The protein cytotoxic T lymphocyte antigen-4 (CTLA-4) is an essential negative regulator of immune responses and its loss causes fatal autoimmunity in mice. We investigated a large autosomal-dominant family with five individuals presenting with a complex immune dysregulation syndrome characterized by hypogammaglobulinemia, recurrent infections and multiple autoimmune features. We identified a heterozygous nonsense mutation in exon 1 of CTLA4. Screening of 71 unrelated patients with comparable clinical phenotypes identified five additional families (nine individuals) with novel splice site and missense mutations in CTLA4. While clinical penetrance was incomplete (eight adults of a total of 19 CTLA4 mutation carriers were considered unaffected), CTLA-4 protein expression was decreased in regulatory T cells (Treg cells) in patients and carriers with CTLA4 mutations. Whilst Treg cells were generally present at elevated numbers, their suppressive function, CTLA-4 ligand binding and transendocytosis of CD80 were impaired. Mutations in CTLA4 were also associated with decreased circulating B cell numbers and antibody levels. Taken together, mutations in CTLA-4 resulting in CTLA-4 haploinsufficiency or impaired ligand binding results in a complex syndrome with features of both autoimmunity and immunodeficiency.

by negative magnetic separation (EasySep Human Naive CD4 + T cell Enrichment Kit, Stem Cell Technologies). Cells were plated at a density of 100,000 per well in a 96-well round bottom plate and stimulated with anti-CD3/28 beads (Human T-Activator Dynabeads, Life Technologies) for 5 days. Where indicated, cultures were treated with 10 ng/ml IL-12 and/or 20 ng/ml IL-2 (both from Peprotech). Statistics. Data were analyzed using Prism statistical software. Statistical significance was assessed using the Mann-Whitney test. Paired data were analyzed using a 2-tailed paired Student's t test. A P value of less than 0.05 was considered significant.

Together our data suggest that H. pylori induces a regulatory T cell response, possibly contributing to its peaceful coexistence with the human host, and that ulcers occur when this regulatory response is inadequate.

Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) is an essential regulator of T-cell responses, and its absence precipitates lethal T-cell hyperactivity. However, whether CTLA-4 acts simply to veto the activation of certain clones or plays a more nuanced role in shaping the quality of T-cell responses is not clear. Here we report that T cells in CTLA-4-deficient mice show spontaneous Tfollicular helper (T FH ) differentiation in vivo, and this is accompanied by the appearance of large germinal centers (GCs). Remarkably, short-term blockade with anti-CTLA-4 antibody in wild-type mice is sufficient to elicit T FH generation and GC development. The latter occurs in a CD28-dependent manner, consistent with the known role of CTLA-4 in regulating the CD28 pathway. CTLA-4 can act by down-regulating CD80 and CD86 on antigen presenting cells (APCs), thereby altering the level of CD28 engagement. To mimic reduced CD28 ligation, we used mice heterozygous for CD28, revealing that the magnitude of CD28 engagement is tightly linked to the propensity for T FH differentiation. In contrast, other parameters of T-cell activation, including CD62L down-regulation and Ki67 expression, were relatively insensitive to altered CD28 level. Altered T FH generation as a result of graded reduction in CD28 was associated with decreased numbers of GC B cells and a reduction in overall GC size. These data support a model in which CTLA-4 control of immunity goes beyond vetoing T-cell priming and encompasses the regulation of T FH differentiation by graded control of CD28 engagement.ontrol of the magnitude and nature of adaptive immune responses is critical for health. The cytotoxic T-lymphocyteassociated antigen-4 (CTLA-4)/CD28 axis has long been known to control the magnitude of T-cell responses, however whether it also influences their nature has not been clear. Early studies suggested that CD28 may be particularly important for Th2 differentiation (1, 2), although others identified roles for CD28 in both Th1 and Th2 responses (3, 4). It is known that CD28 is an absolute requirement for the differentiation of follicular helper T cells (T FH s) that support germinal center (GC) formation (5, 6). However, these studies generally make use of CD28-deficient T cells, and therefore, results may reflect a failure of the cells to properly activate, proliferate, or survive, particularly given the known contribution of CD28 to these processes.A key outstanding question is whether CD28 costimulation in vivo is more complex than a binary checkpoint for T-cell priming. It is clear that expression of costimulatory ligands on antigen presenting cells (APCs) fluctuates in response to environmental stimuli, being up-regulated by inflammatory cytokines and TLR agonists and down-regulated by Treg-expressed CTLA-4 (7-11). Thus, variable levels of costimulatory ligands will be available for CD28 binding depending on the microenvironmental context. However, whether this simply alters the number of T cells that achieve the required threshold to commit to a resp...

To protect the organism against autoimmunity, self-reactive effector/memory T cells (T E/M ) are controlled by cell-intrinsic and -extrinsic regulatory mechanisms. However, how some T E/M cells escape regulation and cause autoimmune disease is currently not understood. Here we show that blocking IL-7 receptor-α (IL-7Rα) with monoclonal antibodies in nonobese diabetic (NOD) mice prevented autoimmune diabetes and, importantly, reversed disease in new-onset diabetic mice. Surprisingly, IL-7-deprived diabetogenic T E/M cells remained present in the treated animals but showed increased expression of the inhibitory receptor Programmed Death 1 (PD-1) and reduced IFN-γ production. Conversely, IL-7 suppressed PD-1 expression on activated T cells in vitro. Adoptive transfer experiments revealed that T E/M cells from anti-IL-7Rα-treated mice had lost their pathogenic potential, indicating that absence of IL-7 signals induces cell-intrinsic tolerance. In addition to this mechanism, IL-7Rα blockade altered the balance of regulatory T cells and T E/M cells, hence promoting cell-extrinsic regulation and further increasing the threshold for diabetogenic T-cell activation. Our data demonstrate that IL-7 contributes to the pathogenesis of autoimmune diabetes by enabling T E/M cells to remain in a functionally competent state and suggest IL-7Rα blockade as a therapy for established T-cell-dependent autoimmune diseases.type 1 diabetes | cytokines | immune regulation

Background: CTLA-4 is an essential regulator of T cell immune responses with unusual intracellular trafficking.Results: Endocytosis of CTLA-4 is continuous with subsequent recycling and degradation.Conclusion: Clathrin-mediated endocytosis of CTLA-4 persists in activated T cells.Significance: This alters our understanding of CTLA-4 behavior and, therefore, how it might function.

IntroductionAlthough regulation is essential for homeostatic control of the immune system, it also presents a barrier to effective tumor surveillance. Professional immune regulation is orchestrated by T cells expressing the transcription factor Foxp3, which fixes a genetic program that imparts suppressive function. The majority of Foxp3-expressing regulatory T cells appear to arise in the thymus and represent, in the main, a remarkably stable population committed to providing life-long immune regulation. 1 Regulatory T cells (Tregs) can call on a wide range of different mechanisms to exert suppressive activity, including pathways involving IL-10, TGF-␤, and CTLA4.In recent years, it has become apparent that the ability of Tregs to elicit effective suppression can be modified, not just by the ratio of suppressors to target cells, but also by the local cytokine environment. Multiple cytokines have reported to interfere with Treg suppression, including 2,3 TNF,3,[4][5][6][7]4,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]7 This raises the possibility that the way in which T cells differentiate may dictate the extent to which a given T-cell response may be regulated. Consistent with this notion, it has been shown that human Th17 clones are significantly less susceptible to Treg suppression than those exhibiting a Th1 or Th2 phenotype. 8 Understanding the rules that govern professional immune regulation has important implications for our ability to alter the magnitude of immune responses therapeutically, for example, to augment antitumor immunity or diminish autoimmunity. In this study, we have focused on the cytokine IL-21, which we and others have previously shown can counteract Treg suppression in vitro and in vivo. 6,7 We have explored the mechanism underlying the capacity of IL-21 to alter Treg suppression and have pinpointed which cell population needs to receive IL-21 signals to permit this effect. We find that IL-21 signaling to Tregs does not impair their suppressive capacity, but instead IL-21 signaling to conventional T cells is responsible for the abrogation of suppression. Our work reveals a novel feedback loop by which IL-21 impacts on Treg homeostasis by down-regulating IL-2 production from conventional T cells. Thus, in addition to inhibiting de novo Treg differentiation, an affect that has been well documented for IL-21, 9-11 this cytokine also negatively regulates the homeostasis of natural Tregs. Methods Mice DO11.10 TCR transgenic and BALB/c mice were purchased from The Jackson Laboratory. IL-21R Ϫ/Ϫ mice were provided by M.K. Rat insulin promoter (RIP)-mOVA mice on a BALB/c background expressing a membrane-bound form of OVA under the control of the RIP (from line 296-1B) were a gift from W. Heath (Walter and Eliza Hall Institute, Melbourne, Australia). DO11.10 mice and RIP-mOVA were crossed as previously described. 12 Mice were housed at the University of Birmingham Biomedical Services Unit and used according to Home Office and institutional guidelines under Home Office Project L...

The CTLA-4 pathway is a key regulator of T cell activation and a critical failsafe against autoimmunity. While early models postulated that CTLA-4 transduced a negative signal, in vivo evidence suggests that CTLA-4 functions in a cell-extrinsic manner. That multiple cell-intrinsic mechanisms have been attributed to CTLA-4, yet its function in vivo appears to be cell-extrinisic, has been an ongoing paradox in the field. Whilst CTLA-4 expressed on conventional T cells (Tconv) can mediate inhibitory function, it is unclear why this fails to manifest as an intrinsic effect. Here we show that Tconv-expressed CTLA-4 can function in a cell-extrinsic manner in vivo. CTLA-4+/+ T cells, from DO11/rag−/− mice that lack Treg, were able to regulate the response of CTLA4−/− T cells in co-transfer experiments. This observation provides a potential resolution to the above paradox, and suggests CTLA-4 function on both Tconv and Treg can be achieved through cell-extrinsic mechanisms.