The autoimmune type 1 diabetes (T1D) that arises spontaneously in NOD mice is considered to be a model of T1D in humans. It is characterized by the invasion of pancreatic islets by mononuclear cells (MNCs), which ultimately leads to destruction of insulin-producing β cells. Although T cell dependent, the molecular mechanisms triggering β cell death have not been fully elucidated. Here, we report that a glycosaminoglycan, heparan sulfate (HS), is expressed at extraordinarily high levels within mouse islets and is essential for β cell survival. In vitro, β cells rapidly lost their HS and died. β Cell death was prevented by HS replacement, a treatment that also rendered the β cells resistant to damage from ROS. In vivo, autoimmune destruction of islets in NOD mice was associated with production of catalytically active heparanase, an HS-degrading enzyme, by islet-infiltrating MNCs and loss of islet HS. Furthermore, in vivo treatment with the heparanase inhibitor PI-88 preserved intraislet HS and protected NOD mice from T1D. Our results identified HS as a critical molecular requirement for islet β cell survival and HS degradation as a mechanism for β cell destruction. Our findings suggest that preservation of islet HS could be a therapeutic strategy for preventing T1D.

Treatment of CBA/H mice with 5 injections of anti-CD4 (GK1.5 mAb) terminating on day 10 posttransplant resulted in long-term survival (≥6 weeks) of fetal pig proislet (pancreatic islet precursor) xenografts. The GK1.5 mAb dose determined the duration of CD4⁺ T cell depletion and the extent to which the survival of pig proislet xenografts was prolonged. Sustained depletion of CD4⁺ T cells (0%, 1%, and 9% of total T cells in peripheral lymph nodes at 2, 4, and 6 weeks, respectively) and survival of proislet xenografts at 6 weeks posttransplant was observed when transplant recipients were treated with 5.4 mg GK1.5 mAb/injection. Treatment of transplanted mice with a suboptimal dose of GK1.5 mAb (0.2 mg/injection) resulted in the same level of depletion at 2 weeks posttransplant but a more rapid recovery of CD4⁺ T cells in the periphery (24% of total T cells at 4 weeks) and only temporary prolongation in xenograft survival (>4 weeks). Control xenografts showed evidence of graft destruction by as early as 6–7 days posttransplant and were completely rejected by 2 weeks. The rejection reaction consisted predominantly of CD4⁺ T cells, eosinophils and F4/80-positive macrophages. Only small numbers of CD8⁺ T cells were identified. CD4⁺ T cells therefore represented the major T cell component of the cellular infiltrate. In contrast, surviving xenografts in GK1.5 mAb-treated recipient mice showed essentially an absence of CD4⁺ T cells but presence of CD8⁺ T cells. This finding may be attributable to the increase (1.7–3.1-fold) in the absolute size of the population of CD8⁺ T cells in the periphery following GK1.5 mAb treatment in vivo. Compared with isolated fetal pig proislets, which contained only a small population of insulin-producing cells in addition to glucagon-and somatostatin-positive cells, surviving pig proislet xenografts contained mainly insulin-positive beta cells with smaller populations of glucagon- and somatostatin-positive cells. Fetal pig proislets therefore differentiate into insulin-producing islet tissue posttransplant and thus show evidence of normal development of endocrine function.

Ross River virus (RRV) is an Australian alphavirus that is often responsible for chronic epidemic polyarthritis and myalgia in humans. Past studies h

Aims/hypothesis This study examined whether the capsule which encases islets of Langerhans in the NOD mouse pancreas represents a specialised extracellular matrix (ECM) or basement membrane that protects islets from autoimmune attack. Methods Immunofluorescence microscopy using a panel of antibodies to collagens type IV, laminins, nidogens and perlecan was performed to localise matrix components in NOD mouse pancreas before diabetes onset, at onset of diabetes and after clinical diabetes was established (2–8.5 weeks post-onset). Results Perlecan, a heparan sulphate proteoglycan that is characteristic of basement membranes and has not previously been investigated in islets, was localised in the peri-islet capsule and surrounding intra-islet capillaries. Other components present in the peri-islet capsule included laminin chains α2, β1 and γ1, collagen type IV α1 and α2, and nidogen 1 and 2. Collagen type IV α3–α6 were not detected. These findings confirm that the peri-islet capsule represents a specialised ECM or conventional basement membrane. The islet basement membrane was destroyed in islets where intra-islet infiltration of leucocytes marked the progression from non-destructive to destructive insulitis. No changes in basement membrane composition were observed before leucocyte infiltration. Conclusions/interpretation These findings suggest that the islet basement membrane functions as a physical barrier to leucocyte migration into islets and that degradation of the islet basement membrane marks the onset of destructive autoimmune insulitis and diabetes development in NOD mice. The components of the islet basement membrane that we identified predict that specialised degradative enzymes are likely to function in autoimmune islet damage.