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

Regulation of B lymphocyte responses to Toll-like receptor ligand binding during diabetes prevention in non-obese diabetic (NOD) mice

BACKGROUND

Interactions between genetic risk factors and the environment drive type 1 diabetes (T1D). The system of Toll-like receptors (TLR) detects these environmental triggers; however, the target cell that intermediates these interactions to drive T1D remains unknown.

METHODS

We investigated the effect of TLR pathway activation (myeloid differentiation primary response 88 [MyD88] vs TIR-domain-containing adapter-inducing interferon-β [TRIF]) on B cell subsets via flow cytometry, including their activation, survival, proliferation, and cytoskeletal mobilization. The effect of polyinosinic-polycytidylic acid (poly(I:C)) on diabetes development was addressed, including the B cell-dependent activation of diabetes-protective DX5+ cells, using genetic models and adoptive transfer.

RESULTS

B lymphocytes from non-obese diabetic (NOD) mice expressed enhanced levels of TLR-responsive proteins. Ex vivo analysis of B lymphocyte subsets demonstrated that TLR3 stimulation via TRIF deletes cells exhibiting a marginal zone phenotype, whereas MyD88-dependent ligands enhance their survival. In vivo, marginal zone B cells were activated by poly(I:C) and were unexpectedly retained in the spleen of NOD mice, in contrast with the mobilization of these cells in non-autoimmune mice, a phenotype we traced to defective actin cytoskeletal dynamics. These activated B cells mediated TLR3-induced diabetes protection.

CONCLUSIONS

Immunotherapies must account for both B cell location and activation, and these properties may differ in autoimmune and healthy settings.

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.

Spectratyping analysis of the islet-reactive T cell repertoire in diabetic NOD Igμ(null) mice after polyclonal B cell reconstitution

BACKGROUND

Non Obese Diabetic mice lacking B cells (NOD.Igμ(null) mice) do not develop diabetes despite their susceptible background. Upon reconstitution of B cells using a chimera approach, animals start developing diabetes at 20 weeks of age.

METHODS

We have used the spectratyping technique to follow the T cell receptor (TCR) V beta repertoire of NOD.Igμ(null) mice following B cell reconstitution. This technique provides an unbiased approach to understand the kinetics of TCR expansion. We have also analyzed the TCR repertoire of reconstituted animals receiving cyclophosphamide treatment and following tissue transplants to identify common aggressive clonotypes.

RESULTS

We found that B cell reconstitution of NOD.Igμ(null) mice induces a polyclonal TCR repertoire in the pancreas 10 weeks later, gradually diversifying to encompass most BV families. Interestingly, these clonotypic BV expansions are mainly confined to the pancreas and are absent from pancreatic lymph nodes or spleens. Cyclophosphamide-induced diabetes at 10 weeks post-B cell reconstitution reorganized the predominant TCR repertoires by removing potential regulatory clonotypes (BV1, BV8 and BV11) and increasing the frequency of others (BV4, BV5S2, BV9, BV16-20). These same clonotypes are more frequently present in neonatal pancreatic transplants under the kidney capsule of B-cell reconstituted diabetic NOD.Igμ(null) mice, suggesting their higher invasiveness. Phenotypic analysis of the pancreas-infiltrating lymphocytes during diabetes onset in B cell reconstituted animals show a predominance of CD19+ B cells with a B:T lymphocyte ratio of 4:1. In contrast, in other lymphoid organs (pancreatic lymph nodes and spleens) analyzed by FACS, the B:T ratio was 1:1. Lymphocytes infiltrating the pancreas secrete large amounts of IL-6 and are of Th1 phenotype after CD3-CD28 stimulation in vitro.

CONCLUSIONS

Diabetes in NOD.Igμ(null) mice appears to be caused by a polyclonal repertoire of T cell accumulation in pancreas without much lymphoid organ involvement and is dependent on the help by B cells.

In vivo islet protection by a nuclear import inhibitor in a mouse model of type 1 diabetes

Background

Insulin-dependent Type 1 diabetes (T1D) is a devastating autoimmune disease that destroys beta cells within the pancreatic islets and afflicts over 10 million people worldwide. These patients face life-long risks for blindness, cardiovascular and renal diseases, and complications of insulin treatment. New therapies that protect islets from autoimmune destruction and allow continuing insulin production are needed. Increasing evidence regarding the pathomechanism of T1D indicates that islets are destroyed by the relentless attack by autoreactive immune cells evolving from an aberrant action of the innate, in addition to adaptive, immune system that produces islet-toxic cytokines, chemokines, and other effectors of islet inflammation. We tested the hypothesis that targeting nuclear import of stress-responsive transcription factors evoked by agonist-stimulated innate and adaptive immunity receptors would protect islets from autoimmune destruction.

Principal Findings

Here we show that a first-in-class inhibitor of nuclear import, cSN50 peptide, affords in vivo islet protection following a 2-day course of intense treatment in NOD mice, which resulted in a diabetes-free state for one year without apparent toxicity. This nuclear import inhibitor precipitously reduces the accumulation of islet-destructive autoreactive lymphocytes while enhancing activation-induced cell death of T and B lymphocytes derived from autoimmune diabetes-prone, non-obese diabetic (NOD) mice that develop T1D. Moreover, in this widely used model of human T1D we noted attenuation of pro-inflammatory cytokine and chemokine production in immune cells.

Conclusions

These results indicate that a novel form of immunotherapy that targets nuclear import can arrest inflammation-driven destruction of insulin-producing beta cells at the site of autoimmune attack within pancreatic islets during the progression of T1D.

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.

Anti-peripherin B lymphocytes are positively selected during diabetogenesis

Rearrangement analysis of immunoglobulin genes is an exceptional opportunity to look back at the B lymphocyte differentiation during ontogeny and the subsequent immune response, and thus to study the selective pressures involved in autoimmune disorders. In a recent study to characterize the antigenic specificity of B lymphocytes during T1D progression, we generated hybridomas of islet-infiltrating B lymphocytes from NOD mice and other related strains developing insulitis, but with different degrees of susceptibility to T1D. We found that a sizable proportion of hybridomas produced monoclonal antibodies reactive to peripherin, an intermediate filament protein mainly found in the peripheral nervous system. Moreover, we found that anti-peripherin antibody-producing hybridomas originated from B lymphocytes that had undergone immunoglobulin class switch recombination, a characteristic of secondary immune response. Therefore, in the present study we performed immunoglobulin VL and VH analysis of these hybridomas to ascertain whether they were derived from B lymphocytes that had undergone antigen-driven selection. The results indicated that whereas some anti-peripherin hybridomas showed signs of oligoclonality, somatic hypermutation and/or secondary rearrangements (receptor edition and receptor revision), others seemed to directly derive from the preimmune repertoire. In view of these results, we conclude that anti-peripherin B lymphocytes are positively selected and primed in the course of T1D development in NOD mice, and reinforce the idea that peripherin is a relevant autoantigen targeted during T1D development in this animal model.

Idd-linked genetic regulation of TACIhigh expressing B cells in NOD mice

In NOD mice, B cells play a key role in the initiation of type 1 diabetes pathogenesis. We have identified a novel NOD-specific B cell-related trait, i.e. the increased percentage of TACI(high)-expressing splenic B cells, by comparing NOD mice with non-autoimmune C57BL/6 mice. Using athymic NOD mice, we determined that this trait was T cell independent. We mapped the loci contributing to the increased proportion of TACI(high) expressing splenic B cells and found that the control of TACI expression was strongly linked to chromosome 1, in a region which includes the insulin-dependent diabetes (Idd) 5 loci. Moreover, another locus potentially involved was detected in the vicinity of Idd22 on chromosome 8. Interestingly, when analyzing age-dependent contribution to the obtained LOD scores we observed that the linkage to chromosome 8 was explained solely by mice > or =61 days of age, suggesting a temporal genetic regulation of TACI expression. In addition, analysis of genetic interaction between chromosome 1 and chromosome 8 indicated that the two loci acted in an additive fashion. Our findings corroborate the notion that B cell deviations contribute to type 1 diabetes development, and suggest a temporal regulation of TACI(high) expression, possibly influenced by the ongoing autoimmune process.

Peripherin Is a Relevant Neuroendocrine Autoantigen Recognized by Islet-Infiltrating B Lymphocytes

Most of our knowledge of the antigenic repertoire of autoreactive B lymphocytes in type 1 diabetes (T1D) comes from studies on the antigenic specificity of both circulating islet-reactive autoantibodies and peripheral B lymphocyte hybridomas generated from human blood or rodent spleen. In a recent study, we generated hybridoma cell lines of infiltrating B lymphocytes from different mouse strains developing insulitis, but with different degrees of susceptibility to T1D, to characterize the antigenic specificity of islet-infiltrating B lymphocytes during progression of the disease. We found that many hybridomas produced mAbs restricted to the peripheral nervous system (PNS), thus indicating an active B lymphocyte response against PNS elements in the pancreatic islet during disease development. The aim of this study was to identify the autoantigen recognized by these anti-PNS mAbs. Our results showed that peripherin is the autoantigen recognized by all anti-PNS mAbs, and, therefore, a relevant neuroendocrine autoantigen targeted by islet-infiltrating B lymphocytes. Moreover, we discovered that the immune dominant epitope of this B lymphocyte immune response is found at the C-terminal end of Per58 and Per61 isoforms. In conclusion, our study strongly suggests that peripherin is a major autoantigen targeted during T1D development and poses a new question on why peripherin-specific B lymphocytes are mainly attracted to the islet during disease.

Phenotype and functional characteristics of islet-infiltrating B-cells suggest the existence of immune regulatory mechanisms in islet milieu

B-cells participate in the autoimmune response that precedes the onset of type 1 diabetes, but how these cells contribute to disease progression is unclear. In this study, we analyzed the phenotype and functional characteristics of islet-infiltrating B-cells in the diabetes-prone NOD mouse and in the insulitis-prone but diabetes-resistant (NOD x NOR)F1 mouse. The results indicate that B-cells accumulate in the islets of both mice influenced by sex traits. Phenotypically and functionally, these B-cells are highly affected by the islet inflammatory milieu, which may keep them in a silenced status. Moreover, although islet-infiltrating B-cells seem to be antigen experienced, they can only induce islet-infiltrating T-cell proliferation when they act as accessory cells. Thus, these results strongly suggest that islet-infiltrating B-cells do not activate islet-infiltrating T-cells in situ, although they may affect the progression of the disease otherwise.

Genes within the Idd5 and Idd9/11 diabetes susceptibility loci affect the pathogenic activity of B cells in nonobese diabetic mice

Autoreactive T cells clearly mediate the pancreatic beta cell destruction causing type 1 diabetes (T1D). However, studies in NOD mice indicate that B cells also contribute to pathogenesis because their ablation by introduction of an Igmunull mutation elicits T1D resistance. T1D susceptibility is restored in NOD.Igmunull mice that are irradiated and reconstituted with syngeneic bone marrow plus NOD B cells, but not syngeneic bone marrow alone. Thus, we hypothesized some non-MHC T1D susceptibility (Idd) genes contribute to disease by allowing development of pathogenic B cells. Supporting this hypothesis was the finding that unlike those from NOD donors, engraftment with B cells from H2g7 MHC-matched, but T1D-resistant, nonobese-resistant (NOR) mice failed to restore full disease susceptibility in NOD.Igmunull recipients. T1D resistance in NOR mice is mainly encoded within the Idd13, Idd5.2, and Idd9/11 loci. B cells from NOD congenic stocks containing Idd9/11 or Idd5.1/5.2-resistance loci, respectively, derived from the NOR or C57BL/10 strains were characterized by suppressed diabetogenic activity. Immature autoreactive B cells in NOD mice have an impaired ability to be rendered anergic upon Ag engagement. Interestingly, both Idd5.1/5.2 and Idd9/11-resistance loci were found to normalize this B cell tolerogenic process, which may represent a mechanism contributing to the inhibition of T1D.

APRIL and BAFF promote increased viability of replicating human B2 cells via mechanism involving cyclooxygenase 2

Of relevance to both protective and pathogenic responses to Ag is the recent finding that soluble molecules of the innate immune system, i.e., IL-4, B cell-activation factor of the TNF family (BAFF), and C3, exhibit significant synergy in promoting the clonal expansion of human B2 cells following low-level BCR ligation. Although IL-4, BAFF, and C3dg each contribute to early cell cycle entry and progression to S phase, only BAFF promotes later sustained viability of progeny needed for continued cycling. The present study sought to further clarify the mechanisms for BAFF's multiple functions. By comparing BAFF and a proliferation-inducing ligand (APRIL) efficacy at different stages in the response (only BAFF binds BR3; both bind transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and B cell maturation Ag, the early role was attributed to BR3, while the later role was attributed to TACI/B cell maturation Ag. Importantly, BAFF- and APRIL-promoted viability of cycling lymphoblasts was associated with sustained expression of cyclooxygenase 2 (COX-2), the rate-limiting enzyme for PGE2 synthesis, within replicating cells. Supernatants of cultures with BAFF and APRIL contained elevated PGE2. Although COX-2 inhibitors diminished daughter cell viability, exogenous PGE2 (1-1000 nM) increased the viability and recovery of lymphoblasts. Increased yield of viable progeny was associated with elevated Mcl-1, suggesting that a BAFF/APRIL --> TACI --> COX-2 --> PGE2--> Mcl-1 pathway reduces activation-related, mitochondrial apoptosis in replicating human B2 cell clones.

B cells in the spotlight: innocent bystanders or major players in the pathogenesis of type 1 diabetes

It has long been established that type 1 diabetes (T1D) is a T cell-mediated autoimmune disease, with CD4+ and CD8+ T cells being largely responsible for the destruction of beta cells within the pancreatic islets of Langerhans. Although autoantibodies specific for islet cell proteins are regularly detected in individuals with T1D and can be utilized as effective markers for predicting the onset of disease, they are not believed to be directly pathogenic to beta cells. Thus, activation of autoantibody-secreting B cells has long been regarded as a secondary consequence of the ongoing self-reactive T cell response. However, recently, studies in the nonobese diabetic mouse model of disease have demonstrated that B cells are an important component in the development of T1D by virtue of their ability to act as the preferential antigen presenting cell population required for efficient expansion of diabetogenic CD4+ T cells. Furthermore, autoantibodies might also be responsible for mediating early beta cell pathogenesis in this model.

Innate immunity and human B cell clonal expansion: effects on the recirculating B2 subpopulation

Foci of autoantigen-specific B lymphocytes in nonlymphoid tissues have been associated with development of autoimmune disease. To better understand the genesis of such ectopic lymphoid tissue, this study investigated whether several B cell-tropic innate immune system molecules, known to be elevated in response to inflammatory stimuli, can cooperate in fostering the T cell-independent clonal expansion of mature human B2 cells under conditions of limiting BCR engagement. Notable synergy was observed between BCR coligation with the C3dg-binding CD21/CD19 costimulatory complex, B cell-activating factor belonging to the TNF family (BAFF), and IL-4 in generating B cell progeny with sustained CD86 and DR expression. The synergy was observed over a wide range of BCR:ligand affinities and involved: 1) cooperative effects at promoting early cell cycle progression and viability; 2) BCR:CD21 coligation-promoted increases in BAFF receptors that were highly regulated by IL-4; 3) reciprocal effects of IL-4 and BAFF at dampening daughter cell apoptosis typical of stimulation by BCR:CD21 and either cytokine alone; and 4) BAFF-sustained expression of antiapoptotic Mcl-1 within replicating lymphoblasts. The results suggest that significant clonal proliferation of recirculating B2 cells occurs upon limited binding to C3dg-coated Ag in an inflammatory in vivo milieu containing both BAFF and IL-4. When rare autoantigen-presenting B cells undergo such expansions, both B cell and T cell autoimmunity may be promoted.

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.

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.