and TNF-α, as compared to WT mice. The changes in liver immune response observed in infected ΔdblGATA mice were accompanied by lower collagen deposition, but higher liver damage and larger granulomas. Moreover, the absence of eosinophils resulted in a higher mortality rate in mice infected with a high parasite load. Therefore, the data indicated that eosinophils participate in the establishment and/or amplification of liver Th-2 and regulatory response induced by S. mansoni, which is necessary for the balance between liver damage and fibrosis, which in turn is essential for modulating disease severity.

Ameliorative effects of eosinophil deficiency on immune response, endoplasmic reticulum stress, apoptosis, and autophagy in fungus-induced allergic lung inflammation

Background

Respiratory fungal exposure is known to be associated with various allergic pulmonary disorders. Eosinophils have been implicated in tissue homeostasis of allergic inflammation as both destructive effector cells and immune regulators. What contributions eosinophils have in Aspergillus fumigatus (Af)-induced allergic lung inflammation is worthy of investigating.

Methods

We established the Af-exposed animal asthmatic model using eosinophil-deficient mice, ∆dblGATA1 mice. Airway inflammation was assessed by histopathological examination and total cell count of bronchoalveolar lavage fluid (BALF). The protein level in BALF and lung mRNA level of type 2 cytokines IL-4, IL-5, and IL-13 were detected by ELISA and qRT-PCR. We further studied the involvement of endoplasmic reticulum (ER) stress, apoptosis, and autophagy by western blots, qRT-PCR, immunofluorescence, TUNEL, or immunohistochemistry. RNA-Seq analysis was utilized to analyze the whole transcriptome of Af-exposed ∆dblGATA1 mice.

Results

Hematoxylin and eosin (HE) staining and periodic acid–Schiff staining (PAS) showed that airway inflammation and mucus production were alleviated in Af-challenged ∆dblGATA1 mice compared with wild-type controls. The protein and mRNA expressions of IL-4, IL-5, and IL-13 were reduced in the BALF and lung tissues in Af-exposed ∆dblGATA1 mice. The results demonstrated that the significantly increased ER stress markers (GRP78 and CHOP) and apoptosis executioner caspase proteases (cleaved caspase-3 and cleaved caspase-7) in Af-exposed wild-type mice were all downregulated remarkably in the lungs of ∆dblGATA1 mice with Af challenge. In addition, the lung autophagy in Af-exposed ∆dblGATA1 mice was found elevated partially, manifesting as higher expression of LC3-II/LC3-I and beclin1, lower p62, and downregulated Akt/mTOR pathway compared with Af-exposed wild-type mice. Additionally, lung RNA-seq analysis of Af-exposed ∆dblGATA1 mice showed that biological processes about chemotaxis of lymphocytes, neutrophils, or eosinophils were enriched but without statistical significance.

Conclusions

In summary, eosinophils play an essential role in the pathogenesis of Af-exposed allergic lung inflammation, whose deficiency may have relation to the attenuation of type 2 immune response, alleviation of ER stress and apoptosis, and increase of autophagy. These findings suggest that anti-eosinophils therapy may provide a promising direction for fungal-induced allergic pulmonary diseases.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Mutant Mice and Animal Models of Airway Allergic Disease

Eosinophilia is a hallmark of allergic airway inflammation, and eosinophils represent an integral effector leukocyte through their release of various granule-stored cytokines and proteins. Numerous mouse models have been developed to mimic clinical disease and they have been instrumental in furthering our understanding of the role of eosinophils in disease. Most of these models consist of intranasal (i.n.) administration of antigenic proteases including papain and house dust mite (HDM) or the neo-antigen ovalbumin, with a resulting Th2-biased immune response and airway eosinophilia. These models have been particularly informative when combined with the numerous transgenic mice available that modulate eosinophil frequency or the mechanisms involved in their migration. Here, we describe the current models of allergic airway inflammation and outline some of the transgenic mice available to study eosinophil disease.

Autoimmunity to neuroretina in the concurrent absence of IFN-γ and IL-17A is mediated by a GM-CSF-driven eosinophilic inflammation

IFN-γ and IL-17A can each elicit ocular autoimmunity independently of the other. Since absence of IFN-γ or IL-17A individually failed to abolish pathology of experimental autoimmune uveitis (EAU), we examined EAU development in the absence of both these cytokines. Ifng-/-Il17a-/- mice were fully susceptible to EAU with a characteristic eosinophilic ocular infiltrate, as opposed to a mononuclear infiltrate in WT mice. Retinal pathology in double-deficient mice was ameliorated when eosinophils were genetically absent or their migration was blocked, supporting a pathogenic role for eosinophils in EAU in the concurrent absence of IFN-γ and IL-17A. In EAU-challenged Ifng-/-Il17a-/- mice, ocular infiltrates contained increased GM-CSF-producing CD4+ T cells, and supernatants of retinal antigen-stimulated splenocytes contained enhanced levels of GM-CSF that contributed to activation and migration of eosinophils in vitro. Systemic or local blockade of GM-CSF ameliorated EAU in Ifng-/-Il17a-/- mice, reduced eosinophil peroxidase levels in the eye and in the serum and decreased eosinophil infiltration to the eye. These results support the interpretation that, in the concurrent absence of IFN-γ and IL-17A, GM-CSF takes on a major role as an inflammatory effector cytokine and drives an eosinophil-dominant pathology. Our findings may impact therapeutic strategies aiming to target IFN-γ and IL-17A in autoimmune uveitis.

IL33 contributes to diesel pollution-mediated increase in experimental asthma severity

BACKGROUND

Exposure to traffic pollution, notably diesel exhaust particles (DEP), increases risk for asthma and asthma exacerbations. The contribution of cytokines generated by stressed lung epithelial cells (IL25, IL33, TSLP) to DEP-induced asthma severity remains poorly understood.

METHODS

BALB/c mice were exposed intratracheally once to DEP or 9 times over 3-weeks to either saline, DEP, and/or house dust mite extract (HDM). Airway hyper-responsiveness (AHR), pulmonary inflammation, and T-cell subsets were assessed 24 hours after the last exposure in mice sufficient and deficient for the IL33 receptor ST2.

RESULTS

DEP exposure induces oxidative stress, IL6, neutrophils and pulmonary accumulation of IL33, but not IL25 or TSLP or other features of allergic disease. When mice are co-exposed to DEP and low doses of HDM, DEP increases IL33 lung levels and Th2 responses. ST2 deficiency partially protected mice from HDM + DEP induced AHR in association with decreased type 2 inflammation and lung levels of IL5⁺ IL17A⁺ co-producing T-cells. Upon in vitro HDM challenge of lung cells from HDM ± DEP exposed ST2^-/- mice, secretion of IL5, IL13, IL6 and IL17A was abrogated by a mechanism involving IL33 signaling in both dendritic cells and T-cells. HDM + DEP exposed bone marrow derived dendritic cells and IL33 pulsed BMDC promote a mixed Th2/Th17 response that was dependent on ST2 expression by CD4⁺ T-cells.

CONCLUSION

IL33 contributes to DEP mediated increase in allergen-induced Th2 inflammation and AHR in a mouse model of severe steroid resistant asthma, potentially through the accumulation of pathogenic IL5⁺ IL17A⁺ CD4⁺ effector T-cells.

Th2 cells promote eosinophil-independent pathology in a murine model of allergic bronchopulmonary aspergillosis

Repeated inhalation of airborne conidia derived from the fungus Aspergillus fumigatus (Af) can lead to a severe eosinophil-dominated inflammatory condition of the lung termed allergic bronchopulmonary aspergillosis (ABPA). ABPA affects about 5 million individuals worldwide and the mechanisms regulating lung pathology in ABPA are poorly understood. Here, we used a mouse model of ABPA to investigate the role of eosinophils and T cell-derived IL-4/IL-13 for induction of allergic lung inflammation. Selective deletion of IL-4/IL-13 in T cells blunted the Af-induced lung eosinophilia and further resulted in lower expression of STAT6-regulated chemokines and effector proteins such as Arginase 1, Relm-α, Relm-β, and Muc5a/c. Eosinophil-deficient ΔdblGata mice showed lower IL-4 expression in the lung and the number of Th2 cells in the lung parenchyma was reduced. However, expression of the goblet cell markers Clca1 and Muc5a/c, abundance of mucin-positive cells, as well as weight gain of lungs were comparable between Af-challenged ΔdblGata and WT mice. Based on these results, we conclude that T cell-derived IL-4/IL-13 is essential for Af-induced lung eosinophilia and inflammation while eosinophils may play a more subtle immunomodulatory role and should not simply be regarded as pro-inflammatory effector cells in ABPA.

Anti-asthmatic effects of lepidii seu Descurainiae Semen plant species in ovalbumin-induced asthmatic mice

ETHNOPHARMACOLOGICAL EVIDENCE

Lepidii seu Descurainiae Semen (LDS) is used as a traditional herbal medicine in northeast Asia, mainly in Korea, Japan, and China to treat lung disorders including coughs and phlegm caused by acute and chronic airway inflammation.

AIM OF THE STUDY

Recently, interest regarding health problems incurred by air pollution has rapidly grown. Herbal medicines are being considered as alternative agents to treat various diseases. In the present study, we evaluated and compared the anti-inflammatory effects of LDS, which is derived from Lepidium apetalum Willd. extracts (LAE) and Descurainia sophia (L.) Webb ex Prantl extracts (DSE), on allergic airway inflammation.

MATERIALS AND METHODS

We established an ovalbumin-induced asthmatic mouse model to evaluate the efficacy of LDS extracts. We performed histological examination and measured relevant inflammatory mediators and cells in bronchoalveolar lavage fluid and lung. Furthermore, we conducted an in vitro T helper 2 (Th2) polarization assay, flow cytometry, and western blot analysis.

RESULTS

Asthmatic phenotypes were attenuated by LDS extract treatments. LDS extract administration significantly reduced mucus production, inflammatory cell infiltration into airways, and eosinophil activation. Furthermore, LDS extracts reduced the expression of type 2 cytokines and inhibited differentiation and activation of Th2 cells.

CONCLUSION

LDS alleviated eosinophilic inflammation by inhibiting Th2 cell differentiation, and DSE was more effective in attenuating allergic lung inflammation than LAE.

Aspergillus fumigatus-Secreted Alkaline Protease 1 Mediates Airways Hyperresponsiveness in Severe Asthma

The hallmark features of allergic asthma are type 2 (eosinophilic) inflammation and airways hyperresponsiveness (AHR). Although these features often comanifest in mouse lungs in vivo, we demonstrate in this study that the serine protease Alp1 from the ubiquitous mold and allergen, Aspergillus fumigatus, can induce AHR in mice unable to generate eosinophilic inflammation. Strikingly, Alp1 induced AHR in mice devoid of protease-activated receptor 2/F2 trypsin-like receptor 1 (PAR2/F2RL1), a receptor expressed in lung epithelium that is critical for allergic responses to protease-containing allergens. Instead, using precision-cut lung slices and human airway smooth muscle cells, we demonstrate that Alp1 directly increased contractile force. Taken together, these findings suggest that Alp1 induces bronchoconstriction through mechanisms that are largely independent of allergic inflammation and point to a new target for direct intervention of fungal-associated asthma.

Potential Mechanisms of T Cell-Mediated and Eosinophil-Independent Bronchial Hyperresponsiveness

Bronchial asthma is a chronic disease characterized by reversible airway obstruction, mucus production, and bronchial hyperresponsiveness (BHR). Although Th2 cell-mediated eosinophilic inflammation is an important disease mechanism in the majority of patients with bronchial asthma, recent studies suggest the possible development of Th2-independent airway inflammation and BHR. These non-Th2 endotype patients seem to consist of multiple subgroups, and often do not respond to inhaled corticosteroids. Therefore, to understand the pathogenesis of asthma, it is important to characterize these non-Th2 subgroups. Recently, we demonstrated that Th9 cells induce eosinophil infiltration and eosinophil-independent BHR, and Th9 cells-mediated BHR may be resistant to glucocorticoid. In this review, we summarize the contribution of several T cell subsets in the development of bronchial asthma and introduce our recent study demonstrating Th9 cell-mediated and eosinophil-independent BHR.

Mesenchymal stem cells for inflammatory airway disorders: promises and challenges

The regenerative and immunomodulatory characteristics of mesenchymal stem cells (MSCs) make them attractive in the treatment of many diseases. Although they have shown promising preclinical studies of immunomodulation and paracrine effects in inflammatory airway disorders and other lung diseases, there are still challenges that have to be overcome before MSCs can be safely, effectively, and routinely applied in the clinical setting. A good understanding of the roles and mechanisms of the MSC immunomodulatory effects will benefit the application of MSC-based clinical therapy. In this review, we summarize the promises and challenges of the preclinical and clinical trials of MSC therapies, aiming to better understand the role that MSCs play in attempt to treat inflammatory airway disorders.

CCL7 Is a Negative Regulator of Cutaneous Inflammation Following Leishmania major Infection

The chemokine CCL7 (MCP3) is known to promote the recruitment of many innate immune cell types including monocytes and neutrophils to sites of bacterial and viral infection and eosinophils and basophils to sites of allergic inflammation. CCL7 upregulation has been associated with many inflammatory settings including infection, cardiovascular disease, and the tumor microenvironment. CCL7's pleotropic effects are due in part to its ability to bind numerous chemokine receptors, namely CCR1, CCR2, CCR3, CCR5, and CCR10. CCL7-blockade or CCL7-deficiency is often marked by decreased inflammation and poor pathogen control. In the context of Leishmania major infection, CCL7 is specifically upregulated in the skin one-2 weeks after infection but its role in L. major control is unclear. To determine CCL7's impact on the response to L. major we infected WT and CCL7^-/- C57BL/6 mice. L. major infection of CCL7-deficient mice led to an unexpected increase in inflammation in the infected skin 2 weeks post-infection. A broad increase in immune cell subsets was observed but was dominated by enhanced neutrophilic infiltration. Increased neutrophil recruitment was associated with an enhanced IL-17 gene profile in the infected skin. CCL7 was shown to directly antagonize neutrophil migration in vitro and CCL7 add-back in vivo specifically reduced neutrophil influx into the infected skin revealing an unexpected role for CCL7 in limiting neutrophil recruitment during L. major infection. Enhanced neutrophilic infiltration in CCL7-deficient mice changed the balance of L. major infected host cells with an increase in the ratio of infected neutrophils over monocytes/macrophages. To determine the consequence of CCL7 deficiency on L. major control we analyzed parasite load cutaneously at the site of infection and viscerally in the draining LN and spleen. The CCL7^-/- mice supported robust cutaneous parasite control similar to their WT C57BL/6 counterparts. In contrast, CCL7-deficiency led to greater parasite dissemination and poor parasite control in the spleen. Our studies reveal a novel role for CCL7 in negatively regulating cutaneous inflammation, specifically neutrophils, early during L. major infection. We propose that CCL7-mediated dampening of the early immune response in the skin may limit the ability of the parasite to disseminate without compromising cutaneous control.

Eosinophil recruitment is dynamically regulated by interplay among lung dendritic cell subsets after allergen challenge

Eosinophil infiltration, a hallmark of allergic asthma, is essential for type 2 immune responses. How the initial eosinophil recruitment is regulated by lung dendritic cell (DC) subsets during the memory stage after allergen challenge is unclear. Here, we show that the initial eosinophil infiltration is dependent on lung cDC1s, which require nitric oxide (NO) produced by inducible NO synthase from lung CD24⁻CD11b⁺ DC2s for inducing CCL17 and CCL22 to attract eosinophils. During late phase responses after allergen challenge, lung CD24⁺ cDC2s inhibit eosinophil recruitment through secretion of TGF-β1, which impairs the expression of CCL17 and CCL22. Our data suggest that different lung antigen-presenting cells modulate lung cDC1-mediated eosinophil recruitment dynamically, through secreting distinct soluble factors during the memory stage of chronic asthma after allergen challenge in the mouse.

Eosinophils are important mediators of allergic responses, but how they are recruited to the inflamed site is still unclear. Here the authors show that CD103⁺ cDC1 cells secrete CCL17 and CCL22 for eosinophil recruitment, with this process promoted by CD24⁻CD11b⁺ DC2s in the early phase but suppressed by CD24⁺ cDC2s in the late phase.

The skin immune response of rainbow trout, Oncorhynchus mykiss (Walbaum), associated with puffy skin disease (PSD)

Puffy skin disease (PSD) is an emerging skin condition which affects rainbow trout, Oncorhynchus mykiss (Walbaum). The transmission pattern of PSD suggests an infectious aetiology, however, the actual causative infectious agent(s) remain(s) unknown. In the present study, the rainbow trout epidermal immune response to PSD was characterised. Skin samples from infected fish were analysed and classified as mild, moderate or severe PSD by gross pathology and histological assessment. The level of expression of 26 immune-associated genes including cytokines, immunoglobulins and cell markers were examined by TaqMan qPCR assays. A significant up-regulation of the gene expression of C3, lysozyme, IL-1β and T-bet and down-regulation of TGFβ and TLR3 was observed in PSD fish compared to control fish. MHCI gene expression was up-regulated only in severe PSD lesions. Histological examinations of the epidermis showed a significant increase in the number of eosinophil cells and dendritic melanocytes in PSD fish. In severe lesions, mild diffuse lymphocyte infiltration was observed. IgT and CD8 positive cells were detected locally in the skin of PSD fish by in situ hybridisation (ISH), however, the gene expression of those genes was not different from control fish. Total IgM in serum of diseased animals was not different from control fish, measured by a sandwich ELISA, nor was significant up regulation of IgM gene expression in PSD lesions observed. Taken together, these results show activation of the complement pathway, up-regulation of a Th17 type response and eosinophilia during PSD. This is typical of a response to extracellular pathogens (i.e. bacteria and parasites) and allergens, commonly associated with acute dermatitis.

pDCs in lung and skin fibrosis in a bleomycin-induced model and patients with systemic sclerosis

Fibrosis is the end result of most inflammatory conditions, but its pathogenesis remains unclear. We demonstrate that, in animals and humans with systemic fibrosis, plasmacytoid DCs (pDCs) are unaffected or are reduced systemically (spleen/peripheral blood), but they increase in the affected organs (lungs/skin/bronchoalveolar lavage). A pivotal role of pDCs was shown by depleting them in vivo, which ameliorated skin and/or lung fibrosis, reduced immune cell infiltration in the affected organs but not in spleen, and reduced the expression of genes and proteins implicated in chemotaxis, inflammation, and fibrosis in the affected organs of animals with bleomycin-induced fibrosis. As with animal findings, the frequency of pDCs in the lungs of patients with systemic sclerosis correlated with the severity of lung disease and with the frequency of CD4+ and IL-4+ T cells in the lung. Finally, treatment with imatinib that has been reported to reduce and/or prevent deterioration of skin and lung fibrosis profoundly reduced pDCs in lungs but not in peripheral blood of patients with systemic sclerosis. These observations suggest a role for pDCs in the pathogenesis of systemic fibrosis and identify the increased trafficking of pDCs to the affected organs as a potential therapeutic target in fibrotic diseases.

Eosinophils in fungal diseases: An overview

Eosinophils are the prominent cells in asthma, allergic bronchopulmonary mycosis (ABPMs), and fungal-sensitization-associated asthma, but their roles in the immunopathology of these disorders are not well understood. Moreover, the immunological mechanisms underlying the molecular direct effector interactions between fungi and eosinophils are rare and not fully known. Here, we provide an overview of eosinophil contributions to allergic asthma and ABPMs. We also revise the major general mechanisms of fungal recognition by eosinophils and consider past and recent advances in our understanding of the molecular mechanisms associated with eosinophil innate effector responses to different fungal species relevant to ABPMs (Alternaria alternata, Candida albicans, and Aspergillus fumigatus). We further examine and speculate about the therapeutic relevance of these findings in fungus-associated allergic pulmonary diseases.

Frontline Science: Eosinophil-deficient MBP-1 and EPX double-knockout mice link pulmonary remodeling and airway dysfunction with type 2 inflammation

Eosinophils and the release of cationic granule proteins have long been implicated in the development of the type 2-induced pathologies linked with respiratory inflammation. Paradoxically, the ablation of the two genes encoding the most abundant of these granule proteins, major basic protein-1 (MBP-1) and eosinophil peroxidase (EPX), results in a near collapse of eosinophilopoiesis. The specificity of this lineage ablation and the magnitude of the induced eosinopenia provide a unique opportunity to clarify the importance of eosinophils in acute and chronic inflammatory settings, as well as to identify potential mechanism(s) of action linked with pulmonary eosinophils in those settings. Specifically, we examined these issues by assessing the induced immune responses and pathologies occurring in MBP-1^-/-/EPX^-/- mice after 1) ovalbumin sensitization/provocation in an acute allergen-challenge protocol, and 2) crossing MBP-1^-/-/EPX^-/- mice with a double-transgenic model of chronic type 2 inflammation (i.e., I5/hE2). Acute allergen challenge and constitutive cytokine/chemokine expression each induced the accumulation of pulmonary eosinophils in wild-type controls that was abolished in the absence of MBP-1 and EPX (i.e., MBP-1^-/-/EPX^-/- mice). The expression of MBP-1 and EPX was also required for induced lung expression of IL-4/IL-13 in each setting and, in turn, the induced pulmonary remodeling events and lung dysfunction. In summary, MBP-1^-/-/EPX^-/- mice provide yet another definitive example of the immunoregulatory role of pulmonary eosinophils. These results highlight the utility of this unique strain of eosinophil-deficient mice as part of in vivo model studies investigating the roles of eosinophils in health and disease settings.

Innate immunity as the orchestrator of allergic airway inflammation and resolution in asthma

The respiratory system is constantly in direct contact with the environment and, has therefore, developed strong innate and adaptive immune responses to combat pathogens. Unlike adaptive immunity which is mounted later in the course of the immune response and is naive at the outset, innate immunity provides the first line of defense against microbial agents, while also promoting resolution of inflammation. In the airways, innate immune effector cells mainly consist of eosinophils, neutrophils, mast cells, basophils, macrophages/monocytes, dendritic cells and innate lymphoid cells, which attack pathogens directly or indirectly through the release of inflammatory cytokines and antimicrobial peptides, and coordinate T and B cell-mediated adaptive immunity. Airway epithelial cells are also critically involved in shaping both the innate and adaptive arms of the immune response. Chronic allergic airway inflammation and linked asthmatic disease is often considered a result of aberrant activation of type 2 T helper cells (Th2) towards innocuous environmental allergens; however, innate immune cells are increasingly recognized as key players responsible for the initiation and the perpetuation of allergic responses. Moreover, innate cells participate in immune response regulation through the release of anti-inflammatory mediators, and guide tissue repair and the maintenance of airway homeostasis. The scope of this review is to outline existing knowledge on innate immune responses involved in allergic airway inflammation, highlight current gaps in our understanding of the underlying molecular and cellular mechanisms and discuss the potential use of innate effector cells in new therapeutic avenues.

Eosinophils are required to suppress Th2 responses in Peyer's patches during intestinal infection by nematodes

Infections with enteric nematodes result in systemic type 2 helper T (Th2) responses, expansion of immunoglobulin (Ig)G1 antibodies, and eosinophilia. Eosinophils have a supportive role in mucosal Th2 induction during airway hyperreactivity. Whether eosinophils affect the local T-cell and antibody response in the gut-associated lymphoid tissue during enteric infections is unknown. We infected eosinophil-deficient ΔdblGATA-1 mice with the Th2-inducing small intestinal nematode Heligmosomoides polygyrus and found that parasite fecundity was decreased in the absence of eosinophils. A lack of eosinophils resulted in significantly augmented expression of GATA-3 and IL-4 by CD4⁺ T cells during acute infection, a finding strictly limited to Peyer's patches (PP). The increase in IL-4-producing cells in ΔdblGATA-1 mice was particularly evident within the CXCR5⁺PD-1⁺ T-follicular helper cell population and was associated with a switch of germinal centre B cells to IgG1 production and elevated serum IgG1 levels. In contrast, infected wild-type mice had a modest IgG1 response in the PP, whereas successfully maintaining a population of IgA⁺ germinal center B cells. Our results suggest a novel role for eosinophils during intestinal infection whereby they restrict IL-4 responses by follicular T helper cells and IgG1 class switching in the PP to ensure maintenance of local IgA production.

Eosinophilic Lung Disease

Eosinophils are involved in the pathogenesis of a number of lung diseases. Recent advances in eosinophil biology have now produced clinically applicable therapies that seek to counter eosinophilia in blood and lungs. This article reviews the basic biology of eosinophils and their role in mediating T-helper 2 cell responses. The current status of anticytokine therapy for eosinophilic lung disease is discussed. A clinical approach to eosinophilic lung disease based on symptoms and radiography is generated. The clinical significance of persistent eosinophilia in lung transplant patients and patients with asthma will receive special emphasis.

Myeloid Cells in Asthma

Asthma is a heterogeneous chronic inflammatory disorder of the airways, and not surprisingly, many myeloid cells play a crucial role in pathogenesis. Antigen-presenting dendritic cells are the first to recognize the allergens, pollutants, and viruses that are implicated in asthma pathogenesis, and subsequently initiate the adaptive immune response by migrating to lymph nodes. Eosinophils are the hallmark of type 2 inflammation, releasing toxic compounds in the airways and contributing to airway remodeling. Mast cells and basophils control both the early- and late-phase allergic response and contribute to alterations in smooth muscle reactivity. Finally, relatively little is known about neutrophils and macrophages in this disease. Although many of these myeloid cells respond well to treatment with inhaled steroids, there is now an increasing armamentarium of targeted biologicals that can specifically eliminate only one myeloid cell population, like eosinophils. It is only with those new tools that we will be able to fully understand the role of myeloid cells in chronic asthma in humans.

Eosinophils in Helminth Infection: Defenders and Dupes

Eosinophilia is a central feature of the host response to helminth infection. Larval stages of parasitic worms are killed in vitro by eosinophils in the presence of specific antibodies or complement. These findings established host defense as the paradigm for eosinophil function. Recently, studies in eosinophil-ablated mouse strains have revealed an expanded repertoire of immunoregulatory functions for this cell. Other reports document crucial roles for eosinophils in tissue homeostasis and metabolism, processes that are central to the establishment and maintenance of parasitic worms in their hosts. In this review, we summarize current understanding of the significance of eosinophils at the host-parasite interface, highlighting their distinct functions during primary and secondary exposure.

p110γ/δ Double-Deficiency Induces Eosinophilia and IgE Production but Protects from OVA-Induced Airway Inflammation

The catalytical isoforms p110γ and p110δ of phosphatidylinositide 3-kinase γ (PI3Kγ) and PI3Kδ play an important role in the pathogenesis of asthma. Two key elements in allergic asthma are increased levels of eosinophils and IgE. Dual pharmacological inhibition of p110γ and p110δ reduces asthma-associated eosinophilic lung infiltration and ameliorates disease symptoms, whereas the absence of enzymatic activity in p110γ^KOδ^D910A mice increases IgE and basal eosinophil counts. This suggests that long-term inhibition of p110γ and p110δ might exacerbate asthma. Here, we analysed mice genetically deficient for both catalytical subunits (p110γ/δ^-/-) and determined basal IgE and eosinophil levels and the immune response to ovalbumin-induced asthma. Serum concentrations of IgE, IL-5 and eosinophil numbers were significantly increased in p110γ/δ^-/- mice compared to single knock-out and wildtype mice. However, p110γ/δ^-/- mice were protected against OVA-induced infiltration of eosinophils, neutrophils, T and B cells into lung tissue and bronchoalveolar space. Moreover, p110γ/δ^-/- mice, but not single knock-out mice, showed a reduced bronchial hyperresponsiveness. We conclude that increased levels of eosinophils and IgE in p110γ/δ^-/- mice do not abolish the protective effect of p110γ/δ-deficiency against OVA-induced allergic airway inflammation.

A Player and Coordinator: The Versatile Roles of Eosinophils in the Immune System

Eosinophils have traditionally been associated with allergic diseases and parasite infection. Research advances in the recent decades have brought evolutionary changes in our understanding of eosinophil biology and its roles in immunity. It is currently recognized that eosinophils play multiple roles in both innate and adaptive immunity. As effector cells in innate immunity, eosinophils exert a pro-inflammatory and destructive role in the Th2 immune response associated with allergic inflammation or parasite infection. Eosinophils can also be recruited by danger signals released by pathogen infections or tissue injury, inducing host defense against parasitic, fungal, bacterial or viral infection or promoting tissue repair and remodeling. Eosinophils also serve as nonprofessional antigen-presenting cells in response to allergen challenge or helminth infection, and, meanwhile, are known to function as a versatile coordinator that actively regulates or interacts with various immune cells including T lymphocytes and dendritic cells. More roles of eosinophils implicated in immunity have been proposed including in immune homeostasis, allograft rejection, and anti-tumor immunity. Eosinophil interactions with structural cells are also implicated in the mechanisms in allergic inflammation and in Helicobacter pylori gastritis. These multifaceted roles of eosinophils as both players and coordinators in immune system are discussed in this review.

Differences in allergic inflammatory responses between urban PM2.5 and fine particle derived from desert-dust in murine lungs

The biological and chemical natures of materials adsorbed onto fine particulate matter (PM2.5) vary by origin and passage routes. The exacerbating effects of the two samples-urban PM2.5 (U-PM2.5) collected during the hazy weather in a Chinese city and fine particles (ASD-PM2.5) collected during Asian sand dust (ASD) storm event days in Japan-on murine lung eosinophilia were compared to clarify the role of toxic materials in PM2.5. The amounts of β-glucan and mineral components were higher in ASD-PM2.5 than in U-PM2.5. On the other hand, organic chemicals, including polycyclic aromatic hydrocarbons (PAHs), were higher in U-PM2.5 than in ASD-PM2.5. When BALB/c mice were intratracheally instilled with U-PM2.5 and ASD-PM2.5 (total 0.4 mg/mouse) with or without ovalbumin (OVA), various biological effects were observed, including enhancement of eosinophil recruitment induced by OVA in the submucosa of the airway, goblet cell proliferation in the bronchial epithelium, synergic increase of OVA-induced eosinophil-relevant cytokines and a chemokine in bronchoalveolar lavage fluid, and increase of serum OVA-specific IgG1 and IgE. Data demonstrate that U-PM2.5 and ASD-PM2.5 induced allergic inflammatory changes and caused lung pathology. U-PM2.5 and ASD-PM2.5 increased F4/80(+) CD11b(+) cells, indicating that an influx of inflammatory and exudative macrophages in lung tissue had occurred. The ratio of CD206 positive F4/80(+) CD11b(+) cells (M2 macrophages) in lung tissue was higher in the OVA+ASD-PM2.5 treated mice than in the OVA+U-PM2.5 treated mice. These results suggest that the lung eosinophilia exacerbated by both PM2.5 is due to activation of a Th2-associated immune response along with induced M2 macrophages and the exacerbating effect is greater in microbial element (β-glucan)-rich ASD-PM2.5 than in organic chemical-rich U-PM2.5.

T cells are the critical source of IL-4/IL-13 in a mouse model of allergic asthma

BACKGROUND

IL-4 and IL-13 play a crucial role during allergic asthma. Both cytokines can be produced by T cells and a variety of cell types of the innate immune system. The relative contribution of T-cell-derived vs innate IL-4/IL-13 for allergic inflammation and airway hyperreactivity remains unclear.

METHODS

We compared the severity of OVA/alum-induced allergic lung inflammation in WT BALB/c mice to mice that lack expression of IL-4/IL-13 only in T cells (4-13Tko) or in all cell types (4-13ko).

RESULTS

T-cell-derived IL-4/IL-13 was required for IgG1 and IgE production, recruitment of eosinophils and basophils to the lung, goblet cell hyperplasia, expression of Muc5ac, Clca3, and RELMβ, differentiation of alternatively activated macrophages, and airway hyperreactivity. Interestingly, ILC2 recruitment to the lung occurred independently of T-cell-derived IL-4/IL-13 but was diminished in the absence of IL-4/IL-13 from all cell types. Thus, the number of IL-4/IL-13-competent ILC2s did not correlate with the severity of lung pathology.

CONCLUSIONS

Th2 cells appear to be the critical IL-4/IL-13-expressing cell type for the induction of allergic airway inflammation and airway hyperreactivity. The translational perspective of our results indicates that inhibition or reprogramming of Th2 cells may be very effective for the treatment of allergic asthma.

Differential activation of airway eosinophils induces IL-13-mediated allergic Th2 pulmonary responses in mice

BACKGROUND

Eosinophils are hallmark cells of allergic Th2 respiratory inflammation. However, the relative importance of eosinophil activation and the induction of effector functions such as the expression of IL-13 to allergic Th2 pulmonary disease remain to be defined.

METHODS

Wild-type or cytokine-deficient (IL-13(-/-) or IL-4(-/-) ) eosinophils treated with cytokines (GM-CSF, IL-4, IL-33) were adoptively transferred into eosinophil-deficient recipient mice subjected to allergen provocation using established models of respiratory inflammation. Allergen-induced pulmonary changes were assessed.

RESULTS

In contrast to the transfer of untreated blood eosinophils to the lungs of recipient eosinophil deficient mice, which induced no immune/inflammatory changes either in the lung or in the lung draining lymph nodes (LDLN), pretreatment of blood eosinophils with GM-CSF prior to transfer elicited trafficking of these eosinophils to LDLN. In turn, these LDLN eosinophils elicited the accumulation of dendritic cells and CD4(+) T cells to these same LDLNs without inducing pulmonary inflammation. However, exposure of eosinophils to GM-CSF, IL-4, and IL-33 prior to transfer induced not only immune events in the LDLN, but also allergen-mediated increases in airway Th2 cytokine/chemokine levels, the subsequent accumulation of CD4(+) T cells as well as alternatively activated (M2) macrophages, and the induction of pulmonary histopathologies. Significantly, this allergic respiratory inflammation was dependent on eosinophil-derived IL-13, whereas IL-4 expression by eosinophils had no significant role.

CONCLUSION

The data demonstrate the differential activation of eosinophils as a function of cytokine exposure and suggest that eosinophil-specific IL-13 expression by activated cells is a necessary component of the subsequent allergic Th2 pulmonary pathologies.

Mouse models of allergic asthma

In the last 20 years, the development of murine models of allergic asthma has provided researchers with a means to explore the mechanisms of this T-helper type 2 (Th2)-driven inflammatory disease. While systemic sensitization and airway challenge with ovalbumin has been the most widely used model, recent emphasis has been placed on the development of models using more naturally occurring antigens. However, the diversity of models currently available makes it hard for investigators new to this field to choose to use the most effective and appropriate model to test their hypothesis. Here we describe three different mouse models of allergic asthma, including the classical ovalbumin model, a modified ovalbumin model that has been shown to be mast-cell dependent, as well as a house dust mite antigen-induced model. We also discuss briefly their characterization and differences, in the aim to facilitate the choice of the appropriate model when working on this intricate Th2 inflammatory disease.

Re-defining the unique roles for eosinophils in allergic respiratory inflammation

The role of eosinophils in the progression and resolution of allergic respiratory inflammation is poorly defined despite the commonality of their presence and in some cases their use as a biomarker for disease severity and/or symptom control. However, this ambiguity belies the wealth of insights that have recently been gained through the use of eosinophil-deficient/attenuated strains of mice that have demonstrated novel immunoregulatory and remodelling/repair functions for these cells in the lung following allergen provocation. Specifically, studies of eosinophil-deficient mice suggest that eosinophils contribute to events occurring in the lungs following allergen provocation at several key moments: (i) the initiating phase of events leading to Th2-polarized pulmonary inflammation, (ii) the suppression Th1/Th17 pathways in lung-draining lymph nodes, (iii) the recruitment of effector Th2 T cells to the lung, and finally, (iv) mechanisms of inflammatory resolution that re-establish pulmonary homoeostasis. These suggested functions have recently been confirmed and expanded upon using allergen provocation of an inducible eosinophil-deficient strain of mice (iPHIL) that demonstrated an eosinophil-dependent mechanism(s) leading to Th2 dominated immune responses in the presence of eosinophils in contrast to neutrophilic as well as mixed Th1/Th17/Th2 variant phenotypes in the absence of eosinophils. These findings highlighted that eosinophils are not exclusively downstream mediators controlled by T cells, dendritic cells (DC) and/or innate lymphocytic cells (ILC2). Instead, eosinophils appear to be more aptly described as significant contributors in complex interrelated pathways that lead to pulmonary inflammation and subsequently promote resolution and the re-establishment of homoeostatic baseline. In this review, we summarize and put into the context the evolving hypotheses that are now expanding our understanding of the roles eosinophils likely have in the lung following allergen provocation.

Eosinophils in mucosal immune responses

Eosinophils, multifunctional cells that contribute to both innate and adaptive immunity, are involved in the initiation, propagation, and resolution of immune responses, including tissue repair. They achieve this multifunctionality by expression of a diverse set of activation receptors, including those that directly recognize pathogens and opsonized targets, and by their ability to store and release preformed cytotoxic mediators that participate in host defense, to produce a variety of de novo pleotropic mediators and cytokines, and to interact directly and indirectly with diverse cell types, including adaptive and innate immunocytes and structural cells. Herein, we review the basic biology of eosinophils and then focus on new emerging concepts about their role in mucosal immune homeostasis, particularly maintenance of intestinal IgA. We review emerging data about their development and regulation and describe new concepts concerning mucosal eosinophilic diseases. We describe recently developed therapeutic strategies to modify eosinophil levels and function and provide collective insight about the beneficial and detrimental functions of these enigmatic cells.

Cutting edge: STAT6 signaling in eosinophils is necessary for development of allergic airway inflammation

Eosinophils are critical cellular mediators in allergic asthma and inflammation; however, the signals that regulate their functions are unclear. The transcription factor STAT6 regulates Th2 cytokine responses, acting downstream of IL-4 and IL-13. We showed previously that eosinophil-derived IL-13 plays an important role in the recruitment of T cells to the lung and the subsequent development of allergic asthma. However, whether eosinophils respond to Th2 signals to control allergic airway inflammation is unclear. In this report, we show that STAT6(-/-) eosinophils are unable to induce the development of allergic lung inflammation, including recruitment of CD4(+) T cells, mucus production, and development of airways hyperresponsiveness. This is likely due to the reduced migration of STAT6(-/-) eosinophils to the lung and in response to eotaxin. These data indicate that, like Th cells, eosinophils need to respond to Th2 cytokines via STAT6 during the development of allergic airway inflammation.

Eosinophils contribute to the resolution of lung-allergic responses following repeated allergen challenge

BACKGROUND

Eosinophils accumulate at the site of allergic inflammation and are critical effector cells in allergic diseases. Recent studies have also suggested a role for eosinophils in the resolution of inflammation.

OBJECTIVE

To determine the role of eosinophils in the resolution phase of the response to repeated allergen challenge.

METHODS

Eosinophil-deficient (PHIL) and wild-type (WT) littermates were sensitized and challenged to ovalbumin (OVA) 7 or 11 times. Airway inflammation, airway hyperresponsiveness (AHR) to inhaled methacholine, bronchoalveolar lavage (BAL) cytokine levels, and lung histology were monitored. Intracellular cytokine levels in BAL leukocytes were analyzed by flow cytometry. Groups of OVA-sensitized PHIL mice received bone marrow from WT or IL-10(-/-) donors 30 days before the OVA challenge.

RESULTS

PHIL and WT mice developed similar levels of AHR and numbers of leukocytes and cytokine levels in BAL fluid after OVA sensitization and 7 airway challenges; no eosinophils were detected in the PHIL mice. Unlike WT mice, sensitized PHIL mice maintained AHR, lung inflammation, and increased levels of IL-4, IL-5, and IL-13 in BAL fluid after 11 challenges whereas IL-10 and TGF-β levels were decreased. Restoration of eosinophil numbers after injection of bone marrow from WT but not IL-10-deficient mice restored levels of IL-10 and TGF-β in BAL fluid as well as suppressed AHR and inflammation. Intracellular staining of BAL leukocytes revealed the capacity of eosinophils to produce IL-10.

CONCLUSIONS

After repeated allergen challenge, eosinophils appeared not essential for the development of AHR and lung inflammation but contributed to the resolution of AHR and inflammation by producing IL-10.