Kristina Lejon

The CD8alpha(+) dendritic cell is responsible for inducing peripheral self-tolerance to tissue-associated antigens.

We previously described a mechanism for the maintenance of peripheral self-tolerance. This involves the cross-presentation of tissue-associated antigens by a bone marrow–derived cell type that stimulates the proliferation and ultimate deletion of self-reactive CD8 T cells. This process has been referred to as cross-tolerance. Here, we characterize the elusive cell type responsible for inducing cross-tolerance as a CD8α+ dendritic cell (DC). To achieve this aim, transgenic mice were generated expressing yellow fluorescent protein (YFP) linked to CTL epitopes for ovalbumin and glycoprotein B (gB) of herpes simplex virus under the rat insulin promoter (RIP). Although tracking of YFP was inconclusive, the use of a highly sensitive gB-specific hybridoma that produced β-galactosidase on encounter with antigen, enabled detection of antigen presentation by cells isolated from the pancreatic lymph node. This showed that a CD11c+CD8α+ cell was responsible for cross-tolerance, the same DC subset as previously implicated in cross-priming. These data indicate that CD8α+ DCs play a critical role in both tolerance and immunity to cell-associated antigens, providing a potential mechanism by which cytotoxic T lymphocyte can be immunized to viral antigens while maintaining tolerance to self.

Up-regulation of cytokines and chemokines predates the onset of rheumatoid arthritis

OBJECTIVE To identify whether cytokines, cytokine-related factors, and chemokines are up-regulated prior to the development of rheumatoid arthritis (RA). METHODS A nested case-control study was performed in 86 individuals who had donated blood samples before experiencing any symptoms of disease (pre-patients) and 256 matched control subjects (1:3 ratio). In 69 of the pre-patients, blood samples were also obtained at the time of the diagnosis of RA. The plasma levels of 30 cytokines, related factors, and chemokines were measured using a multiplex system. RESULTS The levels of several of the cytokines, cytokine receptors, and chemokines were significantly increased in individuals before disease onset compared with the levels in control subjects; i.e., those representing signs of general immune activation (interleukin-1beta [IL-1beta], IL-2, IL-6, IL-1 receptor antagonist, and tumor necrosis factor), activation of Th1 cells (interferon-gamma, IL-12), Th2 cells (IL-4, eotaxin), Treg cells (IL-10), bone marrow-derived factors (IL-7, granulocyte-macrophage colony-stimulating factor, and granulocyte colony-stimulating factor), as well as chemokines (monocyte chemotactic protein 1 and macrophage inflammatory protein 1alpha). The levels were particularly increased in anti-cyclic citrullinated peptide antibody- and rheumatoid factor-positive individuals, and the concentration of most of these increased further after disease onset. The concentration of IL-17 in individuals before disease onset was significantly higher than that in patients after disease onset. Individuals in whom RA subsequently developed were discriminated from control subjects mainly by the presence of Th1 cells, Th2 cells, and Treg cell-related cytokines, while chemokines, stromal cell-derived cytokines, and angiogenic-related markers separated patients after the development of RA from individuals before the onset of RA. CONCLUSION Individuals in whom RA later developed had significantly increased levels of several cytokines, cytokine-related factors, and chemokines representing the adaptive immune system (Th1, Th2, and Treg cell-related factors); after disease onset, the involvement and activation of the immune system was more general and widespread.

CD4(+)CD25(+) T cells facilitate the induction of T cell anergy.

T cell anergy is characterized by the inability of the T cell to produce IL-2 and proliferate. It is reversible by the addition of exogenous IL-2. A similar state of unresponsiveness is observed when the proliferative response of murine CD4+CD25− T cells is suppressed in vitro by coactivated CD4+CD25+ T cells. We have developed a suppression system that uses beads coated with anti-CD3 and anti-CD28 Abs as surrogate APCs to study the interaction of CD4+CD25+ and CD4+CD25− T cells in vitro. CD4+CD25+ T cell-induced suppression, in this model, was not abrogated by blocking the B7-CTLA-4 pathway. When the CD4+CD25− T cells were separated from the CD4+CD25+ suppressor cells after 24 h of coactivation by the Ab-coated beads, the CD4+CD25− T cells were unable to proliferate or to produce IL-2 upon restimulation. The induction of this anergic phenotype in the CD4+CD25− T cells correlated with the up-regulated expression of the gene related to anergy in lymphocytes (GRAIL), a novel anergy-related gene that acts as a negative regulator of IL-2 transcription. This system constitutes a novel mechanism of anergy induction in the presence of costimulation.

EDAR mutation in autosomal dominant hypohidrotic ectodermal dysplasia in two Swedish families

BackgroundHypohidrotic ectodermal dysplasia (HED) is a genetic disorder characterized by defective development of teeth, hair, nails and eccrine sweat glands. Both autosomal dominant and autosomal recessive forms of HED have previously been linked to mutations in the ectodysplasin 1 anhidrotic receptor (EDAR) protein that plays an important role during embryogenesis.MethodsThe coding DNA sequence of the EDAR gene was analyzed in two large Swedish three-generational families with autosomal dominant HED.ResultsA non-sense C to T mutation in exon 12 was identified in both families. This disease-specific mutation changes an arginine amino acid in position 358 of the EDAR protein into a stop codon (p.Arg358X), thereby truncating the protein. In addition to the causative mutation two polymorphisms, not associated with the HED disorder, were also found in the EDAR gene.ConclusionThe finding of the p.Arg358X mutation in the Swedish families is the first corroboration of a previously described observation in an American family. Thus, our study strengthens the role of this particular mutation in the aetiology of autosomal dominant HED and confirms the importance of EDAR for the development of HED.

Establishment and Characterization of RAG-2 Deficient Non-Obese Diabetic Mice

The authors have established a new immunodeficient mouse strain on the genetic background of the diabetes prone non‐obese diabetic (NOD) mouse. A deletion mutant of the RAG‐2 gene was back crossed 10 generations onto the NOD/Bom strain background. The homozygous NODrag−2−/− mice lack functionally mature B and T lymphocytes and do not develop insulitis or diabetes throughout life. In contrast, heterozygous NODrag−2+/− develop both insulitis and diabetes with an incidence similar to the wild type NOD mice. In transfer experiments, spleen cells from diabetic NOD donors were found to transfer disease to NODrag−2−/− recipients similar to what has been previously observed in transfer to irradiated NOD recipients or to immunodeficient NOD‐scid/scid mice. While resembling the recently established NOD‐scid/scid mice in many respects, the NODrag−2−/− mice represents an advantageous model for reconstitution of the pathogenesis of murine IDDM as it does not produce any endogenous, mature T or B lymphocytes.

Altered metabolic signature in Pre-Diabetic NOD Mice

Altered metabolism proceeding seroconversion in children progressing to Type 1 diabetes has previously been demonstrated. We tested the hypothesis that non-obese diabetic (NOD) mice show a similarly altered metabolic profile compared to C57BL/6 mice. Blood samples from NOD and C57BL/6 female mice was collected at 0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 13 and 15 weeks and the metabolite content was analyzed using GC-MS. Based on the data of 89 identified metabolites OPLS-DA analysis was employed to determine the most discriminative metabolites. In silico analysis of potential involved metabolic enzymes was performed using the dbSNP data base. Already at 0 weeks NOD mice displayed a unique metabolic signature compared to C57BL/6. A shift in the metabolism was observed for both strains the first weeks of life, a pattern that stabilized after 5 weeks of age. Multivariate analysis revealed the most discriminative metabolites, which included inosine and glutamic acid. In silico analysis of the genes in the involved metabolic pathways revealed several SNPs in either regulatory or coding regions, some in previously defined insulin dependent diabetes (Idd) regions. Our result shows that NOD mice display an altered metabolic profile that is partly resembling the previously observation made in children progressing to Type 1 diabetes. The level of glutamic acid was one of the most discriminative metabolites in addition to several metabolites in the TCA cycle and nucleic acid components. The in silico analysis indicated that the genes responsible for this reside within previously defined Idd regions.

Enhanced capture of extramembranous IgM and IgG on B cells in the NOD mouse—implications for immune complex trapping

Binding of various antibody isotypes to B cells through either FcgammaRs or complement receptors has been attributed to play several roles, e.g. in immune complex (IC) transportation and regulation of B cell receptor signaling. We have revealed a novel B cell intrinsic receptor for IgM and IgG which is present in C57BL/6 (B6) mice and is more abundant in non-obese diabetic (NOD) mice. As a consequence, the level of extramembranous IgG monomers and IgM pentamers on peripheral blood B cells from NOD mice was significantly higher compared with B6 mice. The effect of this aberration was that all B cells in peripheral blood of (NOD.IgH(a) x B6(IgH(b)))F(1) mice carried both IgM allotypes on their surface. In addition, analysis of IC binding using IgG- or IgM-opsonized bacterial particles revealed a higher degree of binding in NOD mice compared with B6. We hypothesize that this novel Ig-binding receptor is part of the normal immune system function. The aberrant function in the NOD mouse could contribute to the development of Type 1 diabetes by altering normal B cell functions such as activation, IC transportation and B cell homeostasis.

Increased expression of TACI on NOD B cells results in germinal centre reaction anomalies, enhanced plasma cell differentiation and immunoglobulin production.

B cells have an important pathogenic role in the development of type 1 diabetes in the non‐obese diabetic (NOD) mouse. We have previously reported that NOD mice display an increased percentage of TACIhigh‐expressing B cells compared with C57BL/6 mice and this trait is linked to chromosomes 1 and 8. In this paper the genetic association of the transmembrane activator, calcium modulator and cyclophilin ligand interactor (TACI) trait was confirmed using double congenic NOD.B6C1/Idd22 mice. TACI ligation by a proliferation‐inducing ligand (APRIL) has been shown to influence plasma cell differentiation, immunoglobulin production and isotype switch. Hence, the functional consequence of the up‐regulation of TACI on NOD B cells was analysed both in vitro and in vivo. NOD B cells stimulated with APRIL showed an enhanced plasma cell differentiation and class switch to IgG and IgA compared with B cells from C57BL/6 mice. Moreover, flow cytometry analyses revealed that germinal centre B cells in NOD failed to down‐regulate TACI. Availability of the TACI ligand B‐cell activating factor (BAFF) has been shown to be a limiting factor in the germinal centre reaction. In line with this, upon immunization with 4‐hydroxy‐3‐nitrophenylacetyl hapten‐conjugated hen egg lysozyme, NOD mice produced higher titres of low‐affinity antibodies compared with C57BL/6 mice. This observation was supported by the detection of increased levels of BAFF in NOD germinal centres after immunization compared with C57BL/6 by immunofluorescence. Our results support the hypothesis that increased TACI expression on NOD B cells contributes to the pathogenesis of type 1 diabetes in the NOD mouse.

Diabetes induction in C57BL/6 mice reconstituted with lymphocytes of nonobese diabetic C57BL/6 mouse embryo aggregation chimeras.

To determine whether the genetic background of the insulin‐producing β cells of the pancreas contributes to autoimmune diabetes susceptibility, we have used a model of the disease based on tranferring spleen cells from nonobese diabetic (NOD) <−> C57BL/6 (B6) embryo aggregation (EA) chimeras into B6 and NOD irradiated mice. Insulitis and diabetes could be induced into both B6 and NOD hosts, albeit with low incidence. Cyclophosphamide (CY) treatment, known to accelerate diabetes in prediabetic NOD mice, was found to increase diabetes incidence up to 50–60% in both B6 and NOD mice reconstituted with chimeric splenocytes, while diabetes did not occur in CY‐treated B6 mice reconstituted with B6 splenocytes. We conclude that the genetic make‐up of the target organ does not affect the final stage of the pathogenesis of insulin‐dependent diabetes mellitus.

Elevated systemic glutamic acid level in the non-obese diabetic mouse is Idd linked and induces beta cell apoptosis.

Although type 1 diabetes (T1D) is a T‐cell‐mediated disease in the effector stage, the mechanism behind the initial beta cell assault is less understood. Metabolomic differences, including elevated levels of glutamic acid, have been observed in patients with T1D before disease onset, as well as in pre‐diabetic non‐obese diabetic (NOD) mice. Increased levels of glutamic acid damage both neurons and beta cells, implying that this could contribute to the initial events of T1D pathogenesis. We investigated the underlying genetic factors and consequences of the increased levels of glutamic acid in NOD mice. Serum glutamic acid levels from a (NOD×B6)F2 cohort (n = 182) were measured. By genome‐wide and Idd region targeted microsatellite mapping, genetic association was detected for six regions including Idd2, Idd4 and Idd22. In silico analysis of potential enzymes and transporters located in and around the mapped regions that are involved in glutamic acid metabolism consisted of alanine aminotransferase, glutamic‐oxaloacetic transaminase, aldehyde dehydrogenase 18 family, alutamyl‐prolyl‐tRNA synthetase, glutamic acid transporters GLAST and EAAC1. Increased EAAC1 protein expression was observed in lysates from livers of NOD mice compared with B6 mice. Functional consequence of the elevated glutamic acid level in NOD mice was tested by culturing NOD. Rag2−/− Langerhans’ islets with glutamic acid. Induction of apoptosis of the islets was detected upon glutamic acid challenge using TUNEL assay. Our results support the notion that a dysregulated metabolome could contribute to the initiation of T1D. We suggest that targeting of the increased glutamic acid in pre‐diabetic patients could be used as a potential therapy.