Allen Shahin

Effector mechanisms in low-dose streptozotocin-induced diabetes.

The cellular and molecular requirements for β-cell damages in an immune-mediated toxininduced insulin-dependent diabetes mellitus have been studied in the model of multiple low-dose streptozotocin-induced diabetes in rats and mice. It was found that strain-related susceptibility to diabetes induction correlated with a higher level of IL-2, IFN-γ, and TNF-α production, whereas such differences were not observed when IL-1 and NO production by macrophages were analyzed; elimination of immunoregulatory RT6+T cells that increases IFN-γ production, enhances susceptibility to MLD-STZ-induced diabetes; mercury-induced Th-2 cells downregulated the disease; IFN-γ-mediated macrophage activation to produce proinflammatory cytokines rather than NO is an important event in early diabetogenic effects of invading macrophages; inhibition of IL-1 activity downregulates diabetes induction; and generation of NO in β cells appears to be important for diabetogenic effects. Taken together, data indicate that MLD-STZ diabetes is induced by Th-1 lymphocytes that secrete soluble effector molecules that activate macrophages and promote destruction of β cells possibly by both nitric oxide and nonnitric oxide-mediated mechanisms.

Galectin-3 Deficiency Reduces the Severity of Experimental Autoimmune Encephalomyelitis

Galectin-3 (Gal-3) is a member of the β-galactoside-binding lectin family and plays an important role in inflammation. However, the precise role of Gal-3 in autoimmune diseases remains obscure. We have investigated the functional role of Gal-3 in experimental autoimmune encephalomyelitis (EAE) following immunization with myelin oligodendrocyte glycoprotein (MOG)35–55 peptide. Gal-3 deficient (Gal-3−/−) mice developed significantly milder EAE and markedly reduced leukocyte infiltration in the CNS compared with similarly treated wild-type (WT) mice. Gal-3−/− mice also contained fewer monocytes and macrophages but more apoptotic cells in the CNS than did WT mice. Following Ag stimulation in vitro, lymph node cells from the immunized Gal-3−/− mice produced less IL-17 and IFN-γ than did those of the WT mice. In contrast, Gal-3−/− mice produced more serum IL-10, IL-5, and IL-13 and contained higher frequency of Foxp3+ regulatory T cells in the CNS than did the WT mice. Furthermore, bone marrow-derived dendritic cells from Gal-3−/− mice produced more IL-10 in response to LPS or bacterial lipoprotein than did WT marrow-derived dendritic cells. Moreover, Gal-3−/− dendritic cells induced Ag-specific T cells to produce more IL-10, IL-5, and IL-12, but less IL-17, than did WT dendritic cells. Taken together, our data demonstrate that Gal-3 plays an important disease-exacerbating role in EAE through its multifunctional roles in preventing cell apoptosis and increasing IL-17 and IFN-γ synthesis, but decreasing IL-10 production.

IL‐23 leads to diabetes induction after subdiabetogenic treatment with multiple low doses of streptozotocin

IL‐23, a proximal regulator of IL‐17, may be a major driving force in the induction of autoimmune inflammation. We have used a model of subdiabetogenic treatment with multiple low doses of streptozotocin (MLD‐STZ; 4 × 40 mg/kg body weight) in male C57BL/6 mice to study the effect of IL‐23 on immune‐mediated β cell damage and the development of diabetes, as evaluated by blood glucose, quantitative histology, immunohistochemistry and expression of relevant cytokines in the islets. Ten daily injections of 400 ng IL‐23, starting on the first day of MLD‐STZ administration led to significant and sustained hyperglycemia along with weight loss compared with controls (no IL‐23), and a significant increase in the number of infiltrating cells, a lower insulin content, enhanced apoptosis, expression of IFN‐γ and IL‐17 (not seen in the controls) and a significant increase in the expression of TNF‐α and IL‐18 in the pancreatic islets. IL‐23 treatment started 5 days prior to MLD‐STZ administration had no effect on diabetogenesis or cytokines expression in the pancreatic islets. We provide the first evidence in an animal model that IL‐23 is involved in the development of type‐1 diabetes, by inducing IL‐17 and possibly IFN‐γ production in the target tissue.

Targeted disruption of the galectin-3 gene results in decreased susceptibility to multiple low dose streptozotocin-induced diabetes in mice.

Galectin 3 (Gal-3) is an antiapoptotic and a proinflammatory lectin. We hypothesized that the proinflammatory properties of Gal-3 may influence disease induction in the multiple low doses of streptozotocin model of diabetes. Diabetes was induced in C57BL/6 Gal-3(+/+) and Gal-3(-/-) mice and disease monitored by blood glucose level, immuno-histology, insulin content of islets and expression of the proinflammatory cytokines, TNF-alpha, IFN-gamma, IL-17, and iNOS in pancreatic lymph nodes. Gal-3(+/+) mice developed delayed and sustained hyperglycemia, mononuclear cellular infiltration and reduced insulin content of islets accompanied with expression of proinflammatory cytokines. Gal-3(-)/(-) mice were relatively resistant to diabetogenesis as evaluated by glycemia, quantitative histology and insulin content. Further, we observed the weaker expression of IFN-gamma and complete absence of TNF-alpha, and IL-17 in draining pancreatic lymph nodes. Macrophages, the first cells that infiltrate the islet in this model of diabetes, produce less TNF-alpha and NO in Gal-3(-/-) mice. Thus, Gal-3 is involved in immune mediated beta cell damage and is required for diabetogenesis in this model of disease.

Regulatory T cells and ST2 signaling control diabetes induction with multiple low doses of streptozotocin.

Several peripheral mechanisms appear to be operational in limiting autoimmune damage of the islets of Langerhans and organ-specific T cell-mediated autoimmunity in general. These include cyclophosphamide sensitive T regulatory cells (Treg cells) and Th2 derived cytokine downregulation. We used the model of multiple low doses of streptozotocin (MLD-STZ) induced diabetes in susceptible C57BL/6 mice and resistant BALB/c mice to study these regulatory mechanisms. We show that low dose cyclophosphamide (CY) sensitive CD4(+)CD25(+)FoxP3(+) Treg cell-dependent mechanisms can be demonstrated in C57Bl/6 mice susceptible to MLD-STZ diabetes induction. CY pretreatment decreased Foxp3(+) cell count, glycemia, glycosuria and insulitis. In contrast, CY did not overcome resistance to diabetes induction in BALB/c mice. However, in BALB/c mice, deletion of ST2, an orphan member of the IL-1R family responsible for Th2 cell signaling leads to enhanced susceptibility to diabetes induction as evaluated by level of glycemia and glycosuria, number of infiltrating cells and beta cell loss. RT-PCR analysis of mRNA transcripts of diabetogenic cytokines revealed that the expression of TNF-alpha, and IFN-gamma was significantly enhanced in pancreatic lymph nodes by day 10 after diabetes induction in ST2-deficient mice in comparison with wild type BALB/c mice while IL-17 was detected only in ST2(-/-) mice by day 21. Our results are compatible with the notion that Treg cells are involved in MLD-STZ diabetes in susceptible mice and demonstrate that ST2-mediated signaling may also be involved in limiting Th1/Th17-mediated autoimmune pathology in diabetes resistant strain.

Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice

Interleukin 15 (IL-15) and Interleukin 18 (IL-18) are key cytokines produced by macrophages during innate immune response. These cytokines can profoundly affect subsequent adaptive immune responses including autoimmunity. We have investigated the role of IL-15 and IL-18 in the development of autoimmune diabetes in mice induced by multiple low dose streptozotocin (MLD-STZ). To analyze the role of IL-15, we tested the effects of a soluble murine IL-15 receptor alpha-chain (smIL-15Ralpha), on the development of MLD-STZ in C57BL/6 mice. Animals were treated with 10 daily injections of 32 microg of smIL-15Ralpha starting on the first day of diabetes induction. This treatment significantly attenuated the development of diabetes as evaluated by significantly lower glycemia compared with control mice treated with an inactive mutant form of sIL-15Ra. To directly address the role of IL-18 in MLD-STZ we used IL-18 knockout (KO) mice on DBA/1 background. IL-18 deficient mice were significantly more resistant to the induction of diabetes compared with the wild-type controls and did not develop the typical mononuclear cell infiltrates in the islets. Taken together our data suggest that the innate mediators, IL-15 and IL-18, are essential for the development of diabetes and may be important targets in prevention and early treatment of autoimmune diabetes.

Downregulation of apoptosis in the target tissue prevents low-dose streptozotocin-induced autoimmune diabetes

3,7-dimethyl-1-(5-oxohexyl) xanthine, pentoxifylline (PTX) is shown to affect cytokine-induced apoptosis in several experimental models and clinical conditions. It had been also shown to prevent insulitis and hyperglycemia in non-obese diabetic (NOD) mice, and mice and rats susceptible to diabetes induction with multiple low-doses of streptozotocin (MLD-STZ). We therefore analysed the development of diabetes and apoptosis of pancreatic beta islet cells in CBA/mice after diabetes induction with MLD-STZ. We have evaluated the effect of PTX on the level of apoptosis in the islet at different time intervals after diabetes induction. Complementary histological and immunohistochemical studies and analyses of the expression of cytokines and nitric oxide have also been done. It was concluded that PTX significantly attenuated apoptosis of the beta-cells in the islet and suppressed the induction of diabetes. Our data are compatible with the notion that interferon-gamma (IFN-gamma)/tumor necrosis factor (TNF)/nitric oxide (NO)-induced apoptosis of beta-cells in experimental diabetes is attenuated by PTX.

Protein phosphatase 1‐dependent dephosphorylation of Akt is the prime signaling event in sphingosine‐induced apoptosis in Jurkat cells

Sphingosine (SPH) is an important bioactive lipid involved in mediating a variety of cell functions including apoptosis. However, the signaling mechanism of SPH‐induced apoptosis remains unclear. We have investigated whether SPH inhibits survival signaling in cells by inhibiting Akt kinase activity. This study demonstrates that treatment of Jurkat cells with SPH leads to Akt dephosphorylation as early as 15 min, and the cells undergo apoptosis after 6 h. This Akt dephosphorylation is not mediated through deactivation of upstream kinases, since SPH does not inhibit the upstream phosphoinositide‐dependent kinase 1 (PDK1) phosphorylation. Rather, sensitivity to the Ser/Thr protein phosphatase inhibitors (calyculin A, phosphatidic acid, tautomycin, and okadaic acid) indicates an important role for protein phosphatase 1 (PP1) in this process. In vitro phosphatase assay, using Akt immunoprecipitate following treatment with SPH, reveals an increase in Akt‐PP1 association as determined by immunoprecipitation analysis. Moreover, SPH‐induced dephosphorylation of Akt at Ser473 subsequently leads to the activation of GSK‐3β, caspase 3, PARP cleavage, and ultimately apoptosis. Pre‐treatment with caspase 3 inhibitor z‐VAD‐fmk and Ser/Thr phosphatase inhibitor abrogates the effect of SPH on facilitating apoptosis. Altogether, these results demonstrate that PP1‐mediated inhibition of the key anti‐apoptotic protein, Akt, plays an important role in SPH‐mediated apoptosis in Jurkat cells. J. Cell. Biochem. 112: 1138–1153, 2011.

IFN-γ deficiency exacerbates experimental autoimmune neuritis in mice despite a mitigated systemic Th1 immune response

Previous studies have shown that interferon-gamma (IFN-γ) is a proinflammatory cytokine that contributes to the pathogenesis of Guillain-Barré syndrome and its animal model, experimental autoimmune neuritis (EAN). Treatments with anti-IFN-γ antibodies improve clinical outcome in GBS patients and EAN animals and administration of IFN-γ markedly worsens EAN. Paradoxically, the mice deficient in IFN-γ remain susceptible to experimental autoimmune encephalomyelitis, an analogous disease in the central nervous system. These observations raise a question whether IFN-γ might be protective in autoimmune demyelinating diseases. To clarify the role of IFN-γ in the pathogenesis of autoimmune demyelinating diseases, we used P0 protein peptide 180-199 to induce EAN in IFN-γ knockout (KO) mice. After the acute phase of EAN, the clinical signs of IFN-γ KO mice were significantly more severe than those of wild type (WT) controls. After antigenic stimulation, the proliferation of splenic mononuclear cells was significantly higher in IFN-γ KO than in WT mice with EAN. At the peak of EAN, the proportion of interleukin (IL)-17A expressing cells in cauda equina (CE) infiltrating cells, and the levels of IL-17A in sera were elevated in IFN-γ KO mice when compared with their WT counterparts. The proportions of major histocompatibility complex (MHC) II, macrosialin, and IL-12/IL-23p40 expressing cells, relative to total CE infiltrating cells were correspondingly higher in IFN-γ KO than in WT mice with EAN. However, IFN-γ deficiency reduced the production of NO by cultured macrophages in response to proinflammatory stimuli and induced a systemic Th2-oriented immune response. In conclusion, IFN-γ deficiency exacerbates EAN via upregulating Th17 cells despite a mitigated systemic Th1 immune response.

Induction of immunoglobulin G1, interleukin-6 and interleukin-10 by Taenia crassiceps metacestode carbohydrates

T helper type 2 (Th2) ‐polarized immune responses are characteristically dominant in helminth infections. Two murine models that show a Th1 to Th2 polarization with infection progression are those of Schistosoma mansoni and Taenia crassiceps. In both, an early Th1 response is replaced by a late Th2 response. We report that the nucleic acid‐, protein‐ and lipid‐free carbohydrate fraction of T. crassiceps metacestodes (denoted T‐CHO) possesses Th2‐like immunomodulatory activity. Immunization of two strains of rats (Dark Agouti and Albino Oxford) and BALB/c mice with chicken albumin in the presence of T‐CHO resulted in selective enhancement of immunoglobulin G1 (IgG1) antibodies, considered to be associated with Th2 responses in both rats and mice. Interleukin‐6 (IL‐6) followed by IL‐10 were the dominant cytokines detected in in vitro cultures of mouse spleen cells stimulated with T‐CHO. IL‐4 and IL‐5 were not detected in these culture supernates. Furthermore, Taenia carbohydrates were mitogenic to spleen cells, activated serine phosphorylation of proteins and up‐regulated the expression of the anti‐apoptotic protein, Bcl‐2. When mouse spleen cells were cultured in the presence of Taenia carbohydrates, a concentration‐dependent down‐regulation of IL‐2 and an overlapping up‐regulation of IL‐6 secretion were seen.