Genetic control of T and B lymphocyte activation in nonobese diabetic mice

Deletion of Vβ3+CD4+ T cells by endogenous mouse mammary tumor virus 3 prevents type 1 diabetes induction by autoreactive CD8+ T cells

In both humans and NOD mice, type 1 diabetes (T1D) develops from the autoimmune destruction of pancreatic beta cells by T cells. Interactions between both helper CD4+ and cytotoxic CD8+ T cells are essential for T1D development in NOD mice. Previous work has indicated that pathogenic T cells arise from deleterious interactions between relatively common genes which regulate aspects of T cell activation/effector function (Ctla4, Tnfrsf9, Il2/Il21), peptide presentation (H2-A g7, B2m), and T cell receptor (TCR) signaling (Ptpn22). Here, we used a combination of subcongenic mapping and a CRISPR/Cas9 screen to identify the NOD-encoded mammary tumor virus (Mtv)3 provirus as a genetic element affecting CD4+/CD8+ T cell interactions through an additional mechanism, altering the TCR repertoire. Mtv3 encodes a superantigen (SAg) that deletes the majority of Vβ3+ thymocytes in NOD mice. Ablating Mtv3 and restoring Vβ3+ T cells has no effect on spontaneous T1D development in NOD mice. However, transferring Mtv3 to C57BL/6 (B6) mice congenic for the NOD H2 g7 MHC haplotype (B6.H2 g7) completely blocks their normal susceptibility to T1D mediated by transferred CD8+ T cells transgenically expressing AI4 or NY8.3 TCRs. The entire genetic effect is manifested by Vβ3+CD4+ T cells, which unless deleted by Mtv3, accumulate in insulitic lesions triggering in B6 background mice the pathogenic activation of diabetogenic CD8+ T cells. Our findings provide evidence that endogenous Mtv SAgs can influence autoimmune responses. Furthermore, since most common mouse strains have gaps in their TCR Vβ repertoire due to Mtvs, it raises questions about the role of Mtvs in other mouse models designed to reflect human immune disorders.

Role of novel retroviruses in chronic liver disease: assessing the link of human betaretrovirus with primary biliary cirrhosis

A human betaretrovirus resembling mouse mammary tumor virus has been characterized in patients with primary biliary cirrhosis. The agent triggers a disease-specific phenotype in vitro with aberrant cell-surface expression of mitochondrial antigens. The presentation of a usually sequestered self-protein is thought to lead to the loss of tolerance and the production of anti-mitochondrial antibodies associated with the disease. Similar observations have been made in mouse models, where mouse mammary tumor virus infection has been linked with the development of cholangitis and production of anti-mitochondrial antibodies. The use of combination antiretroviral therapy has been shown to impact on histological and biochemical disease in mouse models of autoimmune biliary disease and in clinical trials of patients with primary biliary cirrhosis. However, the HIV protease inhibitors are not well tolerated in patients with primary biliary cirrhosis, and more efficacious regimens will be required to clearly link reduction of viral load with improvement of cholangitis.

The CD19 signalling molecule is elevated in NOD mice and controls type 1 diabetes development

AIMS/HYPOTHESIS

Type 1 diabetes is characterised by early peri-islet insulitis and insulin autoantibodies, followed by invasive insulitis and beta cell destruction. The immunological events that precipitate invasive insulitis are not well understood. We tested the hypothesis that B cells in diabetes-prone NOD mice drive invasive insulitis through elevated expression of CD19 and consequent enhanced uptake and presentation of beta cell membrane-bound antigens to islet invasive T cells.

METHODS

CD19 expression and signalling pathways in B cells from NOD and control mice were compared. Expansion of CD8(+) T cells specific for insulin and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) were compared in CD19-deficient and wild-type NOD mice and this was correlated with insulitis severity. The therapeutic potential of anti-CD19 treatment during the period of T cell activation was assessed for its ability to block invasive insulitis.

RESULTS

CD19 expression and signalling in B cells was increased in NOD mice. CD19 deficiency significantly diminished the expansion of CD8(+) T cells with specificity for the membrane-bound beta cell antigen, IGRP. Conversely the reduction in CD8(+) T cells with specificity for the soluble beta cell antigen, insulin, was relatively small and not significant.

CONCLUSIONS/INTERPRETATION

Elevated CD19 on NOD B cells promotes presentation of the membrane-bound antigen, IGRP, mediating the expansion of autoreactive T cells specific for antigens integral to beta cells, which are critical for invasive insulitis and diabetes. Downregulating the CD19 signalling pathway in insulin autoantibody-positive individuals before the development of type 1 diabetes may prevent expansion of islet-invasive T cells and preserve beta cell mass.

Glucagon-like peptide-1 receptor signalling selectively regulates murine lymphocyte proliferation and maintenance of peripheral regulatory T cells

AIMS/HYPOTHESIS

Glucagon-like peptide-1 receptor (GLP-1R) agonists improve glucose control in animals and humans with type 1 diabetes. However, there is little information on the role of the GLP-1R in the immune system. We studied the role of the GLP-1R in immune function in wild-type (WT) and nonobese diabetic (NOD) and Glp1r-/- mice.

METHODS

Glp1r mRNA expression was examined in sorted immune subpopulations by RT-PCR. The effects of GLP-1R activation were assessed on cAMP production and proliferation, migration and survival of primary immune cells from WT and NOD mice. The ability of primary cells from Glp1r-/- mice to proliferate, migrate or survive apoptosis was determined. Immunophenotyping studies were performed to assess the frequency of immune subpopulations in Glp1r-/- mice.

RESULTS

Ex vivo activation of the GLP-1R resulted in a modest but significant elevation of cAMP in primary thymocytes and splenocytes from both WT and NOD mice. GLP-1R activation did not increase proliferation of primary thymocytes, splenocytes or peripheral lymph node cells. In contrast, Glp1r-/- thymocytes exhibited a hypoproliferative response, whilst peripheral Glp1r-/- lymphocytes were hyperproliferative in response to mitogenic stimulation. Activation or loss of GLP-1R signalling did not modify apoptosis or chemotaxis in primary lymphocytes. Male Glp1r-/- mice exhibited a significantly lower percentage of peripheral regulatory T cells, although no differences were observed in the numbers of CD4+ and CD8+ T cells and B cells in the spleen and lymph nodes of Glp1r-/- mice.

CONCLUSIONS/INTERPRETATION

These studies establish that GLP-1R signalling may regulate lymphocyte proliferation and maintenance of peripheral regulatory T cells.

Differential contributions of APC subsets to T cell activation in nonobese diabetic mice

Despite the pivotal role of dendritic cells (DC) in shaping immunity, little is known about their functionality in type 1 diabetes. Moreover, due to the paucity of DC in vivo, functional studies have relied largely upon in vitro-expanded cells to elucidate type 1 diabetes-associated functional abnormalities. In this study, we provide a comprehensive analysis of the functional capabilities of in vivo-derived DC subsets from NOD mice by comparing DC to other NOD APC types and to DC from autoimmune-resistant strains. NOD DC closely resemble those from nonautoimmune strains with respect to costimulation and cytokine production. The exception is the CD8alpha(+)CD11b(-)DC subset which is numerically reduced in NOD spleens, but not in the pancreatic lymph nodes, while DC from both tissues produce little IL-12 in this strain. This defect results in unusual deferral toward macrophage-derived IL-12 in NOD mice; NOD macrophages produce aberrantly high IL-12 levels that can overcompensate for the DC defect in Th1 polarization. APC subset use for autoantigen presentation also differs in NOD mice. NOD B cells overshadow DC at activating islet-reactive T cells, whereas DC and B cells in NOD-resistant mice are functionally comparable. Differential involvement of APC subsets in T cell activation and tolerance induction may prove to be a crucial factor in the selection and expansion of autoreactive T cells.

B cells in autoimmune diabetes

Autoantibodies have been used as good markers for the prediction of future development of type 1 diabetes mellitus (T1DM), but are not thought to be pathogenic in this disease. The role of B cells that produce autoantibodies in the pathogenesis of human T1DM is largely unknown. In the non-obese diabetic (NOD) mouse model of autoimmune diabetes, it has been shown that B cells may contribute multifariously to the pathogenesis of the disease. Some aspects of deficiencies of B cell tolerance may lead to the circulation of autoreactive B cells. In addition, the antigen-presenting function of autoantigen specific B cells is likely to be particularly important, and autoantibodies are also considered to play a critical role. This review discusses the possible aspects of B cells involved in the development of autoimmune diabetes.

The enlarged population of marginal zone/CD1d(high) B lymphocytes in nonobese diabetic mice maps to diabetes susceptibility region Idd11

The NOD mouse is an important experimental model for human type 1 diabetes. T cells are central to NOD pathogenesis, and their function in the autoimmune process of diabetes has been well studied. In contrast, although recognized as important players in disease induction, the role of B cells is not clearly understood. In this study we characterize different subpopulations of B cells and demonstrate that marginal zone (MZ) B cells are expanded 2- to 3-fold in NOD mice compared with nondiabetic C57BL/6 (B6) mice. The NOD MZ B cells displayed a normal surface marker profile and localized to the MZ region in the NOD spleen. Moreover, the MZ B cell population developed early during the ontogeny of NOD mice. By 3 wk of age, around the time when autoreactive T cells are first activated, a significant MZ B cell population of adult phenotype was found in NOD, but not B6, mice. Using an F2(B6 x NOD) cross in a genome-wide scan, we map the control of this trait to a region on chromosome 4 (logarithm of odds score, 4.4) which includes the Idd11 and Idd9 diabetes susceptibility loci, supporting the hypothesis that this B cell trait is related to the development of diabetes in the NOD mouse.

Dysregulated B7-1 and B7-2 Expression on Nonobese Diabetic Mouse B Cells Is Associated with Increased T Cell Costimulation and the Development of Insulitis

Little is known about the pathogenic role of B cell dysfunction in T cell-mediated autoimmune disease. We previously reported that B cell hyper-responsiveness, resistance to apoptosis, and accumulation in islets occur during the onset of insulitis, but not in type 1 diabetes (T1D), in NOD mice. In this study we extended these studies to further determine how islet-infiltrated B cells contribute to this inflammatory insulitis. We demonstrate the presence of an increased percentage of B7-1(+) and a decreased percentage of B7-2(+) B cells in the spleen of autoimmune disease-prone NOD and nonobese diabetes-resistant mice compared with the spleen of nonautoimmune disease-prone C57BL/6 and BALB/c mice. An age-dependent differential expression of B7-1 and B7-2 was associated with the development of insulitis and CD4(+)CD25(+) T cell deficiency in autoimmune disease-prone mice. Whereas BCR and LPS stimulation increased B7-2 expression on B cells from autoimmune disease-prone and nonautoimmune disease-prone mice, LPS-induced B7-1 expression was higher on NOD than C57BL/6 B cells. Interestingly, increased expression of B7-1 and B7-2 was found on islet-infiltrated B cells, and this increase was associated with enhanced T cell costimulation. Islet-infiltrated B cells were shown to be a source of TNF-alpha production in islets. B7 blockade of BCR-stimulated NOD B cells by anti-B7-1 and anti-B7-2 mAbs during coadoptive transfer with diabetogenic T cells into NOD.scid mice protected these recipients from T1D. These results suggest that increased B7-1 and B7-2 expression on islet-infiltrated NOD B cells is associated with increased T cell costimulation and the development of inflammatory insulitis in NOD mice.

Hyperresponsiveness, resistance to B-cell receptor-dependent activation-induced cell death, and accumulation of hyperactivated B-cells in islets is associated with the onset of insulitis but not type 1 diabetes

B-cells proliferate after B-cell receptor (BCR) stimulation and are deleted by activation-induced cell death (AICD) during negative selection. We report that B-cells from type 1 diabetes-susceptible NOD and type 1 diabetes-resistant but insulitis-prone congenic NOD.B6Idd4B and NOR mice, relative to B-cells from nonautoimmune disease-prone C57BL/6 and BALB/c mice, display a hyperproliferative response to BCR stimulation and lower activation threshold in the absence or presence of interleukin 4 (IL-4). This hyperproliferation is associated with an increased proportion of NOD and NOR B-cells that enter into the S phase of the cell cycle and undergo cell division. The relative resistance to BCR-induced AICD of B-cells from NOD, NOR, and NOD.B6Idd4B mice, all of which develop insulitis, correlates with the presence of a higher percentage of hyperactivated B-cells in the spleen and islets of these mice than in nonautoimmune disease-prone C57BL/6 and BALB/c mice. The NOD islet-infiltrated activated B-cells are more responsive to further stimulation by IL-4 than activated spleen B-cells. Our results suggest that resistance to AICD and accumulation of hyperactivated B-cells in islets is associated with the onset of an inflammatory insulitis, but not type 1 diabetes.

Modulation of insulitis and type 1 diabetes by transgenic HLA-DR3 and DQ8 in NOD mice lacking endogenous MHC class II

To evaluate the contributions of DR3 and DQ8 to the etiopathogenesis of type 1 diabetes in a diabetes-predisposing milieu, we developed human leukocyte antigen (HLA) transgenic mice on the nonobese diabetic (NOD) background in the absence of the endogenous class II molecule, I-A(g7) and studied the incidence of both spontaneous and experimental (induced) autoimmune diabetes. Transgenic expression of HLA-DR3 and -DQ8 (either alone or in combination) did not confer susceptibility to spontaneous or cyclophosphamide-induced type 1 diabetes. Expression of I-A(g7) was mandatory for development of spontaneous or cyclophosphamide-induced diabetes. However, multiple low doses of streptozotocin could induce diabetes in all groups of mice independent of the class II molecules expressed. In unmanipulated mice, only islets from I-A(g7+/+) mice revealed significant intra-islet infiltration. Although a characteristic peri-insulitis/peri-ductulitis was present in Abeta(0)/NOD mice, islets from DR3, DQ8 and DR3 x DQ8 double transgenic mice demonstrated significantly less infiltration. In conclusion, transgenic expression of HLA-DR3 and -DQ8 associated with predisposition to type 1 diabetes alone is not sufficient to induce spontaneous diabetes in NOD mice lacking endogenous class II molecules.