Induction of systemic Th1 and Th2 immune responses by oral administration of soluble antigen and diesel exhaust particles

Different airborne particulates trigger distinct immune pathways leading to peanut allergy in a mouse model

BACKGROUND

Environmental exposure to peanut through non-oral routes is a risk factor for peanut allergy. Early-life exposure to air pollutants, including particulate matter (PM), is associated with sensitization to foods through unknown mechanisms. We investigated whether PM promotes sensitization to environmental peanut and the development of peanut allergy in a mouse model.

METHODS

C57BL/6J mice were co-exposed to peanut and either urban particulate matter (UPM) or diesel exhaust particles (DEP) via the airways and assessed for peanut sensitization and development of anaphylaxis following peanut challenge. Peanut-specific CD4+ T helper (Th) cell responses were characterized by flow cytometry and Th cytokine production. Mice lacking select innate immune signaling genes were used to study mechanisms of PM-induced peanut allergy.

RESULTS

Airway co-exposure to peanut and either UPM- or DEP-induced systemic sensitization to peanut and anaphylaxis following peanut challenge. Exposure to UPM or DEP triggered activation and migration of lung dendritic cells to draining lymph nodes and induction of peanut-specific CD4+ Th cells. UPM- and DEP-induced distinct Th responses, but both stimulated expansion of T follicular helper (Tfh) cells essential for peanut allergy development. MyD88 signaling was critical for UPM- and DEP-induced peanut allergy, whereas TLR4 signaling was dispensable. DEP-induced peanut allergy and Tfh-cell differentiation depended on IL-1 but not IL-33 signaling, whereas neither cytokine alone was necessary for UPM-mediated sensitization.

CONCLUSION

Environmental co-exposure to peanut and PM induces peanut-specific Tfh cells and peanut allergy in mice.

Enhancement of ovalbumin-specific Th1, Th2, and Th17 immune responses by amorphous silica nanoparticles

Nanomaterials present in cosmetics and food additives are used for industrial applications. However, their safety profile is unclear. Amorphous silica nanoparticles (nSPs) are a widely used nanomaterial and have been shown to induce inflammatory cytokines following intratracheal administration in mice. The current study investigated the adjuvant effect of nSP30 (nSP with a diameter of 33 nm) on T helper (Th)1, Th2, and Th17 immune responses as well as immunoglobulin (Ig) levels in mice. BALB/c mice were intraperitoneally administered ovalbumin (OVA) with or without varying doses and varying sizes of nSPs. The adjuvant effect of nSPs was investigated by measuring OVA-specific IgG antibodies in sera, OVA-specific proliferative responses of splenocytes, and the production of Th1, Th2, and Th17 cytokines. Aluminum hydroxide was used as a positive adjuvant control. Anti-OVA IgG production, splenocyte proliferative responses, and secretion of IFN-γ, IL-2, IL-4, IL-5, and IL-17 were increased significantly in mice receiving a combined injection of nSP30 (30 or 300 µg) with OVA compared with OVA alone or a combined injection with nSP30 (3 µg). The responses were nSP30 dose-dependent. When different sized nSPs were used (with 30, 100, and 1000 nm diameters), the responses to OVA were enhanced and were size-dependent. The smaller sized nSP particles had a greater adjuvant effect. nSPs appear to exert a size-dependent adjuvant effect for Th1, Th2, and Th17 immune responses. Understanding the mechanisms of nSP adjuvanticity might lead to the development of novel vaccine adjuvants and therapies for allergic diseases caused by environmental factors.

Effects of diesel exhaust particles on macrophage polarization

BACKGROUND

Exposure to diesel exhaust particles (DEP) has long been associated with increased cardiovascular morbidity and mortality. The development of DEP toxicity seems to be linked to inflammation in which macrophages play a critical role. Macrophages can be polarized into proinflammatory M1 or anti-inflammatory M2 macrophages. The aim of this study was to identify the role of inflammation in DEP-induced toxicity by assessing the effects of DEP on macrophage polarization.

METHODS

Monocyte-derived macrophages (Mϕ) were stimulated with interferon γ and lipopolysaccharide or interleukin (IL)-4 to obtain M1 and M2 subtypes, respectively. To test the polarization capacity of DEP, Mϕ cells were exposed to DEP and compared to Mϕ, M1, and M2. We also studied the effects of DEP on already-polarized M1 or M2. The M1 markers assessed were tumor necrosis factor α (TNF-α) and IL-1β, while the M2 markers were the mannose receptor C type 1 (MRC-1) and transglutaminase 2 (TGM2).

RESULTS

Western blots revealed a 31 kDa band corresponding to pro-IL-1β, but only in M1-polarized macrophages. In M1, we also observed an upregulation of TNF-α messenger RNA (mRNA) expression. MRC-1 and TGM2 mRNA expression were only significantly enhanced in M2. DEP had no effect on any of the M1/M2 markers assessed. Moreover, DEP were not able to modify the phenotype of already-polarized M1 or M2.

CONCLUSION

Mϕ incubation with DEP did not have any effect on macrophage polarization, at least on the markers assessed in this study, namely, TNF-α/IL-1β for M1, and MRC-1/TGM2 for M2. Hence, these data argue against an important role of inflammation in DEP-induced vascular toxicity.

Amorphous nanosilica particles block induction of oral tolerance in mice

The mucosal immune system is exposed to non-self antigens in food and the gut microbiota. Therefore, the recognition of orally ingested non-self antigens is suppressed in healthy individuals to avoid excessive immune responses in a process called "oral tolerance". The breakdown of oral tolerance has been cited as a possible cause of food allergy, and amorphous silica nanoparticles (nSP) have been implicated in this breakdown. As nSP are widely used in foodstuffs and other products, exposure to them is increasing; thus, investigations of any effects of nSP on oral tolerance are urgent. This study evaluated the effects of nSP30 (particle diameter = 39 nm) on immunological unresponsiveness induced in mice with oral ovalbumin (OVA). Specifically, production of OVA-specific antibodies, splenocyte proliferation in response to OVA, and effects on T-helper (TH)-1, TH2, and TH17 responses (in terms of cytokine and IgG/IgE subclass expression) were evaluated. nSP30 increased the levels of OVA-specific IgG in OVA-tolerized mice and induced the proliferation of OVA-immunized splenocytes in response to OVA in a dose-related manner. nSP30 also increased the expression of OVA-specific IgG1, IgE, and IgG2a, indicating stimulation of the TH1 and TH2 responses. The expression of interferon (IFN)-γ (TH1), interleukin (IL)-4 and IL-5 (TH2), and IL-17 (TH17) was also stimulated in a dose-related manner by nSP30 in splenocytes stimulated ex vivo with OVA. The induction of tolerance by OVA, the production of anti-OVA IgG antibodies, and proliferation of splenocytes in response to OVA was inhibited by nSP30 in conjunction with OVA and was dose-related. The nSP30 enhanced TH1 and TH2 responses that might prevent the induction of oral tolerance. Overall, this study showed that the abrogation of OVA-induced oral tolerance in mice by exposure to nSP30 was dose-related and that nSP30 stimulated TH1, TH2, and TH17 responses.

Environment and T regulatory cells in allergy

The central role of T regulatory cells in the responses against harmless environmental antigens has been confirmed by many studies. Impaired T regulatory cell function is implicated in many pathological conditions, particularly allergic diseases. The "hygiene hypothesis" suggests that infections and infestations may play a protective role for allergy, whereas environmental pollutants favor the development of allergic diseases. Developing countries suffer from a variety of infections and are also facing an increasing diffusion of environmental pollutants. In these countries allergies increase in relation to the spreading use of xenobiotics (pesticides, herbicides, pollution, etc.) with a rate similar to those of developed countries, overcoming the protective effects of infections. We review here the main mechanisms of non-self tolerance, with particular regard to relations between T regulatory cell activity, infections and infestations such as helminthiasis, and exposure to environmental xenobiotics with relevant diffusion in developing countries.

The immune effects of naturally occurring and synthetic nanoparticles

Ultrafine particles and engineered nanoparticles have unique aerodynamic and biochemical properties that affect the immune system and human health in ways that are different from or exceed those seen with gases or larger particulates. These effects result from a unique set of physical characteristics and surface moieties, which generate an ability of UFPs to enter tissues and cells, interact with proteins and DNA at a molecular level and directly and indirectly modulate the immune system by novel mechanisms. In recent years, a new field known as nanotechnology has impacted multiple industries by taking advantage of the special qualities of these small "atomic-sized" particles. Nanomedicine has already opened up a new avenue of research in cancer therapy, drug delivery and immune regulation. While the benefits of this new science to human civilization are seemingly immeasurable, it is also important to appreciate that these particles can also lead to harmful effects on human health. In vitro and animal studies are showing that nanoparticles and UFPs are capable of activating proinflammatory cytokines, chemokines and adhesion molecules, with recruitment of inflammatory cells including basophils, macrophages, dendritic cells, T cells, neutrophils and eosinophils. These changes may have an impact on immune defense, but also on the Th1/Th2 balance, and even on non-immunologic function. Resulting immune system derangement can lead to increases in incidence of autoimmune, allergic and even neoplastic diseases. Cardiorespiratory effects have been observed to occur in humans. Much further research is needed to establish safe exposure levels for this important new class of particulates.

Effects of Diesel Exhaust Particles on Antigen-Presenting Cells and Antigen-Specific Th Immunity in Mice

Diesel exhaust particles (DEP) exacerbate antigen-related airway inflammation and hyperresponsiveness in mice; however, the mechanisms remain undefined. The present study characterized more precisely which pathways and cellular events of the allergic response are amplified by DEP in view of the maturation/activation/function of antigen-presenting cells (APC) and the antigen-specific Th response. We evaluated the effects of DEP on the phenotype and function of bone marrow-derived dendritic cells (BMDC) in vitro and on the expression pattern of APC-related molecules in the murine lung in the presence or absence of antigen in vivo. Also, we tested the effects of in vivo DEP co-exposure with antigen on the splenic antigen-specific Th response in the context of cytokine production. DEP significantly increased both allogeneic and antigen (ovalbumin: OVA)-specific syngeneic T-cell proliferation in vitro. In addition, an in vivo experiment showed that repetitive pulmonary exposure to DEP plus antigen (OVA) increased the numbers of MHC class II+cells and those expressing CD11c, DEC205 (DC markers), CD80, CD86 (co-stimulatory molecules), F4/80 (a macrophage marker), and CD19 (a B-cell differentiation antigen) in the lung as compared to that of others (vehicle, DEP, or OVA). Furthermore, an ex vivo assay system demonstrated that splenic mononuclear cells primed by DEP plus OVA produced a greater amount of interleukin (IL)-4, IL-5, and IL-13 after in vitro antigen stimulation compared to those primed by the other treatments. In conclusion, enhancement of allergic responses by DEP can be explained via two novel mechanisms, i.e., enhancement effects on APC including DC and on antigen-specific Th response, which culminate in the promotion of local and systemic dysregulated Th immunity.

(Xeno)estrogen regulation of food allergy

Food allergy and other types of allergies are becoming epidemic in both the developed and developing countries. A large amount of information is available in literature that (xeno)estrogens can regulate the immune response in general, and the development of allergy in particular; however, the effect of (xeno)estrogens on food allergy is basically unknown. With increasing use of xenobiotics worldwide, chemicals with estrogenic activity have been accumulating in our environment. This review has summarized the current literature relating to the topic (xeno)estrogen regulation of food allergy. The effect of (xeno)estrogens on enterocytes, proteases for protein hydrolysis, dendritic cells and T-regulatory cells in the gastrointestinal tract has been discussed. Finally, considering the current confusion in literature regarding the effect of phytoestrogen genistein on the immune system, a brief discussion has been included for its effect on T(H)1-T(H)2 polarization, and possibly food allergy in its relation to windows of exposure. Sufficient evidences exist to support the notion that (xeno)estrogens can regulate food allergy, with the developmental periods more sensitive. Further clinical and animal studies are needed to determine the causal relationship between the exposure of (xeno)estrogens and incidence of food allergy, and the underlying mechanisms.

Diesel particulate material binds and concentrates a proinflammatory cytokine that causes neutrophil migration

Exposure to combustion emissions is associated with adverse health effects, but the properties of the emissions that induce these effects are not fully understood. To examine the direct effects of diesel particulate material (DPM) on alveolar epithelial cells, A549 cells were exposed to DPM. Low concentrations of DPM increased the interleukin-8 (IL-8) detected in the conditioned medium. Higher doses appeared to suppress the response, although this suppression was not related to acute DPM toxicity. In a cell-free system, incubation of IL-8 with DPM resulted in loss of immunoreactive IL-8 from the supernatant of the reaction. In contrast, carbon black did not reduce the concentration of IL-8 in the mixture. The DPM-induced loss was only weakly blocked by a large excess of bovine serum albumin (BSA). High concentrations of salts partially prevented the loss, but extraction of the soot with organic solvents had no effect. To determine biological implications, human blood neutrophils were exposed to DPM that had been preincubated with IL-8, then washed to remove free IL-8. The neutrophils changed shape in a manner suggesting directed movement toward the particles. No morphological change was observed either with carbon black that had been incubated with IL-8 or with DPM alone. These results suggest that DPM not only induces the production of IL-8 by epithelial cells, but also binds biologically active chemokine in a particle- and protein-selective manner. DPM-induced inflammatory responses may therefore be more focused or sustained as a result of this binding of inflammatory mediators by DPM.

Effects of Inula Britannica on the production of antibodies and cytokines and on T cell differentiation in C57BL/6 mice immunized by ovalbumin

In this study, we investigated the effects of Inula Britannica on the production of antibodies against ovalbumin, and the differentiation of T cells, in C57BL/6 mice. The oral administration of Inula Britannica suppressed IL-4 and IL-6 production in lymphocytes collected from an inguinal lymph node in the immunized leg. On the other hand, the intraperitoneal administration of Inula Britannica suppressed IgG1 production, the ratio of IFN-gamma+IL-4-/IFN-gamma-IL-4+ cells and cytokine production of IL-6. It was presumed that the effects of Inula Britannica on the production of antibodies were induced by regulation of the balance of Th1 and Th2. Further, IL-4 and IL-6 production by lymphocytes collected from an inguinal lymph node in the immunized leg were suppressed, and therefore production of antibodies was suppressed.

Diesel fumes and the rising prevalence of atopy: an urban legend?

Recently, the incidence of allergic diseases has increased in most industrialized countries of the world. Persistent exposure to particulate air pollution from motor vehicles has been implicated as one of the factors that is responsible for the observed increased prevalence of atopy. Epidemiologic studies conducted in different parts of the world have demonstrated an important association between ambient levels of motor vehicle traffic emissions and increased symptoms of asthma and rhinitis. Additionally, recent human and animal laboratory-based studies have shown that particulate toxic pollutants, and in particular diesel exhaust particles (DEP), can enhance allergic inflammation and induce the development of allergic immune responses. In this article, our current understanding of the mechanisms by which pollutants such as DEPs enhance the underlying allergic inflammatory response is reviewed, and the evidence that supports the causative link between particulate air pollution from motor vehicles and increasing allergic diseases is discussed.

Diesel exhaust and asthma: hypotheses and molecular mechanisms of action

Several components of air pollution have been linked to asthma. In addition to the well-studied critera air pollutants, such as nitrogen dioxide, sulfur dioxide, and ozone, diesel exhaust and diesel exhaust particles (DEPs) also appear to play a role in respiratory and allergic diseases. Diesel exhaust is composed of vapors, gases, and fine particles emitted by diesel-fueled compression-ignition engines. DEPs can act as nonspecific airway irritants at relatively high levels. At lower levels, DEPs promote release of specific cytokines, chemokines, immunoglobulins, and oxidants in the upper and lower airway. Release of these mediators of the allergic and inflammatory response initiates a cascade that can culminate in airway inflammation, mucus secretion, serum leakage into the airways, and bronchial smooth muscle contraction. DEPs also may promote expression of the T(subscript)H(/subscript)2 immunologic response phenotype that has been associated with asthma and allergic disease. DEPs appear to have greater immunologic effects in the presence of environmental allergens than they do alone. This immunologic evidence may help explain the epidemiologic studies indicating that children living along major trucking thoroughfares are at increased risk for asthmatic and allergic symptoms and are more likely to have objective evidence of respiratory dysfunction.

The influence of diesel exhaust particles on mononuclear phagocytic cell-derived cytokines: IL-10, TGF-beta and IL-1 beta

Diesel exhaust particles (DEP) are known to modulate the production of cytokines associated with acute and chronic respiratory symptoms and allergic respiratory disease. Tolerance is an important mechanism through which the immune system can maintain nonresponsiveness to common environmental antigens. We examined the effect of DEP on IL-10 and TGF-beta, cytokines produced by macrophages and repressor (Tr-like) lymphocytes which influence tolerance. Human PBMCs (n = 22) were incubated with 1-100 ng/ml of DEP, and suboptimally primed with LPS. IL-10 gene expression was assessed by the S1 nuclease protection assay, and production of IL-10, TGF-beta, TNF-alpha, IL-1 beta and IL-4 stimulated CD23 was evaluated by ELISA after 24 and 48 h. The effect of the order of exposure to DEP and LPS was evaluated on IL-10 protein and mRNA in cells (1) preincubated with LPS followed by DEP, or (2) exposed first to DEP followed by LPS. IL-10 was further evaluated using benzo[a]pyrene and [alpha]naphthoflavone as a surrogate for the polyaromatic hydrocarbons (PAHs) adsorbed to DEP. Control cells were incubated with carbon black, without PAHs. In PBMCs exposed to DEP with LPS, or preincubated with LPS before DEP, IL-10 production and mRNA fall significantly. TGF-beta is similarly suppressed, IL-1 beta secretion is significantly stimulated, and IL-4 stimulated CD23 release rises in the atopic subjects. In contrast, when DEP is added prior to LPS, IL-10 production rises, and IL-1 beta falls to zero. These effects on IL-10 are reproduced with benzo[a]pyrene and reversed by the coaddition of [alpha]naphthoflavone, its known antagonist. The carbon black fraction has no effect on IL-10 production. The effect of DEP on IL-10 can be inhibitory or stimulatory, depending on the order of exposure to DEP and LPS. Pro-inflammatory cytokines and factors rise when IL-10 is inhibited, and are suppressed when IL-10 is stimulated. These results are duplicated with benzo[a]pyrene, suggesting that the PAH portion of the DEP is the active agent.