Th17 plasticity and its relevance to inflammatory bowel disease.

It is now clear that previously polarized T cells possess the ability to change their phenotype and repolarize towards different fates. This intrinsic flexibility is commonly referred to as plasticity and is influenced by the cytokine milieu, microbial products and products of metabolism which, in turn, regulate transcription factors and epigenetic machinery in the intestinal lamina propria. The intestinal immune system faces a particularly difficult challenge. It serves to protect the largest mucosal surface against infection and injury while maintaining a state of tolerance towards dietary antigens and the largest population of commensal organisms in the body. This requires a delicate balance between regulatory and effector T cells; loss of this balance is thought to lead to the development of Crohn's disease (CD) and ulcerative colitis (UC), collectively referred to as inflammatory bowel disease (IBD). These unique immune-mediated inflammatory diseases are directed not at self-antigens but rather at the commensal microorganisms which reside within the gut lumen. However, it is thought that owing to persistence of these microbial antigens, intestinal damage and systemic inflammation ensue. New data from mouse models of IBD suggest that T cell plasticity, particularly along the Th1-Th17 and Th17-Treg axes, plays an important role in the regulation of intestinal immune responses. Furthermore, patients with IBD demonstrate increased numbers of "transdifferentiated" T cell populations suggestive of heightened plasticity. This review will consider the mechanisms and roles of Th17 plasticity in the pathogenesis of IBD.

Dietary n-3 PUFA May Attenuate Experimental Colitis.

BACKGROUND: Inflammatory bowel diseases (IBD) occurred in genetically predisposed people exposed to environmental triggers. Diet has long been suspected to contribute to the development of IBD. Supplementation with n-3 polyunsaturated fatty acids (PUFA) protects against intestinal inflammation in rodent models while clinical trials showed no benefits. We hypothesized that intervention timing is crucial and dietary fatty acid pattern may influence intestinal environment to modify inflammation genesis. The aim of this study was to evaluate the dietary effect of PUFA composition on intestinal inflammation. METHODS: Animals received diet varying in their PUFA composition for four weeks before TNBS-induced colitis. Colon inflammatory markers and gut barrier function parameters were assessed. Inflammatory pathway PCR arrays were determined. RESULTS: n-3 diet significantly decreased colon iNOS, COX-2 expression, IL-6 production, and LTB4 production but tended to decrease colon TNFα production (P = 0.0617) compared to control diet. Tight junction protein (claudin-1, occludin) expressions and MUC2 and TFF3 mRNA levels were not different among groups. n-9 diet also decreased colon IL-6 production (P < 0.05). CONCLUSIONS: Dietary n-3 PUFA influence colitis development by attenuating inflammatory markers. Further research is required to better define dietary advice with a scientific rationale.

Crossover Subsets of CD4+ T Lymphocytes in the Intestinal Lamina Propria of Patients with Crohn's Disease and Ulcerative Colitis.

BACKGROUND: Hovhannisyan et al. first showed evidence of plasticity between Treg and Th17 in the inflamed intestine of Crohn's disease (CD) patients. Our previous report suggests that the inflammatory cytokine milieu generates IL-17+ Foxp3+ CD4+ T lymphocytes which is a crossover population converting Treg subset to Th17 in the peripheral blood of IBD patients. This is considered as an evidence of Treg/Th17 plasticity. AIM: The aim of this study was to characterize a variety of helper T cell crossover population, not limited to IL-17+ Foxp3+ CD4+ T lymphocytes, in the lamina propria (LP) of IBD patients. METHODS: Fresh colonoscopic biopsies were obtained from patients with CD (n = 50) and ulcerative colitis (UC, n = 32) and from healthy controls (HC, n = 25). LP mononuclear cells were assessed for intracellular cytokines and transcription factors such as IFNγ, IL-13, IL-17, IL-22, T-bet, Gata-3, RORγt, and Foxp3 using multicolor flow cytometry to detect subsets of LP CD4+ T lymphocytes. RESULTS: Patients with IBD demonstrated increased crossover populations in IL-17+ Foxp3+, T-bet+ Foxp3+, Gata3+ Foxp3+, RORγt+ Foxp3+ populations compared to HC. There was an inverse correlation of Harvey-Bradshaw index with Gata3+ Foxp3+ population in CD patients, while IL-13+ Foxp3+ population was directly correlated with Mayo clinical scores in UC patients. Furthermore, total IL-22 expressing cells as well as Th22 and IL-22+ Th1 populations were decreased in UC compared to CD and HC. CONCLUSION: IBD patients exhibit the increased crossover populations in LP Treg cells toward Th2 and Th17 compared to HC. The prevalence of Treg/Th2 crossover populations is associated with clinical disease score of IBD.

Exaggerated IL-15 and Altered Expression of foxp3+ Cell-Derived Cytokines Contribute to Enhanced Colitis in Nlrp3-/- Mice.

The pathogenesis of Crohn's disease (CD) involves defects in the innate immune system, impairing responses to microbes. Studies have revealed that mutations NLRP3 are associated with CD. We reported previously that Nlrp3-/- mice were more susceptible to colitis and exhibited reduced colonic IL-10 expression. In the current study, we sought to determine how the loss of NLRP3 might be altering the function of regulatory T cells, a major source of IL-10. Colitis was induced in wild-type (WT) and Nlrp3-/- mice by treatment with dextran sulphate sodium (DSS). Lamina propria (LP) cells were assessed by flow cytometry and cytokine expression was assessed. DSS-treated Nlrp3-/- mice exhibited increased numbers of colonic foxp3+ T cells that expressed significantly lower levels of IL-10 but increased IL-17. This was associated with increased expression of colonic IL-15 and increased surface expression of IL-15 on LP dendritic cells. Neutralizing IL-15 in Nlrp3-/- mice attenuated the severity of colitis, decreased the number of colonic foxp3+ cells, and reduced the colonic expression of IL-12p40 and IL-17. These data suggest that the NLRP3 inflammasome can regulate intestinal inflammation through noncanonical mechanisms, providing additional insight as to how NLRP3 variants may contribute to the pathogenesis of CD.

Association of Circulating Fibrocytes With Fibrostenotic Small Bowel Crohn's Disease.

BACKGROUND: Fibrocytes are hematopoietic cells with features of mesenchymal cells found in the circulation and inflammatory sites implicated in promoting fibrosis in many fibroinflammatory diseases. However, their role(s) in the development of intestinal fibrosis is poorly understood. Here, we investigated a potential role of fibrocytes in the development of fibrosis in Crohn's disease (CD) and sought factors that may impact their development and function. METHODS: Plasma and mononuclear cells were collected from patients with and without fibrostenotic CD. Fibrocytes defined as CD11b+, CD34+, and Collagen 1+ were correlated with clinical assessments of fibrosis, including evaluation using intestinal ultrasound. We measured the levels of relevant circulating molecules via Luminex and studied the effect of patient plasma proteins on fibrocyte differentiation. RESULTS: Fibrocyte numbers were increased in CD patients with stricturing Crohn's disease compared with patients with an inflammatory phenotype (P = .0013), with strong correlation between fibrocyte numbers and acoustic radiation force impulse (ARFI), a measure of bowel elasticity on intestinal ultrasound (R = .8383, P = .0127). Fibrostenotic plasma was a more potent inducer of fibrocyte differentiation in both primary human monocytes and cell line and contained increased levels of cytokines implicated in fibrocyte differentiation compared with plasma from inflammatory patients. Interestingly, increased fibrocyte numbers at time of ultrasound were associated with escalation of medical therapy and endoscopic/surgical management of small bowel strictures at 30 months follow-up. CONCLUSIONS: Circulating fibrocytes strongly correlate with fibrostenotic disease in CD, and they may serve as predictors for escalation of medical +/- surgical therapy.

Intestinal strictures are thought to result from excessive deposition of extracellular matrix by activated mesenchymal cells. In this study, we provide evidence that supports a potential role of fibrocytes (bone marrow­derived mesenchymal precursors) in collagen deposition in Crohn's disease strictures. Inasmuch as fibrocyte numbers correlate with sonographic measures of bowel stiffness, fibrocyte numbers may predict the need for therapy escalation.

Increased DNA-incorporated thiopurine metabolite as a possible mechanism for leukocytopenia through cell apoptosis in inflammatory bowel disease patients with NUDT15 mutation.

BACKGROUND AND AIMS: Polymorphisms in the nucleotide diphosphate-linked moiety X-type motif 15 (NUDT15) gene are associated with thiopurine-induced leukopenia in patients with inflammatory bowel disease (IBD). NUDT15-associated subcellular thiopurine metabolism has not been investigated in primary lymphocytes. We hypothesized that NUDT15 mutation increases DNA-incorporated deoxythioguanosine (dTG) and induces apoptosis in lymphocytes. METHODS: DNA-incorporated dTG in peripheral blood mononuclear cells (PBMCs) and 6-thioguanine nucleotides (6-TGN) in red blood cells were measured in patients with IBD undergoing thiopurine treatment. The association of a single nucleotide polymorphism for NUDT15 (rs116855232) with dTGPBMC was examined. The pro-apoptotic effect of DNA-incorporated dTG was examined ex vivo in association with NUDT15 genotypes by co-culturing patient-derived peripheral CD4+ T lymphocytes with 6-thioguanine (6-TG). RESULTS: dTGPBMC was significantly higher in NUDT15 variants than in non-variants. dTGPBMC, but not 6-TGNRBC, negatively correlated with peripheral lymphocyte counts (r = - 0.31 and - 0.12, p = 0.012 and 0.173, respectively). DNA-incorporated dTG significantly accumulated to a greater extent in lymphocytes from NUDT15 variants when co-cultured with 6-TG ex vivo than in those from non-variants and was associated with decreased proliferation and increased apoptosis. CONCLUSION: Increased DNA-incorporated dTG may be responsible for thiopurine-induced leukocytopenia through cell apoptosis in IBD patients with NUDT15 mutation.

Enhanced early expansion and maturation of semi-invariant NK T cells inhibited autoimmune pathogenesis in congenic nonobese diabetic mice.

Semi-invariant NK T cell (iNKT) deficiency has long been associated with the pathogenesis of type 1 diabetes (T1D), but the linkage between this the deficiency and T1D susceptibility gene(s) remains unclear. We analyzed NOD mice subcongenic for resistant alleles of Idd9 locus in search for protective mechanisms against T1D, and found that iNKT cell development was significantly enhanced with a more advanced mature phenotype and function in mice containing Idd9.1 sublocus of B10 origin. The enhanced iNKT cell development and function suppressed effector function of diabetogenic T cells. Elimination of iNKT cells by CD1d deficiency almost abolished T1D protection in these mice. Interestingly, although the iNKT cells were responsible for a Th2 orientated cytokine profile that is often regarded as a mechanism of T1D prevention, our data suggests that the Th2 bias played little if any role for the protection. In addition, dendritic cells from the congenic NOD mice showed increased abilities to engage and potentiate iNKT cells, suggesting that a mechanism mediated by dendritic cells or other APCs may be critical for the enhanced development and maturation of iNKT cells. The products of T1D susceptibility gene(s) in Idd9.1 locus may be a key factor for this mechanism.

Ligand-dependent induction of noninflammatory dendritic cells by anergic invariant NKT cells minimizes autoimmune inflammation.

Stimulated by an agonistic ligand, alpha-galactosylceramide (alphaGalCer), invariant NKT (iNKT) cells are capable of both eliciting antitumor responses and suppressing autoimmunity, while they become anergic after an initial phase of activation. It is unknown how iNKT cells act as either activators or regulators in different settings of cellular immunity. We examined effects of alphaGalCer administration on autoimmune inflammation and characterized phenotypes and functional status of iNKT cells and dendritic cells in alphaGalCer-treated NOD mice. Although iNKT cells became and remained anergic after the initial exposure to their ligand, anergic iNKT cells induce noninflammatory DCs in response to alphaGalCer restimulation, whereas activated iNKT cells induce immunogenic maturation of DCs in a small time window after the priming. Induction of noninflammatory DCs results in the activation and expansion of islet-specific T cells with diminished proinflammatory cytokine production. The noninflammatory DCs function at inflammation sites in an Ag-specific fashion, and the persistence of noninflammatory DCs critically inhibits autoimmune pathogenesis in NOD mice. Anergic differentiation is a regulatory event that enables iNKT cells to transform from promoters to suppressors, down-regulating the ongoing inflammatory responses, similar to other regulatory T cells, through a ligand-dependent mechanism.

Histopathological Features of Inflammatory Bowel Disease are Associated With Different CD4+ T Cell Subsets in Colonic Mucosal Lamina Propria.

BACKGROUND: Inflammatory bowel disease [IBD] results particularly from an aberrance of CD4+ helper and regulatory T cells and comprises histopathologically chronic active enterocolitis with features reflecting both activity and chronicity of mucosal inflammation. The exact immunological-histological correlation in IBD is not understood. METHODS: We studied the correlation between colonic mucosal CD4+ T cell subsets [Th1, Th2, Th17, Th22 and Treg] and mucosal histological changes in ulcerative colitis [UC] and Crohn's disease [CD]. CD4+ T cell subtyping and enumeration were achieved by flow cytometry. Histological features were categorized and assessed semi-quantitatively using three validated histological scoring schemes [ECAP, RHI and D'Haens]. Correlations between prevalence [%] of CD4+ T cell subsets and histological scores were analysed. RESULTS: Treg cells were correlated with ECAP category A [activity] as well as RHI scores. Treg cell were increased particularly in mucosa with severe neutrophilic infiltration in the cryptal/surface epithelium and in lamina propria, and with basal plasmacytosis. Th17 cells were also increased in cases with extensive neutrophil infiltrate in lamina propria, whereas RORc+ cells were increased in cases with severe lymphoplasmacytic infiltration in lamina propria. In both UC and CD, mucosa with marked crypt architectural alteration had increased IL-22+ and Th22 cells. UC with Paneth cell metaplasia had higher Th17 cells. CD with granuloma had increased IL-22+ and IL-22+IFN-γ+ cells. CONCLUSIONS: The Treg subset appears to be associated with the overall severity of IBD histopathology, particularly with active inflammation. Th17 is also associated with activity. By contrast, IL-22+ cells are associated with chronicity and granuloma formation in CD.

Immunogenicity of Influenza Vaccine for Patients with Inflammatory Bowel Disease on Maintenance Infliximab Therapy: A Randomized Trial.

BACKGROUND: In patients with inflammatory bowel disease (IBD) on infliximab, data are limited on immune response to influenza vaccine and the impact of vaccine timing. The study aims were to evaluate immune responses to the influenza vaccine in IBD patients on infliximab and the impact of vaccine timing on immune responses. METHODS: In this randomized study, 137 subjects with IBD on maintenance infliximab therapy were allocated to receive the 2012/2013 inactivated influenza vaccine at the time of infliximab infusion (n = 69) or midway between infusions (n = 68). Serum was collected before and after vaccination for hemagglutination inhibition titers. Serologic protection was defined by postvaccine titer of ≥1:40. RESULTS: Comparing subjects vaccinated at the time of infliximab with those vaccinated midway, serologic protection was achieved in 67% versus 66% to H1N1 (P = 0.8), in 43% versus 49% to H3N2 (P = 0.5), and in 69% versus 79% to influenza B (P = 0.2). Although solicited adverse events were common (60%), no subject experienced a serious adverse event requiring additional medical attention. Only 6% of subjects had a clinically significant increase in disease activity score, not impacted by vaccine timing. CONCLUSIONS: Serologic protection to influenza vaccine is achieved in only approximately 45% to 80% of IBD patients on maintenance infliximab therapy varying by antigen. Yet, importantly, vaccine timing relative to infliximab infusion does not affect the achievement of serologic protection, and the influenza vaccine is well tolerated. Therefore, influenza vaccination at any point during infliximab scheduling is recommended for patients with IBD and opportunities to broaden the availability and convenience of influenza vaccine to optimize coverage should be explored.

Novel CD8+ T-Cell Subsets Demonstrating Plasticity in Patients with Inflammatory Bowel Disease.

BACKGROUND: Distinct CD8+ T-cell subsets such as interleukin-17-expressing Tc17 and Foxp3-expressing Tcreg are functionally similar to CD4+ T cells. Though CD4+ T cells are dysregulated in patients with inflammatory bowel disease (IBD), CD8+ T cells are not well investigated. Vitamin D is an environmental factor which influences T-cell subsets. We assessed the prevalence of CD8+ T-cell subsets among peripheral blood mononuclear cells (PBMC) and lamina propria mononuclear cells (LPMC) of patients with Crohn's disease, patients with ulcerative colitis, and healthy controls. We then tested the effect of 1α,25-dihydroxyvitamin D3 on CD8+ T-cell subsets. METHODS: A total of 73 patients with Crohn's disease, 49 patients with ulcerative colitis, and 47 healthy controls were studied. LPMC or PBMC were isolated and flow cytometry was performed. CD3+ T cells, isolated from PBMC, were cultured with or without 1α,25-dihydroxyvitamin D3, before flow cytometry. RESULTS: In LPMC, the prevalence of Tcreg was higher in patients with IBD (P < 0.05), whereas Tc17 were higher in patients with ulcerative colitis compared with patients with Crohn's disease and healthy controls (P < 0.05). In PBMC, both Tcreg and Tc17 were higher in patients with IBD (P < 0.01). Double-expressing interferon-γ+ interleukin-17+ and Foxp3+ interleukin-17+ CD8+ T cells were also identified indicating possible CD8+ plasticity. 1α,25-dihydroxyvitamin D3 decreased interferon-γ-expressing Tc1 (P < 0.05), but had no effect on Tc17 or Tcreg. CONCLUSIONS: The prevalence of novel CD8+ T-cell subsets is altered in patients with IBD. Double-expressing cells indicate plasticity and were identified in patients with IBD. Vitamin D may have a limited effect on CD8+ T cells by decreasing interferon-γ expression.

Profiles of Lamina Propria T Helper Cell Subsets Discriminate Between Ulcerative Colitis and Crohn's Disease.

BACKGROUND: Distinction between 2 forms of inflammatory bowel disease (IBD), ulcerative colitis (UC) and Crohn's disease (CD), can be challenging. Aberrant mucosal immunity suggests that CD is a T helper type 1 cell (Th1)-driven disease, whereas UC as Th2-driven response. However, whether this paradigm truly distinguishes CD from UC is controversial. We aimed to clarify the discriminating potential of lamina propria Th subsets in patients with IBD. METHODS: Biopsies from 79 patients with IBD and 20 healthy controls were collected for Th subsets analysis (Th1:interferon γ [IFN-γ], T-bet; Th2:interleukin 13 [IL-13], Gata3; Th17:IL-17, RORγt; Treg:FoxP3). The receiver-operating characteristic curves were constructed to assess the discriminating ability by calculating the area under the receiver-operating characteristic curve. The equation with the highest area under the receiver-operating characteristic curve was applied to newly diagnosed patients to evaluate discriminating ability. RESULTS: Patients with CD showed increased IFN-γ or T-bet cells and decreased IL-13 or Gata3 cells compared with UC. A discriminant equation composed of 4 markers (IFN-γ, T-bet, IL-13, and Gata3) yielded the highest area under the receiver-operating characteristic curve. In 36 established CD or UC, the sensitivity, specificity, positive and negative predictive probabilities were 92.6%, 55.6%, 86.2%, and 71.4% and in 14 newly diagnosed patients were 100.0%, 42.9%, 63.6%, and 100.0%. Furthermore, Gata3 cells were increased in tumor necrosis factor inhibitor therapy nonresponders compared with responders in CD. IFN-γ cells were directly and inversely proportional to disease activity in patients with CD and UC, respectively. CONCLUSIONS: The Th1/Th2 paradigm can distinguish CD from UC and may be further associated with response to tumor necrosis factor inhibitor in CD and disease activity in patients with IBD.

Th17 plasticity and its changes associated with inflammatory bowel disease.

CD4 T helper (Th) cell differentiation into distinct T cell subsets is critical to the normal function of the immune system. Until recently, the paradigm held that naïve T cells differentiated into distinct subsets under the guidance of environmental cues (e.g., cytokines) and that once polarized, these cells were committed to a particular functional state. However, the existence of transdifferentiated T cell populations, which express signature transcription factors and cytokines associated with more than one Th subset, challenges the immutability of T helper subsets and suggests that plasticity is a feature of multifaceted immune responses. How this process impacts immune dysregulation in diseases such as inflammatory bowel diseases (IBD) and the machinery that underlies this process is far from fully understood. Interleukin (IL)-17 secreting helper T (Th17) cells have been heavily implicated in tissue-specific immune pathology including murine models of IBD, human Crohn's disease and ulcerative colitis. Plasticity within this subset is suggested by the existence of IL-17 secreting cells, which, can also secrete interferon-γ, the signature cytokine for Th1 cells or, can co-express the anti-inflammatory transcription factor forkhead box p3, a signature transcription factor of regulatory T cells. In this review we mainly discuss evidence for Th17 plasticity, mechanisms, which govern it, and highlight the potential to therapeutically target this process in human IBD.

Opposing effects of smoking in ulcerative colitis and Crohn's disease may be explained by differential effects on dendritic cells.

BACKGROUND: The mechanisms underlying the differential effects of cigarette smoking in patients with Crohn's disease (CD) and ulcerative colitis (UC) remain unknown. Smoking has been demonstrated to be protective in UC, whereas in CD it has been shown to be associated with a more severe course, more frequent relapses, and postoperative recurrence. Dendritic cells (DC) play a critical role in T-cell activation and differentiation. Thus, we examined the effects of in vitro exposure to cigarette smoke extract (CSE) on phenotype/function of DC obtained from patients with UC and CD. METHODS: Sixty-eight subjects were recruited including 30 patients with CD, 19 patients with UC, and 19 healthy controls. Peripheral blood monocytes were differentiated to DC in presence of IL-4 and granulocyte-macrophage colony-stimulating factor. The influence of CSE on Mo-DC subsets, cytokine expression, and ability to drive T cell proliferation and polarization were examined. RESULTS: CSE affected DC phenotypes including increases in class-2 major histocompatibility complex and costimulatory molecules and decreases in CXCL10 and CCL3 levels in UC compared with CD samples. Furthermore, CSE also altered DC function resulting in increasing T cell proliferation and Th1 polarization in CD, whereas it increased Foxp3+ T cells and decreased the Th1 subset in UC samples. CONCLUSIONS: CSE modulates DC phenotype and function in patients with UC leading to increased prevalence of Foxp3+ CD4 T cells, whereas in patients with CD it skews toward Th1 subsets. Differential DC responses to CSE between CD and UC may contribute to the differential effects associated with cigarette smoking status.

Increased prevalence of circulating novel IL-17 secreting Foxp3 expressing CD4+ T cells and defective suppressive function of circulating Foxp3+ regulatory cells support plasticity between Th17 and regulatory T cells in inflammatory bowel disease patients.

BACKGROUND: IL-17 and Foxp3 double-expressing (DE) CD4(+) T lymphocytes are novel crossover immune cell population, but the presence and role of these cells in human intestinal inflammation is unclear. The aim of this study was to investigate the circulating IL-17 and Foxp3 DE CD4(+) T lymphocytes in patients with inflammatory bowel disease (IBD). METHODS: The entire cohort consisted of 79 subjects: 31 patients with Crohn's disease, 28 patients with ulcerative colitis, and 20 healthy control subjects (HC). IBD patients with evidence of active disease at endoscopy were entered into the study. Peripheral blood mononuclear cells were used for ex vivo and in vitro studies to assess the characteristics and generation of these novel cells and the function of circulating Foxp3 CD4(+) regulatory T lymphocytes (Treg) in patients with IBD compared with HC. RESULTS: Patients with IBD had significantly higher prevalence of IL-17 and Foxp3 DE CD4(+) T lymphocytes compared with age- and gender-matched HC. These cells expressed RORγt. The ability of Treg cells to suppress autologous T-cell proliferation was reduced by approximately 60% in patients with IBD compared with HC. Increased generation of these DE cells was demonstrated by the modulation of cytokine environment of CD4(+) lymphocytes in vitro in patients with Crohn's disease. CONCLUSIONS: Prevalence of circulating IL-17 and Foxp3 DE CD4(+) T cells is increased in patients with IBD. Coexpression of RORγt and Foxp3 in these cells implies conversion from Treg cells to Th17 cells. This is associated with a decreased suppressive function of Foxp3 CD4(+) T lymphocytes in patients with IBD.

Transient upregulation of indoleamine 2,3-dioxygenase in dendritic cells by human chorionic gonadotropin downregulates autoimmune diabetes.

OBJECTIVE: Pregnancy induces a state of immunological tolerance that aims at suppressing immune responses against the fetus and has been linked to temporal remission of preexisting autoimmune disorders. To understand the mechanisms of this reversible immune regulation, we investigated the role of a key pregnancy hormone, human chorionic gonadotropin (hCG), in immune tolerance against autoimmune type 1 diabetes in nonobese diabetic (NOD) mice. RESEARCH DESIGN AND METHODS: We injected hCG into cytokine gene-deficient NOD mice and evaluated the effects of hCG administration on T-cells and dendritic cells (DCs). RESULTS: We show that administration of hCG to NOD mice inhibits both the activation of diabetogenic CD4(+) and CD8(+) T-cells, in vitro and in vivo, and the progression of type 1 diabetes by upregulating the expression of indoleamine 2,3-dioxygenase (IDO) in DCs. IDO upregulation is transient and declined shortly after hCG withdrawal. DC depletion restores the diabetetogenic activity of splenic T-cells from hCG-treated mice, and inhibition of IDO activity by 1-methyl-tryptophan abrogates the hCG-induced T-cell suppression and resistance to type 1 diabetes. CONCLUSIONS: We propose that hCG-induced upregulation of IDO in DCs plays a major role in pregnancy-associated resistance to autoimmunity.

Efficient activation of Valpha14 invariant NKT cells by foreign lipid antigen is associated with concurrent dendritic cell-specific self recognition.

A burst release of cytokines by Valpha14 invariant NKT (iNKT) cells upon their TCR engagement critically regulates innate and adaptive immune responses. However, it remains unclear in vivo why iNKT cells respond efficiently to microbial or intracellular lipid Ags that are at low levels or that possess suboptimal antigenicity. We found that dendritic cells (DCs) potentiated iNKT cells to respond to a minimal amount of ligand alpha-galactosylceramide (alphaGalCer) through CD1d-dependent autoreactive responses that require endosomal processing and CD1d trafficking. The ability of potentiation of NKT cells was DC specific and did not depend on costimulatory signals and IL-12 production by DCs. However, DCs that failed to synthesize a major endogenous lipid Ag isoglobotrihexosylceramide were unable to potentiate NKT cells for efficient activation. Further analysis showed that differences in the level and pattern of endogenous lipid Ag presentation differentiate DCs and B cells for effective potentiation and subsequent activation of iNKT cells in the presence of an exogenous Ag. Thus, CD1d-dependent potentiation by DCs may be crucial for iNKT cell-mediated immunity against infectious agents.

Diabetes resistance/susceptibility in T cells of nonobese diabetic mice conferred by MHC and MHC-linked genes.

Polymorphism of MHC and MHC-linked genes is tightly associated with susceptibility to type 1 diabetes (T1D) in human and animal models. Despite the extensive studies, however, the role of MHC and MHC-linked genes expressed by T cells on T1D susceptibility remains unclear. Because T cells develop from TCR(-) thymic precursor (pre-T) cells that undergo MHC restriction mediated by thymic stroma cells, we reconstituted the T cell compartment of NOD.scid-RIP-B7.1 mice using pre-T cells isolated from NOD, NOR, AKR, and C57BL/6 (B6) mice. T1D developed rapidly in the mice reconstituted with pre-T cells derived from NOD or NOR donors. In contrast, most of the NOD.scid-RIP-B7.1 mice reconstituted with pre-T cells from AKR or B6 donors were free of T1D. Further analysis revealed that genes within MHC locus of AKR or B6 origin reduced incidence of T1D in the reconstituted NOD.scid-RIP-B7.1 mice. The expression of MHC class I genes of k, but not b haplotype, in T cells conferred T1D resistance. Replacement of an interval near the distal end of the D region in T cells of B6 origin with an identical allele of 129.S6 origin resulted in T1D development in the reconstituted mice. These results provide evidence that the expression of MHC class I and MHC-linked genes in T cells of NOD mice indeed contributes to T1D susceptibility, while expression of specific resistance alleles of MHC or MHC-linked genes in T cells alone would effectively reduce or even prevent T1D.