On the etiology of type 1 diabetes: a new animal model signifying a decisive role for bacteria eliciting an adverse innate immunity response

Evaluation of RT-PCR and immunohistochemistry as tools for detection of enterovirus in the human pancreas and islets of Langerhans

BACKGROUND

Enteroviruses have been implicated in the etiology of type 1 diabetes, supported by immunoreactivity of enteroviral protein in islets, but presence of enteroviral genome has rarely been reported. Failure to detect enterovirus with RT-PCR has been attributed to the possible presence of PCR inhibitors and that only few cells are infected.

OBJECTIVES

The aim of this study was to evaluate strategies for detection of enterovirus in human islets.

STUDY DESIGN

A scenario was modeled with defined infected islets among a large number of uninfected pancreatic cells and the sensitivity of immunohistochemistry and PCR for detection of enterovirus was evaluated.

RESULTS

Enterovirus was detected with PCR when only one single human islet, infected in vitro with a low dose of virus, was mixed with an uninfected pancreatic biopsy. Enterovirus could not be detected by immunohistochemistry under the same conditions, demonstrating the superior sensitivity of PCR also in pancreatic tissue with only a small fraction of infected cells. In addition, we demonstrate that pancreatic cell culture supernatant does not cause degradation of enterovirus at 37°C, indicating that under normal culture conditions released virus is readily detectable. Utilizing PCR, the pancreases of two organ donors that died at onset of type 1 diabetes were found negative for enterovirus genome despite islet cells being positive using immunohistochemistry.

CONCLUSIONS

These data suggest that PCR should be the preferred screening method for enterovirus in the pancreas and suggest cautious interpretation of immunostaining for enterovirus that cannot be confirmed with PCR.

Insulitis in human type 1 diabetes: a comparison between patients and animal models

Human type 1 diabetes (T1D) is considered to be an autoimmune disease, with CD8+ T-cell-mediated cytotoxicity being directed against the insulin-producing beta cells, leading to a gradual decrease in beta cell mass and the development of chronic hyperglycemia. The histopathologically defining lesion in recent-onset T1D patients is insulitis, a relatively subtle leucocytic infiltration present in approximately 10 % of the islets of Langerhans from children with recent-onset (<1 year) disease. Due to the transient nature of the infiltrate, its heterogeneous distribution in the pancreas and the nature of the patient population, material for research is extremely rare and limited to a cumulative total of approximately 150 cases collected over the past century. Most studies on the etiopathogenesis of T1D have therefore focused on the non-obese diabetic (NOD) mouse model, which shares many genetic and immunological disease characteristics with human T1D, although its islet histopathology is remarkably different. In view of these differences and in view of the limited success of clinical immune interventions based on observations in the NOD mouse, there is a renewed focus on studying the pathogenetic process in patient material.

Gene expression analysis of human islets in a subject at onset of type 1 diabetes

Swollen islet cells have been repeatedly described at onset of type 1 diabetes, but the underlying mechanism of this observation, termed hydropic degeneration, awaits characterization. In this study, laser capture microdissection was applied to extract the islets from an organ donor that died at onset of type 1 diabetes and from an organ donor without pancreatic disease. Morphologic analysis revealed extensive hydropic degeneration in 73% of the islets from the donor with type 1 diabetes. Expression levels of genes involved in apoptosis, ER stress, beta cell function, and inflammation were analyzed in isolated and laser-captured islets by qPCR. The chemokine MCP-1 was expressed in islets from the donor with type 1 diabetes while undetectable in the control donor. No other signs of inflammation were detected. There were no signs of apoptosis on the gene expression level, which was also confirmed by negative immunostaining for cleaved caspase-8. There was an increased expression of the transcription factor ATF4, involved in transcription of ER stress genes, in the diabetic islets, but no further signs of ER stress were identified. In summary, on the transcription level, islets at onset of type 1 diabetes in which many beta cells display hydropic degeneration show no obvious signs of apoptosis, ER stress, or inflammation, supporting the notion that these cells are responding normally to high glucose and eventually succumbing to beta cell exhaustion. Also, this study validates the feasibility of performing qPCR analysis of RNA extracted from islets from subjects with recent onset of T1D and healthy controls by laser capture microdissection.

Distinct function of the head region of human pancreas in the pathogenesis of diabetes

The large size of the human pancreas challenges unbiased quantitative analyses that require a practical stereological approach. While many histological studies of the pancreas in the past lacked regional information, we have shown marked heterogeneity within an individual, where islet distribution/density is relatively low in the head and gradually increases through the body toward the tail region by>2-fold. Studies focusing on the tail region may be prone to overestimation of β-cell/islet mass when normalizing measured values per person by using pancreas weight or volume. In this article, beyond technical issues, we discuss the pathophysiological importance of studying the head region of the human pancreas regarding its unique characteristics in early development, and the anatomical disposition that may lead to a preferential loss of β-cells in patients with type 2 diabetes and the development of pancreatic cancer.

Revisiting the notion of type 1 diabetes being a T-cell-mediated autoimmune disease

PURPOSE OF REVIEW

Type 1 diabetes (T1D) research is at present in a critical period of development and during the past few years several large phase III studies targeting T-cell autoimmunity in recent-onset patients with T1D failed to reach the primary endpoint.

RECENT FINDINGS

Cause and pathogenesis of T1D remain largely unknown. In humans, insulitis is discrete, affects few islets and is present only in about one-third of patients with recent-onset T1D. The rapid increase in incidence of T1D argues against a decisive role for genetic factors and instead for the hypothesis that infectious agents, possibly entering the pancreas via the ductal compartment, are involved in disease pathogenesis. Repeated episodes of bacteria or virus-induced innate inflammations affecting only certain lobes of the pancreas fit well with the reported heterogeneity of the disease within the pancreas as well as with the slow progression over many years.

SUMMARY

In humans there is limited support for T1D being primarily an autoimmune disease; instead available findings support the view that T1D can be regarded as an innate inflammatory disease affecting the entire pancreas, but with its main clinical manifestations emanating from the loss of the insulin-producing cells.

Fecal transplant: a safe and sustainable clinical therapy for restoring intestinal microbial balance in human disease?

Recent studies have suggested an association between intestinal microbiota composition and human disease, however causality remains to be proven. With hindsight, the application of fecal transplantation (FMT) does indeed suggest a causal relation between interfering with gut microbiota composition and a resultant cure of several disease states. In this review, we aim to show the available evidence regarding the involvement of intestinal microbiota and human (autoimmune) disease. Moreover, we refer to (mostly case report) studies showing beneficial or adverse effects of fecal transplantation on clinical outcomes in some of these disease states. If these findings can be substantiated in larger randomized controlled double blind trials also implementing gut microbiota composition before and after intervention, fecal transplantation might provide us with novel insights into causally related intestinal microbiota, that might be serve as future diagnostic and treatment targets in human disease.