Cell-driven Colitis Research Articles

Self antigen-driven, undifferentiated memory-phenotype CD4 T lymphocytes can induce mild and systemic inflammation by differentiating into effector and regulatory T cells

Abstract In adaptive immune responses, naïve CD4 +T lymphocytes that have T cell receptors (TCRs) reactive to challenged foreign antigens are activated to differentiate into antigen-specific effector and memory cells. We have recently reported that in steady state, peripheral naïve precursors can also recognize self antigens to spontaneously acquire a memory phenotype (MP) and that such naturally arising “MP cells” can exert innate immune function in host defense. Given the self-reactivity of MP cells, it is likely that the same T lymphocyte population also has the capacity to induce autoimmune and/or inflammatory disease. Here we show that in lymphopenic environment, self antigen-driven MP cells can evoke mild and persistent inflammation in various organs including colon, lungs, kidneys, and liver. The MP cell-driven colitis is dependent on commensal microbiota as well as cytokines IFN-γ and IL-17A while inflammation in the other organs is independent of these factors. On the other hand, we demonstrate using combined single cell RNA sequencing, TCR sequencing, and flow cytometric approaches that MP as compared to naïve CD4 +T lymphocytes more efficiently differentiate into regulatory T (Treg) cells in a TGF-β-dependent fashion, thereby partially ameliorating inflammation. We further provide evidence arguing that these Th1, Th17, and Treg cells are generated from preexisting, undifferentiated T-bet −rather than T-bet +MP subset. Altogether, our results identify self-driven T-bet −MP cells as a multi-potent CD4 +T lymphocyte population that can induce systemic and mild inflammation by differentiating into Th1 and Th17 effector as well as Treg cells. This work was supported by the Japan Society for the Promotion of Science, Astellas Foundation for Research on Metabolic Disorders, Bristol-Myers Squibb, Cell Science Research Foundation, Chemo-Sero-Therapeutic Research Institute, Daiichi Sankyo Foundation of Life Science, GlaxoSmithKline, Gonryo Foundation for the Promotion of Medical Science, G-7 Scholarship Foundation, Harmonic Ito Foundation, Ichiro Kanehara Foundation for the Promotion of Medical Sciences and Medical Care, Inamori Foundation, Intelligent Cosmos Foundation, Japan Allergy Foundation, Japan Intractable Diseases Research Foundation, Kanae Foundation for the Promotion of Medical Science, Kobayashi Foundation, Life Science Foundation of Japan, Mitsubishi Foundation, Mochida Memorial Foundation for Medical and Pharmaceutical Research, MSD Life Science Foundation, Nakajima Foundation, Nakayama Foundation for Human Science, Ohyama Health Foundation, Okinaka Memorial Institute for Medical Research, Pharmacodynamics Research Foundation, Senri Life Science Foundation, Senshin Medical Research Foundation, Sumitomo Foundation, Takeda Science Foundation, Ube Industries Foundation, Uehara Memorial Foundation, and Waksman Foundation of Japan. Akihisa Kawajiri was supported by the PhD Scholarship (Kibou Project) from Japanese Society for Immunology.

Intestinal epithelial HDAC3 and MHC class II coordinate microbiota-specific immunity.

Aberrant immune responses to resident microbes promote inflammatory bowel disease and other chronic inflammatory conditions. However, how microbiota-specific immunity is controlled in mucosal tissues remains poorly understood. Here, we found that mice lacking epithelial expression of microbiota-sensitive histone deacetylase 3 (HDAC3) exhibited increased accumulation of commensal-specific CD4+ T cells in the intestine, provoking the hypothesis that epithelial HDAC3 may instruct local microbiota-specific immunity. Consistent with this, microbiota-specific CD4+ T cells and epithelial HDAC3 expression were concurrently induced following early-life microbiota colonization. Further, epithelium-intrinsic ablation of HDAC3 decreased commensal-specific Tregs, increased commensal-specific Th17 cells, and promoted T cell-driven colitis. Mechanistically, HDAC3 was essential for NF-κB-dependent regulation of epithelial MHC class II (MHCII). Epithelium-intrinsic MHCII dampened local accumulation of commensal-specific Th17 cells in adult mice and protected against microbiota-triggered inflammation. Remarkably, HDAC3 enabled the microbiota to induce MHCII expression on epithelial cells and limit the number of commensal-specific T cells in the intestine. Collectively, these data reveal a central role for an epithelial histone deacetylase in directing the dynamic balance of tissue-intrinsic CD4+ T cell subsets that recognize commensal microbes and control inflammation.

PH sensing controls tissue inflammation by modulating cellular metabolism and endo-lysosomal function of immune cells.

Extracellular acidification occurs in inflamed tissue and the tumor microenvironment; however, a systematic study on how pH sensing contributes to tissue homeostasis is lacking. In the present study, we examine cell type-specific roles of the pH sensor G protein-coupled receptor 65 (GPR65) and its inflammatory disease-associated Ile231Leu-coding variant in inflammation control. GPR65 Ile231Leu knock-in mice are highly susceptible to both bacterial infection-induced and T cell-driven colitis. Mechanistically, GPR65 Ile231Leu elicits a cytokine imbalance through impaired helper type 17 T cell (TH17 cell) and TH22 cell differentiation and interleukin (IL)-22 production in association with altered cellular metabolism controlled through the cAMP-CREB-DGAT1 axis. In dendritic cells, GPR65 Ile231Leu elevates IL-12 and IL-23 release at acidic pH and alters endo-lysosomal fusion and degradation capacity, resulting in enhanced antigen presentation. The present study highlights GPR65 Ile231Leu as a multistep risk factor in intestinal inflammation and illuminates a mechanism by which pH sensing controls inflammatory circuits and tissue homeostasis.

Th17 Cell-Mediated Colitis Is Positively Regulated by Interferon Regulatory Factor 4 in a T Cell-Extrinsic Manner.

Inflammatory bowel diseases (IBDs) are characterized by chronic, inflammatory gastrointestinal lesions and often require life-long treatment with immunosuppressants and repetitive surgical interventions. Despite progress in respect to the characterization of molecular mechanisms e.g. exerted by TNF-alpha, currently clinically approved therapeutics fail to provide long-term disease control for most patients. The transcription factor interferon regulatory factor 4 (IRF4) has been shown to play important developmental as well as functional roles within multiple immune cells. In the context of colitis, a T cell-intrinsic role of IRF4 in driving immune-mediated gut pathology is established. Here, we conversely addressed the impact of IRF4 inactivation in non-T cells on T cell driven colitis in vivo. Employing the CD4+CD25− naïve T cell transfer model, we found that T cells fail to elicit colitis in IRF4-deficient compared to IRF4-proficient Rag1 −/− mice. Reduced colitis activity in the absence of IRF4 was accompanied by hampered T cell expansion both within the mesenteric lymph node (MLN) and colonic lamina propria (cLP). Furthermore, the influx of various myeloids, presumably inflammation-promoting cells was abrogated overall leading to a less disrupted intestinal barrier. Mechanistically, gene profiling experiments revealed a Th17 response dominated molecular expression signature in colon tissues of IRF4-proficient, colitic Rag1 −/− but not in colitis-protected Rag1 −/− Irf4 −/− mice. Colitis mitigation in Rag1 −/− Irf4 −/− T cell recipients resulted in reduced frequencies and absolute numbers of IL-17a-producing T cell subsets in MLN and cLP possibly due to a regulation of conventional dendritic cell subset 2 (cDC2) known to impact Th17 differentiation. Together, extending the T cell-intrinsic role for IRF4 in the context of Th17 cell driven colitis, the provided data demonstrate a Th17-inducing and thereby colitis-promoting role of IRF4 through a T cell-extrinsic mechanism highlighting IRF4 as a putative molecular master switch among transcriptional regulators driving immune-mediated intestinal inflammation through both T cell-intrinsic and T cell-extrinsic mechanisms. Future studies need to further dissect IRF4 controlled pathways within distinct IRF4-expressing myeloid cell types, especially cDC2s, to elucidate the precise mechanisms accounting for hampered Th17 formation and, according to our data, the predominant mechanism of colitis protection in Rag1 −/− Irf4 −/− T cell receiving mice.

CD4+ T cell activation and concomitant mTOR metabolic inhibition can ablate microbiota-specific memory cells and prevent colitis.

Microbiota-reactive CD4+ T memory (TM) cells are generated during intestinal infections and inflammation, and can revert to pathogenic CD4+ T effector (TE) cells, resulting in chronicity of inflammatory bowel disease (IBD). Unlike TE cells, TM cells have a low rate of metabolism unless they are activated by reencountering cognate antigen. Here, we show that the combination of cell activation and metabolic checkpoint inhibition (CAMCI), by targeting key metabolic regulators mTORC and AMPK, resulted in cell death and anergy, but enhanced the induction of the regulatory subset. Parenteral application of this treatment with a synthetic peptide containing multiple flagellin T cell epitopes (MEP1) and metabolic inhibition successfully prevented the development of CD4+ T cell-driven colitis. Microbiota-specific CD4+ T cells, especially the pathogenic TE subsets, were decreased 10-fold in the intestinal lamina propria. Furthermore, using the CAMCI strategy, we were able to prevent antigen-specific TM cell formation upon initial antigen encounter, and ablate existing TM cells upon reactivation in mice, leading to an altered transcriptome in the remaining CD4+ T cells after ablation. Microbiota flagellin-specific CD4+ T cells from patients with Crohn's disease were ablated in a similar manner after CAMCI in vitro, with half of the antigen-specific T cells undergoing cell death. These results indicate that parenteral activation of microbiota-specific CD4+ T cells with concomitant metabolic inhibition is an effective way to ablate pathogenic CD4+ TM cells and to induce T regulatory (Treg) cells that provide antigen-specific and bystander suppression, supporting a potential immunotherapy to prevent or ameliorate IBD.

Deletion of IRF4 in Dendritic Cells Leads to Delayed Onset of T Cell-Dependent Colitis.

Classical dendritic cells (cDC) can be classified into two major subsets: Irf8-dependent cDC1 and Irf4-expressing cDC2. Although these subsets play distinct roles in intestinal immune homeostasis, their functions in T cell-driven colitis remain unknown. To assess the role of IRF4 expression in cDC2 in T cell-driven colitis, CD11c-Cre.Irf4 fl/fl and Irf4 fl/fl mice were backcrossed onto a Rag-1 -/- background and used as recipients of CD45RBhiCD4+ T cells. Colitis score and innate immune cell influx were reduced in Cre+ mice 4 wk posttransfer, and these changes were associated with reduced CD4+ T cell counts in both the mesenteric lymph nodes and colon. By 7 wk, colitis score and colon CD4+ T cell numbers were similar in Cre+ and Cre- mice despite a selective reduction in Th17 cells in the colon of Cre+ mice and a continued reduction in CD4+ T cell numbers in mesenteric lymph nodes. Cotransfer of CD25+CD45RBlo CD4+ T cells prevented CD45RBhiCD4+ T cell-driven colitis in both Cre+ and Cre- recipients, demonstrating that IRF4 expression by cDC is not required for CD4+ regulatory T cell-mediated control of colitis. Collectively these results suggest a role for IRF4 expression in cDC2 in the generation of colitogenic CD4+ T cells, which becomes redundant as colitis progresses.

Acetylcholine-producing T cells augment innate immune-driven colitis but are redundant in T cell-driven colitis.

Clinical trials suggest that vagus nerve stimulation presents an alternative approach to classical immune suppression in Crohn's disease. T cells capable of producing acetylcholine (ChAT+ T cells) in the spleen are essential mediators of the anti-inflammatory effect of vagus nerve stimulation. Besides the spleen, ChAT+ T cells are found abundantly in Peyer's patches of the small intestine. However, the role of ChAT+ T cells in colitis pathogenesis is unknown. Here, we made use of CD4creChATfl/fl mice (CD4ChAT-/- mice) lacking ChAT expression specifically in CD4+ T cells. Littermates (ChATfl/fl mice) served as controls. In acute dextran sulfate sodium (DSS)-induced colitis (7 days of 2% DSS in drinking water), CD4ChAT-/- mice showed attenuated colitis and lower intestinal inflammatory cytokine levels compared with ChATfl/fl mice. In contrast, in a resolution model of DSS-induced colitis (5 days of 2% DSS followed by 7 days without DSS), CD4ChAT-/- mice demonstrated a worsened colitis recovery and augmented colonic histological inflammation scores and inflammatory cytokine levels as compared with ChATfl/fl mice. In a transfer colitis model using CD4+CD45RBhigh T cells, T cells from CD4ChAT-/- mice induced a similar level of colitis compared with ChATfl/fl T cells. Together, our results indicate that ChAT+ T cells aggravate the acute innate immune response upon mucosal barrier disruption in an acute DSS-induced colitis model, whereas they are supporting the later resolution process of this innate immune-driven colitis. Surprisingly, ChAT expression in T cells seems redundant in the context of T cell-driven colitis.NEW & NOTEWORTHY By using different mouse models of experimental colitis, we provide evidence that in dextran sulfate sodium-induced colitis, ChAT+ T cells capable of producing acetylcholine worsen the acute immune response, whereas they support the later healing phase of this innate immune-driven colitis.

LAG3+ Regulatory T Cells Restrain Interleukin-23-Producing CX3CR1+ Gut-Resident Macrophages during Group 3 Innate Lymphoid Cell-Driven Colitis

Interleukin-22 (IL-22)-producing group 3 innate lymphoid cells (ILC3) maintains gut homeostasis but can also promote inflammatory bowel disease (IBD). The regulation of ILC3-dependent colitis remains to be elucidated. Here we show that Foxp3+ regulatory Tcells (Treg cells) prevented ILC3-mediatedcolitis in an IL-10-independent manner. Treg cells inhibited IL-23 and IL-1β production fromintestinal-resident CX3CR1+ macrophages but notCD103+ dendritic cells. Moreover, Treg cells restrained ILC3 production of IL-22 through suppression of CX3CR1+ macrophage production of IL-23 and IL-1β. This suppression was contact dependent and was mediated by latent activation gene-3 (LAG-3)-an immune checkpoint receptor-expressed on Treg cells. Engagement of LAG-3 on MHC class II drove profound immunosuppression of CX3CR1+ tissue-resident macrophages. Our study reveals that the health of the intestinal mucosa is maintained by an axis driven by Treg cells communication with resident macrophages that withhold inflammatory stimuli required for ILC3 function.

Evaluating IL-21 as a Potential Therapeutic Target in Crohn's Disease.

Background and Aim Interleukin-21 (IL-21) is primarily a T cell-derived cytokine; it is upregulated in patients with Crohn's Disease (CD) and could be a potential new therapeutic target in CD. Methods In human material, IL-21 and IL-21R expression was investigated by in situ hybridization (ISH) and immunohistochemistry (IHC) in noninflammatory bowel disease (non-IBD) controls and patients with CD. The pathologic role of IL-21 was examined in murine models of T cell-dependent and T cell-independent colitis, either with a neutralizing monoclonal antibody against IL-21 or with the transfer of CD4+CD45RBhighIL-21R−/− T cells. Colonic pathology was examined by endoscopy, histopathology, IHC, ELISA, and Luminex. Results In the human intestine, IL-21 and IL-21R mRNA and protein-expressing cells were observed in the mucosa, in lymphoid aggregates of submucosa in non-IBD controls, and in lymphoid aggregates of muscularis externa in patients with CD. IL-21 expression was most abundant in germinal centers (GCs) of the lymphoid aggregates, and IL-21R expression assessed semiquantitatively, was significantly higher in patients with CD compared to non-IBD controls. Following prophylactic and interventive anti-IL-21 mAb treatment in the adoptive transfer (AdTr) model, clinical and pathological parameters were significantly reduced. The most persistent finding was a reduction in colonic infiltrating neutrophils. As well, Rag2−/− mice receiving CD4+CD45RBhighIL-21R−/− T cells developed less severe colitis compared to Rag2−/− mice receiving CD4+CD45RBhighIL-21R+/+ T cells. No effect of reduced IL-21 signalling was observed in T cell-independent colitis. Conclusion Our study shows that patients with CD have significant expression of IL-21 and IL-21R in the gut. As well, we show that neutralization of IL-21 in experimental T cell-driven colitis is associated with a reduction in clinical and pathological findings. This amelioration seems to be associated with a reduction in colon-infiltrating neutrophils.

IL-15 regulates IL-23 production and murine IBD-like disease

Abstract Group 3 innate lymphoid cells (ILC3) have been recently implicated in various autoimmune conditions including inflammatory bowel diseases (IBD). The mechanisms by which ILC3s contibute to IBD pathogenesis remain elusive. In this study, using genetic deleletions that impact ILC3s to varying degrees we sought to determine their contribution to murine IBD development. We show that IL-23-dependent T cell-induced colitis develops independently of ILC3s. Host IL-2 receptor common γ chain (IL-2Rγc) is needed for both innate and adaptive cell-driven colitis, since its deficiency impairs colitogenic T cell proliferation, expansion and recruitment to intestines. We also provide evidence that resistance to colitis in IL-2Rγc Rag2−/− mice may occur as a result of defective IL-15R signaling, and that IL–15−/− Rag1−/− mice recapitulates the murine IBD phenotype of IL-2Rγc Rag2−/− mice. Data we presented herein demonstrates that IL-15 plays an important role in IBD pathogenesis and may contribute to gut inflammation by regulating IL-23 production of antigen presenting cells.

The common mouse protozoaTritrichomonas murisalters mucosal T cell homeostasis and colitis susceptibility

The mammalian gastrointestinal tract hosts a diverse community of microbes including bacteria, fungi, protozoa, helminths, and viruses. Through coevolution, mammals and these microbes have developed a symbiosis that is sustained through the host's continuous sensing of microbial factors and the generation of a tolerant or pro-inflammatory response. While analyzing T cell-driven colitis in nonlittermate mouse strains, we serendipitously identified that a nongenetic transmissible factor dramatically increased disease susceptibility. We identified the protozoan Tritrichomonas muris as the disease-exacerbating element. Furthermore, experimental colonization with T. muris induced an elevated Th1 response in the cecum of naive wild-type mice and accelerated colitis in Rag1-/- mice after T cell transfer. Overall, we describe a novel cross-kingdom interaction within the murine gut that alters immune cell homeostasis and disease susceptibility. This example of unpredicted microbial priming of the immune response highlights the importance of studying trans-kingdom interactions and serves as a stark reminder of the importance of using littermate controls in all mouse research.

Foxp3+ regulatory T cells restrain pathogenic RORγt+ group 3 ILC-mediated colitis (MUC8P.728)

Abstract IL-10 receptor beta (IL-10Rb) is a common receptor chain for both IL-10 and IL-22. Since IL-10 is a protective cytokine that restrains inflammatory responses and IL-22 signaling is required for epithelial cell-dependent tissue repair, targeted deletion of Il10rb should greatly exacerbate inflammatory bowel disease (IBD). Unexpectedly, we found that Il10rb-/- mice are completely resistant to development of spontaneous colitis. In contrast, Il10-/- mice develop IBD by 12 weeks of age and harbor a large number of IL-22-producing RORgt+ innate lymphoid cells (ILCs). Using a CD45RBhi T cell transfer model, we found that induction of intestinal inflammation requires the presence of gut resident RORgt+ ILCs. The IL-22-producing ILCs are essential to perpetuate the disease process initiated by the T cells. Furthermore, Foxp3+ Tregs directly inhibit ILC expression of IL-23R and other tissue injury sensors, thereby suppressing innate cell-driven colitis. Our study has uncovered a novel immune network that maintains intestinal homeostasis.

CD47 fusion protein targets CD172a+ cells in Crohn’s disease and dampens the production of IL-1β and TNF

In mice, the transfer of CD172a(+) (SIRP-α) dendritic cells (DCs) elicits T cell-driven colitis, whereas treatment with CD47-Fc protein, a CD172a-binding agent, confers protection. The aim of this study was to elucidate the nature and functional properties of human CD172a(+) DCs in chronic intestinal inflammation. Here, we show that CD172a(+)CD11c(+) cells accumulate in the mesenteric lymph nodes (mLNs) and inflamed intestinal mucosa in patients with Crohn's disease (CD). These cells are distinct from resident DCs and may coexpress markers typically associated with monocyte-derived inflammatory DCs such as CD14 and/or DC-SIGN, E-Cadherin, and/or CX3CR1. Spontaneous IL-1β and TNF production by HLA-DR(+) cells in CD tissues is restricted to those expressing CD172a. An avidity-improved CD47 fusion protein (CD47-Var1) suppresses the release of a wide array of inflammatory cytokines by CD172a(+) cells, which may include HLA-DR(-)CD172a(+) neutrophils, in inflamed colonic explant cultures and impairs the ability of HLA-DR(+)CD172a(+) cells to activate memory Th17 but not Th1 responses in mLNs. In conclusion, targeting CD172a(+) cells may represent novel therapeutic perspectives for patients with CD.

PPARγ activation drives Th17 cells into a Treg phenotype (163.7)

Abstract Th17 cells mediate inflammatory and effector responses during infectious and immune-mediated diseases. However, the mechanisms of action modulating the plasticity between Th17 and Treg are incompletely understood. To gain a better understanding of the differentiation process we have constructed a computational and mathematical model in COPASI that mimics CD4+ T cell differentiation and contemplates the plasticity between effector Th17 and Treg. Our computer simulations predicted that activation of peroxisome proliferator activated receptor gamma (PPARγ) induces a switch from already differentiated Th17 into Treg. Conducted experimental validation approaches support in silico experimentation. Naive CD4+ T cells obtained from spleens of T cell-specific PPARγ null, RORcGFP+/+ or wild-type donor mice, all in a C57BL6 background, were transferred to SCID and RAG2-/- recipients to induce CD4+ T cell-driven colitis. Our data demonstrate a significant decrease in the expression of FOXP3 and increase of IL-17A and RORγt in recipients of PPARγ null naïve CD4+ T cells when compared to recipients of naïve CD4+ T cells from wild-type mice. Furthermore, administration of PPARγ agonists to recipient mice with colitis decreased the percentages of GFP+ Th17 cells at the gut mucosa. In conclusion, PPARγ promotes differentiation of naïve CD4+ T cells into Treg, downregulates Th17 differentiation and favors phenotype switch from Th17 into Treg CD4+ T cells.

Aged regulatory T cells protect from autoimmune inflammation despite reduced STAT3 activation and decreased constraint of IL‐17 producing T cells

Regulatory T cells (Tregs) are specialized CD4(+) T lymphocytes helping defend against autoimmunity and inflammation. Although age is associated with increased inflammation and autoimmunity, few reports address age effects of immune regulation or auto-aggressive T cells. We show here that young and aged naïve CD4(+) T cells are equivalently auto-aggressive in vivo in T cell-driven autoimmune colitis. Young and aged CD4(+) Tregs equally suppressed age-matched T cell proliferation in vitro and controlled clinical and pathologic T cell-driven autoimmune colitis, suggesting equivalent regulatory function. However, whereas young and aged CD4(+) Tregs suppressed interferon (IFN)-γ(+) T cells equivalently in this model, aged CD4(+) Tregs unexpectedly failed to restrain interleukin (IL)-17(+) T cells. Nonetheless, young and aged CD4(+) Tregs equally restrained IL-17(+) T cells in vivo during acute inflammation, suggesting a chronic inflammation-related defect in aged CD4(+) Tregs. In support, aged Tregs expressed reduced STAT3 activation, a defect associated with poor IL-17-producing T cell restraint. Aged naïve mice had markedly increased programmed death (PD)-1(+) T cells, but these exhibited no significant auto-aggressive or regulatory functions in T cell-driven colitis. Young CD8(+) CD122(-) T cells induce autoimmune bone marrow failure, but we show that aged CD8(+) CD122(-) T cells do not. These data demonstrate no apparent age-related increase in auto-aggressive T cell behavior, but disclose previously unrecognized functional defects in aged CD4(+) Tregs during chronic inflammation. IL-17 can be inflammatory and contributes to certain autoimmune disorders. Reduced aged Treg function during chronic inflammation and reduced IL-17 restraint could contribute to age-related inflammation or autoimmunity.

Defective cell death signalling along the Bcl-2 regulated apoptosis pathway compromises Treg cell development and limits their functionality in mice

The Bcl-2 regulated apoptosis pathway is critical for the elimination of autoreactive lymphocytes, thereby precluding autoimmunity. T cells escaping this process can be kept in check by regulatory T (Treg) cells expressing the transcription and lineage commitment factor Foxp3. Despite the well-established role of Bcl-2 family proteins in shaping the immune system and their frequent deregulation in autoimmune pathologies, it is poorly understood how these proteins affect Treg cell development and function. Here we compared the relative expression of a panel of 40 apoptosis-associated genes in Treg vs. conventional CD4+ T cells. Physiological significance of key-changes was validated using gene-modified mice lacking or overexpressing pro- or anti-apoptotic Bcl-2 family members. We define a key role for the Bim/Bcl-2 axis in Treg cell development, homeostasis and function but exclude a role for apoptosis induction in responder T cells as relevant suppression mechanism. Notably, only lack of the pro-apoptotic BH3-only protein Bim or Bcl-2 overexpression led to accumulation of Treg cells while loss of pro-apoptotic Bad, Bmf, Puma or Noxa had no effect. Remarkably, apoptosis resistant Treg cells showed reduced suppressive capacity in a model of T cell-driven colitis, posing a caveat for the use of such long-lived cells in possible therapeutic settings.

A modified ERG technique and the results obtained in X-linked retinitis pigmentosa.

An electroretinographic (ERG) technique is described in which the relationship between scotopic b wave amplitude and stimulus light intensity is determined. The relative amplitude of scotopic to photopic responses is assessed by means of red light and flicker. The method is applied to the detection of ERG abnormalities in heterozygotes for X-linked retinitis pigmentosa. These have been found in only a proportion of cases. The ERG results can be used to suggest the nature of the retinal abnormality.