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The molecular mechanisms by which worm parasites evade host immunity are incompletely understood. In a mouse model of intestinal helminth infection using Heligmosomoides polygyrus bakeri (Hpb), we show that helminthic glutamate dehydrogenase (heGDH) drives parasite chronicity by suppressing macrophage-mediated host defense. Combining RNA-seq, ChIP-seq, and targeted lipidomics, we identify prostaglandin E2 (PGE2) as a major immune regulatory mechanism of heGDH. The induction of PGE2 and other immunoregulatory factors, including IL-12 family cytokines and indoleamine 2,3-dioxygenase 1, by heGDH required p300-mediated histone acetylation, whereas the enzyme's catalytic activity suppressed the synthesis of type 2–promoting leukotrienes by macrophages via 2-hydroxyglutarate. By contrast, the induction of immunoregulatory factors involved the heGDH N terminus by potentially mediating interactions with cellular targets (CD64 and GPNMB) identified by proteomics. Type 2 cytokines counteracted suppressive effects of heGDH on host defense, indicating that type 2 immunity can limit helminth-driven immune evasion. Thus, helminths harness a ubiquitous metabolic enzyme to epigenetically target type 2 macrophage activation and establish chronicity. Editor's summary: The murine intestinal helminth parasite Heligmosomoides polygyrus bakeri (Hpb) is a key tool in understanding how helminths can suppress type 2 immune responses and facilitate chronic infection. Bohnacker et al. examined how uptake of helminthic glutamate dehydrogenase (heGDH) by macrophages suppresses immune responses. heGDH-driven p300-mediated histone acetylation led to induction of different immune regulatory factors, including prostaglandin E2 (PGE2), which suppressed T helper 2 cell and alternative macrophage activation. In addition, the catalytic activity of heGDH inhibited macrophage production of leukotrienes that also are needed to promote type 2 immunity. These findings provide insights into how heGDH can enable helminth immune evasion by multiple mechanisms. —Christiana N. Fogg [ABSTRACT FROM AUTHOR]

Background: Allergen-specific immunotherapy (AIT) is able to restore immune tolerance to allergens in allergic patients. However, some patients do not or only poorly respond to current treatment protocols. Therefore, there is a need for deeper mechanistic insights and further improvement of treatment strategies. The relevance of the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, has been investigated in several inflammatory diseases, including allergic asthma. However, its potential role in AIT still needs to be addressed. Methods: Amurinemodel of AIT in ovalbumin-induced allergic airway inflammation was performed in AhR-deficient (AhR-/-) and wild-type mice. Furthermore, AIT was combined with the application of the high-affinity AhR agonist 10-chloro-7Hbenzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (10-Cl-BBQ) as an adjuvant to investigate the effects of AhR activation on therapeutic outcome. Results: Although AhR-/- mice suffer stronger allergic responses than wild-type mice, experimental AIT is comparably effective in both. Nevertheless, combining AIT with the administration of 10-Cl-BBQ improved therapeutic effects by an AhRdependent mechanism, resulting in decreased cell counts in the bronchoalveolar fluid, decreased pulmonary Th2 and Th17 cell levels, and lower sIgE levels. Conclusion: This study demonstrates that the success of AIT is not dependent on the AhR. However, targeting the AhR during AIT can help to dampen inflammation and improve tolerogenic vaccination. Therefore, AhR ligands might represent promising candidates as immunomodulators to enhance the efficacy of AIT. [ABSTRACT FROM AUTHOR]

Background: Native allergen extracts or chemically modified allergoids are routinely used to induce allergen tolerance in allergen‐specific immunotherapy (AIT), although mechanistic side‐by‐side studies are rare. It is paramount to balance optimal dose and allergenicity to achieve efficacy warranting safety. AIT safety and efficacy could be addressed by allergen dose reduction and/or use of allergoids and immunostimulatory adjuvants, respectively. In this study, immunological effects of experimental house dust mite (HDM) AIT were investigated applying high‐dose HDM extract and low‐dose HDM allergoids with and without the adjuvants microcrystalline tyrosine (MCT) and monophosphoryl lipid A (MPL) in a murine model of HDM allergy. Methods: Cellular, humoral, and clinical effects of the different AIT strategies were assessed applying a new experimental AIT model of murine allergic asthma based on physiological, adjuvant‐free intranasal sensitization followed by subcutaneous AIT. Results: While low‐dose allergoid and high‐dose extract AIT demonstrated comparable potency to suppress allergic airway inflammation and Th2‐type cytokine secretion of lung‐resident lymphocytes and draining lymph node cells, low‐dose allergoid AIT was less effective in inducing a potentially protective IgG1 response. Combining low‐dose allergoid AIT with MCT or MCT and dose‐adjusted MPL promoted Th1‐inducing mechanisms and robust B‐cell activation counterbalancing the allergic Th2 immune response. Conclusion: Low allergen doses induce cellular and humoral mechanisms counteracting Th2‐driven inflammation by using allergoids and dose‐adjusted adjuvants. In light of safety and efficacy improvement, future therapeutic approaches may use low‐dose allergoid strategies to drive cellular tolerance and adjuvants to modulate humoral responses. [ABSTRACT FROM AUTHOR]

The expression of preprotachykinin gene-I messenger RNA (mRNA) that encodes the tachykinins substance P and neurokinin A in alveolar macrophages was investigated. Adult Sprague-Dawley rats were used as experimental models to examine gene regulation during lung inflammation. Results showed that in vivo or in vitro treatment with lipopolysaccharide stimulated the expression of preprotachykinin gene-I mRNA. Neutrophils produced in the lungs after in vivo lipopolysaccharide exposure also expressed preprotachykinin gene-I mRNA.

Background: Studies show that proallergic TH2 cells decrease after successful allergen‐specific immunotherapy (AIT). It is likely that iatrogenic administration of allergens drives these cells to exhaustion due to chronic T‐cell receptor stimulation. This study aimed to investigate the exhaustion of T cells in connection with allergen exposure during AIT in mice and two independent patient cohorts. Methods: OVA‐sensitized C57BL/6J mice were challenged and treated with OVA, and the development of exhaustion in local and systemic TH2 cells was analyzed. In patients, the expression of exhaustion‐associated surface markers on TH2 cells was evaluated using flow cytometry in a cross‐sectional grass pollen allergy cohort with and without AIT. The treatment effect was further studied in PBMC collected from a prospective long‐term AIT cohort. Results: The exhaustion‐associated surface markers CTLA‐4 and PD‐1 were significantly upregulated on TH2 cells upon OVA aerosol exposure in OVA‐allergic compared to non‐allergic mice. CTLA‐4 and PD‐1 decreased after AIT, in particular on the surface of local lung TH2 cells. Similarly, CTLA‐4 and PD‐1 expression was enhanced on TH2 cells from patients with allergic rhinitis with an even stronger effect in those with concomitant asthma. Using an unbiased Louvain clustering analysis, we discovered a late‐differentiated TH2 population expressing both markers that decreased during up‐dosing but persisted long term during the maintenance phase. Conclusions: This study shows that allergen exposure promotes CTLA‐4 and PD‐1 expression on TH2 cells and that the dynamic change in frequencies of exhausted TH2 cells exhibits a differential pattern during the up‐dosing versus the maintenance phases of AIT. [ABSTRACT FROM AUTHOR]

Abstract Background Exposure to ultrafine particles exerts diverse harmful effects including aggravation of pulmonary diseases like asthma. Recently we demonstrated in a mouse model for allergic airway inflammation that particle-derived oxidative stress plays a crucial role during augmentation of allergen-induced lung inflammation by ultrafine carbon particle (UfCP) inhalation. The mechanisms how particle inhalation might change the inflammatory balance in the lungs, leading to accelerated inflammatory reactions, remain unclear. Lipid mediators, known to be immediately generated in response to tissue injury, might be strong candidates for priming this particle-triggered change of the inflammatory balance. Methods We hypothesize that inhalation of UfCP may disturb the balance of pro- and anti-inflammatory lipid mediators in: i) a model for acute allergic pulmonary inflammation, exposing mice for 24 h before allergen challenge to UfCP inhalation (51.7 nm, 507 μg/m3), and ii) an in-vitro model with primary rat alveolar macrophages (AM) incubated with UfCP (10 μg/1 x 106 cells/ml) for 1 h. Lungs and AM were analysed for pro- and anti-inflammatory lipid mediators, namely leukotriene B4 (LTB4), prostaglandin E2 (PGE2), 15(S)-hydroxy-eicosatetraenoic acid (15(S)-HETE), lipoxin A4 (LXA4) and oxidative stress marker 8-isoprostane by enzyme immunoassays and immunohistochemistry. Results In non-sensitized mice UfCP exposure induced a light non-significant increase of all lipid mediators. Similarly but significantly in rat AM all lipid mediators were induced already within 1 h of UfCP stimulation. Also sensitized and challenge mice exposed to filtered air showed a partially significant increase in all lipid mediators. In sensitized and challenged mice UfCP exposure induced highest significant levels of all lipid mediators in the lungs together with the peak of allergic airway inflammation on day 7 after UfCP inhalation. The levels of LTB4, 8-isoprostane and PGE2 were significantly increased also one day after UfCP exposure. Immunohistochemistry localized highest concentrations of PGE2 especially in AM one day after UfCP exposure. Conclusion Our results suggest that UfCP exposure affects the balance between pro- and anti-inflammatory lipid mediators. In allergic mice, where the endogenous balance of pro- and anti-inflammatory mediators is already altered, UfCP exposure aggravates the inflammation and the increase in anti-inflammatory, pro-resolving lipid mediators is insufficient to counterbalance the extensive inflammatory response. This may be a contributing mechanism that explains the increased susceptibility of asthmatic patients towards particle exposure.

Abstract Background Clara cell protein (CC16), the main secretory product of bronchiolar Clara cells, plays an important protective role in the respiratory tract against oxidative stress and inflammation. The purpose of the study was to investigate the role of elemental carbon ultrafine particles (EC-UFP)-induced oxidative stress on Clara cells and CC16 in a mouse model of allergic lung inflammation. Methods Ovalbumin (OVA)-sensitized mice were exposed to EC-UFP (507 μg/m3 for 24 h) or filtered air immediately prior to allergen challenge and systemically treated with N-acetylcysteine (NAC) or vehicle prior and during EC-UFP inhalation. CC16 was measured up to one week after allergen challenge in bronchoalveolar lavage fluid (BALF) and in serum. The relative expression of CC16 and TNF-α mRNA were measured in lung homogenates. A morphometrical analysis of mucus hypersecretion and electron microscopy served to investigate goblet cell metaplasia and Clara cell morphological alterations. Results In non sensitized mice EC-UFP inhalation caused alterations in CC16 concentration, both at protein and mRNA level, and induced Clara cell hyperplasia. In sensitized mice, inhalation of EC-UFP prior to OVA challenge caused most significant alterations of BALF and serum CC16 concentration, BALF total protein and TNF-α relative expression compared to relevant controls; their Clara cells displayed the strongest morphological alterations and strongest goblet cell metaplasia occurred in the small airways. NAC strongly reduced both functional and morphological alterations of Clara cells. Conclusion Our findings demonstrate that oxidative stress plays an important role in EC-UFP-induced augmentation of functional and morphological alterations of Clara cells in allergic lung inflammation.

Background: Common ragweed has been spreading as a neophyte in Europe. Elevated CO2 levels, a hallmark of global climate change, have been shown to increase ragweed pollen production, but their effects on pollen allergenicity remain to be elucidated. Methods: Ragweed was grown in climate‐controlled chambers under normal (380 ppm, control) or elevated (700 ppm, based on RCP4.5 scenario) CO2 levels. Aqueous pollen extracts (RWE) from control‐ or CO2‐pollen were administered in vivo in a mouse model for allergic disease (daily for 3‐11 days, n = 5) and employed in human in vitro systems of nasal epithelial cells (HNECs), monocyte‐derived dendritic cells (DCs), and HNEC‐DC co‐cultures. Additionally, adjuvant factors and metabolites in control‐ and CO2‐RWE were investigated using ELISA and untargeted metabolomics. Results: In vivo, CO2‐RWE induced stronger allergic lung inflammation compared to control‐RWE, as indicated by lung inflammatory cell infiltrate and mediators, mucus hypersecretion, and serum total IgE. In vitro, HNECs stimulated with RWE increased indistinctively the production of pro‐inflammatory cytokines (IL‐8, IL‐1β, and IL‐6). In contrast, supernatants from CO2‐RWE‐stimulated HNECs, compared to control‐RWE‐stimulated HNECS, significantly increased TNF and decreased IL‐10 production in DCs. Comparable results were obtained by stimulating DCs directly with RWEs. The metabolome analysis revealed differential expression of secondary plant metabolites in control‐ vs CO2‐RWE. Mixes of these metabolites elicited similar responses in DCs as compared to respective RWEs. Conclusion: Our results indicate that elevated ambient CO2 levels elicit a stronger RWE‐induced allergic response in vivo and in vitro and that RWE increased allergenicity depends on the interplay of multiple metabolites. [ABSTRACT FROM AUTHOR]