Differential IL-21 signaling in APCs leads to disparate Th17 differentiation in diabetes-susceptible NOD and diabetes-resistant NOD.Idd3 mice.

Type 1 diabetes (T1D) is an autoimmune disease that shows familial aggregation in humans and likely has genetic determinants. Disease linkage studies have revealed many susceptibility loci for T1D in mice and humans. The mouse T1D susceptibility locus insulin-dependent diabetes susceptibility 3 (Idd3), which has a homologous genetic interval in humans, encodes cytokine genes Il2 and Il21 and regulates diabetes and other autoimmune diseases; however, the cellular and molecular mechanisms of this regulation are still being elucidated. Here we show that T cells from NOD mice produce more Il21 and less Il2 and exhibit enhanced Th17 cell generation compared with T cells from NOD.Idd3 congenic mice, which carry the protective Idd3 allele from a diabetes-resistant mouse strain. Further, APCs from NOD and NOD.Idd3 mice played a central role in this differential Th17 cell development, and IL-21 signaling in APCs was pivotal to this process. Specifically, NOD-derived APCs showed increased production of pro-Th17 mediators and dysregulation of the retinoic acid (RA) signaling pathway compared with APCs from NOD.Idd3 and NOD.Il21r-deficient mice. These data suggest that the protective effect of the Idd3 locus is due, in part, to differential RA signaling in APCs and that IL-21 likely plays a role in this process. Thus, we believe APCs provide a new candidate for therapeutic intervention in autoimmune diseases

Analysis of IL2/IL21 Gene Variants in Cholestatic Liver Diseases Reveals an Association with Primary Sclerosing Cholangitis

Background/Aims: The chromosome 4q27 region harboring IL2 and IL21 is an established risk locus for ulcerative colitis (UC) and various other autoimmune diseases. Considering the strong coincidence of primary sclerosing cholangitis (PSC) with UC and the increased frequency of other autoimmune disorders in patients with primary biliary cirrhosis (PBC), we investigated whether genetic variation in the IL2/IL21 region may also modulate the susceptibility to these two rare cholestatic liver diseases. Methods: Four strongly UC-associated single nucleotide polymorphisms (SNPs) within the KIAA1109/TENR/IL2/IL21 linkage disequilibrium block were genotyped in 124 PBC and 41 PSC patients. Control allele frequencies from 1,487 healthy, unrelated Caucasians were available from a previous UC association study. Results: The minor alleles of all four markers were associated with a decreased susceptibility to PSC (rs13151961: p = 0.013, odds ratio (OR) 0.34; rs13119723: p = 0.023, OR 0.40; rs6822844: p = 0.031, OR 0.41; rs6840978: p = 0.043, OR 0.46). Moreover, a haplotype consisting of the four minor alleles also had a protective effect on PSC susceptibility (p = 0.0084, OR 0.28). A haplotype of the four major alleles was independently associated with PSC when excluding the patients with concomitant inflammatory bowel disease (p = 0.033, OR 4.18). Conclusion: The IL2/IL21 region may be one of the highly suggestive but so far rarely identified shared susceptibility loci for PSC and UC. Copyright (C) 2011 S. Karger AG, Base

Inflammation-Driven Reprogramming of CD4+Foxp3+ Regulatory T Cells into Pathogenic Th1/Th17 T Effectors Is Abrogated by mTOR Inhibition in vivo

While natural CD4+Foxp3+ regulatory T (nTREG) cells have long been viewed as a stable and distinct lineage that is committed to suppressive functions in vivo, recent evidence supporting this notion remains highly controversial. We sought to determine whether Foxp3 expression and the nTREG cell phenotype are stable in vivo and modulated by the inflammatory microenvironment. Here, we show that Foxp3+ nTREG cells from thymic or peripheral lymphoid organs reveal extensive functional plasticity in vivo. We show that nTREG cells readily lose Foxp3 expression, destabilizing their phenotype, in turn, enabling them to reprogram into Th1 and Th17 effector cells. nTREG cell reprogramming is a characteristic of the entire Foxp3+ nTREG population and the stable Foxp3NEG TREG cell phenotype is associated with a methylated foxp3 promoter. The extent of nTREG cell reprogramming is modulated by the presence of effector T cell-mediated signals, and occurs independently of variation in IL-2 production in vivo. Moreover, the gut microenvironment or parasitic infection favours the reprogramming of Foxp3+ TREG cells into effector T cells and promotes host immunity. IL-17 is predominantly produced by reprogrammed Foxp3+ nTREG cells, and precedes Foxp3 down-regulation, a process accentuated in mesenteric sites. Lastly, mTOR inhibition with the immunosuppressive drug, rapamycin, stabilizes Foxp3 expression in TREG cells and strongly inhibits IL-17 but not RORγt expression in reprogrammed Foxp3− TREG cells. Overall, inflammatory signals modulate mTOR signalling and influence the stability of the Foxp3+ nTREG cell phenotype

Cellular mechanisms of restored β-cell tolerance mediated by protective alleles of Idd3 and Idd5

Type 1 diabetes genes within the interleukin (IL)-2, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and natural resistance-associated macrophage protein (NRAMP1) pathways influence development of autoimmune diabetes in humans and NOD mice. In NOD mice, when present together, protective alleles encoding IL-2, Idd3 candidate gene, CTLA-4, NRAMP1, and acetyl-coenzyme A dehydrogenase, long-chain (ACADL) (candidate genes for the Idd5.1, Idd5.2, and Idd5.3 subregions) provide nearly complete diabetes protection. To define where the protective alleles of Idd3 and the Idd5 subregions must be present to protect from diabetes and tolerize islet-specific CD8 T cells, SCID mice were reconstituted so that the host and lymphocytes expressed various combinations of protective and susceptibility alleles at Idd3 and Idd5. Although protective Idd3 alleles in the lymphocytes and protective Idd5 alleles in the SCID host contributed most significantly to CD8 tolerance, both were required together in both lymphocyte and nonlymphocyte cells to recapitulate the potent diabetes protection observed in intact Idd3/5 mice. We conclude that genetic regions involved in autoimmune disease are not restricted in their influence to individual cell types. Even a single protective gene product, such as IL-2, must be expressed in both the lymphocytes and dendritic cells to exert its full extent of disease protection. These studies highlight the pleiotropic effects of genes that determine autoimmune disease susceptibility

Memory CD8+ T cells colocalize with IL-7+ stromal cells in bone marrow and rest in terms of proliferation and transcription

It is believed that memory CD8(+) T cells are maintained in secondary lymphoid tissues, peripheral tissues, and BM by homeostatic proliferation. Their survival has been shown to be dependent on IL-7, but it is unclear where they acquire it. Here we show that in murine BM, memory CD8(+) T cells individually colocalize with IL-7(+) reticular stromal cells. The T cells are resting in terms of global transcription and do not express markers of activation, for example, 4-1BB (CD137), IL-2, or IFN-γ, despite the expression of CD69 on about 30% of the cells. Ninety-five percent of the memory CD8(+) T cells in BM are in G(0) phase of cell cycle and do not express Ki-67. Less than 1% is in S/M/G(2) of cell cycle, according to propidium iodide staining. While previous publications have estimated the extent of proliferation of CD8(+) memory T cells on the basis of BrdU incorporation, we show here that BrdU itself induces proliferation of CD8(+) memory T cells. Taken together, the present results suggest that CD8(+) memory T cells are maintained as resting cells in the BM in dedicated niches with their survival conditional on IL-7 receptor signaling