Activation of CD25(+)CD4(+) regulatory T cells by oral antigen administration

Mechanism of oral tolerance induction to therapeutic proteins

Oral tolerance is defined as the specific suppression of humoral and/or cellular immune responses to an antigen by administration of the same antigen through the oral route. Due to its absence of toxicity, easy administration, and antigen specificity, oral tolerance is a very attractive approach to prevent unwanted immune responses that cause a variety of diseases or that complicate treatment of a disease. Many researchers have induced oral tolerance to efficiently treat autoimmune and inflammatory diseases in different animal models. However, clinical trials yielded limited success. Thus, understanding the mechanisms of oral tolerance induction to therapeutic proteins is critical for paving the way for clinical development of oral tolerance protocols. This review will summarize progress on understanding the major underlying tolerance mechanisms and contributors, including antigen presenting cells, regulatory T cells, cytokines, and signaling pathways. Potential applications, examples for therapeutic proteins and disease targets, and recent developments in delivery methods are discussed.

Early life exposure to antibiotics and the risk of childhood allergic diseases: an update from the perspective of the hygiene hypothesis

The prevalence of allergic diseases has been growing rapidly in industrial countries during recent decades. It is postulated that growing up with less microbial exposure may render the immune system susceptible to a T helper type 2 (Th2)-predominant allergic response-also known as the hygiene hypothesis. This review delineates recent epidemiological and experimental evidence for the hygiene hypothesis, and integrates this hypothesis into the association between early life exposure to antibiotics and the development of allergic diseases and asthma. Several retrospective or prospective epidemiological studies reveal that early exposure to antibiotics may be positively associated with the development of allergic diseases and asthma. However, the conclusion is inconsistent. Experimental studies show that antibiotics may induce the Th2-skewed response by suppressing the T helper type 1 (Th1) response through inhibition of Th1 cytokines and disruption of the natural course of infection, or by disturbing the microflora of the gastrointestinal (GI) tract and therefore jeopardizing the establishment of oral tolerance and regulatory T cell immune responses. The hygiene hypothesis may not be the only explanation for the rapid increase in the prevalence of allergic diseases and asthma. Further epidemiological and experimental studies addressing the issue of the impact of environmental factors on the development of allergic diseases and the underlying mechanisms may unveil novel strategies for the prevention and treatment of allergic diseases in the future.

Antigen-specific effector CD4 T lymphocytes school lamina propria dendritic cells to transfer innate tolerance

Dendritic cells (DCs) have been shown to play a major role in oral tolerance, and this function has been associated with their ability to produce anti-inflammatory cytokines and to induce suppressive regulatory T cells. In this study, we demonstrate that upon oral administration of Ag, lamina propia (LP) DCs engage specific T cells and acquire a novel mechanism by which they transfer tolerance against diverse T cell specificities. Indeed, when Ig-myelin oligodendrocyte glycoprotein (MOG) carrying the MOG(35-55) epitope was orally administered into either T cell-sufficient or -deficient mice, only the T cell-sufficient hosts yielded CD8α(+) and CD8α(-) LP DCs that were able to transfer tolerance to a variety of MHC class II-restricted effector T cells. Surprisingly, these LP DCs upregulated programmed cell death ligand 1 during the initial interaction with MOG-specific T cells and used this inhibitory molecule to suppress activation of T cells regardless of Ag specificity. Furthermore, oral Ig-MOG was able to overcome experimental autoimmune encephalomyelitis induced with CNS homogenate, indicating that the DCs are able to modulate disease involving diverse T cell specificities. This previously unrecognized attribute potentiates DCs against autoimmunity.

B7-H4Ig inhibits mouse and human T-cell function and treats EAE via IL-10/Treg-dependent mechanisms

We evaluated the therapeutic efficacy and mechanisms of action of both mouse and human B7-H4 Immunoglobulin fusion proteins (mB7-H4Ig; hB7-H4Ig) in treating EAE. The present data show that mB7-H4Ig both directly and indirectly (via increasing Treg function) inhibited CD4⁺ T-cell proliferation and differentiation in both Th1- and Th17-cell promoting conditions while inducing production of IL-10. B7-H4Ig treatment effectively ameliorated progression of both relapsing (R-EAE) and chronic EAE correlating with decreased numbers of activated CD4⁺ T-cells within the CNS and spleen, and a concurrent increase in number and function of Tregs. The functional requirement for Treg activation in treating EAE was demonstrated by a loss of therapeutic efficacy of hB7-H4Ig in R-EAE following inactivation of Treg function either by anti-CD25 treatment or blockade of IL-10. Significant to the eventual translation of this treatment into clinical practice, hB7-H4Ig similarly inhibited the in vitro differentiation of naïve human CD4⁺ T-cells in both Th1- and Th17-promoting conditions, while promoting the production of IL-10. B7-H4Ig thus regulates pro-inflammatory T-cell responses by a unique dual mechanism of action and demonstrates significant promise as a therapeutic for autoimmune diseases, including MS.

Mucosal immunology of tolerance and allergy in the gastrointestinal tract

The mucosal immune system typically exists in a state of active tolerance to food antigens and commensal bacteria. Tolerance to food proteins is induced in part by dendritic cells residing in the intestinal mucosa and implemented by regulatory T cells. Food allergy occurs when immune tolerance is disrupted and a sensitizing immune response characterized by food-specific IgE production occurs instead. Experimental food allergy in mice requires use of adjuvant or exploitation of alternate routes of sensitization to induce allergic sensitization, and can aid in understanding the mechanisms of sensitization to food allergens and the pathophysiology of gastrointestinal manifestations of food allergy. Recent work in the understanding of mucosal immunology of tolerance and allergy in the gastrointestinal tract will be discussed.

The effect of oral tolerance on the allergic airway response in younger and aged mice

BACKGROUND

The effect of increased age on the induction of oral tolerance by low-dose antigen feeding and its effect on the response to antigen airway challenge in aged mice have not been well characterized.

OBJECTIVE

To determine whether oral tolerance can be induced in aged mice and its impact on the development of allergic airway inflammation.

METHODS

Younger (6 weeks old) and aged (18 months old) mice were fed ovalbumin (OVA) prior to sensitization to induce antigen tolerance. Serum antigen-specific immunoglobulins (Igs), bronchoalveolar lavage fluid (BALF), lung histology, enumeration of CD4 + Foxp3+ Treg cells, and airway hyperresponsiveness (AHR) were determined after the final antigen challenge.

RESULTS

Feeding antigen to aged mice prior to sensitization induced oral tolerance as determined by a decrease in antigen-specific IgE and IgG(1); however, the effect was greater in younger mice. Induction of oral tolerance was associated with a greater increase in airway Treg cells in the younger mice. Despite these differences, oral tolerance significantly suppressed features of asthma in aged mice, including BALF total cell and eosinophil numbers, cytokine production, and AHR.

CONCLUSIONS

Aged mice developed oral tolerance to antigen, which suppressed several features of allergic airway inflammation.

Low plasma antibodies specific for phosphatidylethanol in alcohol abusers and patients with alcoholic pancreatitis

Phosphatidylethanol (PEth) is a group of alcohol-modified phospholipids present in cell membranes after heavy drinking. Our aim was to demonstrate the presence of human plasma antibodies binding to PEth and to address their specificity and value in detecting subjects engaged in heavy alcohol consumption. Antibodies to PEth were analyzed in plasma from heavy drinkers (n=20), patients with alcoholic pancreatitis (n=58) and control subjects (n=24), using chemiluminescent immunoassay. Heavy drinkers and patients with alcoholic pancreatitis demonstrated significantly lower levels of plasma IgG, IgA and IgM titers to PEth compared with controls (P<0.001). The specificity of the antibodies to PEth was demonstrated with competitive liquid phase immunoassays and flow cytometry. The plasma IgG, but not IgA or IgM, titers to PEth in heavy drinkers correlated with the whole blood PEth concentration determined by liquid chromatography-mass spectrometry (r=0.655, P=0.002). Compared with traditional markers for alcohol abuse (aspartate aminotransferase, gamma-glutamyl transpeptidase and mean corpuscular volume), receiver operating characteristic curve analysis showed that a low plasma IgA to PEth had the highest area under the curve (AUC 0.940, P<0.001). In conclusion, plasma IgG, IgA and IgM antibodies binding specifically to PEth were found in subjects of all study groups. Subjects with heavy alcohol consumption showed markedly lower plasma immunoglobulin levels to PEth, potentially making them useful as a biomarker to distinguish heavy from moderate alcohol use.

The microbiome of the lung

Investigation of the lung microbiome is a relatively new field. Although the lungs were classically believed to be sterile, recently published investigations have identified microbial communities in the lungs of healthy humans. At the present time, there are significant methodologic and technical hurdles that must be addressed in ongoing investigations, including distinguishing the microbiota of the upper and lower respiratory tracts. However, characterization of the lung microbiome is likely to provide important pathogenic insights into cystic fibrosis, respiratory disease of the newborn, chronic obstructive pulmonary disease, and asthma. In addition to characterization of the lung microbiome, the microbiota of the gastrointestinal tract have profound influence on the development and maintenance of lung immunity and inflammation. Further study of gastrointestinal-respiratory interactions is likely to yield important insights into the pathogenesis of pulmonary diseases, including asthma. As this field advances over the next several years, we anticipate that studies using larger cohorts, multicenter designs, and longitudinal sampling will add to our knowledge and understanding of the lung microbiome.

Compromised intestinal epithelial barrier induces adaptive immune compensation that protects from colitis

Mice lacking junctional adhesion molecule A (JAM-A, encoded by F11r) exhibit enhanced intestinal epithelial permeability, bacterial translocation, and elevated colonic lymphocyte numbers, yet do not develop colitis. To investigate the contribution of adaptive immune compensation in response to increased intestinal epithelial permeability, we examined the susceptibility of F11r(-/-)Rag1(-/-) mice to acute colitis. Although negligible contributions of adaptive immunity in F11r(+/+)Rag1(-/-) mice were observed, F11r(-/-)Rag1(-/-) mice exhibited increased microflora-dependent colitis. Elimination of T cell subsets and cytokine analyses revealed a protective role for TGF-β-producing CD4(+) T cells in F11r(-/-) mice. Additionally, loss of JAM-A resulted in elevated mucosal and serum IgA that was dependent upon CD4(+) T cells and TGF-β. Absence of IgA in F11r(+/+)Igha(-/-) mice did not affect disease, whereas F11r(-/-)Igha(-/-) mice displayed markedly increased susceptibility to acute injury-induced colitis. These data establish a role for adaptive immune-mediated protection from acute colitis under conditions of intestinal epithelial barrier compromise.

Oral gene application using chitosan-DNA nanoparticles induces transferable tolerance

Oral tolerance is a promising approach to induce unresponsiveness to various antigens. The development of tolerogenic vaccines could be exploited in modulating the immune response in autoimmune disease and allograft rejection. In this study, we investigated a nonviral gene transfer strategy for inducing oral tolerance via antigen-encoding chitosan-DNA nanoparticles (NP). Oral application of ovalbumin (OVA)-encoding chitosan-DNA NP (OVA-NP) suppressed the OVA-specific delayed-type hypersensitivity (DTH) response and anti-OVA antibody formation, as well as spleen cell proliferation following OVA stimulation. Cytokine expression patterns following OVA stimulation in vitro showed a shift from a Th1 toward a Th2/Th3 response. The OVA-NP-induced tolerance was transferable from donor to naïve recipient mice via adoptive spleen cell transfer and was mediated by CD4(+)CD25(+) T cells. These findings indicate that nonviral oral gene transfer can induce regulatory T cells for antigen-specific immune modulation.

IgA plasma cells express the negative regulatory co-stimulatory molecule programmed cell death 1 ligand and have a potential tolerogenic role in the intestine

To maintain immune homeostasis in the intestine, the intestinal immune system has evolved several tolerogenic mechanisms toward intestinal microflora and food antigens. Although programmed cell death-1 (PD-1) protein has been implicated in immunological tolerance in the intestine and gut-associated lymphoid tissues (GALTs), distribution of its ligands PD-L1 and PD-L2 in the small intestine lamina propria (LP) are unknown. We investigated PD-L1 expression in intestinal LP and found that IgA plasma cells (PCs) were major PD-L1 expressing cells. PD-L1 expression levels on IgA PCs were higher than that on IgG PCs in peripheral lymphoid tissues. IgA PCs expressed antigen-presenting molecule MHC class II and co-stimulatory molecules CD80, CD86, and PD-L2. IgA PCs isolated from intestinal LP exhibited antigen presentation activity, and in the presence of TGF-β induced FoxP3(+) regulatory T cells, but not IFN-γ(+) Th1 cells, from naïve T cells. Thus, IgA PCs in the intestine may be involved in an immune regulatory role in the intestinal immune system.

Regulation of CD8(+) T Cell Responses to Retinal Antigen by Local FoxP3(+) Regulatory T Cells

While pathogenic CD4 T cells are well known mediators of autoimmune uveoretinitis, CD8 T cells can also be uveitogenic. Since preliminary studies indicated that C57BL/6 mice were minimally susceptible to autoimmune uveoretinitis induction by CD8 T cells, the basis of the retinal disease resistance was sought. Mice that express β-galactosidase (βgal) on a retina-specific promoter (arrβgal mice) were backcrossed to mice expressing green fluorescent protein (GFP) and diphtheria toxin (DTx) receptor (DTR) under control of the Foxp3 promoter (Foxp3-DTR/GFP mice), and to T cell receptor transgenic mice that produce βgal-specific CD8 T cells (BG1 mice). These mice were used to explore the role of regulatory T cells in the resistance to retinal autoimmune disease. Experiments with T cells from double transgenic BG1 × Foxp3-DTR/GFP mice transferred into Foxp3-DTR/GFP × arrβgal mice confirmed that the retina was well protected from attempts to induce disease by adoptive transfer of activated BG1 T cells. The successful induction of retinal disease following unilateral intraocular administration of DTx to deplete regulatory T cells showed that the protective activity was dependent on local, toxin-sensitive regulatory T cells; the opposite, untreated eye remained disease-free. Although there were very few Foxp3(+) regulatory T cells in the parenchyma of quiescent retina, and they did not accumulate in retina, their depletion by local toxin administration led to disease susceptibility. We propose that these regulatory T cells modulate the pathogenic activity of βgal-specific CD8 T cells in the retinas of arrβgal mice on a local basis, allowing immuno regulation to be responsive to local conditions.

Thymic stromal lymphopoietin (TSLP)-mediated dermal inflammation aggravates experimental asthma

Individuals with one atopic disease are far more likely to develop a second. Approximately half of all atopic dermatitis (AD) patients subsequently develop asthma, particularly those with severe AD. This association, suggesting a role for AD as an entry point for subsequent allergic disease, is a phenomenon known as the "atopic march." Although the underlying cause of the atopic march remains unknown, recent evidence suggests a role for the cytokine thymic stromal lymphopoietin (TSLP). We have established a mouse model to determine whether TSLP plays a role in this phenomenon, and in this study show that mice exposed to the antigen ovalbumin (OVA) in the skin in the presence of TSLP develop severe airway inflammation when later challenged with the same antigen in the lung. Interestingly, neither TSLP production in the lung nor circulating TSLP is required to aggravate the asthma that was induced upon subsequent antigen challenge. However, CD4 T cells are required in the challenge phase of the response, as was challenge with the sensitizing antigen, demonstrating that the response was antigen specific. This study, which provides a clean mouse model to study human atopic march, indicates that skin-derived TSLP may represent an important factor that triggers progression from AD to asthma.

Enterocytes: active cells in tolerance to food and microbial antigens in the gut

Enterocytes used to be studied particularly in terms of digestion protagonists. However, as the immune functions of the intestinal tract were better understood, it became clear that enterocytes are not mere bystanders concerning the induction of immune tolerance to dietary peptides and gut microbiota. In fact, enterocytes are involved actively in shaping the intestinal immune environment, designed for maintaining a non-belligerent state. This tolerant milieu of the gut immune system is achieved by keeping a balance between suppression and stimulation of the inflammatory responses. Our review presents the current state of knowledge concerning the relationship between enterocytes and immune cells (dendritic cells, lymphocytes), with emphasis on the enterocytes' impact on the mechanisms leading to the induction of oral tolerance.

T regulatory cell responses to immunization with a soluble egg antigen in Schistosoma mansoni-infected mice

The aim of the study is to characterize the phenotypes of CD4⁺ CD25⁺ T regulatory cells within the liver granulomas and association with both Foxp-3 gene expression and splenic cytokines. Naïve C57BL/6 mice were intravenously injected with multiple doses of the soluble egg antigen (SEA) 7 days before cercarial infection. The immunized and infected control groups were sacrificed 8 and 16 weeks post-infection (PI). Histopathology, parasitological parameters, splenic phenotypes for T regulatory cells, the FOXP-3 expression in hepatic granuloma using real-time PCR, and the associated splenic cytokines were studied. Histopathological examination of the liver revealed remarkable increase in degenerated ova within hepatic granuloma which decreased in diameter at weeks 8 and 16 PI (P<0.01). The percentage of T regulatory cells (CD4⁺ CD25⁺) increased significantly (P<0.01) in the immunized group compared to the infected control at weeks 8 and 16 PI. The FOXP-3 expression in hepatic granulomas increased from 10 at week 8 to 30 fold at week 16 PI in the infected control group. However, its expression in the immunized group showed an increase from 30 at week 8 to 70 fold at week 16 PI. The splenic cytokine levels of pro-inflammatory cytokines, IFN-γ, IL-4, and TNF-α, showed significant decreases (P<0.05) compared to the infected control group. In conclusion, the magnitude and phenotype of the egg-induced effects on T helper responses were found to be controlled by a parallel response within the T regulatory population which provides protection in worm parasite-induced immunopathology.

Immunomodulation of antigen presenting cells promotes natural regulatory T cells that prevent autoimmune diabetes in NOD mice

Progression towards type 1 diabetes (T1D) in susceptible patients is linked to a progressive decline in the capacity of regulatory T cells (Treg) to maintain tolerance. As such, therapies aimed at redressing the failing Treg compartment have been the subject of intense investigation. Treg dysfunction in T1D has recently been linked to a reduced capacity of antigen presenting cells (APCs) to maintain Treg function rather than Treg intrinsic defects. This suggests that therapies aimed simply at addressing the failing Treg compartment are unlikely to provide long-term protection. Here, we demonstrate that modulation of the inflammatory status of CD11b+CD11c− APCs favors the upregulation of protective Tregs in a mouse model of T1D. We further demonstrate that reduced expression of the costimulatory molecule CD40 plays a role in this increased immunoregulatory capacity. Strikingly, Treg upregulation resulted exclusively from an increase in natural Tregs rather than the peripheral conversion of conventional T cells. This suggests that modulation of CD11b+ CD11c− APCs inflammatory properties favors the establishment of natural Treg responses that, unlike adaptive Treg responses, are likely to maintain tolerance to a broad range of antigens. As such, modulation of this APC subset represents a potential therapeutic avenue to reestablish peripheral tolerance and protect from autoimmune diseases such as T1D.

Induced CD4+Foxp3+ regulatory T cells in immune tolerance

Regulatory T lymphocytes are essential to maintain homeostasis of the immune system, limiting the magnitude of effector responses and allowing the establishment of immunological tolerance. Two main types of regulatory T cells have been identified--natural and induced (or adaptive)-and both play significant roles in tuning down effector immune responses. Adaptive CD4(+)Foxp3(+) regulatory T (iTreg) cells develop outside the thymus under a variety of conditions. These include not only antigen presentation under subimmunogenic or noninflammatory conditions, but also chronic inflammation and infections. We speculate that the different origin of iTreg cells (noninflammatory versus inflammatory) results in distinct properties, including their stability. iTreg cells are also generated during homeostasis of the gut and in cancer, although some cancers also favor expansion of natural regulatory T (nTreg) cells. Here we review how iTreg cells develop and how they participate in immunological tolerance, contrasting, when possible, iTreg cells with nTreg cells.

Regulatory T cells induced by mucosal B cells alleviate allergic airway hypersensitivity

Asthma is one of the most common chronic airway inflammatory diseases. The induction of immunologic tolerance via mucosa has been used for treating allergic diseases. B cells, which comprise the major cell population in Peyer's patches, were shown to induce the development of regulatory T (Treg) cells. This study investigated the role of B cells in Peyer's patches regarding the induction of tolerance and Treg cell functions. An in vitro suppressive assay and ELISA were used to evaluate the function of T cells stimulated by Peyer-patch B cells (Treg-of-B cells). The therapeutic potential of Treg-of-B cells was then evaluated by an animal model of airway inflammation. Treg-of-B cells were found to exert a suppressive function on T-cell proliferation. Antigen-loaded B cells isolated from Peyer's patches were more tolerogenic, and had the potential to generate more suppressive Treg-of-B cells via the production of IL-10 and cell-cell contacts. Treg-of-B cells expressed cytotoxic T lymphocyte antigen 4, inducible costimulator, OX40 (CD134), programmed death 1, and TNF-RII, and produced lower concentrations of IL-2 and higher concentrations of IL-10. In a murine model of asthma, an adoptive transfer of Treg-of-B cells before or after immunization sufficiently suppressed Th2 cytokine production and eosinophilic infiltration, and alleviated asthmatic symptoms. B cells isolated from gut-associated lymphoid tissues can generate regulatory T cells that may be important in oral tolerance, and that may be applicable to the alleviation of allergic symptoms.

Oral tolerance induction by partially hydrolyzed whey protein in mice is associated with enhanced numbers of Foxp3+ regulatory T-cells in the mesenteric lymph nodes

BACKGROUND

Hypoallergenic formulas are considered a good option for infants at risk for cow's milk allergy. The aim of this animal study was to investigate whether whey hydrolyzates (WH) have the capacity to induce oral tolerance to whey.

METHODS

Whey, partial or extensive WH was given via gavages to naïve mice prior to oral whey sensitization using cholera toxin as an adjuvant. The acute allergic skin response, mouse mast cell protease-1 (mMCP-1), whey-specific IgE, IgG(1) and effector Th2-cells, Th1-cells, and Foxp3(+) regulatory T-cells were determined in the mesenteric lymph nodes (MLN). MLN cells from tolerized mice were adoptively transferred to naïve recipient mice prior to whey sensitization.

RESULTS

In contrast to the extensive WH, pre-treatment of naïve mice with whey or partial WH reduced the acute allergic skin response and mast cell degranulation after whey challenge. However, only treatment with whey prevented the generation of serum-specific IgE/IgG(1) . In partial WH tolerized mice, Foxp3(+) regulatory T-cell numbers in the MLN were increased compared to whey-sensitized mice. Both whey and partial WH treatment showed a tendency toward a decreased number of effector Th2-cells. Transfer of MLN cells from tolerized mice protected recipient mice from developing an acute allergic skin response.

CONCLUSION

These results show that partial WH with limited sensitizing properties reduced the effector response upon whey challenge. This effect is transferable using MLN cells and was associated with enhanced Foxp3(+) regulatory T-cell numbers in the MLN. Partial WH retained the capacity to induce active immune suppression in mice which may be relevant for allergy prevention.

Acquisition of pneumococci specific effector and regulatory Cd4+ T cells localising within human upper respiratory-tract mucosal lymphoid tissue

The upper respiratory tract mucosa is the location for commensal Streptococcus (S.) pneumoniae colonization and therefore represents a major site of contact between host and bacteria. The CD4⁺ T cell response to pneumococcus is increasingly recognised as an important mediator of immunity that protects against invasive disease, with data suggesting a critical role for Th17 cells in mucosal clearance. By assessing CD4 T cell proliferative responses we demonstrate age-related sequestration of Th1 and Th17 CD4⁺ T cells reactive to pneumococcal protein antigens within mucosal lymphoid tissue. CD25^hi T cell depletion and utilisation of pneumococcal specific MHCII tetramers revealed the presence of antigen specific Tregs that utilised CTLA-4 and PDL-1 surface molecules to suppress these responses. The balance between mucosal effector and regulatory CD4⁺ T cell immunity is likely to be critical to pneumococcal commensalism and the prevention of unwanted pathology associated with carriage. However, if dysregulated, such responses may render the host more susceptible to invasive pneumococcal infection and adversely affect the successful implementation of both polysaccharide-conjugate and novel protein-based pneumococcal vaccines.

The S. pneumoniae bacteria is a major cause of disease (e.g. pneumonia and meningitis) particularly affecting infants. In most cases bacteria can colonise the nose without causing harm, however colonisation is thought to be a prerequisite of disease. With increasing age colonization and disease, rates gradually decrease which is likely due to the development of immunity to the pneumococcus with age. The CD4 T cells of the immune system may contribute to the defence against bacterial colonisation by producing factors that promote pneumococcal killing. Herein, we show that CD4 T cells reactive to pneumococci are found in greater numbers at the site of colonisation and gradually increase in their levels from infancy. However, at the peak of CD4 T cell responses from late teens, we detected the presence of regulatory T cells (Tregs) which suppressed anti-pneumococci CD4 T cell activity greatly. Our finding shows that pneumococcal reactive CD4 T cells selectively populate colonisation sites and increase with age as a result of ongoing bacterial exposure throughout life, inversely correlating with colonisation and disease rates. As factors that utilise CD4 T cells become increasingly advocated as potential preventative strategies against pneumococcal carriage and disease, the observed effect of Tregs must be considered.

Gut-tropic T cells that express integrin α4β7 and CCR9 are required for induction of oral immune tolerance in mice

BACKGROUND & AIMS

Induction of oral immune tolerance (OT) blocks proinflammatory responses to orally administered antigens and might be used to treat autoimmune conditions. We investigated whether gut-tropic T cells that express the integrin α4β7 and the chemokine receptor CCR9 are required for OT.

METHODS

Skin delayed-type hypersensitivity and experimental autoimmune encephalomyelitis were used to monitor OT in mice. To assess the role of receptors that mediate localization of lymphocytes to the gut (gut-homing receptors) in induction of OT, we studied CCR9(-/-) and β7(-/-) mice and also blocked the α4β7 ligand MAdCAM-1 in wild-type mice. We used DEREG and Scurfy mice to assess the role of Foxp3(+) regulatory T cells (Treg) and IL-10(-/-) and IL-10Rβ(-/-) mice to examine the role of interleukin (IL)-10 in induction of OT.

RESULTS

OT could not be induced in CCR9(-/-) or β7(-/-) mice, or when MAdCAM-1 was blocked in wild-type mice, indicating that gut-homing receptors are required for oral tolerization. Consistent with the role of all-trans retinoic acid in inducing gut-homing T cells, OT could not be induced in mice depleted of vitamin A. OT was rescued in CCR9(-/-) mice following adoptive transfer of wild-type T cells, but not CCR9(-/-) or β7(-/-) T cells. Gut-homing T cells are therefore necessary and sufficient to induce OT. Wild-type Treg and IL-10 were required to restore OT to CCR9(-/-) mice, indicating that homing and functional differentiation of IL-10-producing Treg in the gut is required for OT. Conversely, transfer of CCR9(-/-) or β7(-/-) T cells to wild-type mice partially inhibited OT.

CONCLUSIONS

Expression of CCR9 and α4β7 on T cells and their subsequent localization to the gut is required for induction of OT in mice. Therapies designed to block gut-homing receptors might, under some conditions, interfere with normal tolerogenic mechanisms in the intestinal mucosa.

Vitamin A and immune regulation: role of retinoic acid in gut-associated dendritic cell education, immune protection and tolerance

The vitamin A (VA) metabolite all-trans retinoic acid (RA) plays a key role in mucosal immune responses. RA is produced by gut-associated dendritic cells (DC) and is required for generating gut-tropic lymphocytes and IgA-antibody-secreting cells (IgA-ASC). Moreover, RA modulates Foxp3(+) regulatory T cell (T(REG)) and Th17 effector T cell differentiation. Thus, although RA could be used as an effective "mucosal adjuvant" in vaccines, it also appears to be required for establishing intestinal immune tolerance. Here we discuss the roles proposed for RA in shaping intestinal immune responses and tolerance at the gut mucosal interface. We also focus on recent data exploring the mechanisms by which gut-associated DC acquire RA-producing capacity.

Caloric restriction modifies both innate and adaptive immunity in the mouse small intestine

Although caloric restriction (CR) apparently has beneficial effects on the immune system, its effects on the immunological function of the intestinal mucosa are little known. The present study explored the effect of CR on the innate and adaptive intestinal immunity of mice. Balb/c mice were either fed ad libitum (control) or on alternate days fed ad libitum and fasted (caloric restriction). After 4 months, an evaluation was made of IgA levels in the ileum, the gene expression for IgA and its receptor (pIgR), as well as the expression of two antimicrobial enzymes (lysozyme and phospholipase A2) and several cytokines of the intestinal mucosa. CR increased the gene expression of lysozyme and phospholipase A2. The levels of IgA were diminished in the ileum, which apparently was a consequence of the reduced transport of IgA by pIgR. In ileum, CR increased the gene expression for most cytokines, both pro- and anti-inflammatory. Hence, CR differentially modified the expression of innate and adaptive immunity mediators in the intestine.

Regulatory T cells accumulate in the lung allergic inflammation and efficiently suppress T-cell proliferation but not Th2 cytokine production

Foxp3⁺CD25⁺CD4⁺ regulatory T cells are vital for peripheral tolerance and control of tissue inflammation. In this study, we characterized the phenotype and monitored the migration and activity of regulatory T cells present in the airways of allergic or tolerant mice after allergen challenge. To induce lung allergic inflammation, mice were sensitized twice with ovalbumin/aluminum hydroxide gel and challenged twice with intranasal ovalbumin. Tolerance was induced by oral administration of ovalbumin for 5 consecutive days prior to OVA sensitization and challenge. We detected regulatory T cells (Foxp3⁺CD25⁺CD4⁺ T cells) in the airways of allergic and tolerant mice; however, the number of regulatory T cells was more than 40-fold higher in allergic mice than in tolerant mice. Lung regulatory T cells expressed an effector/memory phenotype (CCR4^highCD62L^lowCD44^highCD54^highCD69⁺) that distinguished them from naive regulatory T cells (CCR4^intCD62L^highCD44^intCD54^intCD69⁻). These regulatory T cells efficiently suppressed pulmonary T-cell proliferation but not Th2 cytokine production.

Induction of immunological tolerance by oral anti-CD3

In recent years, our knowledge about immunoregulation and autoimmunity has significantly advanced, but nontoxic and more effective treatments for different inflammatory and autoimmune diseases are still lacking. Oral tolerance is of unique immunologic importance because it is a continuous natural immunologic event driven by exogenous antigen and is an attractive approach for treatment of these conditions. Parenteral administration of anti-CD3 monoclonal antibody is an approved therapy for transplantation in humans and is effective in autoimmune diabetes. Orally administered anti-CD3 monoclonal antibody is biologically active in the gut and suppresses experimental models of autoimmune diseases. Orally delivered antibody does not have side effects including cytokine release syndromes, thus oral anti-CD3 antibody is clinically applicable for chronic therapy. Here we review findings that identify a novel and powerful immunologic approach that is widely applicable for the treatment of human autoimmune conditions.

Oral tolerance and Treg cells are induced in BALB/c mice after gavage with bovine β-lactoglobulin

BACKGROUND

Food allergy is considered as resulting from an impaired development or a breakdown of oral tolerance. We aimed to induce oral tolerance to the major cow's milk allergen bovine β-lactoglobulin (BLG) or corresponding trypsin hydrolysates (BLG-Try) and to investigate the mechanisms involved.

METHODS

Wild-type BALB/cJ mice were gavaged on days 1-3 and 8-10 with different doses of native BLG (nBLG) or with nBLG-Try and were then sensitized on day 14 by i.p. administration of BLG in alum. Sensitization was assessed by measurement of BLG-specific antibodies in sera and of cytokines secreted by BLG-reactivated splenocytes. Elicitation of the allergic reaction was assessed by measurement of cytokines and mMCP-1 in sera collected 35 min after an oral challenge. Cellular and biochemical markers of the allergic reaction were also analysed in bronchoalveolar lavage fluids (BAL) collected 24 h after intra-nasal challenge. Analysis of the CD4(+) CD25(+) Foxp3(+) cells in different organs obtained 3 days after gavage and in vivo depletion of CD25(+) cells before oral tolerance induction were then performed.

RESULTS

Systemic sensitization and elicitation of the allergic reaction were totally inhibited in mice gavaged with 2 mg of nBLG whereas nBLG-Try was far less efficient. A high percentage of CD4(+) Foxp3(+) cells were observed in BAL from tolerant mice, and a negative correlation between the number of eosinophils and the percentage of Foxp3(+) cells was evidenced. Efficient induction of CD4(+) CD25(+) Foxp3(+) cells after nBLG gavage and impaired oral tolerance induction after in vivo depletion of CD25 cells were then demonstrated.

CONCLUSION

For the first time, allergen-induced Treg cells that inhibited both the sensitization and the elicitation of the allergic reaction were evidenced in gavaged wild-type mice.

Down-regulation of Treg cells and up-regulation of TH1/TH2 cytokine ratio were induced by polysaccharide from Radix Glycyrrhizae in H22 hepatocarcinoma bearing mice

Radix Glycyrrhizae polysaccharide (GP) possesses multiple pharmacological activities. However, the effect of GP on CD4+CD25+ regulatory T (Treg) cells has not been elucidated. This study aimed to investigate the effects of GP on Treg cells and Th1/Th2 cytokines in H22 hepatocarcinoma tumor-bearing mice. The results demonstrated that GP inhibits tumor progression. In the lymph nodes of the tumor microenvironment and spleen, the proportion of Treg cells was significantly higher in the tumor-bearing mice. GP administration down-regulated the population of Treg cells (P < 0.01) and decreased lymph node Foxp3 and IL-10 mRNA expression (P < 0.01). In addition, GP treatment decreased IL-10 and TGF-β level (P < 0.01) and increased IL-2 and IL-12p70 level in serum (P < 0.01). In conclusion, GP reduced the proportion of Treg cells and Foxp3 lowered expression in Treg cells, and up-regulated Th1/Th2 cytokine ratio in serum in the tumor bearing mice, which might partially cause the inhibition of tumor growth.

Oral tolerance

The gut-associated lymphoid tissue is the largest immune organ in the body and is the primary route by which we are exposed to antigens. Tolerance induction is the default immune pathway in the gut, and the type of tolerance induced relates to the dose of antigen fed: anergy/deletion (high dose) or regulatory T-cell (Treg) induction (low dose). Conditioning of gut dendritic cells (DCs) by gut epithelial cells and the gut flora, which itself has a major influence on gut immunity, induces CD103(+) retinoic acid-dependent DC that induces Tregs. A number of Tregs are induced at mucosal surfaces. Th3 type Tregs are transforming growth factor-β dependent and express latency-associated peptide (LAP) on their surface and were discovered in the context of oral tolerance. Tr1 type Tregs (interleukin-10 dependent) are induced by nasal antigen and forkhead box protein 3(+) iTregs are induced by oral antigen and by oral administration of aryl hydrocarbon receptor ligands. Oral or nasal antigen ameliorates autoimmune and inflammatory diseases in animal models by inducing Tregs. Furthermore, anti-CD3 monoclonal antibody is active at mucosal surfaces and oral or nasal anti-CD3 monoclonal antibody induces LAP(+) Tregs that suppresses animal models (experimental autoimmune encephalitis, type 1 and type 2 diabetes, lupus, arthritis, atherosclerosis) and is being tested in humans. Although there is a large literature on treatment of animal models by mucosal tolerance and some positive results in humans, this approach has yet to be translated to the clinic. The successful translation will require defining responsive patient populations, validating biomarkers to measure immunologic effects, and using combination therapy and immune adjuvants to enhance Treg induction. A major avenue being investigated for the treatment of autoimmunity is the induction of Tregs and mucosal tolerance represents a non-toxic, physiologic approach to reach this goal.

Obstructive jaundice expands intrahepatic regulatory T cells, which impair liver T lymphocyte function but modulate liver cholestasis and fibrosis

Although obstructive jaundice has been associated with a predisposition toward infections, the effects of bile duct ligation (BDL) on bulk intrahepatic T cells have not been clearly defined. The aim of this study was to determine the consequences of BDL on liver T cell phenotype and function. After BDL in mice, we found that bulk liver T cells were less responsive to allogeneic or syngeneic Ag-loaded dendritic cells. Spleen T cell function was not affected, and the viability of liver T cells was preserved. BDL expanded the number of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg), which were anergic to direct CD3 stimulation and mediated T cell suppression in vitro. Adoptively transferred CD4(+)CD25(-) T cells were converted into Treg within the liver after BDL. In vivo depletion of Treg after BDL restored bulk liver T cell function but exacerbated the degrees of inflammatory cytokine production, cholestasis, and hepatic fibrosis. Thus, BDL expands liver Treg, which reduce the function of bulk intrahepatic T cells yet limit liver injury.

Increased frequency of CD4+CD25(high)FoxP3+ regulatory T cells in patients with hepatocellular carcinoma

Accumulating evidence suggests regulatory T cells (Tregs) are associated with impaired antitumor responses. However, the relationship between the CD4(+)CD25(high)FoxP3(+) Treg and hepatocellular carcinoma (HCC) has not been well investigated. Levels of CD4(+)CD25(high)FoxP3(+) Tregs in peripheral blood mononuclear cells (PBMCs) from HCC patients and healthy donors, tumor infiltrating lymphocytes (TILs) extracted from HCC, and hepatic lymphocytes extracted from resected liver were measured by flow cytometry, and their effects on T-cell proliferation was determined by (3)H-thymidine incorporation. Serum levels of interleukin (IL)-10 and transforming growth factor (TGF)-β1 were measured by enzyme linked immunosorbent assay. The frequency of Tregs in PBMCs from HCC patients was higher than that from healthy donors. Similarly, the frequency of Tregs in TILs was higher than that of hepatic lymphocytes. On the other hand, the (3)H-thymidine uptake by TILs and PBMCs from HCC patients was decreased drastically when compared to the counterparts from normal controls. Furthermore, serum IL-10 and TGF-β1 levels increased significantly in HCC patients when compared to the healthy donors. This study identified an increased frequency of CD4(+)CD25(high)FoxP3(+) Tregs in patients with HCC. The elevated serum IL-10, TGF-β1 levels also correlated with impaired antitumor responses in these patients. Further effort is needed to establish new immunotherapeutic strategies designed to modulate Tregs to promote a competent antitumor response.

Construction of a Der p2-transgenic plant for the alleviation of airway inflammation

In clinical therapy, the amount of antigen administered to achieve oral tolerance for allergic diseases is large, and the cost is a major consideration. In this study, we used tobacco plants to develop a large-scale protein production system for allergen-specific immunotherapy, and we investigated the mechanisms of oral tolerance induced by a transgenic plant-derived antigen. We used plants (tobacco leaves) transgenic for the Dermatophagoides pteronyssinus 2 (Der p2) antigen to produce Der p2. Mice received total protein extract from Der p2 orally once per day over 6 days (days 0-2 and days 6-8). Mice were also sensitized and challenged with yeast-derived recombinant Der p2 (rDer p2), after which the mice were examined for airway hyper-responsiveness and airway inflammation. After sensitization and challenge with rDer p2, mice that were fed with total protein extracted from transgenic plants showed decreases in serum Der p2-specific IgE and IgG1 titers, decreased IL-5 and eotaxin levels in bronchial alveolar lavage fluid, and eosinophil infiltration in the airway. In addition, hyper-responsiveness was also decreased in mice that were fed with total protein extracted from transgenic plants, and CD4(+)CD25(+)Foxp3(+) regulatory T cells were significantly increased in mediastinal and mesenteric lymph nodes. Furthermore, splenocytes isolated from transgenic plant protein-fed mice exhibited decreased proliferation and increased IL-10 secretion after stimulation with rDer p2. The data here suggest that allergen-expressing transgenic plants could be used for therapeutic purposes for allergic diseases.

Ulcerative colitis: immune function, tissue fibrosis and current therapeutic considerations

BACKGROUND

Ulcerative colitis (UC) is a complex disease in which the interaction of genetic, environmental and microbial factors drives chronic intestinal inflammation that finally leads to extensive tissue fibrosis.

DISCUSSION

The present review discusses the current knowledge on genetic susceptibility, especially of the IL-12/IL-23 pathway, the pathophysiologic role of the involved cytokines (e.g. IL-13, IL-23, TGFβ1) and immune cells (e.g. T cells, epithelial cells, fibroblasts) in UC followed by an overview on actual therapeutic considerations. These future therapies will target selectively the involved cell types by blocking their activation and its downstream signalling, by inhibiting their migration to the inflamed site and by anti-cytokine strategies. This may avoid-when initiated in time-the perpetuation of the inflammatory mechanisms thus preventing fibrosis. With respect to animal models that have guided the most productive efforts for understanding human inflammatory bowel disease, these will be shortly discussed in the respective context.

Ulcerative colitis: immune function, tissue fibrosis and current therapeutic considerations

BACKGROUND

Ulcerative colitis (UC) is a complex disease in which the interaction of genetic, environmental and microbial factors drives chronic intestinal inflammation that finally leads to extensive tissue fibrosis.

DISCUSSION

The present review discusses the current knowledge on genetic susceptibility, especially of the IL-12/IL-23 pathway, the pathophysiologic role of the involved cytokines (e.g. IL-13, IL-23, TGFβ1) and immune cells (e.g. T cells, epithelial cells, fibroblasts) in UC followed by an overview on actual therapeutic considerations. These future therapies will target selectively the involved cell types by blocking their activation and its downstream signalling, by inhibiting their migration to the inflamed site and by anti-cytokine strategies. This may avoid-when initiated in time-the perpetuation of the inflammatory mechanisms thus preventing fibrosis. With respect to animal models that have guided the most productive efforts for understanding human inflammatory bowel disease, these will be shortly discussed in the respective context.

Tissue-based class control: the other side of tolerance

In this Essay, we offer a new perspective on how immune responses are regulated. We do not cover how they are turned on and off, but focus instead on the second major aspect of an immune response: the control of effector class. Although it is generally thought that the class of an immune response is tailored to fit the invading pathogen, we suggest here that it is primarily tailored to fit the tissue in which the response occurs. To this end, we cover such topics as the nature of T helper (T(H)) cell subsets (current and yet to be discovered), the nature of privileged sites, the difference between oral tolerance and oral vaccination, why the route of immunization matters, whether the T(H)1-type response is really the immune system's primary defense, and whether there might be a different role for some regulatory T cells.

Adaptive T-cell responses regulating oral tolerance to protein antigen

The term oral (or mucosal) tolerance has been classically defined as the suppression of T- and B-cell responses to an antigen by prior administration of the antigen by the oral route. In recent years, it has become clear that both innate and acquired regulatory immune responses are essential for the development of oral tolerance. As such, mucosal microenvironmental factors such as transforming growth factor- β, prostaglandins but also dietary vitamin A create conditioning of an adaptive regulatory T-cell response that suppresses subsequent antigen-specific responses. Particular resident subsets of antigen presenting dendritic cells are pivotal to convey conditioning signals next to the presentation of antigen. This review discusses the primary mechanisms of adaptive regulatory T-cell induction to ingested soluble protein antigen. However, we also discuss the limitations of our knowledge with respect to understanding the very common food hypersensitivity Celiac disease caused by an aberrant adaptive immune response to the food protein gluten.

Suppression of oral tolerance by Lactococcus lactis in mice

Although oral ovabumin (OVA) administration suppressed the antibody (Ab) response in OVA-immunized mice, Lactococcus lactis increased OVA-specific IgG2a in these mice. L. lactis increased the casein-specific IgG level in NC/Nga mice fed on a casein diet. The percentage of CD4(+)CD25(+) cells was increased in DO11.10 mice orally given OVA, but this increase of CD4(+)CD25(+) cells were suppressed in L. lactis-fed DO11.10 mice.

Differential regulation of Toll-like receptor signalling in spleen and Peyer's patch dendritic cells

Toll-like receptor (TLR) signalling shapes dendritic cell (DC) responses by inducing co-stimulatory molecule up-regulation and cytokine secretion while TLR regulatory proteins inhibit this process. We aimed to determine if gene expression of TLRs and TLR regulatory proteins underpins the functionally different lipopolysaccharide (LPS) responses of DCs from murine Peyer's patches (PP) and spleen and of murine bacteria-conditioned bone-marrow-derived cells. Isolated spleen and PP DCs were analysed for basal expression of TLRs by flow cytometry and real time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The DCs were stimulated with LPS to determine cytokine secretion by enzyme-linked immunosorbent assay and expression of TLR regulatory proteins by qRT-PCR. In vitro results were confirmed following in vivo intraperitoneal LPS injection. In addition, changes in gene expression of TLR regulatory proteins were assessed in bacteria-conditioned bone-marrow-derived cells. Results indicated that surface expression of TLR2 and TLR4 on PP DCs was decreased compared with spleen DCs. The PP DCs secreted a limited profile of cytokines compared with spleen DCs following LPS stimulation. In vivo LPS exposure up-regulated sigirr, tollip and tmed1 messenger RNA in PP DCs, but not spleen DCs. Similar gene expression changes were observed in bacteria-conditioned bone-marrow-derived cells. Therefore, functionally different LPS responses in PP and spleen DCs reflect their characteristic expression of TLRs and TLR regulatory proteins. Differential regulation of TLR signalling was also evident in bacteria-conditioned bone-marrow-derived cells indicating that bacterial signalling may be a mechanism for inducing altered gene regulation in PP DCs.

Impaired thymic selection and abnormal antigen-specific T cell responses in Foxn1(Δ/Δ) mutant mice

Background

Foxn1^Δ/Δ mutant mice have a specific defect in thymic development, characterized by a block in TEC differentiation at an intermediate progenitor stage, and blocks in thymocyte development at both the DN1 and DP cell stages, resulting in the production of abnormally functioning T cells that develop from an atypical progenitor population. In the current study, we tested the effects of these defects on thymic selection.

Methodology/Principal Findings

We used Foxn1^Δ/Δ; DO11 Tg and Foxn1^Δ/Δ; OT1 Tg mice as positive selection and Foxn1^Δ/Δ; MHCII I-E mice as negative selection models. We also used an in vivo system of antigen-specific reactivity to test the function of peripheral T cells. Our data show that the capacity for positive and negative selection of both CD4 and CD8 SP thymocytes was reduced in Foxn1^Δ/Δ mutants compared to Foxn1^+/Δ control mice. These defects were associated with reduction of both MHC Class I and Class II expression, although the resulting peripheral T cells have a broad TCR Vβ repertoire. In this deficient thymic environment, immature CD4 and CD8 SP thymocytes emigrate from the thymus into the periphery. These T cells had an incompletely activated profile under stimulation of the TCR signal in vitro, and were either hypersensitive or hyporesponsive to antigen-specific stimulation in vivo. These cell-autonomous defects were compounded by the hypocellular peripheral environment caused by low thymic output.

Conclusions/Significance

These data show that a primary defect in the thymic microenvironment can cause both direct defects in selection which can in turn cause indirect effects on the periphery, exacerbating functional defects in T cells.

Helminth secretions induce de novo T cell Foxp3 expression and regulatory function through the TGF-β pathway

Foxp3-expressing regulatory T (T reg) cells have been implicated in parasite-driven inhibition of host immunity during chronic infection. We addressed whether parasites can directly induce T reg cells. Foxp3 expression was stimulated in naive Foxp3⁻ T cells in mice infected with the intestinal helminth Heligmosomoides polygyrus. In vitro, parasite-secreted proteins (termed H. polygyrus excretory-secretory antigen [HES]) induced de novo Foxp3 expression in fluorescence-sorted Foxp3⁻ splenocytes from Foxp3-green fluorescent protein reporter mice. HES-induced T reg cells suppressed both in vitro effector cell proliferation and in vivo allergic airway inflammation. HES ligated the transforming growth factor (TGF) β receptor and promoted Smad2/3 phosphorylation. Foxp3 induction by HES was lost in dominant-negative TGF-βRII cells and was abolished by the TGF-β signaling inhibitor SB431542. This inhibitor also reduced worm burdens in H. polygyrus-infected mice. HES induced IL-17 in the presence of IL-6 but did not promote Th1 or Th2 development under any conditions. Importantly, antibody to mammalian TGF-β did not recognize HES, whereas antisera that inhibited HES did not affect TGF-β. Foxp3 was also induced by secreted products of Teladorsagia circumcincta, a related nematode which is widespread in ruminant animals. We have therefore identified a novel pathway through which helminth parasites may stimulate T reg cells, which is likely to be a key part of the parasite's immunological relationship with the host.

Food allergy: separating the science from the mythology

Numerous genes are involved in innate and adaptive immunity and these have been modified over millions of years. During this evolution, the mucosal immune system has developed two anti-inflammatory strategies: immune exclusion by the use of secretory antibodies to control epithelial colonization of microorganisms and to inhibit the penetration of potentially harmful agents; and immunosuppression to counteract local and peripheral hypersensitivity against innocuous antigens, such as food proteins. The latter strategy is called oral tolerance when induced via the gut. Homeostatic mechanisms also dampen immune responses to commensal bacteria. The mucosal epithelial barrier and immunoregulatory network are poorly developed in newborns. The perinatal period is, therefore, critical with regard to the induction of food allergy. The development of immune homeostasis depends on windows of opportunity during which innate and adaptive immunity are coordinated by antigen-presenting cells. The function of these cells is not only orchestrated by microbial products but also by dietary constituents, including vitamin A and lipids, such as polyunsaturated omega-3 fatty acids. These factors may in various ways exert beneficial effects on the immunophenotype of the infant. The same is true for breast milk, which provides immune-inducing factors and secretory immunoglobulin A, which reinforces the gut epithelial barrier. It is not easy to dissect the immunoregulatory network and identify variables that lead to food allergy. This Review discusses efforts to this end and outlines the scientific basis for future food allergy prevention.

A double-edged sword in B-cell-targeted therapy for inflammatory diseases

Cells of the immune system, including B cells, perform inflammatory functions against microbial invasion, accompanied by anti-inflammatory responses to avoid host damage. B-cell-depletion therapy using anti-CD20 monoclonal antibodies against inflammatory diseases has beneficial or adverse effects depending on the timing and/or microenvironment in which they are used. To achieve effective B-cell-targeted therapy, it is necessary to identify and understand the modes of action of pathogenic and regulatory B cells, which include antibody production, formation of immune complexes, cytokine and chemokine production, cytotoxic killing, lymphoid neogenesis and antigen presentation. B cells interact with multiple cells, including dendritic cells, T cells and natural killer T cells, creating a complex regulatory network. Specific targeting of B-cell subsets and/or their interaction partners might lead to clinical benefits with minimal host damage.

Treating arthritis by immunomodulation: is there a role for regulatory T cells?

The discovery of regulatory T cells almost 15 years ago initiated a new and exciting research area. The growing evidence for a critical role of these cells in controlling autoimmune responses has raised expectations for therapeutic application of regulatory T cells in patients with autoimmune arthritis. Here, we review recent studies investigating the presence, phenotype and function of these cells in patients with RA and juvenile idiopathic arthritis (JIA) and consider their therapeutic potential. Both direct and indirect methods to target these cells will be discussed. Arguably, a therapeutic approach that combines multiple regulatory T-cell-enhancing strategies could be most successful for clinical application.