Germ-Free Mice Exhibit Mast Cells With Impaired Functionality and Gut Homing and Do Not Develop Food Allergy.

Background: Mucosal mast cells (MC) are key players in IgE-mediated food allergy (FA). The evidence on the interaction between gut microbiota, MC and susceptibility to FA is contradictory. Objective: We tested the hypothesis that commensal bacteria are essential for MC migration to the gut and their maturation impacting the susceptibility to FA. Methods: The development and severity of FA symptoms was studied in sensitized germ-free (GF), conventional (CV), and mice mono-colonized with L. plantarum WCFS1 or co-housed with CV mice. MC were phenotypically and functionally characterized. Results: Systemic sensitization and oral challenge of GF mice with ovalbumin led to increased levels of specific IgE in serum compared to CV mice. Remarkably, despite the high levels of sensitization, GF mice did not develop diarrhea or anaphylactic hypothermia, common symptoms of FA. In the gut, GF mice expressed low levels of the MC tissue-homing markers CXCL1 and CXCL2, and harbored fewer MC which exhibited lower levels of MC protease-1 after challenge. Additionally, MC in GF mice were less mature as confirmed by flow-cytometry and their functionality was impaired as shown by reduced edema formation after injection of degranulation-provoking compound 48/80. Co-housing of GF mice with CV mice fully restored their susceptibility to develop FA. However, this did not occur when mice were mono-colonized with L. plantarum. Conclusion: Our results demonstrate that microbiota-induced maturation and gut-homing of MC is a critical step for the development of symptoms of experimental FA. This new mechanistic insight into microbiota-MC-FA axis can be exploited in the prevention and treatment of FA in humans.

Oocyst-Derived Extract of Toxoplasma Gondii Serves as Potent Immunomodulator in a Mouse Model of Birch Pollen Allergy.

INTRODUCTION: Previously, we have shown that oral infection with Toxoplasma gondii oocysts prevented type I allergy in mice. Here we investigated whether the application of a T. gondii oocyst lysate antigen (OLA) could also reduce allergy development. BALB/c mice were immunised twice with OLA followed by sensitisation with the major birch pollen (BP) allergen Bet v 1 and an aerosol challenge with BP extract. METHODS: First, we tested OLA in vitro. Stimulation of splenocytes and bone marrow-derived dendritic cells (BMDC) with OLA led to the production of pro-inflammatory and regulatory cytokines such as IL-6, IFN-γ and IL-10. Moreover, BMDC exposed to OLA upregulated the maturation markers CD40, CD80, CD86, and MHCII. Furthermore, OLA was recognised by TLR2-transfected human embryonic kidney cells. RESULTS: Immunisation of mice with OLA induced high levels of Toxoplasma-specific IgG antibodies in sera along with increased production of IFN-γ and IL-10 in Toxoplasma-antigen restimulated splenocytes. OLA reduced allergic airway inflammation as manifested by significant reduction of eosinophils in bronchoalveolar fluids, decreased cellular infiltrates and mucus production in the lungs. Accordingly, Bet v 1-specific IgE was decreased in OLA-pretreated mice. The reduced allergic immune responses were accompanied by increased numbers of CD4+CD25highFoxp3+ regulatory T cells in spleens as well as by increased numbers of granulocytic myeloid-derived suppressor cells in lungs when compared to sensitised controls suggesting that these two cell populations might be involved in the suppression of the allergic immune responses. CONCLUSION: Our data demonstrate that pretreatment with the oocyst extract can exert anti-allergic effects comparable to T. gondii infection. Thus, the immunomodulatory properties of the parasite extract indicate that this extract and in the future defined molecules thereof might serve as immunomodulatory adjuvants in allergy treatment and prophylaxis.

The Role of Alveolar Epithelial Type II-Like Cells in Uptake of Structurally Different Antigens and in Polarisation of Local Immune Responses.

BACKGROUND: Our previous studies on intranasal tolerance induction demonstrated reduction of allergic responses with different allergen constructs. The underlying mechanisms varied depending on their conformation or size. OBJECTIVE: The aim of the present study was to compare the uptake of two structurally different allergen molecules within the respiratory tract following intranasal application. METHODS: The three-dimensional Bet v 1 (Bv1-Protein) and the T cell epitope peptide of Bet v 1 (Bv1-Peptide) were labelled with 5,6-Carboxyfluorescein (FAM) and their uptake was investigated in lung cells and cells of the nasal associated lymphoid tissue from naive and sensitised BALB/c mice. Phenotypic characterisation of FAM+ lung cells after antigen incubation in vitro and after intranasal application was performed by flow cytometry. Impact of Bv1-Protein and Bv1-Peptide on cytokine profiles and gene expression in vivo or in an alveolar epithelial type II (ATII) cell line were assessed in mono- and co-cultures with monocytes using ELISA and quantitative real-time PCR. RESULTS: Both antigens were taken up preferably by ATII-like cells (ATII-LCs) in naive mice, and by macrophages in sensitised mice. After intranasal application, Bv1-Peptide was taken up faster and more efficiently than Bv1-Protein. In vivo and in vitro experiments revealed that Bv1-Protein induced the transcription of thymic stromal lymphopoietin mRNA while Bv1-Peptide induced the transcription of IL-10 and MCP1 mRNA in ATII-LCs. CONCLUSION AND CLINICAL RELEVANCE: Both tested antigens were taken up by ATII-LCs under steady state conditions and induced different polarisation of the immune responses. These data may have an important impact for the generation of novel and more effective prophylactic or therapeutic tools targeting the respiratory mucosa.

Langerhans cell precursors acquire RANK/CD265 in prenatal human skin.

The skin is the first barrier against foreign pathogens and the prenatal formation of a strong network of various innate and adaptive cells is required to protect the newborn from perinatal infections. While many studies about the immune system in healthy and diseased adult human skin exist, our knowledge about the cutaneous prenatal/developing immune system and especially about the phenotype and function of antigen-presenting cells such as epidermal Langerhans cells (LCs) in human skin is still scarce. It has been shown previously that LCs in healthy adult human skin express receptor activator of NF-κB (RANK), an important molecule prolonging their survival. In this study, we investigated at which developmental stage LCs acquire this important molecule. Immunofluorescence double-labeling of cryostat sections revealed that LC precursors in prenatal human skin either do not yet [10-11 weeks of estimated gestational age (EGA)] or only faintly (13-15 weeks EGA) express RANK. LCs express RANK at levels comparable to adult LCs by the end of the second trimester. Comparable with adult skin, dermal antigen-presenting cells at no gestational age express this marker. These findings indicate that epidermal leukocytes gradually acquire RANK during gestation - a phenomenon previously observed also for other markers on LCs in prenatal human skin.

Neonatal colonization of germ-free mice with Bifidobacterium longum prevents allergic sensitization to major birch pollen allergen Bet v 1.

The main goal in reversing the allergy epidemic is the development of effective prophylactic strategies. We investigated the prophylactic effect of neonatal mother-to-offspring mono-colonization with Bifidobacterium longum ssp. longum CCM 7952 on subsequent allergic sensitization. Adult male and female germ-free (GF) mice were mono-colonized with B. longum, mated and their offspring, as well as age-matched GF controls, were sensitized with the major birch pollen allergen Bet v 1. Furthermore, signaling pathways involved in the recognition of B. longum were investigated in vitro. Neonatal mono-colonization of GF mice with B. longum suppressed Bet v 1-specific IgE-dependent ß-hexosaminidase release as well as levels of total IgE and allergen-specific IgG2a in serum compared to sensitized GF controls. Accordingly, Bet v 1-induced production of both Th1- and Th2-associated cytokines in spleen cell cultures was significantly reduced in these mice. The general suppression of Bet v 1-specific immune responses in B. longum-colonized mice was associated with increased levels of regulatory cytokines IL-10 and TGF-ß in serum. In vitro, B. longum induced low maturation status of bone marrow-derived dendritic cells and production of IL-10 in TLR2-, MyD88-, and MAPK-dependent manner. Our data demonstrate that neonatal mono-colonization with B. longum reduces allergic sensitization, likely by activation of regulatory responses via TLR2, MyD88, and MAPK signaling pathways. Thus, B. longum might be a promising candidate for perinatal intervention strategies against the onset of allergic diseases in humans.

Oesophagostomum dentatum extract modulates T cell-dependent immune responses to bystander antigens and prevents the development of allergy in mice.

One third of the human population is currently infected by one or more species of parasitic helminths. Certain helminths establish long-term chronic infections resulting in a modulation of the host's immune system with attenuated responsiveness to "bystander" antigens such as allergens or vaccines. In this study we investigated whether parasite-derived products suppress the development of allergic inflammation in a mouse model. We show that extract derived from adult male Oesophagostomum dentatum (eMOD) induced Th2 and regulatory responses in BALB/c mice. Stimulation of bone marrow-derived dendritic cells induced production of regulatory cytokines IL-10 and TGF-beta. In a mouse model of birch pollen allergy, co-administration of eMOD with sensitizing allergen Bet v 1 markedly reduced the production of allergen-specific antibodies in serum as well as IgE-dependent basophil degranulation. Furthermore, eMOD prevented the development of airway inflammation, as demonstrated by attenuation of bronchoalveolar lavages eosinophil influx, peribronchial inflammatory infiltrate, and mucus secretion in lungs and IL-4 and IL-5 levels in lung cell cultures. Reduced secretion of Th2-related cytokines by birch pollen-re-stimulated splenocytes and mesenteric lymph node cells was observed in eMOD-treated/sensitized and challenged mice in comparison to sensitized and challenged controls. The suppressive effects of eMOD were heat-stable. Immunization with model antigens in the presence of eMOD reduced production of antibodies to thymus-dependent but not to thymus-independent antigen, suggesting that suppression of the immune responses by eMOD was mediated by interference with antigen presenting cell or T helper cell function but did not directly suppress B cell function. In conclusion, we have shown that eMOD possesses immunomodulatory properties and that heat-stable factors in eMOD are responsible for the dramatic suppression of allergic responses in a mouse model of type I allergy. The identification and characterization of parasite-derived immune-modulating molecules might have potential for designing novel prophylactic/therapeutic strategies for immune-mediated diseases.

Differential effects of corticosteroids and pimecrolimus on the developing skin immune system in humans and mice.

Atopic dermatitis arises primarily in early infancy. In these patients, corticosteroids are used especially with great caution because of their side effects. Calcineurin inhibitors such as pimecrolimus (PIM) could be useful, but safety concerns have been raised in particular because of the lack of knowledge about their effects on the developing skin immune system. This study was designed to investigate the impact of PIM and corticosteroids on epidermal cells (EC) in infants and newborn mice. We found that the percentage of unfractionated viable infant ECs was significantly decreased in the presence of beta-methasone-17-valerate (BMV) but not PIM. Exposure of unfractionated infant ECs to BMV but not to PIM and vehicle control caused a significant inhibition of the upregulation of CD86 molecules on Langerhans cells (LC). The release of cytokines by LCs and ECs, cultured in the presence of BMV and PIM, was not significantly reduced compared with controls. Topical corticosteroid but not PIM application onto newborn mice induced apoptosis in some LC precursors. Our data suggest that similar to the situation in adult skin, corticosteroids may impair LC maturation as well as viability of ECs in infants, effects not seen with PIM.