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The gut immune system and its modification by diet have been implicated in the pathogenesis of type 1 diabetes (T1D). Therefore, we investigated gut immune status in non-diabetes-prone LEW.1AR1 and diabetes-prone LEW.1AR1-iddm rats and evaluated the effect of a low antigen, hydrolysed casein (HC)-based diet on gut immunity and T1D. Rats were weaned onto a cereal-based or HC-based diet and monitored for T1D. Strain and dietary effects on immune homeostasis were assessed in non-diabetic rats (50-60 days old) and rats with recent-onset diabetes using flow cytometry and immunohistochemistry. Immune gene expression was analysed in mesenteric lymph nodes (MLN) and jejunum using quantitative RT-PCR and PCR arrays. T1D was prevented in LEW.1AR1-iddm rats by feeding an HC diet. Diabetic LEW.1AR1-iddm rats had fewer lymphoid tissue T cells compared with LEW.1AR1 rats. The percentage of CD4(+) Foxp3(+) regulatory T (Treg) cells was decreased in pancreatic lymph nodes (PLN) of diabetic rats. The jejunum of 50-day LEW.1AR1-iddm rats contained fewer CD3(+) T cells, CD163(+) M2 macrophages and Foxp3(+) Treg cells. Ifng expression was increased in MLN and Foxp3 expression was decreased in the jejunum of LEW.1AR1-iddm rats; Ifng/Il4 was decreased in jejunum of LEW.1AR1-iddm rats fed HC. PCR arrays revealed decreased expression of M2-associated macrophage factors in 50-day LEW.1AR1-iddm rats. Wheat peptides stimulated T-cell proliferation and activation in MLN and PLN cells from diabetic LEW.1AR1-iddm rats. LEW.1AR1-iddm rats displayed gut immune cell deficits and decreased immunoregulatory capacity, which were partially corrected in animals fed a low antigen, protective HC diet consistent with other models of T1D.

BACKGROUND: A complex interplay between a failing intestinal barrier and low-grade inflammation leading to sensorimotor disturbances is an often-cited mechanism in the pathogenesis of functional gastrointestinal disorders (FGID). However, the cause-consequence relationship between these features has not been clearly established. We previously described jejunal alterations in the normoglycemic BB-rat (BBDP-N) model proposing this model as a suitable animal model to study FGID pathophysiology. The current study explores colonic permeability, inflammation, and sensitivity of the BB-rat. METHODS: Colonic tissue of BBDP-N and control (BBDR) rats at 50, 90, 110, 160, and 220 days (n ≥ 7 per group) was used to assess intestinal permeability in Ussing chambers and inflammation, including infiltration by eosinophils, mast cells, and eosinophil peroxidase (EPO) activity. Anxiety-like symptoms were evaluated at 50, 90, and 220 days and colonic sensitivity at 160 and 220 days by measuring the visceromotor response (VMR) to isobaric colorectal distensions. KEYS RESULTS: Lamina propria eosinophil and mast cell infiltration and increased EPO activity were demonstrated from 90 days onward. Increased permeability and myenteric ganglionitis were observed in the oldest BBDP-N rats. At 220 days, the VMR was significantly increased suggesting colonic hypersensitivity. At the same age, increased anxiety-like behavior was observed. CONCLUSION AND INFERENCES: We demonstrated a lamina propria eosinophil and mast cell infiltration preceding visceral hypersensitivity in the colon of the BBDP-N rat, reminiscent of patients with FGID. These findings help elucidating pathogenetic pathways in FGID and further validate the BBDP-N rat as an attractive model to study pathophysiology and therapy of FGID. ispartof: NEUROGASTROENTEROLOGY AND MOTILITY vol:31 issue:7 ispartof: location:England status: published

In our previous work, we found that feeding Lactobacillus johnsonii to BioBreeding diabetes-prone (BBDP) rats decreased the incidence of diabetes development. The aim of this study was to investigate host pathways affected by L. johnsonii, with specific focus on the rate-limiting enzyme of tryptophan catabolism, indoleamine 2,3-dioxygenase (IDO). Suspensions of L. johnsonii or an equal volume of vehicle were orally administered to BBDP rats. Tissue IDO was investigated using quantitative RT-PCR and Western blot, whereas tryptophan, kynurenine, and 5-hydroxytryptamine (5-HT) concentrations were quantified by HPLC and ELISA. IDO activity was also investigated using L. johnsonii culture cell-free supernatant (CFS) with affinity-purified IDO and HT-29 intestinal epithelial cells. L. johnsonii feeding resulted in a 17% reduction in serum kynurenine compared with that in vehicle-fed controls, correlating with a 1.4-fold elevation in 5-HT levels. H₂O₂ produced by L. johnsonii abolished IDO activity in vitro, and L. johnsonii feeding resulted in a 3.9-fold increase in ileum lumen H₂O₂. L. johnsonii CFS significantly reduced IDO activity in HT-29 intestinal epithelial cells (47% reduction) compared with that in vehicle-treated controls, an effect abolished by catalase treatment. These data support the role of H₂O₂ in commensal bacteria-host interactions and highlight the influence of commensal bacteria-derived H₂O₂ on host physiology.

Scope: To identify genes involved in the susceptibility to iodine-induced autoimmune thyroiditis. Methods and results: Diabetes, thyroiditis-prone (BBdp) and -resistant (BBc) rats were fed either a control or a high-iodine diet for 9 wk. Excess iodine intake increased the incidence of insulitis and thyroiditis in BBdp rats. BBdp rats fed the high-iodine diet that did not develop thyroiditis had higher mRNA levels of Fabp4, Cidec, perilipin, Pparγ and Slc36a2 than BBdp rats fed the control diet and BBc rats fed either the control or the high-iodine diet. BBdp rats fed the high-iodine diet that did develop thyroiditis had higher mRNA levels of Cidec, Icam1, Ifitm1, and Slpi than BBdp rats fed the control diet and BBc rats fed either the control or the high-iodine diet. BBdp rats that did develop thyroiditis had lower mRNA levels of Fabp4, perilipin and Slc36a2 but higher mRNA levels of Icam1, Ifitm1 and Slpi than BBdp that did not develop thyroiditis. Excess dietary iodine also increased the protein levels of Fabp4, Cidec and perilipin in BBdp rats. Conclusion: Differential expression of thyroid genes in BBdp versus BBc rats caused by excess dietary iodine may be implicated in autoimmune thyroiditis and insulitis pathogenesis.

Background Rat models of diabetes have emerged as a powerful experimental tool for addressing the role of microbial pathogens in the mechanism of autoimmune diabetes. We have used the biobreeding diabetes resistant and LEW1.WR1 rat models to identify the role of virus-induced innate immunity in the mechanism of type 1 diabetes. Methods Groups of rats 21–25 days of age were left untreated, injected i.p. with 1 × 107 PFU of Kilham rat virus (KRV) only, or with 1–3 µg/g body-weight-purified toll-like receptor agonists on three consecutive days and infected with 1 × 107 PFU of KRV on the following day. Spleens and pancreatic lymph nodes were recovered 5 days after infection and used for gene array analysis. To test the role of inflammation in diabetes, rats injected with KRV only or Poly(I:C) plus KRV were also administered with 2 or 0.2 µg/g body weight of dexamethasone and followed for diabetes for 40 days. Results KRV induced the expression of a vast array of proinflammatory genes in pancreatic lymph nodes on day 5 following infection. Brief dexamethasone therapy downmodulated inflammation and completely blocked diabetes. Conclusions Our data suggest a strong association between early virus-induced proinflammatory responses and islet destruction and raise the possibility that targeting innate immune pathways in the early stages of diabetes may be a useful strategy for disease prevention. Copyright © 2011 John Wiley & Sons, Ltd.

Diabetes mellitus is a common systemic disease that has been associated with poor fracture healing outcomes. The mechanism through which diabetes impairs bone regeneration is unknown. One possible mechanism may be related to either decreased or uncoordinated release of local growth factors at the fracture site. Indeed, previous studies have found reduced platelet-derived growth factor (PDGF) levels in the fracture callus of diabetic rats, suggesting that local application of PDGF may overcome the negative effects of diabetes and promote fracture healing. To test this hypothesis, low (22 microg) and high (75 ug) doses of recombinant human PDGF-BB (rhPDGF-BB) were applied directly to femur fracture sites in BB Wistar diabetic rats that were then compared to untreated or vehicle-treated animals. rhPDGF-BB treatment significantly increased early callus cell proliferation compared to that in control specimens. Low dose rhPDGF-BB treatment significantly increased callus peak torque values (p < 0.05) at 8 weeks after fracture as compared to controls. High dose rhPDGF-BB treatment increased callus bone area at 12 weeks postfracture. These data indicate that rhPDGF-BB treatment ameliorates the effects of diabetes on fracture healing by promoting early cellular proliferation that ultimately leads to more bone formation. Local application of rhPDGF-BB may be a new therapeutic approach to treat diabetes-impaired fracture healing.

Type 1 diabetes (T1D) occurs when the immune system attacks the insulin-producing beta cells located in the islets of Langerhans within the pancreas. Animal models have played a prominent role in developing an understanding of this disease process, through studies of genetic susceptibility, progression of hyperglycemia, and novel approaches to therapy. Here, we critically evaluate the currently available diabetic animal models and their propensity to match and predict disease outcomes in man as well as propose new in vitro and in vivo systems that may facilitate progress in the T1D field.

The morphology of the vitreoretinal border region, also termed the inner limiting membrane, was examined in spontaneously diabetic rats (BB rats), in non-diabetes-prone rats (WB rats) and in Buffalo rats (BUF rats) by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This was performed in order to visualize a possible increase in thickness of the lamina densa or in the whole vitreoretinal border region complex with duration of diabetes. The median thickness of the lamina densa in the three groups varied between 34 and 68 nm. In BB rats the thickness decreased with age and duration of diabetes. In WB rats the lamina densa thickened up to the 9th month and then decreased to the level of the young rats. In BUF rats the lamina densa decreased in thickness with age. The median thickness of the whole vitreoretinal border region varied between: BB rats: 84 and 126 nm (SEM) and 68 and 119 nm (TEM); WB rats: 42 and 84 nm (SEM) and 51 and 68 nm (TEM); BUF rats: 42 nm (SEM) and 34 and 68 nm (TEM). In BB rats the whole vitreoretinal border region appeared in SEM to thicken with duration of diabetes > or = 27 weeks, whereas in TEM no specific pattern could be statistically demonstrated. In WB rats the whole vitreoretinal border region was thinner in 3-month-old animals than in 9-month-old animals in (SEM) and TEM. In BUF rats there was no difference in thickness between young and older animals. Light microscopy of older diabetic animals showed neovascularization of the iris stroma.

We recently hypothesized that Toll-like receptor-induced innate upregulation by Kilham rat virus (KRV) in the BioBreeding diabetes-resistant (BBDR) rat model plays a key role in the mechanism of diabetes induction. To address this hypothesis, we analyzed innate immune signaling pathways upregulated by KRV in vitro and in vivo. We demonstrate that KRV activates the signal transducer and activator of transcription (STAT)-1 in spleen cells in vitro and that this activation can be blocked by TLR9 inhibition. We also show that KRV upregulates STAT-1 in pancreatic lymph nodes early after virus infection. Our data may implicate TLR9-induced STAT-1 signaling pathways in KRV-induced innate immune activation in the BBDR rat and raise the possibility that these pathways are involved in mediating autoimmune diabetes.

Allogeneic and autoimmune islet destruction limits the success of islet transplantation in autoimmune diabetic patients. This study was designed to investigate whether ex vivo gene transfer of viral interleukin-10 (vIL-10) protects BioBreeding (BB) rat islets from autoimmune destruction after transplantation into diabetic BB recipients. Islets were transduced with adenoviral constructs (Ad) expressing the enhanced green fluorescent protein (eGFP), α-1 antitrypsin (AAT) or vIL-10. Transduction efficiency was demonstrated by eGFP-positive cells and vIL-10 production. Islet function was determined in vitro by measuring insulin content and insulin secretion and in vivo by grafting AdvIL-10-transduced islets into syngeneic streptozotocin (SZ)-diabetic, congenic Lewis (LEW.1 W) rats. Finally, gene-modified BB rat islets were grafted into autoimmune diabetic BB rats. Ad-transduction efficiency of islets increased with virus titre and did not interfere with insulin content and insulin secretion. Ad-transduction did not induce Fas on islet cells. AdvIL-10-transduced LEW.1 W rat islets survived permanently in SZ-diabetic LEW.1 W rats. In diabetic BB rats AdvIL-10-transduced BB rat islets were rapidly destroyed. Prolongation of islet culture prior to transplantation improved the survival of gene-modified islets in BB rats. Several genes including those coding for chemokines and other peptides associated with inflammation were down-regulated in islets after prolonged culture, possibly contributing to improved islet graft function in vivo. Islets transduced ex vivo with vIL-10 are principally able to cure SZ-diabetic rats. Autoimmune islet destruction in diabetic BB rats is not prevented by ex vivo vIL-10 gene transfer to grafted islets. Graft survival in autoimmune diabetic rats may be enhanced by improvements in culture conditions prior to transplantation.

During the last decades, the incidence of type 1 diabetes (T1D) has increased significantly, reaching percentages of 3% annually worldwide. This increase suggests that besides genetical factors environmental perturbations (including viral infections) are also involved in the pathogenesis of T1D. T1D has been associated with viral infections including enteroviruses, rubella, mumps, rotavirus, parvovirus and cytomegalovirus (CMV). Although correlations between clinical presentation with T1D and the occurrence of a viral infection that precedes the development of overt disease have been recognized, causalities between viruses and the diabetogenic process are still elusive and difficult to prove in humans. The use of experimental animal models is therefore indispensable, and indeed more insight in the mechanism by which viruses can modulate diabetogenesis has been provided by studies in rodent models for T1D such as the biobreeding (BB) rat, nonobese diabetic (NOD) mouse or specific transgenic mouse strains. Data from experimental animals as well as in vitro studies indicate that various viruses are clearly able to modulate the development of T1D via different mechanisms, including direct beta-cell lysis, bystander activation of autoreactive T cells, loss of regulatory T cells and molecular mimicry. Data obtained in rodents and in vitro systems have improved our insight in the possible role of viral infections in the pathogenesis of human T1D. Future studies will hopefully reveal which human viruses are causally involved in the induction of T1D and this knowledge may provide directions on how to deal with viral infections in diabetes-susceptible individuals in order to delay or even prevent the diabetogenic process. Copyright (c) 2006 John Wiley & Sons, Ltd.

Insulin-dependent diabetes mellitus (IDDM), also known as type 1 diabetes, is an organ-specific autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells. The hypothesis that IDDM is an autoimmune disease has been considerably strengthened by the study of animal models such as the BioBreeding (BB) rat and the nonobese diabetic (NOD) mouse, both of which spontaneously develop a diabetic syndrome similar to human IDDM. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T cells have been shown to be involved in the pathogenesis of autoimmune diabetes. Among the beta cell autoantigens identified, glutamic acid decarboxylase (GAD) has been extensively studied and is the best characterized. Beta cell-specific suppression of GAD expression in NOD mice results in the prevention of IDDM. Macrophages and/or dendritic cells are the first cell types to infiltrate the pancreatic islets. Macrophages play an essential role in the development and activation of beta cell-cytotoxic T cells. B lymphocytes play a role as antigen-presenting cells, and T cells have been shown to play a critical role as final effectors that kill beta cells. Cytokines secreted by immunocytes, including macrophages and T cells, may regulate the direction of the immune response toward Th1 or Th2 as well as cytotoxic effector cell or suppressor cell dominance. Beta cells are destroyed by apoptosis through Fas-Fas ligand and TNF-TNF receptor interactions and by granzymes and perforin released from cytotoxic effector T cells. Therefore, the activated macrophages and T cells, and cytokines secreted from these immunocytes, act synergistically to destroy beta cells, resulting in the development of autoimmune IDDM.

The Bio Breeding (BB) rat is a useful animal model of type 1 autoimmune diabetes. The aim of this study was to observe and follow the cytokine and antigenic expressions within the islets of Langerhans in young non-diabetic, in pre-diabetic hyperglycemic, and in overtly diabetic animals. BB rats were therefore checked at day 21 up to day 90 of life for blood glucose, insulin levels, degree of islet infiltration, expression of proinflammatory and protective cytokines and antibodies including CD4, CD8, CD25, LFA-1, and ICAM-1. Animals were treated with insulin as they became diabetic. We found that islets of non-diabetic BB rats became positive to both IL-1beta and IL-4 very early on, confirming a local but intense production of both cytokines within the islets during the initial non-diabetic period. In addition, we observed that the production of these interleukins together with the expression levels of CD4 and CD25 are events predictive for type 1 diabetes onset in non-diabetic BB rats, as for non-obese diabetic (NOD) mice. In particular, the production of IL-1beta and IL-4 during the non-diabetic period together with the lack of enhancement of CD4 and CD25, indicating selective recruitment of activated T cells, may explain the failure of anti-diabetic treatments in this animal model of type 1 diabetes.

Background Type 1 diabetes mellitus (DM) has been shown to alter the properties of bone and impair fracture healing in both humans and animals. The objective of this study was to examine changes in the histomorphometrical, histological and mechanical parameters of bone and remodeling during fracture healing, depending on the diabetic metabolic state in spontaneously diabetic BB/O(ttawa)K(arlsburg) rats, a rat strain that represents a close homology to DM in man. Methods On the basis of blood glucose values at the time of surgery, postoperative blood glucose course and postoperative insulin requirements, 90 spontaneously diabetic BB/OK rats were divided into groups with well-compensated or poorly compensated metabolic state. Forty-five LEW.1A rats served as the normoglycemic controls. The femurs were fractured in a standardized procedure and then allowed to heal for 2, 4 and 6 weeks. Results Our study showed that, in terms of bone histomorphometry, within the first 4 weeks after fracture, severe mineralization disorders occurred exclusively in the rats with poorly compensated diabetic metabolic states with a significant decrease of all fluorochrome-based parameters of mineralization, apposition, formation and timing of mineralization, as well as a delay in cellular differentiation and significantly decreased values of biomechanical properties in comparison to the spontaneously diabetic rats with well-compensated metabolic states and to the control rats. Conclusions With a controlled insulin therapy and a resulting well-compensated diabetic metabolic state, mineralization and cellular differentiation disorders, as well as the decreased values of biomechanical properties in the fracture repair in the poorly compensated diabetic metabolic state with very severe hyperglycemia can be avoided. Copyright © 2005 John Wiley & Sons, Ltd.

Background The development of immune-mediated diabetes in BB rats may involve an inflammatory lesion of the intestinal tract. Methods In order to further explore this issue, the activity of peroxidase was measured, in the absence and presence of either bromide or dapsone, at day 10, 30, 45, 70, 95 and 120 in three segments (top, mid and bottom) of the intestinal tract from Wistar–Furth rats and both diabetes-resistant and diabetes-prone BB rats fed after weaning either diabetes-promoting diets or a protective diet, which decreases the incidence of diabetes in the BB rats. Results In the present study, from day 30 onwards, an age-related increase in peroxidase activity was found in the intestine of diabetes-prone BB rats (BBdp rats) fed diabetogenic diets, when compared with either Wistar–Furth or diabetes-resistant BB rats (BBc rats). This increase was most pronounced in the distal segments of the intestinal tract. Even when fed a protective diet, higher peroxidase activity was found in BBdp than BBc rats. Yet, in BBc rats, and to a lesser extent in BBdp rats, the diabetogenic diets lowered peroxidase activity below the value found in rats of the same strain fed the protective diet. There was a tight correlation between the activity of peroxidase and its susceptibility to be increased by bromide. Conclusion It is proposed that diabetogenic diets may decrease peroxidase activity in intestinal cells, this effect becoming masked in BBdp rats by an age-related increase in the contribution of inflammatory cells. The latter phenomenon affects preferentially the distal segments of the intestinal tract. Copyright © 2004 John Wiley & Sons, Ltd.

Diabetes-prone BB (dpBB) rats develop autoimmune insulin-dependent diabetes mellitus (IDDM) at high frequency as a consequence of a defect in T cell development, caused by a mutation in a single gene locus on rat chromosome 4 (lyp) which has recently been identified as immune-associated nucleotide 4 (ian4). A phenotype similar to dpBB rat lymphopenia has recently been described in the mouse as the result of the targeted inactivation of the gene for the transcription factor LKLF (Lung Kruppel-like factor, KLF2) in the immune system. We cloned the LKLF gene of the rat and screened a panel of rat/hamster radiation hybrid cell lines to determine its chromosomal localization. We conclude that the LKLF gene is not defective in dpBB rats and that its expression is not compromised by the lyp mutation.

Alterations in rat's nerve collagens due to diabetes may be related to the permanence of damage due to diabetic neuropathy. We (1) provide a methodology for determining the diameters of collagen fibers accounting for atomic force microscope (AFM) imaging artifacts, (2) present data on structural differences in sciatic nerve endoneurial, epineurial and tail tendon collagens of control and diabetic Sprague-Dawley and BioBreeding rats, and (3) compare results with literature values.We measured collagen diameters and band spacing on endoneurial and epineurial sciatic nerve tissue, and tail tendon, in control and diabetic rats (STZ-induced 12-week diabetic SD and 16-week spontaneously diabetic BB rats). We also developed a model to interpret the raw AFM data.All types of fibrillar collagen diameters studied became larger for diabetic versus control animals. Values for diabetic and control collagen fiber diameters in SD rats were 78 nm and 72 nm for SN epineurium, and 49 nm and 43 nm for SN endoneurium. For diabetic and control BB rats, these values were 83 nm and 77 nm (SN epineurium) and 49 nm and 43 nm (SN endoneurium). Values of 161 nm and 125 nm were found for diabetic and control tail tendon of BB rats. No significant changes were observed in any of the five comparisons made in D-band spacings that ranged from 63 to 69 nm.The best means we have found to reduce raw AFM data is to measure several diameters with a single scan, using valley-to-valley measurements. Structural, fibrillar collagens of the nerve and tendon become larger in rats exposed to prolonged diabetes.

Several clinical series, analyzing fracture healing in patients with diabetes mellitus (DM). demonstrated significant incidence of delayed union, non-union, and pseudarthrosis. In this study, analysis was performed to evaluate the effects of blood glucose (BG) control on fracture healing in the DM BB Wistar rat, a rat strain that represents a close homology to Type I DM in man. Our study showed decreased cell proliferation at the fracture site as well as decreased mechanical stiffness and bony content in the poorly controlled DM rats. To determine the effect of BG control, DM rats were treated with insulin sufficient to maintain physiologic BG levels throughout the course of the study. Values of cellular proliferation, biomechanical properties and callus bone content in tightly controlled DM animals were not significantly different from values of non-DM control values. This study suggests that insulin treatment with resultant improved BG control will ameliorate the impaired early and late parameters of DM fracture healing.

This study was designed to determine the level of inhibition of gene transcription by the reduction in insulin levels upon the onset of diabetes in spontaneously diabetic B/B rats and if reducing the level of polyunsaturated fatty acids (PUFA) in the diet will increase lipogenic enzyme activity. Control (eight animals per group) and spontaneously diabetic B/B male weanling rats (25 animals per group) were fed semipurified diets containing 20% (w/w) fat of either low (0.25) or high (1.0) polyunsaturated to saturated (P/S) fatty acid ratio. Rats were killed at the onset of diabetes [blood glucose level of approximately/= 100 mg/dL (5.55 mM)] and as they became highly diabetic [blood glucose level of approximately/= 400 mg/dL (22.22 mM)]. Total RNA was extracted from liver, and the relative amount of mRNA coding for fatty acid synthase (FAS), acetyl-CoA carboxylase, malic enzyme, pyruvate kinase, and phosphoenolpyruvate carboxykinase was determined. Liver enzyme activities were also measured. The mRNA levels for FAS, acetyl-CoA carboxylase, and malic enzyme decreased compared to control animals. The mRNA level for pyruvate kinase decreased at the onset of diabetes as compared to control animals. Feeding animals the low P/S diet treatment elevated the level of mRNA and lipogenic enzyme activity compared to animals fed the high P/S diet treatment, suggesting that the effect of PUFA on lipogenic enzymes is through a direct effect on gene expression.

We develop a mathematical formula that provides the number of cells in an isolated population that have divided k times in n days (0 ≤k≤n). This differential cell division formula is applied to the kinetics of peripheral T cells in the diabetes‐prone BB rat following thymectomy. These rats received daily intraperitoneal injections of the DNA precursor, bromodeoxyuridine (BrdUrd), over a period of 12–13 days. As the cells divided, they incorporated BrdUrd progressively into their DNA molecules, and the differential formula provides a close prediction of the fraction of BrdUrd‐positive T cells present each day during this ‘pulse’ phase. No further BrdUrd was administered after 13 days, and the diminishing fraction of BrdUrd‐positive cells was recorded for several more weeks. The differential cell division formula was capable of describing the rather complex form of the retention curve as BrdUrd‐tagged DNA molecules passed to progeny cells during this ‘chase’ phase. We believe that this simple formula may be found generally useful in describing cell kinetic data in mitotically active cells.

Correlation studies between cytokines expressed in islets and autoimmune diabetes development in NOD mice and BB rats have demonstrated that beta-cell destructive insulitis is associated with increased expression of proinflammatory cytokines (IL-1, TNF alpha, and IFN alpha) and type 1 cytokines (IFN gamma, TNF beta, IL-2 and IL-12), whereas non-destructive (benign) insulitis is associated with increased expression of type 2 cytokines (IL-4 and IL-10) and the type 3 cytokine (TGF beta). Cytokines (IL-1, TNF alpha, TNF beta and IFN gamma) may be directly cytotoxic to beta-cells by inducing nitric oxide and oxygen free radicals in the beta-cells. In addition, cytokines may sensitize beta-cells to T-cell-mediated cytotoxicity in vivo by upregulating MHC class I expression on the beta-cells (an action of IFN gamma), and inducing Fas (CD95) expression on beta-cells (actions of IL-1, and possibly TNF alpha and IFN gamma). Transgenic expression of cytokines in beta-cells of non-diabetes-prone mice and NOD mice has suggested pathogenic roles for IFN alpha, IFN gamma, IL-2 and IL-10 in insulin-dependent diabetes mellitus (IDDM) development, and protective roles for IL-4, IL-6 and TNF alpha. Systemic administrations of a wide variety of cytokines can prevent IDDM development in NOD mice and/or BB rats; however, a given cytokine may retard or accelerate IDDM development, depending on the dose and frequency of administration, and the age and the diabetes-prone animal model studied (NOD mouse or BB rat). Islet-reactive CD4+ T-cell lines and clones that adoptively transfer IDDM into young NOD mice have a Th1 phenotype (IFN gamma-producing), but other islet-specific Th1 clones that produce TGF beta can adoptively transfer protection against IDDM in NOD mice. NOD mice with targeted deletions of IL-12 and IFN gamma genes still develop IDDM, albeit delayed and slightly less often. In contrast, post-natal deletions of IL-12 and IFN gamma, also IL-1, TNF alpha, IL-2, and IL-6--by systemic administrations of neutralizing antibodies, soluble receptors and receptor antagonists, and receptor-targeted cytotoxic drugs--significantly decrease IDDM incidence in NOD mice and/or BB rats. These cytokine deletion studies have provided the best evidence for pathologic roles for proinflammatory cytokines (IL-1, TNF alpha, and IL-6) and type 1 cytokines (IFN gamma, IL-2 and IL-12) in IDDM development.