Concomitant exposure to ovalbumin and endotoxin augments airway inflammation but not airway hyperresponsiveness in a murine model of asthma

Endotoxin contamination in ovalbumin as viewed from a nano-immunotherapy perspective

Ovalbumin (OVA) is a model antigen commonly incorporated in smartly designed nanoparticles for delivery into antigen-presenting cells (APC), aiming to investigate the immune activity and therapeutic efficacy of nanoparticles that contain immunoregulatory compounds. However, the immunoresponse observed in nano-immunotherapy may unexpectedly arise from endotoxin impurity of OVA in the nanoparticles. Literature review shows that most researchers did not notice the importance of endotoxin-free OVA when used in nano-immunotherapy studies. Concentration at as low as 5 μg/ml OVA from Sigma-Aldrich (contains 0.625 ng/ml endotoxin) was able to activate APC such as dendritic cells and macrophages. Here, we proposed that the endotoxin impurity in OVA or the finished nanoproducts should be determined by both Limulus Amebocyte Lysate (LAL) and cell-based assay, to ensure the endotoxin-free quality of the nanoparticles. The endotoxin in OVA can be removed by endotoxin removal column and phase separation methods and endotoxin-free OVA can be purchased. This perspective alerts the researchers of endotoxin impurity of OVA that may transfer into the finished nanoparticles and introduce an unfavorable immunoregulatory function with false-positive results. OVA with minimal endotoxin level should be used in nano-immunotherapy studies to accurately reflect the true effects of nanoparticles on the immune system. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Global Gene Expression of T Cells Is Differentially Regulated by Peritoneal Dendritic Cell Subsets in an IL-2 Dependent Manner

Dendritic cells (DCs) in peripheral tissues may have a unique role to regulate innate and adaptive immune responses to antigens that enter the tissues. Peritoneal cavity is the body compartment surrounding various tissues and organs and housing diverse immune cells. Here, we investigated the specialized features of classical DC (cDC) subsets following the intraperitoneal injection of a model antigen ovalbumin (OVA). Peritoneal cDC1s were superior to cDC2s in activating OVA-specific CD8 T cells, while both cDCs were similar in stimulating OVA-specific CD4 T cells. Each peritoneal cDC subset differentially regulated the homing properties of CD8 T cells. CD8 T cells stimulated by cDC1s displayed a higher level of lung-homing receptor CCR4, whereas those stimulated by cDC2s prominently expressed various homing receptors including gut-homing molecules CCR9 and α4β7. Also, we found that cDC1s played a dominating role over cDC2s in controlling the overall gene expression of CD8 T cells. Soluble factor(s) emanating from CD8 T cells stimulated by peritoneal cDC1s were responsible for mediating this dominance of cDC1s, and we identified IL-2 as a soluble factor regulating the global gene expression of T cells. Collectively, our study indicates that different peritoneal cDC subsets effectively diversify T cell responses by altering the level of cytokines, such as IL-2, in the milieu.

The Role of Heat Shock Protein 70 kDa in Asthma

Asthma is a complex chronic disorder of the airways, affecting immune and structural cells and inducing both protein and tissue remodeling. Heat shock proteins 70 kDa (HSP70s) are highly conserved members of the stress-induced family, possessing precisely described chaperone activity. There is growing evidence of a tight relationship between inflammatory diseases of different origins and the elevation of local HSP70 expression and secretion. Although extracellular HSP70 does not serve as a common marker of asthma, elevated HSP70 levels have been detected in the peripheral blood serum and sputum of patients with asthma, as well as in the bronchoalveolar lavage fluid of mice with induced allergic airway inflammation. Possessing diverse immunomodulating properties, extracellular HSP70 can manifest different activities in airway inflammatory processes and asthma, acting either as a pro-inflammatory trigger, or an anti-inflammatory agent. This review will discuss the effects and possible mechanisms concerning HSP70 implication in airway inflammation regulation in asthma. We examine ATPase and chaperone activities of HSP70 as potential modulators of immune responses in asthma. Given the crucial role of a chronic inflammatory response in asthma, understanding the effects of HSP70 on immune and structural cells may reveal new perspectives for the therapeutic control of inflammation.

Topical Adjuvant Application during Subcutaneous Vaccination Promotes Resident Memory T Cell Generation

Skin tissue resident memory T cells (T_RM) provide superior protection to a second infection. In this study, we evaluated the use of topical CpG oligodeoxynucleotide (ODN) as adjuvant to generate skin T_RM in mice. Topical or s.c. CpG ODN adjuvant administration at the time of a s.c. Ag injection led to an accumulation of CD103^- CD8 T cells in the epidermis. However, only mice with CpG ODN administered topically had significant numbers of CD103⁺ Ag-specific CD8 T cells persisting in the local epidermal skin, enhanced circulating memory cells in the blood, and showed protection from intradermal challenge with melanoma cells. Generation of Ag-specific CD8 T cells was dependent on TLR9 expression on hematopoietic cells and partially dependent on receptor expression on stromal cells. Topical challenge of immunized mice at a distal site led to significant expansion of Ag-specific T cells in the blood and accumulation in the challenged skin. We demonstrate that local and systemic T cell memory can be generated with topical CpG ODN at the time of s.c. immunization, suggesting a new method of enhancing current vaccine formulations to generate tissue T_RM.

Involvement of PM2.5-bound protein and metals in PM2.5-induced allergic airway inflammation in mice

BACKGROUND

The aim of this study was to investigate the protein and trace element components of PM2.5 and their contribution to the allergic airway inflammation in BALB/c mice.

METHODS

PM2.5, treated at high temperature and with a strong acid to hydrolyze any protein content and remove trace elements, was administered to BALB/c mice. Allergic airway inflammation was compared between the three groups (saline, pure PM2.5 and treated PM2.5) by evaluating airway hyperresponsiveness (AHR), bronchoalveolar lavage fluid (BALF) cells, serum IgE, the mRNA of various cytokine (IL-4, IL-5, IL-13, eotaxin-1 and CXCL3), mucus protein mRNA (MUC5ac and MUC5b) and the filtration of inflammatory cells in the lung.

RESULTS

The treatment of PM2.5 with a strong acid at a high temperature attenuated AHR, eosinophil percentage in BALF, mRNA levels of IL-13 and CXCL3 and peribronchial inflammation. On the contrary, the percentage of neutrophils in BALF, mRNA expression of MIP2α, EGFR, Nrf2, and TLR4 and 4-OH-2-nonenal levels in the lung was increased. Moreover, the treatment of the PM2.5 reduced PM2.5-bound proteins as well as the percentages of the trace elements in PM2.5 in the order Zn > Cu >  Pb > P > S > Mn > Fe > Ca > Ni, whereas the percentage of C, Si and Cl increased.

CONCLUSIONS

PM2.5 collected by of the cyclone system induced allergic airway inflammation in mice. PM2.5-bound proteins and acid-soluble metals may be involved in the pathogenesis of PM2.5-induced allergic airway inflammation.

Sputum cytology during late-phase responses to inhalation challenge with different allergens

BACKGROUND

In mouse models of allergic asthma, exposure to different allergens can trigger distinct inflammatory subtypes in the airways. We investigated whether this observation extends to humans.

METHODS

We compared the frequency of sputum inflammatory subtypes between mild allergic asthma subjects (n = 129) exposed to different allergens in inhalation challenge tests. These tests were performed using a standardized protocol as part of clinical trials of experimental treatments for asthma, prior to drug randomization. Five allergen types were represented: the house dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae, ragweed, grass, and cat.

RESULTS

Of 118 individuals with a sputum sample collected before allergen challenge (baseline), 45 (38%) had paucigranulocytic, 51 (43%) eosinophilic, 11 (9%) neutrophilic, and 11 (9%) mixed granulocytic sputum. Of note, most individuals with baseline paucigranulocytic sputum developed eosinophilic (48%) or mixed granulocytic (43%) sputum 7 hours after allergen challenge, highlighting the dynamic nature of sputum inflammatory subtype in asthma. Overall, there was no difference in the frequency of sputum inflammatory subtypes following challenge with different allergen types. Similar results were observed at 24 hours after allergen challenge.

CONCLUSIONS

Unlike reported in mice, in humans the sputum inflammatory subtype observed after an allergen-induced asthma exacerbation is unlikely to be influenced by the type of allergen used.

Lipopolysaccharide Exposure Alleviates Asthma in Mice by Regulating Th1/Th2 and Treg/Th17 Balance

Background

It is generally believed that endotoxin exposure exacerbates risk of developing asthmatic symptoms. However, recent studies have indicated that prior bacterial exposure may prevent future symptoms of asthma. Here, we evaluated the influence of pre-exposure to different concentrations of lipopolysaccharide (LPS) to subsequent ovalbumin (OVA) allergen sensitization and challenge.

Material/Methods

Four-week-old Balb/c mice were treated intranasally with varying concentrations of LPS (1 ug, 10 ug, and 100 ug) or sterile PBS for 10 days, then 2 weeks later they were exposed to OVA. Both the molecular and functional airway responses to OVA administration were assessed following prior exposure to different doses of LPS or controls. Additionally, the Th1/Th2 and Treg/Th17 balance was measured.

Results

Airway responsiveness and immune cell recruitment in the bronchoalveolar lavage (BALF) were decreased in animals exposed to a low dose of LPS (1 ug) treatment compared with the asthma group. Moderate-dose (10 ug) and high-dose (100 ug) LPS administration showed no differences from controls. Further, low-dose LPS (1 ug) exposure was associated with increased Th1 cytokines, T-bet, Treg cytokine (IL-10, TGF-β), and Foxp3 expression, but decreased Th2 cytokines (IL-4,5,13), GATA3, Th17, and ROR-γt expression compared with the asthma group. Finally, higher numbers of CD4+CD25+Foxp3+Treg cells, and CD4+INF-γ+T cells, and lower CD4+IL-4+T cells and CD4+IL-17+T cells were observed in the low-dose LPS-treated groups compared to controls.

Conclusions

Our findings suggest that prior exposure to low doses of LPS may protect from OVA-induced airway hyperresponsiveness (AHR) and histopathologic changes through regulation of the Th1/Th2 and Treg/Th17 balance.

Enhanced expression of PD-L1 and IFN-γ on dendritic cells is associated with BCG-induced Th2 inhibition

Accumulating evidence indicates that the exposure to Mycobacterium bovis bacillus Calmette-Guérin (BCG) prevents the development of allergy and the airway dendritic cells (DCs) may be involved in this protective effect. However, studies to better characterize the specific interactions between BCG and DCs and their role in this mycobacteria-mediated Th2 cell suppression are still ongoing. This study aimed to evaluate the effect of the neonatal BCG vaccination in the innate immune response in a mouse model of ovalbumin (OVA)-induced airway inflammation. BCG treated neonatal BALB/c mice were sensitized and challenged with aerosolized OVA. Twenty-four hours after the last challenge, samples were collected for analysis. The intranasal BCG treatment inhibited the allergic Th2-response by decreasing the allergen-induced eosinophilic inflammation, EPO activity, CCL11, IL-25, TSLP, IL-4 and IL-5 lung levels, and serum levels of IgE. Mycobacteria treatment increased lung levels of IL-10 and TGF-β, and the TLR2 and TLR4 expressions by pulmonary CD11c⁺CD103⁺CD8α⁺ DCs. Additionally an enhanced expression of PD-L1 was observed besides an increased production of IFN-γ by these cells. These results indicated that neonatal BCG vaccination inhibits key features of allergic airway inflammation, probably by promoting T regulatory immune response via an enhanced expression of TLR2, TLR4 and PD-L1 on DCs.

Revisiting asthma therapeutics: focus on WNT signal transduction

Asthma is a complex disease of the airways that develops as a consequence of both genetic and environmental factors. This interaction has highlighted genes important in early life, particularly those that control lung development, such as the Wingless/Integrase-1 (WNT) signalling pathway. Although aberrant WNT signalling is involved with an array of human conditions, it has received little attention within the context of asthma. Yet it is highly relevant, driving events involved with inflammation, airway remodelling, and airway hyper-responsiveness (AHR). In this review, we revisit asthma therapeutics by examining whether WNT signalling is a valid therapeutic target for asthma.

Lipopolysaccharide/TLR4 Stimulates IL-13 Production through a MyD88-BLT2-Linked Cascade in Mast Cells, Potentially Contributing to the Allergic Response

In an experimental asthma model, the activation of TLR4 by bacterial LPS occasionally exacerbates allergic inflammation through the production of Th2 cytokines, and mast cells have been suggested to play a central role in this response. However, the detailed mechanism underlying how LPS/TLR4 stimulates the production of Th2 cytokines, especially IL-13, remains unclear in mast cells. In the current study, we observed that the expression levels of leukotriene B4 receptor-2 (BLT2) and the synthesis of its ligands were highly upregulated in LPS-stimulated bone marrow-derived mast cells and that BLT2 blockade with small interfering RNA or a pharmacological inhibitor completely abolished IL-13 production, suggesting a mediatory role of the BLT2 ligand-BLT2 axis in LPS/TLR4 signaling to IL-13 synthesis in mast cells. Moreover, we demonstrated that MyD88 lies upstream of the BLT2 ligand-BLT2 axis and that this MyD88-BLT2 cascade leads to the generation of reactive oxygen species through NADPH oxidase 1 and the subsequent activation of NF-κB, thereby mediating IL-13 synthesis. Interestingly, we observed that costimulation of LPS/TLR4 and IgE/FcεRI caused greatly enhanced IL-13 synthesis in mast cells, and blockading BLT2 abolished these effects. Similarly, in vivo, the IL-13 level was markedly enhanced by LPS administration in an OVA-induced asthma model, and injecting a BLT2 antagonist beforehand clearly attenuated this increase. Together, our findings suggest that a BLT2-linked cascade plays a pivotal role in LPS/TLR4 signaling for IL-13 synthesis in mast cells, thereby potentially exacerbating allergic response. Our findings may provide insight into the mechanisms underlying how bacterial infection worsens allergic inflammation under certain conditions.

Encapsulating an Immunosuppressant Enhances Tolerance Induction by Siglec-Engaging Tolerogenic Liposomes

Unwanted antibody responses significantly impact human health, and current options for treating deleterious antibody responses largely rely on broad immunosuppressants that can compromise overall immunity. A desirable alternative is to induce antigen-specific immune tolerance. We have shown that co-presentation of antigen and ligands of B cell sialic acid-binding immunoglobulin-like lectins (Siglecs) on a liposomal nanoparticle induces antigen-specific tolerance. Although Siglec-engaging tolerance-inducing antigenic liposomes (STALs) induce robust B cell tolerance in naïve mice, the full potential of STALs requires long-term tolerance induction and suppression of an ongoing immune response. We hypothesized that STALs encapsulated with rapamycin (RAPA), an immunomodulator, could improve the efficacy of STALs and potentially enable their use in the context of immunological memory. Here, we showed that formulation of STALs with RAPA produced enhanced tolerance induction in naïve mice compared to STALs without RAPA but had minimal impact on inducing tolerance in previously sensitized mice. These findings indicate that the addition of immunomodulators to STALs could be beneficial in tolerance induction and support future development of STALs for the treatment of allergy and autoimmune diseases.

Association of MBL With Work-Related Respiratory Symptoms in Bakery Workers

Baker's asthma is the most prevalent occupational asthma, and IgE-mediated response is known as a major pathogenesis. However, recent studies have suggested the involvement of innate immune response because wheat flour contains bacterial endotoxins or lipopolysaccharides. To further understand a role of innate immune response in the development of work-related respiratory symptoms (WRS) in bakery workers, we investigated mannose-binding lectin (MBL), one of the initiating components of the complement cascade in a single cohort of bakery workers. A total of 373 bakery workers completed a questionnaire regarding WRS. The bakery workers were divided into 2 groups according to previous history of allergic rhinitis (AR)/bronchial asthma (BA): those with history of AR/BA (group I) and those without (group II). We measured serum MBL levels by using enzyme-linked immunosorbant assay and genotyped 4 single nucleotide polymorphisms of the MBL2 gene (226G>A in exon 1, -554G>C, -431A>C, and -225G>C in the promoter) by using TaqMan assays. Fifty-nine subjects (15.5%) were previously diagnosed with AR/BA, and 64 subjects (16.8%) complained of WRS. No significant differences were found in serum MBL levels between groups I and II. However, in group II subjects, but not in group I subjects, the serum MBL levels were significantly higher in bakery workers with WRS than in those without. In addition, the serum MBL levels were significantly different according to genetic polymorphisms of the MBL2 gene and its haplotypes. In conclusion, serum MBL, affected by genetic polymorphisms, may be associated with WRS in bakery workers with no previous history of AR/BA.

IgE-mediated enhancement of CD4(+) T cell responses requires antigen presentation by CD8α(-) conventional dendritic cells

IgE, forming an immune complex with small proteins, can enhance the specific antibody and CD4(+) T cell responses in vivo. The effects require the presence of CD23 (Fcε-receptor II)(+) B cells, which capture IgE-complexed antigens (Ag) in the circulation and transport them to splenic B cell follicles. In addition, also CD11c(+) cells, which do not express CD23, are required for IgE-mediated enhancement of T cell responses. This suggests that some type of dendritic cell obtains IgE-Ag complexes from B cells and presents antigenic peptides to T cells. To elucidate the nature of this dendritic cell, mice were immunized with ovalbumin (OVA)-specific IgE and OVA, and different populations of CD11c(+) cells, obtained from the spleens four hours after immunization, were tested for their ability to present OVA. CD8α(-) conventional dendritic cells (cDCs) were much more efficient in inducing specific CD4(+) T cell proliferation ex vivo than were CD8α(+) cDCs or plasmacytoid dendritic cells. Thus, IgE-Ag complexes administered intravenously are rapidly transported to the spleen by recirculating B cells where they are delivered to CD8α(-) cDCs which induce proliferation of CD4(+) T cells.

CD8+ T Cells Mediate Female-Dominant IL-4 Production and Airway Inflammation in Allergic Asthma

The prevalence and severity of bronchial asthma are higher in females than in males after puberty. Although antigen-specific CD8+ T cells play an important role in the development of asthma through their suppressive effect on cytokine production, the contribution of CD8+ T cells to sex differences in asthmatic responses remains unclear. In the present study, we investigated the sex-specific effect of CD8+ T cells in the suppression of asthma using an ovalbumin mouse model of asthma. The number of inflammatory cells in bronchoalveolar lavage (BAL) fluid, lung type 2 T-helper cytokine levels, and interleukin-4 (IL-4) production by bronchial lymph node cells were significantly higher in female wild-type (WT) mice compared with male mice, whereas no such sex differences were observed between male and female cd8α-disrupted mice. The adaptive transfer of male, but not female, CD8+ T cells reduced the number of inflammatory cells in the recovered BAL fluid of male recipient mice, while no such sex difference in the suppressive activity of CD8+ T cells was observed in female recipient mice. Male CD8+ T cells produced higher levels of IFN-γ than female CD8+ T cells did, and this trend was associated with reduced IL-4 production by male, but not female, CD4+ T cells. Interestingly, IFN-γ receptor expression on CD4+ T cells was significantly lower in female mice than in male mice. These results suggest that female-dominant asthmatic responses are orchestrated by the reduced production of IFN-γ by CD8+ T cells and the lower expression of IFN-γ receptor on CD4+ T cells in females compared with males.

Higher Sensitivity of Foxp3+ Treg Compared to Foxp3- Conventional T Cells to TCR-Independent Signals for CD69 Induction

T lymphocytes elicit specific responses after recognizing cognate antigen. However, antigen-experienced T cells can also respond to non-cognate stimuli, such as cytokines. CD4⁺ Foxp3⁺ regulatory T cells (Treg) exhibit an antigen-experienced-like phenotype. Treg can regulate T cell responses in an antigen-specific or bystander way, and it is still unclear as to which extent they rely on T cell receptor (TCR) signals. The study of the antigen response of Treg has been hampered by the lack of downstream readouts for TCR stimuli. Here we assess the effects of TCR signals on the expression of a classical marker of early T cell activation, CD69. Although it can be induced following cytokine exposure, CD69 is commonly used as a readout for antigen response on T cells. We established that upon in vitro TCR stimulation CD69 induction on Foxp3⁺ Treg cells was more dependent on signaling via soluble factors than on TCR activation. By contrast, expression of the activation marker Nur77 was only induced after TCR stimulation. Our data suggest that Treg are more sensitive to TCR-independent signals than Foxp3^- cells, which could contribute to their bystander activity.

Pneumococcal pneumonia suppresses allergy development but preserves respiratory tolerance in mice

Colonization with Streptococcus pneumoniae (S. pneumoniae) is associated with an increased risk for recurrent wheeze and asthma. Killed S. pneumoniae showed some potential as an effective immunomodulatory therapy in a murine model of asthma. Murine studies demonstrated protection against allergic asthma by symbiotic bacteria via triggering regulatory T cell response: treatment with killed S. pneumoniae resulted in suppressed levels of allergen-specific Th2 cytokines, while early immunization generated a protective Th1 response. We investigated the impact of lung infection with live S. pneumoniae on both the development and maintenance of allergic airway inflammation and respiratory tolerance in mice. BALB/c mice were infected intratracheally with S. pneumoniae either prior to or after tolerance or allergy were induced, using ovalbumin (OVA) as model allergen. Infection of mice with S. pneumoniae prior to sensitization or after manifestation of allergic airway inflammation suppressed the development of an allergic phenotype as judged by reduced eosinophil counts in bronchoalveolar lavage fluid, decreased IgE serum levels and Th2 cytokines, relative to non-infected allergic control mice. In contrast, infection of mice with S. pneumoniae after manifestation of allergic airway inflammation combined with late mucosal re-challenge did not affect the allergic response. Moreover, induction and maintenance of respiratory tolerance to OVA challenge were not altered in S. pneumoniae-infected mice, demonstrating that mice remained tolerant to the model allergen and were protected from the development of allergic airway inflammation regardless of the time point of infection. Our results suggest that a bacterial infection may decrease the manifestation of an allergic phenotype not only prior to sensitization but also after manifestation of allergic airway inflammation in mice, whereas both, induction and maintenance of respiratory tolerance are not affected by pneumococcal pneumonia. These data may point to a role for undisturbed development and maintenance of mucosal tolerance for the prevention of allergic inflammation also in humans.