The pathology of the endocrine pancreas in type 1 (insulin-dependent) diabetes mellitus

Ultrastructure characterization of pancreatic β-cells is accompanied by modulatory effects of the HDAC inhibitor sodium butyrate on the PI3/AKT insulin signaling pathway in juvenile diabetic rats

Genetic and epigenetic factors contribute equally to the pathogenesis of type 1 diabetes mellitus. Sodium butyrate (NaB) has been reported to improve glucose homeostasis by modulation of the p38/ERK MAPK pathway. This work aims to evaluate the effect of NaB on the ultrastructure of pancreatic β-cells and the PI3/AKT pathway. Juvenile albino male rats were used to establish a type 1 diabetes model using streptozotocin injection and NaB in a pre- and post-treatment schedule. Plasma glucose, insulin levels, and glucose tolerance were evaluated. Light and electron microscopy and immunohistochemistry were performed using Ki-67, caspase-3, and insulin. NaB treatment resulted in a significant improvement in plasma glucose levels, plasma insulin levels/expression, and ameliorated diabetes-induced histological alternations. Additionally, it increased the expression of phosphorylated AKT. These findings provide evidence that NaB may be useful in the treatment of juvenile diabetes.

Enterovirus infection and type 1 diabetes: unraveling the crime scene

Enteroviruses (EV) have been historically associated to type 1 diabetes. Definitive proof for their implication in disease development is lacking, but growing evidence suggests that they could be involved in beta cell destruction either directly by killing beta cells or indirectly by creating an exacerbated inflammatory response in the islets, capable of attracting autoreactive T cells to the 'scene of the crime'. Epidemiological and serological studies have been associated with the appearance of islet autoimmunity and EV RNA has been detected in prospective studies. In addition, the EV capsid protein has been detected in the islets of recent-onset type 1 diabetic donors, suggesting the existence of a low-grade EV infection that could become persistent. Increasing evidence in the field shows that a 'viral signature' exists in type 1 diabetes and involves interferon responses that could be sustained during prolonged periods. These include the up-regulation of markers such as protein kinase R (PKR), melanoma differentiation-associated protein 5 (MDA5), retinoic acid inducible gene I (RIG-I), myxovirus resistance protein (MxA) and human leukocyte antigen-I (HLA-I) and the release of chemokines able to attract immune cells to the islets leading to insulitis. In this scenario, the hyperexpression of HLA-I molecules would promote antigen presentation to autoreactive T cells, favoring beta cell recognition and, ultimately, destruction. In this review, an overview is provided of the standing evidence that implicates EVs in beta cell 'murder', the time-line of events is investigated from EV entry in the cell to beta cell death and possible accomplices are highlighted that might be involved in beta cell demise.

An important step towards a prevascularized islet microencapsulation device: in vivo prevascularization by combination of mesenchymal stem cells on micropatterned membranes

Extrahepatic transplantation of islets of Langerhans could aid in better survival of islets after transplantation. When islets are transfused into the liver 60-70% of them are lost immediately after transplantation. An important factor for a successful extrahepatic transplantation is a well-vascularized tissue surrounding the implant. There are many strategies known for enhancing vessel formation such as adding cells with endothelial potential, the combination with angiogenic factors and / or applying surface topography at the exposed surface of the device. Previously we developed porous, micropatterned membranes which can be applied as a lid for an islet encapsulation device and we showed that the surface topography induces human umbilical vein endothelial cell (HUVEC) alignment and interconnection. This was achieved without the addition of hydrogels, often used in angiogenesis assays. In this work, we went one step further towards clinical implementation of the device by combining this micropatterned lid with Mesenchymal Stem Cells (MSCs) to facilitate prevascularization in vivo. As for HUVECs, the micropatterned membranes induced MSC alignment and organization in vitro, an important contributor to vessel formation, whereas in vivo (subcutaneous rat model) they contributed to improved implant prevascularization. In fact, the combination of MSCs seeded on the micropatterned membrane induced the highest vessel formation score in 80% of the sections.

Type I Interferon Is a Catastrophic Feature of the Diabetic Islet Microenvironment

A detailed understanding of the molecular pathways and cellular interactions that result in islet beta cell (β cell) destruction is essential for the development and implementation of effective therapies for prevention or reversal of type 1 diabetes (T1D). However, events that define the pathogenesis of human T1D have remained elusive. This gap in our knowledge results from the complex interaction between genetics, the immune system, and environmental factors that precipitate T1D in humans. A link between genetics, the immune system, and environmental factors are type 1 interferons (T1-IFNs). These cytokines are well known for inducing antiviral factors that limit infection by regulating innate and adaptive immune responses. Further, several T1D genetic risk loci are within genes that link innate and adaptive immune cell responses to T1-IFN. An additional clue that links T1-IFN to T1D is that these cytokines are a known constituent of the autoinflammatory milieu within the pancreas of patients with T1D. The presence of IFNα/β is correlated with characteristic MHC class I (MHC-I) hyperexpression found in the islets of patients with T1D, suggesting that T1-IFNs modulate the cross-talk between autoreactive cytotoxic CD8⁺ T lymphocytes and insulin-producing pancreatic β cells. Here, we review the evidence supporting the diabetogenic potential of T1-IFN in the islet microenvironment.

Islet cell hyperexpression of HLA class I antigens: a defining feature in type 1 diabetes

AIMS/HYPOTHESIS

Human pancreatic beta cells may be complicit in their own demise in type 1 diabetes, but how this occurs remains unclear. One potentially contributing factor is hyperexpression of HLA class I antigens. This was first described approximately 30 years ago, but has never been fully characterised and was recently challenged as artefactual. Therefore, we investigated HLA class I expression at the protein and RNA levels in pancreases from three cohorts of patients with type 1 diabetes. The principal aims were to consider whether HLA class I hyperexpression is artefactual and, if not, to determine the factors driving it.

METHODS

Pancreas samples from type 1 diabetes patients with residual insulin-containing islets (n = 26) from the Network for Pancreatic Organ donors with Diabetes (nPOD), Diabetes Virus Detection study (DiViD) and UK recent-onset type 1 diabetes collections were immunostained for HLA class I isoforms, signal transducer and activator of transcription 1 (STAT1), NLR family CARD domain containing 5 (NLRC5) and islet hormones. RNA was extracted from islets isolated by laser-capture microdissection from nPOD and DiViD samples and analysed using gene-expression arrays.

RESULTS

Hyperexpression of HLA class I was observed in the insulin-containing islets of type 1 diabetes patients from all three tissue collections, and was confirmed at both the RNA and protein levels. The expression of β2-microglobulin (a second component required for the generation of functional HLA class I complexes) was also elevated. Both 'classical' HLA class I isoforms (i.e. HLA-ABC) as well as a 'non-classical' HLA molecule, HLA-F, were hyperexpressed in insulin-containing islets. This hyperexpression did not correlate with detectable upregulation of the transcriptional regulator NLRC5. However, it was strongly associated with increased STAT1 expression in all three cohorts. Islet hyperexpression of HLA class I molecules occurred in the insulin-containing islets of patients with recent-onset type 1 diabetes and was also detectable in many patients with disease duration of up to 11 years, declining thereafter.

CONCLUSIONS/INTERPRETATION

Islet cell HLA class I hyperexpression is not an artefact, but is a hallmark in the immunopathogenesis of type 1 diabetes. The response is closely associated with elevated expression of STAT1 and, together, these occur uniquely in patients with type 1 diabetes, thereby contributing to their selective susceptibility to autoimmune-mediated destruction.

Oxidative stress and beta cell dysfunction

Autoimmune Type 1 A Diabetes (T1D) is characterized by dependence on exogenous insulin consequential to the autoimmune attack and destruction of insulin-producing islet beta cells. Pancreatic islet cell inflammation, or insulitis, precedes beta cell death and T1D onset. In the insulitic lesion, innate immune cells produce chemokines and cytokines that recruit and activate adaptive immune cells (Eizirik D et al., Nat Rev Endocrinol 5:219-226, 2009). Locally produced cytokines not only increase immune surveillance of beta cells (Hanafusa T and Imagawa A, Ann NY Acad Sci 1150:297-299, 2008), but also cause beta cell dysfunction and decreased insulin secretion due to the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) by the beta cells. This, coupled to the high levels of ROS and RNS secreted by activated macrophages and the low antioxidant capacities of beta cells (Huurman VA, PLoS One 3:e2435, 2008; Schatz D, Pediatr Diabetes 5:72-79, 2004; Verge CF, Diabetes 44:1176-1179, 1995), implicates free radicals as important effectors in T1D pathogenesis (Eizirik D et al., Nat Rev Endocrinol 5:219-226, 2009; Hanafusa T and Imagawa A, Ann NY Acad Sci 1150:297-299, 2008; Eisenbarth GS and Jeffrey J, Arq Bras Endocrinol Metabol 52:146-155, 2008; Pietropaolo M et al., Pediatr Diabetes 6:184-192, 2005).

Collecting high-quality pancreatic tissue for experimental study from organ donors with signs of β-cell autoimmunity

BACKGROUND

The aim of this study was to create a new research strategy to obtain high-quality pancreatic tissues from subjects with preclinical or clinical type 1 diabetes, which would open up new avenues for studying the mechanisms of the β-cell damaging process in humans.

RESEARCH DESIGN AND METHODS

A nationwide collaboration network (the PanFin network) was established in Finland to start an on-call screening of diabetes-associated autoantibodies from deceased organ donors and subsequent processing of pancreases from autoantibody-positive donors. This protocol was integrated into the national organ transplantation procedure.

RESULTS

Only a few modifications were needed to the normal transplantation practices. One additional blood sample was obtained from donors for autoantibody analyses, the transplantation team was informed about the autoantibody result and the pancreas of autoantibody-positive donors was transported to the core laboratory. Altogether, 307 donors were screened and 22 (7.2%) were positive for at least one autoantibody and 3 tested positive for two or more autoantibodies out of the five tested (islet cell antibodies, insulin autoantibodies and autoantibodies to glutamic acid decarboxylase, islet antigen 2 and zinc transporter 8). The quality of collected pancreatic tissue was superior to that from autopsies and allowed the detection of both RNA and proteins.

CONCLUSIONS

The study protocol was proven feasible to be carried out on a nationwide scale. It did not interfere with the normal transplantation activities and provided valuable tissue material for research.

Evidence of increased islet cell proliferation in patients with recent-onset type 1 diabetes

AIMS/HYPOTHESIS

In adults, the rate of beta cell replication is normally very low, but recent evidence suggests that it may increase during insulitis. We therefore studied tissue from donors with recent-onset type 1 diabetes to establish whether islet cell proliferation is increased during the disease process.

METHODS

Paraffin-embedded pancreatic sections from ten donors with recent-onset type 1 diabetes and a range of relevant controls were stained by immunohistochemical techniques with antibodies against the proliferation markers Ki67 and minichromosome maintenance protein-2 (MCM-2). A combination staining technique involving immunoperoxidase and immunofluorescence methods was developed to quantify the numbers of alpha and beta cells with Ki67-positive nuclei and to investigate the relationship between insulitis and islet cell proliferation.

RESULTS

In non-diabetic control donors, only 1.1 +/- 0.3% (mean +/- SEM) of islets contained one or more Ki67(+) islet cells, whereas this proportion was increased markedly in recent-onset type 1 diabetes (10.88 +/- 2.5%; p < 0.005). An equivalent increase in Ki67(+) staining occurred in alpha and beta cells and was correlated positively with the presence of insulitis. A significant increase in the labelling of islet cells from type 1 diabetic donors was also seen when MCM-2 staining was employed. Increased islet cell proliferation was not evident in three donors with longer duration type 1 diabetes or in ten type 2 diabetic donors.

CONCLUSIONS/INTERPRETATION

Alpha and beta cells undergo a marked increase in proliferation during the progression of type 1 diabetes in humans. The results imply that islet cell proliferation is re-initiated in response to the autoimmune attack associated with type 1 diabetes.

Insulin: a critical autoantigen and potential therapeutic agent in Type 1 diabetes

Insulin is a polypeptide hormone secreted by pancreatic beta-cells and is critical for glucose homeostasis. Abnormalities in insulin secretion result in various forms of diabetes. Type 1A diabetes is an autoimmune form in which insulin has been identified as a critical autoantigen. Recent studies have identified genetic determinants of insulin-specific autoimmune responses and insulin epitopes targeted by autoreactive T lymphocytes. The study of insulin as an autoantigen has also led to discoveries about basic mechanisms of immunological tolerance and autoimmunity. Experimental and clinical evidence suggests that insulin and insulin-derived peptides may delay and perhaps prevent the development of diabetes. Further clinical trials may identify effective treatment modalities for inhibiting diabetogenic autoimmunity and preventing disease development.

The pancreas in human type 1 diabetes

Type 1 diabetes (T1D) is considered a disorder whose pathogenesis is autoimmune in origin, a notion drawn in large part from studies of human pancreata performed as far back as the 1960s. While studies of the genetics, epidemiology, and peripheral immunity in T1D have been subject to widespread analysis over the ensuing decades, efforts to understand the disorder through analysis of human pancreata have been far more limited. We have reviewed the published literature pertaining to the pathology of the human pancreas throughout all stages in the natural history of T1D. This effort uncovered a series of findings that challenge many dogmas ascribed to T1D and revealed data suggesting the marked heterogeneity in terms of its pathology. An improved understanding and appreciation for pancreatic pathology in T1D could lead to improved disease classification, an understanding of why the disorder occurs, and better therapies for disease prevention and management.

Type 1 diabetes mellitus: primary, secondary, and tertiary prevention

We have entered the era of clinical trials to prevent type 1 diabetes mellitus (T1DM). Before 1922, when insulin was first given to a patient with diabetes, a diagnosis of T1DM was considered a death sentence. Advances in treatment for subjects with diabetes are not yet sufficient to prevent the deleterious impact of diabetes on both day-to-day activities and the early morbidity and mortality still associated with the disease. We now understand a great deal about blood glucose regulation and potential health complications associated with long-term T1DM, but the mystery of why, or the pathogenesis of this devastating disease, remains elusive. Great strides toward unraveling this mystery have been made over the past several decades. Even without definitive answers, we are moving from the period of discovery and animal research to the era of clinical trials. In this review, we wish to convey the palpable excitement in the field. It is time to determine if we can safely change the course of T1DM.

Analysis of pancreas tissue in a child positive for islet cell antibodies

AIMS/HYPOTHESIS

Type 1 diabetes is caused by an immune-mediated process, reflected by the appearance of autoantibodies against pancreatic islets in the peripheral circulation. Detection of multiple autoantibodies predicts the development of diabetes, while positivity for a single autoantibody is a poor prognostic marker. The present study assesses whether positivity for a single autoantibody correlates with pathological changes in the pancreas.

METHODS

We studied post mortem pancreatic tissue of a child who repeatedly tested positive for islet cell antibodies (ICA) in serial measurements. Paraffin sections were stained with antibodies specific for insulin, glucagon, somatostatin, interferon alpha, CD3, CD68, cyclooxygenase-2 (COX-2), beta-2-microglobulin, coxsackie B and adenovirus receptor (CAR), natural killer and dendritic cells. Apoptosis was detected using Fas-specific antibody and TUNEL assay. Enterovirus was searched for using immunohistochemistry and in situ hybridisation, as well as enterovirus-specific RT-PCR from serum samples.

RESULTS

The structure of the pancreas did not differ from normal. The number of beta cells was not reduced and no signs of insulitis were observed. Beta-2-microglobulin and CAR were strongly produced in the islets, but not in the exocrine pancreas. Enterovirus protein was detected selectively in the islets by two enterovirus-specific antibodies, but viral RNA was not found.

CONCLUSIONS/INTERPRETATION

These observations suggest that positivity for ICA alone, even when lasting for more than 1 year, is not associated with inflammatory changes in the islets. However, it is most likely that the pancreatic islets were infected by an enterovirus in this child.

The molecular genetics of type 1 diabetes: new genes and emerging mechanisms

Susceptibility to type 1 diabetes (T1D) is determined by complex interactions between several genetic loci and environmental factors. Alleles at the human leukocyte antigen (HLA) locus explain up to 50% of the familial clustering of T1D, and the remainder is contributed to by multiple loci, of which only four were known until recently. First-stage results of genome-wide association (GWA) studies performed with high-density genotyping arrays have already produced four novel loci and the promise that, with the completion of the second stage of the GWA studies, most of the genetic basis of T1D will be known. We will review what is known to date about the mechanisms of genetic susceptibility to T1D, with special emphasis on possible diagnostic and therapeutic applications of these recent genetic findings.

Interferons induce an antiviral state in human pancreatic islet cells

Enterovirus infections, in particular those with Coxsackieviruses, have been linked to the development of type 1 diabetes (T1D). Although animal models have demonstrated that interferons (IFNs) regulate virus-induced T1D by acting directly on the beta cell, little is known on the human pancreatic islet response to IFNs. Here we show that human islet cells respond to IFNs by expressing signature genes of antiviral defense. We also demonstrate that they express three intracellular sensors for viral RNA, the toll like receptor 3 (TLR3) gene, the retinoic acid-inducible gene I (RIG-I) and the melanoma differentiation-associated gene-5 (MDA-5), which induce type I IFN production in infected cells. Finally, we show for the first time that the IFN-induced antiviral state provides human islets with a powerful protection from the replication of Coxsackievirus. This may be critical for beta cell survival and protection from virus-induced T1D in humans.

Enteroendocrine cell dysgenesis and malabsorption, a histopathologic and immunohistochemical characterization

Enteroendocrine cell dysgenesis was observed in 3 patients with intestinal failure of unknown cause. Enteroendocrine cell dysgenesis is a congenitally acquired life-threatening malabsorptive condition with a unique clinical phenotype paired with a histologically identifiable disease pattern. Two cases were first presented at the Ninth International Small Bowel Transplantation Symposium, Brussels 2005, and were subsequently published (N Engl J Med 2006;355:270). We now present the histopathologic and immunohistochemical findings of the gastric antrum, small bowel, and colon in greater detail. The clinical phenotype of the patients was unusual in that the affected patients demonstrated profound malabsorption of all nutrients, except water, from birth. The small intestine in each patient demonstrated almost no abnormality, except a near absence of endocrine cells in the mucosa. The colon appeared similarly affected. Known causes of congenital malabsorption, inflammatory, and infectious causes of diarrhea were excluded. The defect is secondary to point mutations in NEUROG3, which result in an arrest of endocrine cell development in the small intestine and colon. This work describes the pathologic characterization of enteroendocrine cell dysgenesis using routine techniques. The pattern of injury is distinct from other histopathologically assessed congenital malabsorptive conditions such as microvillus inclusion disease, tufting enteropathy, and abetalipoproteinemia. It is also easily distinguished from inflammatory conditions such as food allergy, gluten-sensitive enteropathy, autoimmune enteropathy, IPEX (immune dysfunction, polyendocrinopathy, enteropathy, and X-linked inheritance), and inflammatory bowel disease. The histopathology of disease is similar to what has been found transiently in a single patient with autoimmune polyglandular syndrome type I.

Interferon-gamma-induced regulation of the pancreatic derived cytokine FAM3B in islets and insulin-secreting betaTC3 cells

The pancreatic-derived factor (PANDER, FAM3B) is a novel protein that is beta-cell specific and induces beta-cell death. PANDER is localized to insulin-containing granules-based on confocal microscopy and immunogold electron microscopy. PANDER protein was detected in the conditioned medium of betaTC3 cells. Using real-time reverse transcription-polymerase chain reaction, treatment of betaTC3 cells with IL-1beta + TNFalpha + IFNgamma induced a significant seven-fold increase in PANDER mRNA expression (n = 3; p < 0.01 at 24 h, p < 0.05 at 48 h), while IFNgamma alone caused a 3.2-fold increase (n = 3; p < 0.01 at 24 h) compared to unstimulated and time-matched vehicle controls. IL-1beta or TNFalpha alone had no effect. Under those conditions, a similar up-regulation was also observed in mouse islet cells, with increases in PANDER mRNA of 5.9-fold and 5.0-fold after treatment with IL-1beta + TNFalpha + IFNgamma or IFNgamma alone. Because PANDER mRNA expression is up-regulated by IFNgamma, a cytokine implicated in the pathogenesis of type 1 diabetes, PANDER may contribute to the pathogenesis of beta-cell death.

No evidence for association of the TATA-box binding protein glutamine repeat sequence or the flanking chromosome 6q27 region with type 1 diabetes

Susceptibility to the autoimmune disease type 1 diabetes has been linked to human chromosome 6q27 and, moreover, recently associated with one of the genes in the region, TATA box-binding protein (TBP). Using a much larger sample of T1D families than those studied by others, and by extensive re-sequencing of nine other genes in the proximity, in which we identified 279 polymorphisms, 83 of which were genotyped in up to 725 T1D multiplex and simplex families, we obtained no evidence for association of the TBP CAG/CAA (glutamine) microsatellite repeat sequence with disease, or for nine other genes, PDCD2, PSMB1, KIAA1838, DLL1, dJ894D12.4, FLJ25454, FLJ13162, FLJ11152, PHF10 and CCR6. This study also provides an exon-based tag single nucleotide polymorphism map for these 10 genes that can be used for analysis of other diseases.

CTLA-4 gene polymorphisms and susceptibility to type 1 diabetes mellitus: a HuGE Review and meta-analysis

The authors performed a meta-analysis of 33 studies examining the association of type 1 diabetes mellitus with polymorphisms in the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) gene, including the A49G (29 comparisons), C(-318)T (three comparisons), and (AT)n microsatellite (six comparisons) polymorphisms. The studies included 5,637 cases of type 1 diabetes and 6,759 controls (4,775 and 5,829, respectively, for analysis of the A49G polymorphism). The random-effects odds ratio for the *G (Ala) allele versus the *A (Thr) allele was 1.45 (95% confidence interval (CI): 1.28, 1.65), with significant between-study heterogeneity (p < 0.001). The effect size tended to be higher in type 1 diabetes cases with age of onset <20 years (odds ratio (OR) = 1.61), and there was a significant association between the presence of glutamic acid decarboxylase-65 autoantibodies and the *G allele among type 1 diabetes cases (OR = 1.49). Larger studies showed more conservative results (p = 0.011). After exclusion of studies with fewer than 150 subjects and studies with significant deviation from Hardy-Weinberg equilibrium in the controls, the summary odds ratio was 1.40 (95% CI: 1.28, 1.54). Available data showed no strong association for the 106-base-pair allele of the microsatellite polymorphism (OR = 0.99, 95% CI: 0.64, 1.55) or the *T allele of the C(-318)T polymorphism (OR = 0.92, 95% CI: 0.45, 1.89). This meta-analysis demonstrates that the CTLA-4*G genotype is associated with type 1 diabetes.

Inflammatory cytokine regulation of TRAIL-mediated apoptosis in thyroid epithelial cells

Death receptor-mediated apoptosis has been implicated in target organ destruction in chronic autoimmune thyroiditis. Depending on the circumstances, inflammatory cytokines such as IL-1, TNF and IFNgamma have been shown to contribute to either the induction, progression or inhibition of this disease. Here we demonstrate that the death ligand TRAIL can induce apoptosis in primary, normal, thyroid epithelial cells under physiologically relevant conditions, specifically, treatment with the combination of inflammatory cytokines IL-1beta and TNFalpha. In contrast, IFNgamma is capable of blocking TRAIL-induced apoptosis in these cells. This regulation of TRAIL-mediated apoptosis by inflammatory cytokines appears to be due to alterations of cell surface expression of TRAIL receptor DR5 and not DR4. We also show the in vivo presence of TRAIL and TRAIL receptors DR5 and DcR1 in both normal and inflamed thyroids. Our data suggests TRAIL-mediated apoptosis may contribute to target organ destruction in chronic autoimmune thyroiditis.

Expression of pancreatic islet MHC class I, insulin, and ICA 512 tyrosine phosphatase in low-dose streptozotocin-induced diabetes in mice

Activated immune cells contribute to the development of diabetes mellitus in multiple low-dose streptozotocin-treated mice. However, a role in the process for MHC Class I restricted T-cells remains a matter of debate. In this study, we examined by confocal microscopy the pancreatic expression of MHC Class I protein, insulin, and ICA 512 protein tyrosine phosphatase in C57BL/Ks mice given 40 mg/kg bw streptozotocin IP on 5 consecutive days. All animals were hyperglycemic from Day 7 and onwards. A loss of ICA 512 from the central portions of the islets was noted on Day 3. On Day 7, an increase in MHC Class I expression, confined primarily to immune cells in the exocrine pancreas and the periinsular areas, was detected. Later, several MHC class I/glucagon and some MHC class I/insulin double-positive cells were found. The insulitis was maximal on Day 14 and declined thereafter. The induction of MHC Class I expression in endocrine cells, occuring only after the cellular infiltration and when the animals were diabetic, indicates that the immune component of the disease does not depend on MHC Class I-restricted cytotoxic T-cells but rather comprises a non-antigen-specific process. (J Histochem Cytochem 48:761-767, 2000)

Apoptosis and thyroiditis

The origin of the various forms of autoimmune thyroiditis remains unclear. Most investigations into the pathogenesis of these disorders have focused on immune abnormalities that might lead to an autoimmune response. However, no unique immune response to thyroid autoantigens has been identified that either is limited to patients with thyroiditis or is absolutely correlated with clinical disease expression. CD8 T-cell-mediated cytotoxicity is thought to be a major cause of thyroid follicular cell damage in thyroiditis. This damage is produced in part through the induction of apoptosis in thyroid cells. Recent studies have demonstrated that programmed cell death is regulated in thyroid cells and that a major pathway for immune-mediated apoptosis, the Fas pathway, is blocked by labile inhibitors in a manner that could prevent cytotoxicity. This review also examines several other types of regulation of apoptotic pathways in thyrocytes. We hypothesize that the regulation of programmed cell death pathways in the thyroid may alter the expression of autoimmune thyroid diseases by modifying the susceptibility of thyroid cells to immune-mediated apoptosis.