The role of regulatory T cells in allergy

Role of regulatory T-cells in autoimmunity

There has been considerable historical interest in the concept of a specialist T-cell subset which suppresses over-zealous or inappropriate T-cell responses. However, it was not until the discovery that CD4(+)CD25(+) T-cells had suppressive capabilities both in vitro and in vivo that this concept regained credibility and developed into one of the most active research areas in immunology today. The notion that in healthy individuals there is a subset of T(reg)-cells (regulatory T-cells) involved in 'policing' the immune system has led to the intensive exploration of the role of this subset in disease resulting in a number of studies concluding that a quantitative or qualitative decline in T(reg)-cells is an important part of the breakdown in self-tolerance leading to the development of autoimmune diseases. Although T(reg)-cells have subsequently been widely postulated to represent a potential immunotherapy option for patients with autoimmune disease, several studies of autoimmune disorders have demonstrated high numbers of T(reg)-cells in inflamed tissue. The present review highlights the need to consider a range of other factors which may be impairing T(reg)-cell function when considering the mechanisms involved in the breakdown of self-tolerance rather than focussing on intrinsic T(reg)-cell factors.

The interaction between Helicobacter pylori and atopy: does inverse association really exist?

AIM

To date, cross-sectional and case-control studies suggest an inverse association between Helicobacter pylori infection and atopic diseases, whereas the immunologic basis has not been studied yet. In this study we investigated T helper (Th) cell function in H. pylori-infected children and compared cytokine responses in atopic and non-atopic groups.

METHODS

The study groups was recruited from a cohort of 327 healthy children evaluated and followed-up for 6 years to assess the natural history of H. pylori infection. Seventy-four of 136 healthy children who underwent (13)C urea breath test were eligible and accepted to participate. All participants were evaluated by a questionnaire, and skin-prick testing. According to the results, children were divided into four groups with respect to the presence or absence of H. pylori and atopy. Peripheral blood mononuclear cells isolated from 34 of 74 children were cultured with H. pylori, Der p 1, and phytohemagglutinin (PHA). Interferon-gamma (IFN-gamma), interleukin (IL)-4 and IL-10, transforming growth factor-beta (TGF-beta) levels were measured in supernatants.

RESULTS

The frequency of atopy was lower in H. pylori-infected group (31.9% vs. 48.1, p = .22), while atopic symptoms were similar between infected and non-infected children. While PHA and H. pylori induced IFN-gamma levels were significantly higher in H. pylori-infected children, concomitant presence of both atopy and H. pylori decreased the level of PHA and H. pylori induced IFN-gamma production. PHA and Der p 1-induced IL-4 levels were higher in atopic children, and IL-4 production was suppressed when they were concomitantly infected with H. pylori. The production of TGF-beta was found to be suppressed in atopic children irrespective of the presence of H. pylori infection.

CONCLUSION

The results of the current study demonstrated a counteractive Th1 and Th2 cytokine interaction between H. pylori infection and atopy. However, this counteractive immunologic balance did not protect against atopy.

Primary immune deficiencies with aberrant IgE production

IgE antibodies play a central role in the pathogenesis of atopic diseases and in host immunity against parasitic infections. IgE has potent activities on mast cells and basophils. IgE class switching is a very tightly controlled process, and serum IgE levels are very low compared with other immunoglobulin isotypes. Transcription factors that activate or inhibit the IgE gene promoter, as well as T(H)1 and T(H)2 cytokines are important in the regulation of IgE levels. Hyper-IgE syndrome; Wiskott-Aldrich syndrome; immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX); Omenn syndrome; and atypical complete DiGeorge syndrome are primary immune deficiencies that are associated with elevated serum IgE levels. Increased IgE levels in IPEX, Wiskott-Aldrich syndrome and Omenn syndrome are likely related to increased T(H)2 cytokine production caused by decreased a number or function of CD4(+)CD25(+)forkhead box protein P3(+) regulatory T cells. The link between signal transducer and activator of transcription 3 mutations and elevated serum IgE levels in hyper-IgE syndrome is unclear. Insight into IgE regulation provided by the study of primary immune deficiencies with elevated IgE has important implications for allergic diseases.

Primary immunodeficiencies unravel critical aspects of the pathophysiology of autoimmunity and of the genetics of autoimmune disease

BACKGROUND

Primary Immunodeficiencies (PIDs) represent unique opportunities to understand the operation of the human immune system. Accordingly, PIDs associated with autoimmune manifestations provide insights into the pathophysiology of autoimmunity as well as into the genetics of autoimmune diseases (AID). Epidemiological data show that there are PIDs systematically associated with AID, such as immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX), Omenn syndrome, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), autoimmune lymphoproliferative syndrome (ALPS), and C1q deficiency, while strong associations are seen with a handful of other deficits.

CONCLUSION

We interpret such stringent disease associations, together with a wealth of observations in experimental systems, as indicating first of all that natural tolerance to body components is an active, dominant process involving many of the components that ensure responsiveness, rather than, as previously believed, the result of the mere purge of autoreactivities. More precisely, it seems that deficits of Treg cell development, functions, numbers, and T cell receptor repertoire are among the main factors for autoimmunity pathogenesis in many (if not all) PIDs most frequently presenting with autoimmune features. Clearly, other pathophysiological mechanisms are also involved in autoimmunity, but these seem less critical in the process of self-tolerance. Comparing the clinical picture of IPEX cases with those, much less severe, of ALPS or APECED, provides some assessment of the relative importance of each set of mechanisms.

Heme oxygenase-1 attenuates ovalbumin-induced airway inflammation by up-regulation of foxp3 T-regulatory cells, interleukin-10, and membrane-bound transforming growth factor- 1

Cumulative evidence suggests the up-regulation of interleukin (IL)-10 and T-regulatory (Treg) cells is implicated in anti-inflammatory effect of heme oxygenase-1 (HO-1). Thus, we postulated that induction of HO-1 could augment IL-10 and transforming growth factor (TGF)-beta production and foxp3+CD4+CD25+ Treg cell function, thereby leading to attenuation of airway inflammation. In this study, CD4+CD25+ Treg cells isolated from mouse spleen were either transfected with a HO-1 expression vector (pcDNA3HO-1) or treated with a HO-1 inducer (hemin). Up-regulation of HO-1 enhanced foxp3 expression and IL-10 secretion in the Treg cells in vitro. Next, BALB/c, C57/B6.129, and IL-10-deficient B6.129P2-Il10tm1Cgn/J mice were challenged by ovalbumin to induce airway inflammation. Consistent with in vitro findings, hemin treatment resulted in induction of HO-1 and foxp3 and production of IL-10 and membrane-bound TGF-beta1 in vivo. This was further correlated with decrease of ovalbumin-specific immunoglobulin E level and eosinophil infiltration in bronchial alveolar lavage fluid from the asthmatic mice. Furthermore, hemin significantly enhanced the biological activity of CD4+CD25+ Treg cells. This protective effect was specifically blocked by Sn-protoporphyrin, a HO-1 enzymatic inhibitor. Finally, hemin failed to up-regulate the function of CD4+CD25+ Treg cells from IL-10-deficient mice. Our study indicates that HO-1 exerts its protective effect on asthma through a mechanism mediated by foxp3+CD4+CD25+ Treg cells, IL-10, and membrane-bound TGF-beta1.

Murine models of Omenn syndrome

In the 40 years since Harvard medical student Gilbert Omenn first described a rare, inherited disorder producing a paradoxical combination of immunodeficiency and immune dysregulation, the pathogenesis of Omenn syndrome (OS) has remained mysterious. In separate studies reported in this issue of the JCI, two mouse models bearing mutations in the V(D)J recombinase analogous to those causing human OS have been shown to recapitulate the disease and provide insight into the genesis of immunodeficiency combined with autoimmunity and atopy in OS and other disease settings (see the related articles beginning on pages 1260 and 1270).

Changes in immune regulation in response to examination stress in atopic and healthy individuals

BACKGROUND

Stress can aggravate the allergic inflammation, but determinants of disturbed immune regulation are largely unknown.

OBJECTIVE

To determine systemic immunological, local inflammatory and functional airway responses to stress in healthy and atopic individuals.

METHODS

Forty-one undergraduate students, 22 with allergy of whom 16 had asthma, and 19 healthy controls, were studied in a low-stress period and in association with a large exam. Subjects completed questionnaires on stress and health behaviours, underwent lung function tests, bronchial methacholine challenge, measurements of exhaled nitric oxide and urine cortisol. Blood cells were phenotyped, and cytokines from mononuclear blood cells were analysed.

RESULTS

Perceived stress and anxiety increased in both groups during the exam period while cortisol increased only in the atopy group. Cytokine production decreased broadly in response to stress in both groups, which was paralleled by an increase in the proportion of regulatory T cells (CD4(+)CD45RO(+)CD25(bright)). Interestingly, atopic individuals, but not controls, reacted with a decreased T-helper type 1/T-helper type 2 (Th1/Th2) ratio and a decrease in natural killer (NK) cell numbers in response to stress. In control subjects only, exhaled nitric oxide decreased and forced expiratory volume in one second increased during stress.

CONCLUSION

Atopic and non-atopic subjects shared some immune changes in response to stress, such as a dramatic decline in cytokines and an increase in the number of regulatory T cells in peripheral blood. However, other stress-induced immune changes were unique to atopic individuals, such as a skewed Th1/Th2 ratio and reduced NK cell numbers, indicating that some pathogenic mechanisms in atopics may be more strongly affected by stress than others.

New aspects on inflammation in allergic diseases

BACKGROUND

Allergic disease has currently reached epidemic proportions, with a high percentage of individuals in the developed world exhibiting an allergic response after exposure to some common environmental factors. Although new strategies for the treatment and management of allergic diseases have decreased the mortality rate, a high percentage of affected persons still require frequent hospitalization and experience decreased quality of life.

METHODS

An internet-based literature search was performed for recent contributions on the underlying mechanisms provoking an allergic response and their potential for therapeutic approaches.

RESULTS

Novel concepts on allergic responses have emerged: allergic disease may result from an imbalance between allergen activation of regulatory T cells and effector T helper 2 cells (Th2), a process in which dendritic cells are key players. Cytokines such as interleukin (IL)-6, IL-21, IL-25, and human thymic stromal lymphopoietin (TSLP) seem to be important contributors in allergic processes. New data on IgE effector responses and on the IgE-independent mechanisms involved in allergic reactions have resolved some unanswered questions about these reactions.

CONCLUSIONS

These new findings on allergic diseases have important implications for diagnosis and management, with potential improvements in prevention and treatment, which could provide a cure in the future.

Disconnection of man and the soil: reason for the asthma and atopy epidemic?

Intense search has been going on to find factors responsible for the asthma and atopy epidemic in Western societies. Attention has increasingly been devoted to environmental saprophytes, which, in addition to gut commensals, might be the major players in the development and fine tuning of immunologic homeostasis. This review outlines current evidence for the role of environmental saprophytes in the development of atopic disease and considers the consequences of urbanization in reducing contacts with soil microorganisms. The major microbial components that have been shown to possess immunomodulatory capacity and their respective Toll-like receptors are also discussed, as are the possible mechanisms underlying the ability of saprophytes to confer protection against atopic disease.