Adjuvant activity of pollen grains

Pulmonary delivery of mucosal nanovaccines

Mucosal vaccination can elicit both systemic and mucosal immunity, and therefore has the potential to not only treat mucosal immune diseases, prevent the pathogen infection at the mucosal entry sites, but also treat distant or systemic immune disorders. However, only a few mucosal vaccines have been approved for human use in the clinic. Effective mucosal immunization requires the delivery of immunogenic agents to appropriate mucosal surfaces, which remains significantly challenging due to the essential biological barriers presenting at mucosal tissues. In the past decade, remarkable progress has been made in the development of pulmonary mucosal nanovaccines. The nanovaccines leverage advanced nanoparticle-based pulmonary delivery technologies on the characteristics of large surface area and rich antigen presentation cell environment of the lungs for triggering robust immune protection against various mucosal diseases. Herein, we review current methods and formulations of pulmonary delivery, discuss the design strategies of mucosal nanovaccines for potent and long-lasting immune responses, and highlight recent advances in the application of lipid-based pulmonary nanovaccines against mucosal diseases. These advances promise to accelerate the development of novel mucosal nanovaccines for the prophylaxis and therapy of infectious diseases, and cancer, as well as autoimmune disorders at mucosal tissues.

Latent 1,3-β-D-glucan acts as an adjuvant for allergen-specific IgE production induced by Japanese cedar pollen exposure

BACKGROUND

The pollen grains of several plant species contain 1,3-β-D-glucan (BG). BG activates dendritic cells (DCs) and subsequently regulates the innate immune responses. Within Japan, the most common disease associated with type-I hypersensitivity is Japanese cedar pollinosis. However, the role of BG in Japanese cedar pollen (JCP) remains unclear. This study examined the localization and immunological effects of BG in JCP.

METHODS

The localization of BG in JCP grain was determined by immunohistochemical staining using a soluble dectin-1 protein probe and a BG recognition protein (BGRP). The content of BG extracted from JCP was measured by a BGRP-based ELISA-like assay. The cytokine production by bone marrow-derived DCs (BMDCs) obtained from wild-type and BG receptor (dectin-1) knock-out mice was examined in vitro. The mice were intranasally administered JCP grains and the specific serum Ig levels were then quantified.

RESULTS

BG was detected in the exine and cell wall of the generative cell and tube cell of the JCP grain. Moreover, BG in the exine stimulated production of TNF-α and IL-6 in the BMDCs via a dectin-1-dependent mechanism. Meanwhile, JCP-specific IgE and IgG were detected in the serum of wild-type mice that had been intranasally administered with JCP grains. These mice also exhibited significantly enhanced sneezing behavior. However, dectin-1 knock-out mice exhibited significantly lower JCP-specific IgE and IgG levels compared to wild-type mice.

CONCLUSIONS

Latent BG in JCP can act as an adjuvant to induce JCP-specific antibody production via dectin-1.

Chemical modification of coating of Pinus halepensis pollen by ozone exposure

Pollen coating, located on the exine, includes an extractible lipid fraction. The modification of the pollen coating by air pollutants may have implications on the interactions of pollen with plant stigmas and human cells. Pinus halepensis pollen was exposed to ozone in vitro and the pollen coating was extracted with organic solvent and analyzed by GC-MS. Ozone has induced chemical changes in the coating as observed with an increase in dicarboxylic acids, short-chain fatty acids and aldehydes. 4-Hydroxybenzaldehyde was identified as the main reaction product and its formation was shown to occur both on native pollen and on defatted pollen. 4-Hydroxybenzaldehyde is very likely formed via the ozonolysis of acid coumaric-like monomers constitutive of the sporopollenin. Modification of pollen coating by air pollutants should be accounted for in further studies on effect of pollution on germination and on allergenicity.

Ragweed pollen extract intensifies lipopolysaccharide-induced priming of NLRP3 inflammasome in human macrophages

Ragweed pollen extract (RWE) possesses intrinsic NADPH oxidase activity that induces oxidative stress by initiating the production of intracellular reactive oxygen species (ROS). The ROS are important contributors to the manifestation of allergic inflammation; furthermore, concomitant exposure to an allergen and an endotoxin trigger a stronger inflammatory response. One of the main pro-inflammatory cytokines produced in inflammatory responses is interleukin-1β (IL-1β), and its production is associated with caspase-1-containing inflammasome complexes. Intracellular ROS have been implicated in NLRP3 inflammasome-mediated IL-1β production, therefore, we aimed to study whether RWE influences the function of NLRP3 inflammasome. Here we describe that, in the presence of NADPH, RWE significantly elevates lipopolysaccharide-induced IL-1β production of THP-1 cells as well as human primary macrophages and dendritic cells. We also demonstrate that increased IL-1β production is mediated through NLRP3 inflammasome in THP-1 macrophages. We provide evidence that RWE elevates cytosolic ROS level in these cells, and ROS inhibitors abolish IL-1β production. Furthermore, we show that RWE enhances lipopolysaccharide-induced gene transcription/expression of pro-IL-1β and key components of the inflammasome via a ROS-dependent mechanism.

Ragweed subpollen particles of respirable size activate human dendritic cells

Ragweed (Ambrosia artemisiifolia) pollen grains, which are generally considered too large to reach the lower respiratory tract, release subpollen particles (SPPs) of respirable size upon hydration. These SPPs contain allergenic proteins and functional NAD(P)H oxidases. In this study, we examined whether exposure to SPPs initiates the activation of human monocyte-derived dendritic cells (moDCs). We found that treatment with freshly isolated ragweed SPPs increased the intracellular levels of reactive oxygen species (ROS) in moDCs. Phagocytosis of SPPs by moDCs, as demonstrated by confocal laser-scanning microscopy, led to an up-regulation of the cell surface expression of CD40, CD80, CD86, and HLA-DQ and an increase in the production of IL-6, TNF-α, IL-8, and IL-10. Furthermore, SPP-treated moDCs had an increased capacity to stimulate the proliferation of naïve T cells. Co-culture of SPP-treated moDCs with allogeneic CD3⁺ pan-T cells resulted in increased secretion of IFN-γ and IL-17 by T cells of both allergic and non-allergic subjects, but induced the production of IL-4 exclusively from the T cells of allergic individuals. Addition of exogenous NADPH further increased, while heat-inactivation or pre-treatment with diphenyleneiodonium (DPI), an inhibitor of NADPH oxidases, strongly diminished, the ability of SPPs to induce phenotypic and functional changes in moDCs, indicating that these processes were mediated, at least partly, by the intrinsic NAD(P)H oxidase activity of SPPs. Collectively, our data suggest that inhaled ragweed SPPs are fully capable of activating dendritic cells (DCs) in the airways and SPPs' NAD(P)H oxidase activity is involved in initiation of adaptive immune responses against innocuous pollen proteins.

Gram-positive bacteria on grass pollen exhibit adjuvant activity inducing inflammatory T cell responses

BACKGROUND

Recently, it has been established that pollen grains contain Th2-enhancing activities besides allergens.

OBJECTIVE

The aim of this study was to analyse whether pollen carry additional adjuvant factors like microbes and what immunological effects they may exert.

METHODS

Timothy pollen grains were collected and disseminated on agar plates, and the growing microorganisms were cultivated and defined. Furthermore, the immunologic effects of microbial products on DC and T cell responses were analysed.

RESULTS

A complex mixture of bacteria and moulds was detected on grass pollen. Besides Gram-negative bacteria that are known to favour Th1-directed immune responses, moulds were identified as being sources of allergens themselves. Herein, we focused on Gram-positive bacteria that were found in high numbers, e.g. Bacillus cereus and Bacillus subtilis. Contact of immature dendritic cells (DC) from grass pollen allergic donors with supernatants of homogenized Gram-positive bacteria induced maturation of DC as measured by up-regulation of CD80, CD83 and CD86 and by enhanced production of IL-6, IL-12p40 and TNF-α, which was less pronounced compared with effects induced by lipopolysaccharide (LPS). Consequently, stimulation of autologous CD4(+) T cells with supernatants of homogenized Gram-positive bacteria plus grass pollen allergen-pulsed DC led to an enhanced proliferation and production of IL-4, IL-13, IL-10, IL-17, IL-22 and IFN-γ production compared with T cells that were stimulated with allergen-pulsed immature DC alone, whereas production of the transcription factor for regulatory T cells FoxP3 was not significantly affected.

CONCLUSIONS AND CLINICAL RELEVANCE

These data indicate that grass pollen is colonized by several microorganisms that influence the immune response differently. Similar to LPS, supernatants of homogenized Gram-positive bacteria may serve as adjuvants by augmenting DC maturation and inflammatory Th1, Th2 and Th17 responses helping to initiate allergic immune responses.

Mite allergen decreases DC-SIGN expression and modulates human dendritic cell differentiation and function in allergic asthma

House dust mites (HDMs) induce allergic asthma in sensitized individuals, although how HDMs activate immature mucosal dendritic cells (DCs) to render the T helper cell type 2 (Th2)-mediated immune response is unclear. In this study, our results showed a significant calcium-dependent lectin binding of Dermatophagoides pteronyssinus (Der p) extracts to DC-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), the C-type lectin receptors (CLRs) of DCs. Moreover, monocyte-derived DCs (MDDCs) of Der p-sensitized asthmatics (AS) exhibited decreased expression of DC-SIGN, increased endocytosis, and impaired differentiation of DC precursors. The Der p-induced downregulation of DC-SIGN expression in the differentiation of immature MDDCs may be because of the internalization of Der p-DC-SIGN complex. MDDCs of AS produced more interleukin (IL)-6 and less IL-12p70 cytokines when stimulated with lipopolysaccharide (LPS) or Der p than those of nonallergic controls (NC). In the co-culture experiments, MDDCs pretreated with Der p induced GATA-3 expression and IL-4 cytokine productions in naive CD4(+) T cells. These effects of Der p on the differentiation and function of MDDCs could be partially blocked by anti-DC-SIGN antibodies. In conclusion, our results suggest a critical step of allergen sensitization that involves CLRs in the innate immune response of DCs, which may provide a therapeutic or preventive potential for allergic asthma.

Characterization of Phleum pratense pollen extracts by 2-D DIGE and allergen immunoreactivity

The allergen content of standardized pollen material is crucial for an effective diagnosis and treatment. However, variations in IgE reactivities of allergic patients to different preparations of Phleum pratense pollen have been reported. In order to define and directly compare the allergen composition of pollen preparations provided by different suppliers, a comprehensive proteome analysis of three different timothy grass pollen extracts was performed. More than 140 proteins were annotated comprising the pollen proteome/allergome in a global 2-D map. With regard to the individual pollen preparations, several major differences in the overall protein composition were detected that also affected known Phleum allergens and their isoforms. Importantly, these differences were also reflected at the level of antibody reactivities in 1-D and 2-D immunoblots. As a consequence, it is suggested that the observed differences should be taken into consideration aiming for a standardized diagnosis and therapy of grass pollen allergies as recommended by international medical agencies.

Pollen-induced oxidative stress influences both innate and adaptive immune responses via altering dendritic cell functions

It has been demonstrated that pollen grains contain NAD(P)H oxidases that induce oxidative stress in the airways, and this oxidative insult is critical for the development of allergic inflammation in sensitized mice. On the basis of this observation, we have examined whether pollen grain exposure triggers oxidative stress in dendritic cells (DCs), altering their functions. To test this hypothesis, human monocyte-derived DCs were treated with ragweed pollen grains. Our findings show that exposure to pollen grains induces an increase in the intracellular levels of reactive oxygen species in DCs. Our data also indicate that besides the NAD(P)H oxidases, other component(s) of pollen grains contributes to this phenomenon. Elevated levels of intracellular reactive oxygen species triggered the production of IL-8 as well as proinflammatory cytokines, such as TNF-alpha and IL-6. Treatment with pollen grains initiated the maturation of DCs, strongly upregulated the membrane expression of CD80, CD86, CD83, and HLA-DR, and caused only a slight increase in the expression of CD40. The pollen-treated DCs induced the development of naive T lymphocytes toward effector T cells with a mixed profile of cytokine production. Antioxidant inhibited both the phenotypic and functional changes of DCs, underlining the importance of oxidative stress in these processes. Collectively, these data show that pollen exposure-induced oxidative stress may contribute to local innate immunity and participate in the initiation of adaptive immune responses to pollen Ags.

Cupressaceae pollen grains modulate dendritic cell response and exhibit IgE-inducing adjuvant activity in vivo

Pollen is considered a source of not only allergens but also immunomodulatory substances, which could play crucial roles in sensitization and/or the exacerbation of allergies. We investigated how allergenic pollens from different plant species (Japanese cedar and Japanese cypress, which belong to the Cupressaceae family, and birch, ragweed, and grass) modulate murine bone marrow-derived dendritic cell (DC) responses and examined the effect of Cupressaceae pollen in vivo using mice. DCs were stimulated with pollen extracts or grains in the presence or absence of LPS. Cell maturation and cytokine production in DCs were analyzed by flow cytometry, ELISA, and/or quantitative PCR. Pollen extracts suppressed LPS-induced IL-12 production and the effect was greatest for birch and grass. Without LPS, pollen grains induced DC maturation and cytokine production without IL-12 secretion and the response, for which TLR 4 was dispensable, was greatest for the Cupressaceae family. Intranasal administration of Cupressaceae pollen in mice induced an elevation of serum IgE levels and airway eosinophil infiltration. Coadministration of ovalbumin with Cupressaceae pollen grains induced ovalbumin-specific IgE responses associated with eosinophil infiltration. The results suggest that modulation of DC responses by pollen differs among the plant families via (1) the promotion of DC maturation and cytokine production by direct contact and/or (2) the inhibition of IL-12 production by soluble factors. The strong DC stimulatory activity in vitro and IgE-inducing activity in mice support the clinical relevance of Cupressaceae pollen to allergies in humans.

Nuclear erythroid 2 p45-related factor 2 inhibits the maturation of murine dendritic cells by ragweed extract

Oxidative stress plays an important role in immune regulation and dendritic cell (DC) maturation. Recent studies indicate that allergens, including ragweed extract (RWE), possess prooxidant activities, but how RWE interacts with DCs is not well understood. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a key transcription factor that regulates constitutive and coordinated induction of a battery of antioxidant genes. We hypothesized that RWE would activate DCs and that this response would be augmented in the absence of Nrf2. We generated bone marrow-derived DCs (BM-DCs) and isolated lung DCs from Nrf2(+/+) and Nrf2(-/-) mice and studied the effects of RWE on DCs in vitro. Under resting conditions, Nrf2(-/-) BM-DCs exhibited constitutively greater levels of inflammatory cytokines and costimulatory molecules than Nrf2(+/+) BM-DCs. Exposure to RWE impaired endocytic activity, significantly induced oxidative stress, and enhanced the expression of CD80, CD86, and MHCII in Nrf2(-/-) BM-DCs when compared with Nrf2(+/+) BM-DC, in association with reduced expression of Nrf2-regulated antioxidant genes. RWE significantly induced the secretion of inflammatory cytokines IL-6 and TNF-alpha in BM-DCs and lung DCs from Nrf2(-/-) mice than Nrf2(+/+) mice and significantly inhibited the secretion of IL-12 in Nrf2(+/+) BM-DCs and IL-18 in Nrf2(+/+) and Nrf2(-/-) BM-DCs. The stimulatory effects of RWE on DC activation were inhibited to varying degrees by the antioxidant N-acetyl cysteine. Our findings indicate that a defect in Nrf2-mediated signaling mechanisms alters the response of DCs to a common environmental allergen, which may contribute to the susceptibility to allergic diseases.

Pollen generates nitric oxide and nitrite: a possible link to pollen-induced allergic responses

Reactive nitrogen species (RNS), such as nitric oxide (NO), are ubiquitous and diverse signalling molecules involved in a wide range of physiological and pathophysiological processes in both animals and plants. Nitrite, a metabolite of NO turnover, has also been recently characterised as an important mediator of fundamental physiological mechanisms in mammalian cells, and is a substrate for NO production in several plant cell signalling processes. A previous study demonstrated that during plant reproductive processes, intracellular NO is produced by pollen, and that such NO could be important in signalling interactions between pollen and stigma. The aim of this study was to establish whether pollen releases NO and nitrite, using a wide range of plant species. Using a fluorimetric assay in conjunction with electron paramagnetic resonance (EPR) spectroscopy, the present study demonstrated that all hydrating pollen examined released NO, although some appeared to have more activity than others. Additionally, gas phase ozone-based chemiluminescence data showed that nitrite is also released from hydrating pollen. Given that pollen has interactions with other cells, for example in allergenic rhinitis (hay fever) in humans, it suggests that NO might be involved in mediating the responses of both plant and animal cells to pollen. These findings may have important implications for future allergy research, as it is possible that pollen-derived NO and nitrite may impact on mammalian cells during pollen-induced allergic responses.

Allergen-enhanced thrombomodulin (blood dendritic cell antigen 3, CD141) expression on dendritic cells is associated with a TH2-skewed immune response

BACKGROUND

Dendritic cells (DCs) are important in allergic diseases such as asthma, although little is known regarding the mechanisms by which DCs induce T(H)2-polarized responses in atopic individuals. It has been suggested that intrinsic properties of allergens can directly stimulate T(H)2 polarizing functions of DCs, but little is known of the underlying mechanisms.

OBJECTIVE

To identify novel genes expressed by house dust mite (HDM) allergen-exposed DCs.

METHODS

We screened for allergen-induced gene expression by microarray, and validated differentially expressed genes at the mRNA and protein levels.

RESULTS

Thrombomodulin (CD141, blood dendritic cell antigen 3) expression by microarray was higher on HDM-stimulated DCs from atopic (relative to nonatopic) individuals. These findings were confirmed at both the mRNA and protein levels in an independent group. Purified thrombomodulin(+) DCs induced a strongly T(H)2-polarized cytokine response by allergen-specific T cells compared with DCs lacking thrombomodulin. In vivo, thrombomodulin(+) circulating DCs were significantly more frequent in subjects with HDM allergy and asthma, compared with control subjects. Furthermore, thrombomodulin expression in blood leukocytes was higher in children with acute asthma than at convalescence 6 weeks later.

CONCLUSION

Thrombomodulin expression on DCs may be involved in the pathogenesis of atopy and asthma.

Allergenic pollen and pollen allergy in Europe

The allergenic content of the atmosphere varies according to climate, geography and vegetation. Data on the presence and prevalence of allergenic airborne pollens, obtained from both aerobiological studies and allergological investigations, make it possible to design pollen calendars with the approximate flowering period of the plants in the sampling area. In this way, even though pollen production and dispersal from year to year depend on the patterns of preseason weather and on the conditions prevailing at the time of anthesis, it is usually possible to forecast the chances of encountering high atmospheric allergenic pollen concentrations in different areas. Aerobiological and allergological studies show that the pollen map of Europe is changing also as a result of cultural factors (for example, importation of plants such as birch and cypress for urban parklands), greater international travel (e.g. colonization by ragweed in France, northern Italy, Austria, Hungary etc.) and climate change. In this regard, the higher frequency of weather extremes, like thunderstorms, and increasing episodes of long range transport of allergenic pollen represent new challenges for researchers. Furthermore, in the last few years, experimental data on pollen and subpollen-particles structure, the pathogenetic role of pollen and the interaction between pollen and air pollutants, gave new insights into the mechanisms of respiratory allergic diseases.

The expression of CD40 on monocytes of children with primary humoral immunodeficiencies

The interactions between CD40 and CD40L (CD154) are critical for effective humoral immune response. CD40 signaling facilitates T lymphocyte dependent B cell proliferation and immunoglobulin isotype switch. The objective of our study was to investigate the CD40 and CD40L expression on peripheral blood mononuclear cells (PBMC) of children with symptomatic transient hypogammaglobulinemia (THI), common variable immunodeficiency (CVID) and selective IgA deficiency (SIgAD). Additionally we studied the production of IL-12 and IL-18 by PBMC stimulated with soluble CD40L. CD40 expression was analyzed on B cells and monocytes, CD40L on activated T lymphocytes, using flow cytometry following staining of the cells with appropriate MAb. We found that CD40 expression on B cells and CD40L on activated T cells were essentially similar in the control and patient groups, while the decreased CD40 expression on monocytes was observed in THI and SIgAD patients compared with normal subjects. The most significant decrease of CD40 expression was observed in THI (37% of positive cells) in comparison with control (81% of positive cells). IL-12, but not IL-18, release by PBMC was increased in THI and CVID, but not in SIgAD. In conclusion we suggest that the decreased expression of CD40 on monocytes of children with THI and SIgAD, but not CVID, may be involved in the pathomechanism of these immunodeficiencies.