Assessing the effectiveness of Interleukin-2 therapy in experimental type 1 diabetes

AIM

Much focus of immunotherapy for type 1 diabetes (T1D) has been devoted on selectively boosting regulatory T (Treg) cells using low dose IL-2 due to their constitutive expression of IL-2Rα, CD25. However, several clinical trials using a low dose of IL-2 only showed a limited improvement of metabolic control. It can therefore be hypothesized that further decreasing IL-2 dosage may increase the selective responsiveness of Treg cells.

METHODS

We induced experimental T1D using multiple low dose streptozotocin (STZ) injections and treated the mice with an ultra-low dose IL-2 (uIL-2, approximately 7-fold lower than low dose). Immune response was studied using multicolor flow cytometry.

RESULTS

We found that uIL-2 did not protect STZ mice from developing hyperglycemia. It did neither increase Treg cell proportions, nor did it correct the phenotypic shift of Treg cells seen in T1D. It only partially decreased the proportion of IFN-γ+ T cells. Likewise, uIL-2 also did not protect the dysfunction of regulatory B (Breg) cells. Strikingly, when administered in combination with an anti-inflammatory cytokine IL-35, uIL-2 abrogated IL-35's protective effect. Low dose IL-2, on the other hand, protected half of the STZ mice from developing hyperglycemia. No difference was found in the Treg and Breg response, and it only tended to decrease CD80 expression in macrophages and dendritic cells.

CONCLUSION

In conclusion, further decreasing IL-2 dosage may not be a suitable approach for T1D therapy, and the limited success suggests that an alternative low dose IL-2 therapy strategy or other immunotherapies should be considered.

IL-35 producing antigen presenting cells in type 1 diabetes

In type 1 diabetes (T1D), the insulin producing β cells are damaged by unknown factors. Antigen presenting cells (APCs) are believed to present autoantigens to T cells, thus initiating the immune attacks to β cells. However, several types of APCs also possess regulatory functions by producing anti-inflammatory cytokines like IL-35. We found the proportions of IL-35+ cells among both CD11c+CD123− dendritic cells (DCs) and CD11c−CD123+ DCs were decreased in the peripheral blood mononuclear cells from T1D patients than healthy controls. Multiple low dose streptozotocin (MLDSTZ) mouse model of T1D was used to study the immune response of IL-35 producing APCs. Male CD-1 mice were injected with STZ for five consecutive days to induce experimental T1D. We found the proportions of IL-35 expressing MHC-II+CD11b−CD11chigh conventional DCs (cDCs) were decreased in the spleens of MLDSTZ mice than in control mice on day 21 after the first STZ injection. We next investigated which subtype of cDCs contribute to the IL-35 production, and found that it is CD8+XCR1+ cDC1s that produce IL-35 while cDC2s do not. After the five day STZ injections, male CD-1 mice further received recombinant mouse IL-35 injection or PBS daily for 8 days. We found increased proportions of IL-35+ cells among cDC1s in IL-35 treated mice than PBS treated mice. Only a minority of plasmacytoid DCs (pDCs) produce IL-35, and IL-35 treatment did not increase the proportion of IL-35+ pDCs. We further investigated macrophage polarization, finding that IL-35 treatment increased Arg1+ M2 proportions and decreased TNF-α+ M1 proportions. Our results illustrate that the decrease in IL-35 producing APCs may contribute to the development of T1D.

Kinetics of immune cell responses in the multiple low-dose streptozotocin mouse model of type 1 diabetes

In type 1 diabetes (T1D), the insulin-producing β cells are destructed by immune mechanisms. It has been hypothesized that the very first immune response in T1D onset comes from innate immune cells, which further activates the adaptive immune cells to attack the islets. Despite intensive research on characterization of islet-infiltrating immune cells, the kinetics of different immune cells in multiple low-dose streptozotocin (MLDSTZ)-induced T1D mouse model is still much unclear. Therefore, we investigated the proportions of innate immune cells such as neutrophils, dendritic cells (DCs), plasmacytoid dendritic cells (pDCs), macrophages, natural killer (NK) cells, and adaptive immune cells (T and B lymphocytes) in thymi, pancreatic-draining lymph nodes, and spleens of MLDSTZ mice on days 3, 7, 10, and 21 after the first injection of STZ by flow cytometry. The proportions of DCs and B cells were increased from day 3, while the proportions of B-1a lymphocytes and interferon-γ+ cells among NK cells were increased, but NK cells were decreased on day 10 in MLDSTZ-treated mice, illustrating that the initial immune response is induced by DCs and B cells. Later, the proportions of T helper 1 and cytotoxic T cells were increased from day 7, suggesting that the innate immune cells precede adaptive immune cell response in MLDSTZ mice. Altogether, our data demonstrate a possible sequence of events regarding the involvement of DCs, pDCs, NK cells, B-1a lymphocytes, B, and T cells at the early stage of T1D development.

Kinetics of immune cell responses in the multiple low dose streptozotocin mouse model of type 1 diabetes

In type 1 diabetes (T1D), the insulin producing β cells are damaged by immune attacks. It has been hypothesized that the very first response in T1D onset comes from innate immune cells, which further activates the adaptive immune cells to attack the β cells. The kinetics of the infiltration of different immune cells in the multiple low dose streptozotocin (MLDSTZ) induced T1D mouse model is still unclear. Therefore, we used flow cytometry to investigate the proportions of innate immune cells such as neutrophils, dendritic cells (DCs), plasmacytoid DCs (pDCs) and macrophages, and adaptive immune cells (T and B lymphocytes) in thymi, pancreatic draining lymph nodes (PDLNs) and spleens of MLDSTZ mice on days 3, 7, 10 and 21 after the first injection of MLDSTZ. The proportions of DCs and pDCs were increased on day 3 while the proportions of B-1a lymphocytes and neutrophils were increased on day 10 in MLDSTZ treated mice, illustrating that the initial immune response is induced by DCs and pDCs. The proportions of T helper 1, Helios+ T cells and cytotoxic T cells were increased from day 7, suggesting that the innate immune cells precede the adaptive immune cell response in MLDSTZ mice. We also found the proportions of interleukin-35 (IL-35) expressing tolerogenic antigen presenting cells (tolAPCs) were decreased in the spleens of MLDSTZ mice than in control mice on day 21. Furthermore, we found the proportions of IL-35+ tolAPCs were decreased in the peripheral blood mononuclear cells from T1D patients than from healthy controls. Altogether, our data demonstrate a possible sequence of events regarding the involvement of DCs, pDCs, B-1a lymphocytes, neutrophils, and Helios+ T-cells at the early stage of T1D development.

Determination of Regulatory T Cell Subsets in Murine Thymus, Pancreatic Draining Lymph Node and Spleen Using Flow Cytometry

Our immune system consists of a number and variety of immune cells including regulatory T cells (Treg) cells. Treg cells can be divided into two subsets, thymic derived Treg (tTreg) cells and peripherally induced Treg (pTreg) cells. They are present in different organs of our body and can be distinguished by specific markers, such as Helios and Neuropilin 1. It has been reported that tTreg cells are functionally more suppressive than pTreg cells. Therefore, it is important to determine the proportion of both tTreg and pTreg cells when investigating heterogeneous cell populations. Herein, we collected thymic glands, pancreatic draining lymph nodes and spleens from normoglycemic non-obese diabetic mice to distinguish tTreg cells from pTreg cells using flow cytometry. We manually prepared single cell suspensions from these organs. Fluorochrome conjugated surface CD4, CD8, CD25, and Neuropilin 1 antibodies were used to stain the cells. They were kept in the fridge overnight. On the next day, the cells were stained with fluorochrome conjugated intracellular Foxp3 and Helios antibodies. These markers were used to characterize the two subsets of Treg cells. This protocol demonstrates a simple but practical way to prepare single cells from murine thymus, pancreatic draining lymph node and spleen and use them for subsequent flow cytometric analysis.

Pancreatic islets of bank vole show signs of dysfunction after prolonged exposure to high glucose concentrations in vitro

Bank voles develop glucose intolerance/diabetes mellitus when kept in captivity. We have characterized beta-cell function of glucose intolerant/diabetic animals, and found that this animal model has features of both human type 1 and type 2 diabetes. The aim of this study was to study the functional alterations of islets isolated from glucose tolerant bank voles after a prolonged exposure to various glucose concentrations in vitro. For this purpose, pancreatic islets from normal (glucose tolerant) male and female bank voles were cultured at different glucose concentrations (5.6, 11.1 (control), or 28 mM) whereupon islet functions were examined. Overall, islet insulin output was lowered at 5.6 mM glucose, and similar to control, or enhanced after culture in 28 mM glucose. High glucose culture led to decreased insulin contents, but there was no change in islet DNA content and in morphological assessments of cell death, with the latter findings suggesting that the so-called glucotoxicity had not evolved. A slight gender difference was observed in that islets isolated from females exhibited a glucose-regulated (pro)insulin biosynthesis rate and insulin gene expression. In conclusion, we have found that islets isolated from female and male bank voles are affected by glucose concentrations in vitro in that some signs of dysfunction were observed upon high glucose exposure. A minor gender difference was observed suggesting that the islets of the females may more readily adapt to the elevated glucose concentration than islets of the male bank voles. It could be that these in vitro gender differences observed may represent a mechanism underlying the gender difference in diabetes development observed among bank voles.

Suppression of bank vole pancreatic islet function by proinflammatory cytokines

Bank voles kept in captivity may develop diabetes. We recently characterized beta-cell function of pancreatic islets from normal and glucose intolerant/diabetic bank voles. These animals had features of both human type 1 and type 2 diabetes. Cytokines may impair beta-cell function in both types of diabetes. Presently, we studied how pancreatic islets isolated from normal, i.e. glucose tolerant bank voles are affected by proinflammatory cytokines in vitro. Islets were exposed to hIL-1beta (25U/ml) alone or in combination with hTNF-alpha (1000U/ml)+mIFN-gamma (1000U/ml) for 48h, whereupon islet functions were assessed. Cytokines markedly reduced insulin gene expression and the (pro)insulin biosynthesis rate, which was accompanied by a profound depletion of the islet insulin content. The cytokines did not affect the culture medium insulin accumulation and the glucose oxidation rate, but caused a modest increase in medium nitrite, an indicator of nitric oxide (NO) generation. Cytokine-induced decrease in islet insulin content was not prevented by the preferential inducible NO synthase inhibitor aminoguanidine. These findings suggest that the reduction in islet insulin content is not attributed to enhanced exocytosis or related to altered glucose metabolism, but is rather due to a decline in insulin production. The suppressive effects of islet functions elicited by cytokines seem to be mediated by an NO-independent mechanism. In relation to previous studies on cytokine effects on islets from various species, the bank vole islets show a pattern which more resembles human islets than rat or murine islets.

Characterization of beta-cell function of pancreatic islets isolated from bank voles developing glucose intolerance/diabetes: an animal model showing features of both type 1 and type 2 diabetes mellitus, and a possible role of the Ljungan virus

Bank voles (Clethrionomys glareolus) kept in captivity develop diabetes mellitus to a significant extent. Also in wild bank voles, elevated blood glucose has been observed. A newly isolated picornavirus named Ljungan virus (LV) has been found in the pancreas of these bank voles. Moreover, LV infection in combination with environmental factors may cause glucose intolerance/diabetes (GINT/D) in normal mice. The aim of the present study was to investigate the functional characteristics of pancreatic islets, isolated from bank voles, bred in the laboratory but considered LV infected. About 20% of all males and females were classified as GINT/D following a glucose tolerance test. Of these animals the majority had become diabetic by 20 weeks of age, with a tendency towards an earlier onset in the males. GINT/D animals had increased serum insulin levels. Islets were tested on the day of isolation (day 0) and after 1 week of culture for their insulin content and their capacity to synthesize (pro)insulin, secrete insulin and metabolize glucose. Functional differences could be observed between normal and GINT/D animals as well as between genders. An elevated basal insulin secretion was observed on day 0 indicating beta-cell dysfunction among islets isolated from diabetic males. In vitro culture could reverse some functional changes. The increased serum insulin level and the increased basal islet insulin secretion may suggest that the animals had developed a type 2 diabetes-like condition. It is likely that the putative stress imposed in the laboratory, maybe in combination with LV infection, can lead to an increased functional demand on the beta-cells.

Prenatal viral exposure followed by adult stress produces glucose intolerance in a mouse model

AIMS/HYPOTHESIS

It has been suggested that the uterine environment may influence metabolic disease occurring later in adult life, and that adult stress may promote disease outcome. Using a mouse model, we tested whether in utero exposure to Ljungan virus (LV) followed by adult exposure to stress produces diabetes. The influence of the timing of viral exposure over the course of pregnancy was also tested.

MATERIALS AND METHODS

Pregnant CD-1 mice were exposed i.p. to LV on pregnancy days 4, 8, 12 or 17. Adult male mice from these pregnancies were stressed by being kept in shared cages. Stress only, LV exposure in utero only, and no-stress/no virus exposure groups were also followed. Outcome variables included bodyweight, epididymal fat weight, baseline glucose, glucose tolerance tests (60 and 120 min) and serum insulin.

RESULTS

We demonstrated that male mice developed a type 2-like diabetes, including obesity, as adults if infected during pregnancy with LV. Diabetes at the age of 11 weeks was more severe in mice whose mothers were infected earlier than in those whose mothers were infected later in pregnancy. Only animals infected in utero and kept under stress developed diabetes; infection or stress alone did not cause disease.

CONCLUSIONS/INTERPRETATION

This work demonstrates that a type 2 diabetes-like disease can be virus-induced in a mouse model. Early in utero viral insults can set the stage for disease occurring during adult life, but the final manifestation of diabetes is dependent on the combination of early viral exposure and stress in adult life.

Bonding to densely sintered alumina surfaces: effect of sandblasting and silica coating on shear bond strength of luting cements

PURPOSE

An important determinant of the clinical success of ceramic restorations is the bond strength of the luting agent to the seating surface and the prepared tooth structures. Manufacturers of ceramic systems frequently specify both the luting agent and preluting treatment of the seating surface of the crown. Procera AllCeram is an all-ceramic crown comprising a porcelain-veneered coping of densely sintered, high-purity aluminum oxide. This study evaluated the shear bond strength of 4 luting agents: zinc-phosphate, glass-ionomer, resin-modified glass-ionomer, and resin cement (dual cured) to Procera aluminum oxide coping material. The luting agents were subjected to different surface treatments: untreated, sandblasted, or silica coated by the Rocatec system.

MATERIALS AND METHODS

Cylindric and cubic specimens of the coping material were luted together, and the shear force necessary to separate the cylinder from the cube was measured with a universal testing machine. The surfaces of the specimens were also analyzed.

RESULTS

No significant differences were recorded for the shear bond strengths of the luting agents to the untreated aluminum oxide. Glass-ionomer and the resin-modified glass-ionomer cements had the highest values (4.2 +/- 2.5 MPa and 4.3 +/- 1.9 MPa, respectively), and the lowest were 3.3 +/- 2.3 MPa for the resin cement and 3.2 +/- 1.0 MPa for the zinc-phosphate cement. Similar results were recorded for the sandblasted aluminum oxide surfaces, except with the glass-ionomer, which was significantly higher (12.9 +/- 2.4 MPa). For all 4 luting agents, the highest shear bond strength values were recorded for the silica-coated specimens; the highest was for the resin cement, at 36.2 +/- 7.8 MPa.

CONCLUSION

The bond strengths between resin cement and aluminum oxide specimens treated by the Rocatec system were significantly higher than those of the other materials and surface treatments evaluated.

Passive adsorption of immunologically active and inactive synthetic peptides to polystyrene is influenced by the proportion of non-polar residues in the peptide

A well-known drawback in the use of synthetic peptides as solid-phase antigens in immunoassays is that positive controls confirming the presence of the peptide on the solid phase are not always present. We therefore evaluated the applicability of a recently described enzyme immunoassay (EIA) method by which the presence of peptides is detected by biotinylation (BioEIA) of alpha- and/or epsilon-amino groups after passive adsorption. This approach allows the rapid screening of a large number of proteins and peptides in respect to passive adsorption to plastic surfaces. When using irradiated polystyrene microplates we found that 240 (94%) of 256 synthetic peptides, covering 85% of the complete hepatitis C virus (HCV) sequence, passively adsorbed to polystyrene. When comparing the results from the BioEIA to the peptide reactivity of human sera it was obvious that the absence of serum reactivities was not due to lack of peptide adsorption to the plates. Using 192 peptides the relation between the signal-to-cutoff ratio (S/CO) in the BioEIA and the amino acid content of the individual peptides was further analyzed. The S/CO ratio was related to the number of epsilon NH2 groups (Lys residues) present in the peptide (P < 0.001, Kruskal-Wallis). We separately related the amino acid content of 68 peptides with Lys and 124 peptides lacking Lys to the S/CO ratio in the BioEIA. In both cases it was found that an increasing amount of nonpolar residues such as Ala, Phe, Ile, Met, and Val (P < 0.05, respectively) in the peptides was related to a lower S/CO ratio in the BioEIA.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of lining techniques on the marginal seal of Class II composite resin restorations

Various sealing techniques using a light-curing dental adhesive (Scotchbond 2) and bulk application of a light-curing resin-bonded ceramic were examined in 203 Class II cavities. Different pretreatment procedures and lining materials were used, and in one series resin impregnation of the contraction gap was included. The presence of gaps or leakage was disclosed either by a dye or a fluorescent resin penetration technique. In many restorations, Scotchbond 2 and a light-curing glass-ionomer lining did not prevent gap formation at the cervical wall. The gap usually occurred between the liner and the dentin, with dye penetration into the dentin. Three liners, one containing polytrifluorethylene sodium fluoride and calcium fluoride, one containing polyamide resin, and one containing calcium hydroxide, did not prevent dye penetration to the dentin at all; good dentinal protection was frequently observed, however, in cavities treated with a hydrophilic shellac film prior to placement of a polystyrene liner. The best results were observed when dentinal treatment with this lining system was followed by resin impregnation of the contraction gap after the composite resin had set.

The effect of cervical grooves on the contraction gap in class 2 composites

The extent and the width of the cervical contraction gap in class 2 composite resin restorations were examined using a fluorescent resin-penetrating technique. In all restorations Scotchbond 2 bonding system and P-50 were used. The cervical wall was prepared either with no groove or with one or two grooves. The results indicated that the extent of the contraction gap was reduced when two retention grooves were prepared. The difference between no groove and two grooves was statistically significant. The width of the gap was also reduced, but not with statistical significance. A statistical difference was also found when one retention groove was compared with no groove.

Effect of tooth storage and cavity cleansing on cervical gap formation in Class II glass-ionomer/composite restorations

Class II cavities with the cervical margin just below the C-E junction and with two cervical retention grooves were prepared in intact human premolars, 31 cavities in teeth stored frozen and 29 cavities in teeth stored in 1% chloramine solution. The teeth from both storage conditions were assigned to two groups; in one group, the cavities were cleaned with a water spray, in the other group, with a cleaner containing 0.2% EDTA and 1% NaF. All cavities were lined with Vitrebond and restored with P50. Cervical contraction gaps were disclosed by a fluorescent resin penetration technique. The length and width of each gap were analysed. A contraction gap was revealed in 17 of the 31 cavities in teeth stored frozen (54.8%) and in 22 of the 29 restorations in the teeth stored in chloramine (75.8%). The width of the gap was significantly greater in teeth stored in chloramine (p = 0.0004). No statistical difference in gap formation was found between cavities cleaned with water or with the detergent containing 0.2% EDTA and sodium fluoride. Since the cavity cleansing procedure was not a significant factor in gap formation, apparently removing the superficial smear layer with the cavity cleaner does not impair the bonding of Vitrebond to the dentin. However, gap formation appeared to be significantly affected by the storage conditions of the extracted teeth. It is suggested that teeth to be used in bond strength and leakage experiments should be stored frozen rather than stored in 1% chloramine solution.