New insights into mechanisms of immunoregulation in 2007

Targeting of tolerogenic dendritic cells to heat-shock proteins in inflammatory arthritis

Background

Autologous tolerogenic dendritic cells (tolDC) are a promising therapeutic strategy for inflammatory arthritis (IA) as they can regulate autoantigen-specific T cell responses. Here, we investigated two outstanding priorities for clinical development: (i) the suitability of using heat-shock proteins (HSP), abundant in inflamed synovia, as surrogate autoantigens to be presented by tolDC and (ii) identification of functional biomarkers that confirm tolDC regulatory activity.

Methods

Cell proliferation dye-labelled human peripheral blood mononuclear cells of IA (rheumatoid arthritis (RA) and psoriatic arthritis (PsA)) patients or healthy donors were cultured with HSP40-, HSP60- and HSP70-derived peptides or recall antigens (e.g. tuberculin purified protein derivative (PPD)) in the presence or absence of tolDC or control DC for 9 days. Functional characteristics of proliferated antigen-specific T-cells were measured using flow cytometry, gene expression profiling and cytokine secretion immunoassays. Repeated measures analysis of variance (ANOVA) with Bonferroni correction for comparisons between multiple groups and paired Student t test for comparisons between two groups were used to determine significance.

Results

All groups showed robust CD4⁺ T-cell responses towards one or more HSP-derived peptide(s) as assessed by a stimulation index > 2 (healthy donors: 78%, RA: 73%, PsA: 90%) and production of the cytokines IFNγ, IL-17A and GM-CSF. Addition of tolDC but not control DC induced a type 1 regulatory (Tr1) phenotype in the antigen-specific CD4⁺ T-cell population, as identified by high expression of LAG3, CD49b and secretion of IL-10. Furthermore, tolDC inhibited bystander natural killer (NK) cell activation in a TGFβ dependent manner.

Conclusions

HSP-specific CD4⁺ T-cells are detectable in the majority of RA and PsA patients and can be converted into Tr1 cells by tolDC. HSP-loaded tolDC may therefore be suitable for directing T regulatory responses to antigens in inflamed synovia of IA patients. Tr1 markers LAG3, CD49b and IL-10 are suitable biomarkers for future tolDC clinical trials.

Inflammation in Respiratory Allergy Treated by Sublingual Immunotherapy

The most common allergic diseases, such as rhinitis, asthma and atopic dermatitis, are sustained by allergic inflammation, the treatment of which requires anti-inflammatory activity. Among the available treatments, allergen immunotherapy (IT) has a documented impact on allergic inflammation which persists after its discontinuation and modifies the natural course of allergy. The anti-inflammatory effects of IT, and particularly of sublingual IT (SLIT), are based on the ability to modify the phenotype of T cells which, in allergic subjects, are characterized by a prevalence of the Th2 type, with production of IL-4, IL-5, IL-13, IL-17, and IL-32 cytokines. IT-induced changes result in a Th1-type response (immune deviation) related to an increased IFN-gamma and IL-2 production or in a Th2 reduced activity, through a mechanism of anergy or tolerance. It is now known that T cell tolerance is characterized by the generation of allergen-specific Treg cells, which produce cytokines such as IL-10 and TGF-beta with immunosuppressant and/or immunoregulatory activity. Recent studies suggest that the anti-inflammatory mechanism of SLIT is similar to classical, subcutaneous IT, with a prominent role in SLIT for mucosal dendritic cells. The tolerance pattern induced by Treg accounts for the suppressed or reduced activity of inflammatory cells and for the isotypic switch of antibody synthesis from IgE to IgG, and especially to IgG4. Data obtained from biopsies clearly indicate that the pathophysiology of the oral mucosa plays a pivotal role in inducing tolerance to the sublingually administered allergen.

Therapeutic targets for olive pollen allergy defined by gene markers modulated by Ole e 1-derived peptides

Two regions of Ole e 1, the major olive-pollen allergen, have been characterized as T-cell epitopes, one as immunodominant region (aa91-130) and the other, as mainly recognized by non-allergic subjects (aa10-31). This report tries to characterize the specific relevance of these epitopes in the allergic response to olive pollen by analyzing the secreted cytokines and the gene expression profiles induced after specific stimulation of peripheral blood mononuclear cells (PBMCs). PBMCs from olive pollen-allergic and non-allergic control subjects were stimulated with olive-pollen extract and Ole e 1 dodecapeptides containing relevant T-cell epitopes. Levels of cytokines were measured in cellular supernatants and gene expression was determined by microarrays, on the RNAs extracted from PBMCs. One hundred eighty-nine differential genes (fold change >2 or <-2, P<0.05) were validated by qRT-PCR in a large population. It was not possible to define a pattern of response according the overall cytokine results but interesting differences were observed, mainly in the regulatory cytokines. Principal component (PCA) gene-expression analysis defined clusters that correlated with the experimental conditions in the group of allergic subjects. Gene expression and functional analyses revealed differential genes and pathways among the experimental conditions. A set of 51 genes (many essential to T-cell tolerance and homeostasis) correlated with the response to aa10-31 of Ole e 1. In conclusion, two peptides derived from Ole e 1 could regulate the immune response in allergic patients, by gene-expression modification of several regulation-related genes. These results open new research ways to the regulation of allergy by Oleaceae family members.

Iron oxide particles modulate the ovalbumin-induced Th2 immune response in mice

This study was designed to investigate the modulatory effects of submicron and nanosized iron oxide (Fe(2)O(3)) particles on the ovalbumin (OVA)-induced immune Th2 response in BALB/c mice. Particles were intratracheally administered four times to mice before and during the OVA sensitization period. For each particle type, three different doses, namely 4×100, 4×250 or 4×500 μg/mouse, were used and for each dose, four groups of mice, i.e. group saline solution (1), OVA (2), particles (3), and OVA plus particles (4), were constituted. Mice exposed to OVA alone exhibited an allergic Th2-dominated response with a consistent increase in inflammatory scores, eosinophil numbers, specific IgE levels and IL-4 production. When the mice were exposed to OVA and to high and intermediate doses of iron oxide submicron- or nanoparticles, the OVA-induced allergic response was significantly inhibited, as evidenced by the decrease in eosinophil cell influx and specific IgE levels. However, the low dose (4×100 μg) of submicron particles had no significant effect on the OVA allergic response while the same dose of nanoparticles had an adjuvant effect on the Th2 response to OVA. In conclusion, these data demonstrate that the pulmonary immune response to OVA is a sensitive target for intratracheally instilled particles. Depending on the particle dose and size, the allergic response was suppressed or enhanced.

Identification of contact and respiratory sensitizers according to IL-4 receptor α expression and IL-2 production

Identification of allergenic chemicals is an important occupational safety issue. While several methods exist to identify contact sensitizers, there is currently no validated model to predict the potential of chemicals to act as respiratory sensitizers. Previously, we reported that cytometry analysis of the local immune responses induced in mice dermally exposed to the respiratory sensitizer trimellitic anhydride (TMA 10%) and contact sensitizer dinitrochlorobenzene (DNCB 1%) could identify divergent expression of several immune parameters. The present study confirms, first, that IgE-positive B cells, MHC class II molecules, interleukin (IL)-2, IL-4 and IL-4Rα can differentiate the allergic reactions caused by high doses of strong respiratory (TMA, phthalic anhydride and toluene diisocyanate) and contact sensitizers (DNCB, dinitrofluorobenzene and oxazolone). The second part of the study was designed to test the robustness of these markers when classing the weakly immunogenic chemicals most often encountered. Six respiratory allergens, including TMA (2.5%), five contact allergens, including DNCB (0.25%), and two irritants were compared at doses of equivalent immunogenicity. The results indicated that IL-4Rα and IL-2 can be reliably used to discriminate sensitizers. Respiratory sensitizers induced markedly higher IL-4Rα levels than contact allergens, while irritants had no effect on this parameter. Inversely, contact allergens tended to induce higher percentages of IL-2⁺CD8⁺ cells than respiratory allergens. In contrast, the markers MHC-II, IgE and IL-4 were not able to classify chemicals with low immunogenic potential. In conclusion, IL-4Rα and IL-2 have the potential to be used in classifying a variety of chemical allergens.

Mechanisms of subcutaneous allergen immunotherapy

Allergen-specific immunotherapy (SIT) is the only curative approach in the treatment of allergic diseases defined up-to-date. Peripheral T-cell tolerance to allergens, the goal of successful allergen-SIT, is the primary mechanism in healthy immune responses to allergens. By repeated administration of increased doses of the causative allergen, allergen-SIT induces a state of immune tolerance to allergens through the constitution of T regulatory (Treg) cells, including allergen-specific interleukin (IL)-10-secreting Treg type 1 cells and CD4(+)CD25(+)Treg cells; induction of suppressive cytokines, such as IL-10 and transforming growth factor β; suppression of allergen-specific IgE and induction of IgG4 and IgA; and suppression of mast cells, basophils, eosinophils, and inflammatory dendritic cells. This review summarizes the current knowledge on the mechanisms of allergen-SIT with emphasis on the roles of Treg cells in allergen-SIT.

Experimentally induced accumulation of Foxp3⁺ T cells in upper airway allergy

BACKGROUND

It has been suggested that Foxp3(+) regulatory T (Treg) cells inhibit allergic inflammation in humans by suppressing the activation of allergen-specific effector T cells. Whether this occurs at the site of allergen exposure has not been determined.

OBJECTIVE

To determine the occurrence of Foxp3(+) Treg cells in the nasal mucosa of allergic rhinitis (AR) patients and non-allergic controls after a nasal allergen challenge.

METHODS

Pollen-allergic patients (n=18) and non-allergic volunteers (n=7) were challenged locally with pollen extract or placebo for 7 days outside the pollen season. Mucosal biopsies were obtained from the inferior turbinate on days 0, 1 and 7 and subjected to multi-colour immunofluorescence and blood was drawn for eosinophil counts on days 0, 2, 5 and 7.

RESULTS

Only AR patients receiving pollen extract experienced typical allergic symptoms and demonstrated increased levels of eosinophils in peripheral blood and nasal mucosa. In allergic patients, a transient early increase (day 1) in CD3(+) T cells was observed in the nasal mucosa, followed by a significant increase of Foxp3(high) T cells at day 7. No changes were found in the control group. The majority of Foxp3(high) cells co-expressed CTLA-4, CD25 and CD4, and a substantial fraction expressed the proliferation marker Ki67.

CONCLUSION AND CLINICAL RELEVANCE

Experimentally induced inflammation in AR patients leads to an early inflammatory response followed by accumulation of Foxp3(high) T cells in the nasal mucosa. Our findings are similar to that observed in allergic airways of experimental mice, which suggest that Treg cells are operative in allergic upper airway inflammation. It should be explored whether Treg cells accumulating in the nasal mucosa could be targets for therapeutic intervention.

Clinical immunology review series: an approach to desensitization

Allergen immunotherapy describes the treatment of allergic disease through administration of gradually increasing doses of allergen. This form of immune tolerance induction is now safer, more reliably efficacious and better understood than when it was first formally described in 1911. In this paper the authors aim to summarize the current state of the art in immunotherapy in the treatment of inhalant, venom and drug allergies, with specific reference to its practice in the United Kingdom. A practical approach has been taken, with reference to current evidence and guidelines, including illustrative protocols and vaccine schedules. A number of novel approaches and techniques are likely to change considerably the way in which we select and treat allergy patients in the coming decade, and these advances are previewed.

Blunted HPA axis responsiveness to stress in atopic patients is associated with the acuity and severeness of allergic inflammation

Previously we could demonstrate attenuated responsiveness of the hypothalamus-pituitary-adrenal (HPA) axis to stress in patients with chronic allergic inflammatory disease (i.e., atopic dermatitis, allergic asthma). The present study was designed to investigate HPA axis function in an acute manifestation of allergy. Patients with seasonal allergic rhinitis (SAR; n = 20) and non-atopic controls (n = 20) were exposed to a standardized laboratory stressor ('Trier Social Stress Test'; TSST). Cortisol responses to the TSST and cortisol awakening responses (CAR) were measured in SAR subjects while suffering from acute symptoms of SAR (pollen season), and during a non-active state of their disease (pollen-free season). To assess the acuity and severity of SAR, eosinophil and basophil numbers and SAR symptomatology were determined. Non-allergic control subjects were examined at identical times during the year. To control for possible sequence effects, a cross-over design was used. SAR patients showed significantly increased symptom severity (t = 9.4; p<.001) as well as eosinophil (F(1,31) = 9.8; p<.01) and basophil (F(1,38) = 6.4; p<.05) numbers during the pollen season when compared to a pollen-free period. When exposed to the TSST, significantly attenuated cortisol responses were found in SAR subjects during acute manifestation of the disease (pollen season) when compared to the pollen-free season (F(16,456) = 1.65; p<.05). In SAR patients, there was a significant negative correlation between symptom severity and the cortisol response to the stressor (r = .53; p<.05). No significant between-group or between-condition differences with respect to the CAR could be determined (all p>.05). These findings support previous data of attenuated HPA axis responsiveness to stress in atopic conditions and further, suggest that HPA axis hyporesponsiveness in atopy may be linked to the severity of the allergic inflammatory process.

The leukocyte activation antigen CD69 limits allergic asthma and skin contact hypersensitivity

BACKGROUND

Allergic diseases have a major health care impact in industrialized countries. The development of these diseases is influenced by exposure to allergen and to immunological and genetic factors. However, the molecular mechanisms underlying the inflammatory response that triggers allergy are not well defined.

OBJECTIVE

We have investigated the role of the leukocyte activation antigen CD69 in the regulation of two allergic diseases, asthma and contact dermatitis.

METHODS

Analysis of two models of allergic diseases in CD69 knockout and wild-type mice: ovalbumin-induced allergic airway inflammation (BALB/c genetic background) and contact hypersensitivity to oxazolone (C57BL/6J genetic background).

RESULTS

CD69 deficiency dramatically enhanced the inflammatory response in the ovalbumin-induced asthma model of antigen-induced airway allergy. CD69 knockout mice showed exacerbated pulmonary eosinophil recruitment, high vascular cell adhesion molecule 1 expression levels in lung vasculature, and enhanced T(H)2 and T(H)17 cytokines in the bronchoalveolar space and lung tissue. In the hapten-induced cutaneous contact hypersensitivity model, both CD69 deficiency and treatment with anti-CD69 mAb increased inflammation. Treatment with contact allergens induced enhanced T(H)1 and T(H)17 responses in CD69 deficient mice, and neutralizing anti-IL-17 antibodies reduced skin inflammation. In both experimental systems, adoptive transfer of lymph node cells from CD69 knockout mice increased the inflammatory response in recipient mice.

CONCLUSION

These results demonstrate that the early activation receptor CD69 is an intrinsic modulator of immune allergic processes through the negative regulation of allergen-induced T-cell effector responses.

An immunological overview of allergen specific immunotherapy -- subcutaneous and sublingual routes

Allergen-specific immunotherapy remains the most likely effective treatment modality for allergic disorders by targeting the underlying immune mechanisms and possibly causing modifications in the disease course, as well as treating the symptoms. Treatment and compliance experiences been gained over nearly a century in injection-type allergen-specific immunotherapy have motivated the development of newer, alternative routes. Adverse events and safety concerns, efficacy and ease of application seem to be the stimulating factors for the development of a sublingual form of this treatment modality, wherein the principal factor is the capture of the antigen (allergen) by dendritic cells, in the location where oral tolerance arises. Due to the presence of high numbers of tolerogenic dendritic cell subsets in this region, programming of the immune system towards a regulatory state with unresponsiveness to specific allergens occurs. Induction of peripheral tolerance through the generation of regulatory T cells is the key event, with several functional modulations in the allergic immune response. With an increase in understanding of the mechanism of regulatory pathways, promising progresses in the field of allergen-specific immunotherapy will ensue and may provide new options for the treatment of allergic disorders.

Ebastine in the light of CONGA recommendations for the development of third-generation antihistamines

In 2003 a consensus group on new-generation antihistamines (CONGA) defined the characteristics required for a third-generation H(1) antihistamine as there had been much controversy about this issue since the early 1990s. One of the antihistamines that had been claimed to belong to such a group is the second-generation antihistamine, ebastine. The objective of this review is to analyze the pharmacology of ebastine, in light of the CONGA recommendations for the development of new-generation antihistamines: (1) anti-inflammatory properties, (2) potency, efficacy and effectiveness, (3) lack of cardiotoxicity, (4) lack of drug interactions, (5) lack of CNS effects, and (6) pharmacological approach. Ebastine seems to have anti-inflammatory properties that help to ameliorate nasal congestion, though this has not yet been conclusively demonstrated. Its pharmacological-therapeutic profile does not differ greatly from that of other second-generation antihistamines. Its cardiac safety has been widely assessed and no cardiac toxicity has been found at therapeutic doses despite initial concerns. The risk of potentially relevant drug interactions has been investigated and ruled out. Ebastine does not produce sedation at therapeutic doses and drug interaction studies with classical CNS depressants have not demonstrated a synergistic effect. Pharmacologically, ebastine is an H(1) inverse agonist. Perhaps the answer to the quest for new-generation antihistamines lies not only in H(1) but in a combined approach with other histamine receptors.