Orally tolerized T cells can form conjugates with APCs but are defective in immunological synapse formation

Dietary Regulation of the Crosstalk between Gut Microbiome and Immune Response in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), a chronic, recurring inflammatory response, is a growing global public health issue. It results from the aberrant crosstalk among environmental factors, gut microbiota, the immune system, and host genetics, with microbiota serving as the core of communication for differently-sourced signals. In the susceptible host, dysbiosis, characterized by the bloom of facultative anaerobic bacteria and the decline of community diversity and balance, can trigger an aberrant immune response that leads to reduced tolerance against commensal microbiota. In IBD, such dysbiosis has been profoundly proven in animal models, as well as clinic data analysis; however, it has not yet been conclusively ascertained whether dysbiosis actually promotes the disease or is simply a consequence of the inflammatory disorder. Better insight into the complex network of interactions between food, the intestinal microbiome, and host immune response will, therefore, contribute significantly to the diagnosis, treatment, and management of IBD. In this article, we review the ways in which the mutualistic circle of dietary nutrients, gut microbiota, and the immune system becomes anomalous during the IBD process, and discuss the roles of bacterial factors in shaping the intestinal inflammatory barrier and adjusting immune capacity.

Comprehensive analysis of DNA methylation and gene expression in orally tolerized T cells

T cell anergy is known to be a crucial mechanism for various types of immune tolerance, including oral tolerance. The expression of several anergy-specific genes was reportedly up-regulated in anergic T cells, and played important roles in the cells. However, how the genes were up-regulated has not been understood. In this study, we comprehensively analyzed the altered gene expression and DNA methylation status in T cells tolerized by oral antigen in vivo. Our results showed that many genes were significantly up-regulated in the orally tolerized T cells, and most of the genes found in this study have not been reported previously as anergy related genes; for example, ribosomal protein L41 (FC = 3.54E06, p = 3.70E-09: Fisher's exact test; the same applies hereinafter) and CD52 (FC = 2.18E05, p = 3.44E-06). Furthermore, we showed that the DNA methylation statuses of many genes; for example, enoyl-coenzyme A delta isomerase 3 (FC = 3.62E-01, p = 3.01E-02) and leucine zipper protein 1 (FC = 4.80E-01, p = 3.25E-02), including the ones distinctly expressed in tolerized T cells; for example, latexin (FC = 3.85E03, p = 4.06E-02 for expression; FC = 7.75E-01, p = 4.13E-01 for DNA methylation) and small nuclear ribonucleoprotein polypeptide F (FC = 3.12E04, p = 4.46E-04 for expression; FC = 8.56E-01, p = 5.15E-01 for DNA methylation), changed during tolerization, suggesting that the distinct expression of some genes was epigenetically regulated in the tolerized T cells. This study would contribute to providing a novel clue to the fine understanding of the mechanism for T cell anergy and oral tolerance.

Immunomodulation by food: impact on gut immunity and immune cell function

Recent studies have revealed that various food components affect the immune response. These components act on various immune cells, and their effects are mediated through the intestinal immune system and, in some cases, the intestinal microbiota. In this review, we describe the immunomodulating effects of various food components, including probiotics, prebiotics, polysaccharides, vitamins, minerals, fatty acids, peptides, amino acids and polyphenols. Some of these components enhance immune responses, leading to host defense against infection, whereas others inhibit immune responses, thus suppressing allergy and inflammation.

Lactococcus lactis As a Versatile Vehicle for Tolerogenic Immunotherapy

Genetically modified Lactococcus lactis bacteria have been engineered as a tool to deliver bioactive proteins to mucosal tissues as a means to exert both local and systemic effects. They have an excellent safety profile, the result of years of human consumption in the food industry, as well as a lack of toxicity and immunogenicity. Also, containment strategies have been developed to promote further application as clinical protein-based therapeutics. Here, we review technological advancements made to enhanced the potential of L. lactis as live biofactories and discuss some examples of tolerogenic immunotherapies mediated by mucosal drug delivery via L. lactis. Additionally, we highlight their use to induce mucosal tolerance by targeted autoantigen delivery to the intestine as an approach to reverse autoimmune type 1 diabetes.

Comprehensive analysis of epigenetically regulated genes in anergic T cells

T cell anergy is one of the important mechanisms for immune tolerance. The results of many studies investigating the mechanism for T cell anergy induction have revealed that the expression of several genes was up-regulated in anergic T cells. It has also been demonstrated that the molecules encoded on those genes played a critical role in anergy induction. However, the mechanism for their up-regulation has not previously been clarified. We examined in this study the changes in gene expression and DNA methylation status caused by anergy induction. Our results demonstrate that the expression of many genes was changed by anergy induction, and that the DNA methylation status of some of these genes was also changed. We show here by a GO analysis that the extent of the change in methylation status caused by anergy induction was distinct between the groups of genes that were categorized.

Mechanisms of Oral Tolerance

Oral tolerance is an active process of local and systemic immune unresponsiveness to orally ingested antigens such as food. The gut immune system must balance responses to commensal bacteria (microbiome), innocuous antigens, and pathogens. Although it is clear that specialized populations of immune cells and lymph nodes create a unique environment in the gut, there remains evidence to suggest that systemic effector sites also are critical to establishing and maintaining oral tolerance.

Impaired T-Cell Function in B-Cell Lymphoma: A Direct Consequence of Events at the Immunological Synapse?

Tumors can escape immune destruction through the development of antigen loss variants and loss of antigen processing/presentation pathways, thereby rendering them invisible to T cells. Alternatively, mechanisms of peripheral T-cell tolerance that would normally be important for protection from the development of autoimmunity may also be co-opted to (i) generate an immuno-inhibitory tumor environment, (ii) promote development of regulatory cell populations, or (iii) cell-intrinsically inactivate tumor-specific T cells. Emerging evidence suggests that T-cell function is impaired in hematological malignancies, which may manifest from cognate interactions between T cells and the tumor. The immunological synapse forms the cognate T-cell and antigen-presenting cell interaction and is the site where key signalling events, including those delivered by co-inhibitory receptors, that determine the fate of T cells occur. Here, we review evidence that events at the immune synapse between T cells and malignant B cells and alterations in immune synapse function may contribute to loss of T-cell function in B-cell malignancies.

Cholera toxin subunit B peptide fusion proteins reveal impaired oral tolerance induction in diabetes-prone but not in diabetes-resistant mice

The cholera toxin B subunit (CTB) has been used as adjuvant to improve oral vaccine delivery in type 1 diabetes. The effect of CTB/peptide formulations on Ag-specific CD4(+) T cells has remained largely unexplored. Here, using tetramer analysis, we investigated how oral delivery of CTB fused to two CD4(+) T-cell epitopes, the BDC-2.5 T-cell 2.5 mi mimotope and glutamic acid decarboxylase (GAD) 286-300, affected diabetogenic CD4(+) T cells in nonobese diabetic (NOD) mice. When administered i.p., CTB-2.5 mi activated 2.5 mi(+) T cells and following intragastric delivery generated Ag-specific Foxp3(+) Treg and Th2 cells. While 2.5 mi(+) and GAD-specific T cells were tolerized in diabetes-resistant NODxB6.Foxp3(EGFP) F1 and nonobese resistant (NOR) mice, this did not occur in NOD mice. This indicated that NOD mice had a recessive genetic resistance to induce oral tolerance to both CTB-fused epitopes. In contrast to NODxB6.Foxp3(EGFP) F1 mice, oral treatment in NOD mice lead to strong 2.5 mi(+) T-cell activation and the sequestration of these cells to the effector-memory pool. Oral treatment of NOD mice with CTB-2.5 mi failed to prevent diabetes. These findings underline the importance of investigating the effect of oral vaccine formulations on diabetogenic T cells as in selected cases they may have counterproductive consequences in human patients.

A deficient translocation of CD3ζ, ZAP-70 and Grb2 to lipid raft, as a hallmark of defective adaptive immune response during chronic hepatitis B infection

Hepatitis B is considered to be a worldwide public health problem. An immunosuppressor microenvironment has been proposed to contribute to viral persistence during chronic disease. Understanding the intracellular signaling cascade in T-cells from HBV-infected patients, will contribute to unravel the mechanisms that control the development of immune response during hepatitis B. We analyze lipid rafts formation and early activation signals in chronic HBV infected patients, compared to naturally immune subjects (NIS). Patients show: (1) diminished GM1 clustering, (2) A deficient lipid rafts recruitment of CD3ζ/ZAP-70/Grb2, and (3) these proteins do not merge with GM1 within the lipid rafts. Finally, immunoprecipitation assays proved that ZAP-70 does not associate to CD3ζ. These results show for the first time, defects regarding early key events in T-cell activation, in chronically infected HBV patients, which may contribute not only to understand HBV immune tolerance, but to reveal new potential therapeutic targets to control the infection.

Anergy in CD4 memory T lymphocytes. II. Abrogation of TCR-induced formation of membrane signaling complexes

Memory and naive CD4 T cells have unique regulatory pathways for self/non-self discrimination. A memory cell specific regulatory pathway was revealed using superantigens to trigger the TCR. Upon stimulation by bacterial superantigens, like staphylococcal enterotoxin B (SEB), TCR proximal signaling is impaired leading to clonal tolerance (anergy). In the present report, we show that memory cell anergy results from the sequestration of the protein tyrosine kinase ZAP-70 away from the TCR/CD3ζ chain. During SEB-induced signaling, ZAP-70 is excluded from both detergent-resistant membrane microdomains and the immunological synapse, thus blocking downstream signaling. We also show that the mechanism underlying memory cell anergy must involve Fyn kinase, given that the suppression of Fyn activity restores the movement of ZAP-70 to the immunological synapse, TCR proximal signaling, and cell proliferation. Thus, toleragens, including microbial toxins, may modulate memory responses by targeting the organizational structure of memory cell signaling complexes.

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.

Impairment of immunological synapse formation in adaptively tolerant T cells

Adaptive tolerance is a hyporesponsive state in which lymphocyte Ag receptor signaling becomes desensitized after prolonged in vivo encounter with Ag. The molecular mechanisms underlying this hyporesponsive state in T cells are not fully understood, although a major signaling block has been shown to be present at the level of ZAP70 phosphorylation of linker for activation of T cells (LAT). In this study, we investigated the ability of adaptively tolerant mouse T cells to form conjugates with Ag-bearing APCs and to translocate signaling molecules into the interface between the T cells and APCs. Compared with naive or preactivated T cells, adaptively tolerant T cells showed no dramatic impairment in their formation of conjugates with APCs. In contrast, there was a large impairment in immunological synapse formation. Adaptively tolerant T cells were defective in their translocation of signaling molecules, such as ZAP70, LAT, and phospholipase C γ1, into the T cell-APC contact sites. Although Ag-induced activation of VAV1 was normal, VAV's recruitment into the synapse was also impaired. Interestingly, expressions of both IL-2-inducible T cell kinase and growth factor receptor-bound protein 2-related adaptor downstream of SHC were decreased by 60-80% in adaptively tolerant T cells. These decreases, in addition to the impairment in LAT phosphorylation by ZAP70, appear to be the major impediments to the phosphorylation of SLP76 (SRC homology 2 domain-containing leukocyte protein of 76 kDa) and the recruitment of VAV1, which are important for stable immunological synapse formation.

Primary human CD4+ T cells have diverse levels of membrane lipid order that correlate with their function

Membrane lipid microdomains (lipid rafts) play an important role in T cell function by forming areas of high lipid order that facilitate activation. However, their role in regulating T cell differentiation and function remains controversial. In this study, by applying a new approach involving microscopy and flow cytometry, we characterize membrane lipid order in ex vivo primary human CD4(+) T cells. We reveal that differential membrane lipid order dictates the response to TCR stimulation. T cells with high membrane order formed stable immune synapses and proliferated robustly, intermediate order cells had reduced proliferative ability accompanied by unstable immune synapse formation, whereas low order T cells were profoundly unresponsive to TCR activation. We also observed that T cells from patients with autoimmune rheumatic disease had expanded intermediate order populations compared with healthy volunteers. This may be important in dictating the nature of the immune response since most IFN-γ(+)CD4(+) T cells were confined within intermediate membrane order populations, whereas IL-4(+)CD4(+) T cells were contained within the high order populations. Importantly, we were able to alter T cell function by pharmacologically manipulating membrane order. Thus, the results presented from this study identify that ex vivo CD4(+) T cells sustain a gradient of plasma membrane lipid order that influences their function in terms of proliferation and cytokine production. This could represent a new mechanism to control T cell functional plasticity, raising the possibility that therapeutic targeting of membrane lipid order could direct altered immune cell activation in pathology.

Diversity in immunological synapse structure

Immunological synapses (ISs) are formed at the T cell-antigen-presenting cell (APC) interface during antigen recognition, and play a central role in T-cell activation and in the delivery of effector functions. ISs were originally described as a peripheral ring of adhesion molecules surrounding a central accumulation of T-cell receptor (TCR)-peptide major histocompatibility complex (pMHC) interactions. Although the structure of these 'classical' ISs has been the subject of intense study, non-classical ISs have also been observed under a variety of conditions. Multifocal ISs, characterized by adhesion molecules dispersed among numerous small accumulations of TCR-pMHC, and motile 'immunological kinapses' have both been described. In this review, we discuss the conditions under which non-classical ISs are formed. Specifically, we explore the profound effect that the phenotypes of both T cells and APCs have on IS structure. We also comment on the role that IS structure may play in T-cell function.

Anergic CD4+ T cells form mature immunological synapses with enhanced accumulation of c-Cbl and Cbl-b

CD4(+) T cell recognition of MHC:peptide complexes in the context of a costimulatory signal results in the large-scale redistribution of molecules at the T cell-APC interface to form the immunological synapse. The immunological synapse is the location of sustained TCR signaling and delivery of a subset of effector functions. T cells activated in the absence of costimulation are rendered anergic and are hyporesponsive when presented with Ag in the presence of optimal costimulation. Several previous studies have looked at aspects of immunological synapses formed by anergic T cells, but it remains unclear whether there are differences in the formation or composition of anergic immunological synapses. In this study, we energized primary murine CD4(+) T cells by incubation of costimulation-deficient, transfected fibroblast APCs. Using a combination of TCR, MHC:peptide, and ICAM-1 staining, we found that anergic T cells make mature immunological synapses with characteristic central and peripheral supramolecular activation cluster domains that were indistinguishable from control synapses. There were small increases in total phosphotyrosine at the anergic synapse along with significant decreases in phosphorylated ERK 1/2 accumulation. Most striking, there was specific accumulation of c-Cbl and Cbl-b to the anergic synapses. Cbl-b, previously shown to be essential in anergy induction, was found in both the central and the peripheral supramolecular activation clusters of the anergic synapse. This Cbl-b (and c-Cbl) accumulation at the anergic synapse may play an important role in anergy maintenance, induction, or both.

Characterization of CD4+ T-cell-dendritic cell interactions during secondary antigen exposure in tolerance and priming

Despite the recent advances in our understanding of the dynamics of the cellular interactions associated with the induction of immune responses, comparatively little is known about the in vivo behaviour of antigen-experienced T cells upon secondary antigen exposure in either priming or tolerance. Such information would provide an insight into the functional mechanisms employed by memory T cells of distinct phenotypes and provide invaluable knowledge of how a specific tolerogenic or immunogenic state is maintained. Using real-time imaging to follow the in vivo motility of naïve, primed and tolerized CD4(+) T cells and their interactions with dendritic cells (DCs), we demonstrate that each of these distinct functional phenotypes is associated with specific patterns of behaviour. We show that antigen-experienced CD4(+) T cells, whether primed or tolerized, display inherently slower migration, making many short contacts with DCs in the absence of antigen. Following secondary exposure to antigen, primed T cells increase their intensity or area of interaction with DCs whereas contacts between DCs and tolerized T cells are reduced. Importantly, this was not associated with alterations in the contact time between DCs and T cells, suggesting that T cells that have previously encountered antigen are more effective at surveying DCs. Thus, our studies are the first to demonstrate that naïve, primed and tolerized T cells show distinct behaviours before and after secondary antigen-encounter, providing a novel mechanism for the increased immune surveillance associated with memory T cells. These findings have important consequences for many immunotherapeutics, which aim to manipulate secondary immune responses.

IL-10 and IL-27 producing dendritic cells capable of enhancing IL-10 production of T cells are induced in oral tolerance

Oral tolerance is a key feature of intestinal immunity, generating systemic tolerance to ingested antigens (Ag). Dendritic cells (DC) have been revealed as important immune regulators, however, the precise role of DC in oral tolerance induction remains unclear. We investigated the characteristics of DC in spleen, mesenteric lymph node (MLN), and Peyer's patch (PP) after oral Ag administration in a TCR-transgenic mouse model. DC from PP and MLN of tolerized mice induced IL-10 production but not Foxp3 expression in cocultured T cells. IL-10 production was markedly increased after 5-7-day Ag administration especially in PP DC. On the other hand, IL-27 production was increased after 2-5-day Ag administration. CD11b(+) DC, which increased after ingestion of Ag, prominently expressed IL-10 and IL-27 compared with CD11b(-) DC. These results suggest that IL-10 and IL-27 producing DC are increased by interaction with antigen specific T cells in PP, and these DC act as an inducer of IL-10 producing T cells in oral tolerance.

The molecular makeup and function of regulatory and effector synapses

Physical interactions between T cells and antigen-presenting cells (APCs) form the basis of any specific immune response. Upon cognate contacts, a multimolecular assembly of receptors and adhesion molecules on both cells is created, termed the immunological synapse (IS). Very diverse structures of ISs have been described, yet the functional importance for T-cell differentiation is largely unclear. Here we discuss the principal structure and function of ISs. We then focus on two characteristic T-cell-APC pairs, namely T cells contacting dendritic cells (DCs) or naive B cells, for which extremely different patterns of the IS have been observed as well as fundamentally different effects on the function of the activated T cells. We provide a model on how differences in signaling and the involvement of adhesion molecules might lead to diverse interaction kinetics and, eventually, diverse T-cell differentiation. We hypothesize that the preferred activation of the adhesion molecule leukocyte function-associated antigen-1 (LFA-1) and of the negative regulator for T-cell activation, cytotoxic T-lymphocyte antigen-4 (CTLA-4), through contact with naive B cells, lead to prolonged cell-cell contacts and the generation of T cells with regulatory capacity. In contrast, DCs might have evolved mechanisms to avoid LFA-1 overactivation and CTLA-4 triggering, thereby promoting more dynamic contacts that lead to the preferential generation of effector cells.

Regulation of intestinal immunity: effects of the oral adjuvant Escherichia coli heat-labile enterotoxin on migrating dendritic cells

Escherichia coli heat-labile enterotoxin (Etx) is an oral adjuvant in mice. We show that this is also true for rats. To understand this adjuvant activity we examined lymph dendritic cells (DC) migrating from the intestine to mesenteric lymph nodes (MLN) in animals fed Etx. These DC can prime antigen-specific antibody responses. We show that in rats the small intestine contains 7-24 million DC and 8 x 10(5 )of these migrate to MLN each day. Surprisingly, Etx does not stimulate increased migration of lymph DC. However, oral Etx affects the activation, antigen transport and localization of migratory DC. Specifically, expression of CD25 increases on the CD172a(high) subset of lymph DC. Oral Etx also increases the number of CD172a(high) lymph DC containing co-administered ovalbumin. CD172a(high) lymph DC treated with Etx in vitro, or purified from the lymph of animals fed Etx, stimulate stronger proliferative responses from primed T cells. Etx also directs more of the CD172a(high) lymph DC into the central region of the MLN T cell areas. This change in DC localization is associated with an increase in the expression of CCR7. These data help advance our understanding of the role of DC in initiating mucosal immune responses in vivo.

Modulation of immunological synapse by membrane-bound and soluble ligands

An efficient adaptive immune response should prevent pathogen infections and tumor growth without causing significant damage to host constituents. A crucial event determining the balance between tolerance and immunity is antigen recognition by T cells on the surface of antigen presenting cells (APC). Several molecular contacts at the interface between T cells and APCs contribute to define the nature of the adaptive immune response against a particular antigen. Upon TCR engagement by a peptide-MHC complex (pMHC) on the surface of an APC, a specialized supra-molecular structure known as immunological synapse (IS) assembles at the interface between these two cells. This structure involves massive re-distribution of membrane proteins, including TCR and pMHC complexes, as well as co-stimulatory and adhesion molecules. Furthermore, IS assembly leads to several important intracellular events necessary for T cell activation, such as recruitment of signaling molecules and cytoskeleton rearrangements. Because IS assembly leads to major consequences on the function of T cells, several studies have attempted to identify both soluble and membrane-bound molecules that could contribute to modulate the IS function. Here we describe recent literature on the regulation of IS assembly and modulation by TCR/pMHC binding kinetics, chemokines and cytokines focusing on their role at controlling the balance between adaptive immunity and tolerance.

In vivo anergized T cells form altered immunological synapses in vitro

T cells contact allogeneic antigen presenting cells (APCs) and assemble, at their contact interface, a molecular platform called the immunological synapse. Synapse-based molecules provide directional signals for the T cell--either positive signals, resulting in T-cell activation, or negative signals causing T-cell inactivation or anergy. To better understand the molecular basis of in vivo T-cell anergy we analyzed the contacts made between in vivo anergized T cells and APCs, and determined which signaling molecules were included or excluded from their immunological synapses. Anergy was induced in TCR transgenic mice by the intravenous injection of semiallogeneic donor spleen cells. T cells from anergized mice were mixed with APCs, the T-cell/APC synapses imaged using deconvolution microscopy, and their molecular compositions were determined. T cells from anergic mice formed unstable immunological synapses in vitro with allogeneic APCs and failed to recruit the signaling proteins necessary to initiate T-cell activation. These findings suggest that T-cell anergy induced by exposure to semiallogeneic donor cells is associated with defects in the earliest events of T-cell activation, immunological synapse formation and recruitment of TCR-mediated signaling proteins.

Impairment of T cell interactions with antigen-presenting cells by immunosuppressive drugs reveals involvement of calcineurin and NF-κB in immunological synapse formation

A stable supramolecular cluster in T cells at the contact site of APCs, the immunological synapse (IS), is essential for full T cell activation. Failure of IS maturation, as determined by defective relocalization of the TCR/CD3 complex at the T cell/APC contact site, is linked with T cell hyporesponsiveness. The effects of clinically used immunosuppressants on these critical events, however, are undefined. Here, we show that treatment of T cells with cyclosporin A, FK506, and dexamethasone, which are known to inhibit calcineurin and NF-kappaB, respectively, but not rapamycin, the inhibitor of mammalian target of rapamycin, selectively prevented TCR/CD3 relocalization into the IS, while relocalization of adhesion and cytoskeletal proteins as well as T cell/APC conjugate formation remained unaltered. The involvement of calcineurin and NF-kappaB in IS maturation was confirmed by using specific inhibitors of these molecules (FR901725, gossypol, SN50). FK778, as an inhibitor of DNA replication and also TCR/CD3-activated tyrosine kinases, globally abrogated cytoskeletal, adhesion, and signaling molecule relocalization, thereby preventing formation of an IS at an earlier, immature stage along with impaired, antigen-specific T cell/APC conjugate formation. Collectively, blocking IS formation at distinct stages may mediate effects on T cell activation of currently used immunosuppressants, apart from their capacity to block gene transcription, cytokine signaling, and DNA replication. Furthermore, these data imply novel functions of calcineurin and NF-kappaB for successful IS maturation.

Ethanol suppresses LPS-induced Toll-like receptor 4 clustering, reorganization of the actin cytoskeleton, and associated TNF-alpha production

BACKGROUND

Ethanol (EtOH) suppresses cytokine responses induced through most Toll-like receptors (TLRs), but the mechanism of action is unclear. We recently found that acute EtOH alters lipopolysaccharide (LPS)-induced partitioning of CD14, a critical component of the LPS receptor complex, within lipid raft fractions in the macrophage-like cell line RAW264.7.

METHODS

Here we investigated the role of receptor clustering in alteration of the responses of cells to LPS caused by EtOH both in vitro and in vivo. The cellular distribution of CD14, TLR4, actin cytoskeleton, and tumor necrosis factor-alpha (TNF-alpha) were studied by confocal microscopy following exposure of cells to LPS with or without EtOH. TLR4 and CD14 were clustered into highly colocalized patches on the cell membrane accompanied by the reorganization of the actin cytoskeleton in some of the RAW264.7 cells as well as peritoneal cells following LPS treatment.

RESULTS

Addition of EtOH reduced the number of cells that had LPS-induced receptor patches and in which this reorganization occurred. Cells on which CD14 and TLR4 formed clusters or caps had substantially higher levels of membrane-bound TNF-alpha compared with cells without clustering or capping of these molecules. Interference with the actin cytoskeleton by cytochalasin D suppressed the production of TNF-alpha and receptor clustering, as EtOH did.

CONCLUSIONS

These data confirm our previous observations, suggest a novel mechanism of EtOH action that involves interference with receptor clustering, and indicate a potential role of actin filaments in the formation of receptor patches, subsequent activation of macrophages by LPS, and production of TNF-alpha.

Oral tolerance and allergic responses to food proteins

PURPOSE OF REVIEW

The default response to protein antigens in the intestine is the induction of systemic and local hyporesponsiveness, ensuring the prevention of coeliac disease and food allergies. Interest is increasing in the role of dietary manipulation and probiotics in treating allergic and other diseases, but less is known about how these regimens might influence systemic and local immune responses. This paper addresses the mechanisms at the interface of innate and adaptive immunity that determine how the body responds to orally administered proteins and how local bacteria modify these.

RECENT FINDINGS

This paper discusses evidence that dendritic cells in the intestinal mucosa are the critical cells that take up dietary proteins and migrate to the draining mesenteric lymph node, where they induce regulatory CD4 T-cell differentiation. The properties of tolerized T cells are discussed and it is proposed that the gut microenvironment maintains homeostasis by conditioning dendritic cells to remain in a quiescent state. Inhibitory signalling by commensal bacteria possibly contributes to this process.

SUMMARY

A regulatory network controls how dietary antigens are taken up and presented to T lymphocytes by specialized antigen-presenting cells. Elucidating their nature and how they are influenced by external factors such as probiotics may help develop novel therapies for allergy and help understand diseases such as coeliac disease.

NKT cells play critical roles in the induction of oral tolerance by inducing regulatory T cells producing IL-10 and transforming growth factor beta, and by clonally deleting antigen-specific T cells

Oral tolerance is the systemic unresponsiveness induced by orally administered proteins. To explore the roles of natural killer T (NKT) cells in oral tolerance, we induced oral tolerance to ovalbumin (OVA) in NKT cell-deficient mice. In CD1d-/- mice, the induction of tolerance to orally administered high- or low-dose OVA was impaired. Dendritic cells (DCs) in the Peyer's patches (PPs) of CD1d-/- mice fed OVA showed high expression of major histocompatibility complex (MHC) class II and B7 molecules, whereas DCs of control mice fed OVA expressed low levels of these molecules. The adoptive transfer of NKT cells restored oral tolerance and induction of tolerogenic DCs in the PPs and spleens of CD1d-/- mice. Moreover, interleukin (IL)-10 and transforming growth factor (TGF)-beta1 production in vitro were reduced in cells from the spleen and PPs of CD1d-/- mice compared with those of control mice fed OVA. The numbers of OVA-specific CD4+ KJ1-26+ T cells were significantly reduced in the PPs and spleens of DO11.10 mice fed OVA. In contrast, OVA-specific CD4+ KJ1-26+ T cells were not deleted in the PPs or spleens of DO11.10 CD1d-/- mice. In conclusion, NKT cells were found to play an indispensable role in oral tolerance by inducing regulatory T cells, and clonally deleting antigen-specific CD4+ T cells.

Regulatory T cells inhibit protein kinase C theta recruitment to the immune synapse of naive T cells with the same antigen specificity

The precise mechanisms by which regulatory T cells operate, particularly their effect on signaling pathways leading to T cell activation, are poorly understood. In this study we have used regulatory T (Treg) cells of known Ag specificity, generated in vivo, to address their effects on early activation events occurring in naive T cells of the same Ag specificity. We found that the Treg cells need to be present at the moment of priming to suppress activation and proliferation of the naive T cell. Furthermore, the Treg cells significantly inhibit the recruitment of protein kinase Ctheta (PKCtheta) to the immune synapse of the naive T cell as long as both T cells are of the same Ag specificity and are contacting the same APC. Finally, naturally occurring CD4(+)25(+) T cells seem to have the same effect on PKCtheta recruitment in CD25(-) T cells of the same Ag specificity. These results suggest that although additional mechanisms of regulation are likely to exist, inhibition of PKCtheta recruitment in the effector T cell may be a common regulatory pathway leading to the absence of NF-kappaB activation and contributing to the block of IL-2 secretion characteristic of immune suppression.

Impaired Activation and Localization of LAT in Anergic T Cells as a Consequence of a Selective Palmitoylation Defect

The molecular basis of T cell anergy is not completely understood. We show that in antigen-primed anergic murine CD4(+) T cells the linker for activation of T cells (LAT) is hypophosphorylated upon CD3/CD28 restimulation. Signaling events downstream of LAT (PLCgamma1 phosphorylation and p85 [PI3-K] association) were impaired, whereas upstream events (CD3zeta and ZAP-70 phosphorylation) remained intact. LAT recruitment to the immunological synapse and its localization in detergent-resistant membrane (DRM) fractions were defective in anergic T cells. These defects resulted from impaired palmitoylation of LAT and were selective since the DRM localization and palmitoylation of Fyn were intact. This LAT defect was independent of Cbl-b and did not reflect enhanced LAT degradation. These results identify LAT as the most upstream target of anergy induction; moreover, they suggest that regulation of the amount of LAT in the immunological synapse and DRM by posttranslational palmitoylation contributes to the induction of T cell anergy.

Cholesterol and sphingolipids as lipid organizers of the immune cells’ plasma membrane: Their impact on the functions of MHC molecules, effector T-lymphocytes and T-cell death

The possible regulatory mechanisms by which glycosphingolipid- and cholesterol-rich membrane microdomains, caveolar and non-caveolar lipid rafts, control the immune response are continuously expanding. In the present overview we will focus on how these membrane-organizing lipids are involved, in collaboration with tetraspanin proteins, in the formation of distinct MHC-I and MHC-II microdomains at the cell surface and will analyze the possible roles of MHC compartmentation in the processes of antigen presentation and regulation of various stages of the cellular immune response. Some basic, lipid raft- and tetraspan mediated mechanisms involved in the formation and function of immunological synapses between various APCs and T-cells will also be discussed. Finally, a new aspect of immune regulation by sphingolipids will be briefly described, namely how can the death or stress signals, leading to ceramide accumulation, result in raft-associated regulatory platforms controlling cell death or antigen-induced, TCRmediated signaling of T-lymphocytes. The influence of these signals and their cross-talk on the fate (death or survival) of T-cells and the outcome of T-cell response will also be discussed.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.