Toxoplasma gondii as a possible causative pathogen of type-1 diabetes mellitus: Evidence from case-control and experimental studies.

Toxoplasma gondii is the causative parasite of an important worldwide disease. This obligate intracellular parasite can infect and replicate inside any nucleated cells including those of pancreas. Insulin is a hormone secreted by the pancreas and is responsible for controlling blood glucose concentration. Deficiency of insulin production accounts for the occurrence of type-1 diabetes mellitus (T1D). Thus, theoretically, toxoplasmosis could play a possible role in the development of T1D. However, the studies on this theory are still insufficient; therefore, this work was designed. Interestingly, in the case-control study, seropositivity of anti-Toxoplasma IgG was significantly higher among T1D (86.37%) in comparison with T2D (66.67%) and the control group (60%). Moreover, the odd ratio of chronic toxoplasmosis was 4.2 folds higher among T1D patients than among controls. The experimental study included acute and chronic Me49 T. gondii infected mice groups in addition to a control group. Pathological examination revealed the presence of T. gondii zoites adjacent to the islets of Langerhans and in pancreatic parenchyma of acutely infected mice. With chronic infection, there was a significant reduction of islets number and sizes in association with grade-1 insulitis. Additionally, the immunohistochemical study showed significant infiltration of the islets of chronically infected mice by CD8+ and CD45+ immune cells. In contrary to the control group, the islets of the chronic group showed significantly higher expression of the apoptotic marker caspase-3 and a significantly lower expression of the proliferation marker Ki69. Finally, a significant reduction of insulin expression in the islets of chronic infection group was detected in association with a significant increase in serum glucose concentrations; however, the establishment of diabetes did not occur throughout this work. Thus, this study presents an evidence for the probable role of chronic toxoplasmosis in the development of T1D which should be considered in further studies.

Host-Parasite Interactions in Individuals with Type 1 and 2 Diabetes Result in Higher Frequency of Ascaris lumbricoides and Giardia lamblia in Type 2 Diabetic Individuals.

Host-parasite interactions in diabetic patients might influence diabetes complications and intestinal parasitosis. The aim was to investigate the occurrence of enteroparasites in individuals with diabetes types 1 and 2. A descriptive study was designed to estimate frequencies of parasites and to compare them in individuals with diabetes types 1 and 2 from two Health Centers and one hospital in the Federal District of Brazil. Patients were allocated to the study by convenience. Three fecal samples of 156 diabetic individuals (120 type 1 and 36 type 2) were analyzed using two parasitological methods. Enteroparasites or commensals frequency in diabetics was 64%. Diabetics infected with up to six species of intestinal parasites or commensals were found. Frequencies of Ascaris lumbricoides and Giardia lamblia were higher in individuals with type 2 diabetes. The lower frequency of A. lumbricoides found in type 1 diabetes may be related to a strong Th2 response to parasites. Autoimmune response developed in type 1 diabetic individuals characterized by the production of Th1 cytokines could explain low frequency of G. lamblia. High frequency of parasites found in type 2 diabetes emphasizes the importance of periodic parasitological examinations in these individuals.

Toxoplasma gondii Infection in Diabetes Mellitus Patients in China: Seroprevalence, Risk Factors, and Case-Control Studies.

The association between Toxoplasma gondii (T. gondii) infection and diabetes mellitus remains controversial. With the improvement of living standards, the prevalence rate of diabetes is steadily increasing in China. Thus, it is necessary to explore the possible association between toxoplasmosis and diabetes mellitus in China. Hence, case-control studies were conducted to explore the T. gondii seroprevalence and identify the risk factors and possible transmission routes of T. gondii infection in different types of diabetes, including type 1 diabetes (T1DM), type 2 diabetes (T2DM), and gestational diabetes (GDM) patients in China. Four hundred serum samples for each type of diabetes mellitus, matched with 400 control subjects for each group, were collected and examined for anti-T. gondii IgG and IgM antibodies using commercially available enzyme immunoassay kits. The total T. gondii seroprevalence in T1DM, T2DM, and GDM patients was 16.50%, 23.50%, and 21.25%, respectively. Each type of diabetes mellitus patients had a significantly higher T. gondii seroprevalence than the control subjects. Multivariate regression identified three variables as risk factors for T. gondii infection in diabetes patients, including keeping cats at home and consumption of raw oysters for T1DM patients and consumption of raw/undercooked meat and raw oysters for T2DM patients, which may help to guide future research and control policies in diabetes mellitus patients.

Therapeutic potential of helminths in autoimmune diseases: helminth-derived immune-regulators and immune balance.

Helminths have accompanied human throughout history by releasing immune-evasion molecules that could counteract an aberrant immune response within the host. In the past decades, helminth infections are becoming less prevalent possibly due to the developed sanitation. Meanwhile, the incidence of autoimmune diseases is increasing, which cannot be exclusively explained by the changes of susceptibility genes. While the hygiene hypothesis casts light on the problem. The infections of helminths are believed to interact with and regulate human immunity with the byproduct of suppressing the autoimmune diseases. Thus, helminths are potential to treat or cure the autoimmune diseases. The therapeutic progresses and possible immune suppression mechanisms are illustrated in the review. The helminths that are studied most intensively include Heligmosomoides polygyrus, Hymenolepis diminuta, Schistosoma mansoni, Trichinella spiralis, and Trichuris suis. Special attentions are paid on the booming animal models and clinical trials that are to detect the efficiency of immune-modulating helminth-derived molecules on autoimmune diseases. These trials provide us with a prosperous clinical perspective, but the precise mechanism of the down-regulatory immune response remains to be clarified. More efforts are needed to be dedicated until these parasite-derived immune modulators could be used in clinic to treat or cure the autoimmune diseases under a standard management.

Dual genetic absence of STAT6 and IL-10 does not abrogate anti-hyperglycemic effects of Schistosoma mansoni in streptozotocin-treated diabetic mice.

Schistosoma mansoni (Sm) is known to exert protective effects against various allergic and autoimmune disorders. It has been reported that this parasite protects NOD mice from spontaneous type 1 diabetes (T1D) and ameliorates streptozotocin (STZ)-induced T1D in wild-type mice. Here, we tried to clarify the anti-diabetic mechanisms of Sm in the latter model. Sm infection partially prevented the degradation of pancreatic islets and hyperglycemia in multiple low-dose (MLD) STZ-treated mice. Neither Treg cell depletion nor genetic absences of IL-10 and/or STAT6 abrogated the anti-hyperglycemic effects of Sm. Among M2 macrophage markers, Arg-1 and Ym1, but not Retnla, remained up-regulated in the pancreatic lymph nodes and in the spleens of STAT6/IL-10 double deficient (DKO) mice. Collectively, it is suggested that Sm exerts anti-diabetic effects on this experimental T1D model via Treg/IL-4/IL-13/IL-10-independent mechanisms. Augmented expressions of Arg-1 and Ym1 in the lymphoid organs adjacent to pancreas may be relevant to the anti-diabetic effects of Sm.

Immunomodulation by helminths: Similar impact on type 1 and type 2 diabetes?

The incidence of both type 1 (T1D) and type 2 diabetes (T2D) is drastically increasing, and it is predicted that the global prevalence of diabetes will reach almost 600 million cases by 2035. Even though the pathogenesis of both types of diabetes is distinct, the immune system is actively involved in both forms of the disease. Genetic and environmental factors determine the risk to develop T1D. On the other hand, sedentary life style, surplus of food intake and other lifestyle changes contribute to the increase of T2D incidence. Improved sanitation with high-quality medical treatment is such an environmental factor that has led to a continuous reduction of infectious diseases including helminth infections over the past decades. Recently, a growing body of evidence has implicated a negative association between helminth infections and diabetes in humans as well as animal models. In this review, we discuss studies that have provided evidence for the beneficial impact of helminth infections on T1D and T2D. Possible mechanisms are presented by which helminths prevent T1D onset by mitigating pancreatic inflammation and confer protection against T2D by improving insulin sensitivity, alleviating inflammation, augmenting browning of adipose tissue and improving lipid metabolism and insulin signalling.

Secreted proteins from the helminth Fasciola hepatica inhibit the initiation of autoreactive T cell responses and prevent diabetes in the NOD mouse.

Infections with helminth parasites prevent/attenuate auto-inflammatory disease. Here we show that molecules secreted by a helminth parasite could prevent Type 1 Diabetes (T1D) in nonobese diabetic (NOD) mice. When delivered at 4 weeks of age (coincident with the initiation of autoimmunity), the excretory/secretory products of Fasciola hepatica (FhES) prevented the onset of T1D, with 84% of mice remaining normoglycaemic and insulitis-free at 30 weeks of age. Disease protection was associated with suppression of IFN-γ secretion from autoreactive T cells and a switch to the production of a regulatory isotype (from IgG2a to IgG1) of autoantibody. Following FhES injection, peritoneal macrophages converted to a regulatory M2 phenotype, characterised by increased expression levels of Ym1, Arg-1, TGFß and PD-L1. Expression of these M2 genetic markers increased in the pancreatic lymph nodes and the pancreas of FhES-treated mice. In vitro, FhES-stimulated M2 macrophages induced the differentiation of Tregs from splenocytes isolated from naïve NOD mice. Collectively, our data shows that FhES contains immune-modulatory molecules that mediate protection from autoimmune diabetes via the induction and maintenance of a regulatory immune environment.

Helminth mediated modulation of Type 1 diabetes (T1D).

Type 1 diabetes is increasing dramatically in incidence in the developed world. While there may be several reasons for this, improved sanitation and public health measures have altered our interactions with certain infectious agents such as helminths. There is increasing interest in the use of helminths or their products to alleviate inflammatory or allergic conditions. Using rodent models of diabetes, it has been possible to explore the therapeutic potential of both live infections as well as helminth-derived products on the development of autoimmunity. This review provides an overview of the findings from animal models and additionally explores the potential for translation to the clinic.

Helminth protection against autoimmune diabetes in nonobese diabetic mice is independent of a type 2 immune shift and requires TGF-ß.

Leading hypotheses to explain helminth-mediated protection against autoimmunity postulate that type 2 or regulatory immune responses induced by helminth infections in the host limit pathogenic Th1-driven autoimmune responses. We tested these hypotheses by investigating whether infection with the filarial nematode Litomosoides sigmodontis prevents diabetes onset in IL-4-deficient NOD mice and whether depletion or absence of regulatory T cells, IL-10, or TGF-ß alters helminth-mediated protection. In contrast to IL-4-competent NOD mice, IL-4-deficient NOD mice failed to develop a type 2 shift in either cytokine or Ab production during L. sigmodontis infection. Despite the absence of a type 2 immune shift, infection of IL-4-deficient NOD mice with L. sigmodontis prevented diabetes onset in all mice studied. Infections in immunocompetent and IL-4-deficient NOD mice were accompanied by increases in CD4(+)CD25(+)Foxp3(+) regulatory T cell frequencies and numbers, respectively, and helminth infection increased the proliferation of CD4(+)Foxp3(+) cells. However, depletion of CD25(+) cells in NOD mice or Foxp3(+) T cells from splenocytes transferred into NOD.scid mice did not decrease helminth-mediated protection against diabetes onset. Continuous depletion of the anti-inflammatory cytokine TGF-ß, but not blockade of IL-10 signaling, prevented the beneficial effect of helminth infection on diabetes. Changes in Th17 responses did not seem to play an important role in helminth-mediated protection against autoimmunity, because helminth infection was not associated with a decreased Th17 immune response. This study demonstrates that L. sigmodontis-mediated protection against diabetes in NOD mice is not dependent on the induction of a type 2 immune shift but does require TGF-ß.

Helminth infection and type 1 diabetes.

The increasing incidence of type 1 diabetes (T1D) and autoimmune diseases in industrialized countries cannot be exclusively explained by genetic factors. Human epidemiological studies and animal experimental data provide accumulating evidence for the role of environmental factors, such as infections, in the regulation of allergy and autoimmune diseases. The hygiene hypothesis has formally provided a rationale for these observations, suggesting that our co-evolution with pathogens has contributed to the shaping of the present-day human immune system. Therefore, improved sanitation, together with infection control, has removed immunoregulatory mechanisms on which our immune system may depend. Helminths are multicellular organisms that have developed a wide range of strategies to manipulate the host immune system to survive and complete their reproductive cycles successfully. Immunity to helminths involves profound changes in both the innate and adaptive immune compartments, which can have a protective effect in inflammation and autoimmunity. Recently, helminth-derived antigens and molecules have been tested in vitro and in vivo to explore possible applications in the treatment of inflammatory and autoimmune diseases, including T1D. This exciting approach presents numerous challenges that will need to be addressed before it can reach safe clinical application. This review outlines basic insight into the ability of helminths to modulate the onset and progression of T1D, and frames some of the challenges that helminth-derived therapies may face in the context of clinical translation.

Regulation of type 1 diabetes, tuberculosis, and asthma by parasites.

Helminth infection is a worldwide health problem. In addition to directly causing disease, helminthic infection also affects the incidence and progression of other diseases by exerting immune modulatory effects. In animal models, infection with helminthic parasites can prevent autoimmune diseases and allergic inflammatory diseases, but worsens protective immunity to certain infectious pathogens. In this review, we summarize current findings regarding the effects of helminth infection on type 1 diabetes, tuberculosis, and asthma and discuss possible mechanisms through which helminthic parasites modulate host immunity. Investigating these mechanisms could lead to treatment strategies that specifically modulate the immune response as well as address fundamental questions in immunobiology.

Helminth infection can reduce insulitis and type 1 diabetes through CD25- and IL-10-independent mechanisms.

Parasitic helminth infection has been shown to modulate pathological inflammatory responses in allergy and autoimmune disease. The aim of this study was to examine the effects of infection with a helminth parasite, Heligmosomoides polygyrus, on type 1 diabetes (T1D) in nonobese diabetic (NOD) mice and to elucidate the mechanisms involved in this protection. H. polygyrus inoculation at 5 weeks of age protected NOD mice from T1D until 40 weeks of age and also inhibited the more aggressive cyclophosphamide-induced T1D. Moreover, H. polygyrus inoculation as late as 12 weeks of age reduced the onset of T1D in NOD mice. Following H. polygyrus inoculation of NOD mice, pancreatic insulitis was markedly inhibited. Interleukin-4 (IL-4), IL-10, and IL-13 expression and the frequency of CD4(+) CD25(+) FoxP3(+) regulatory T cells were elevated in mesenteric and pancreatic lymph nodes. Depletion of CD4(+) CD25(+) T cells in vivo did not abrogate H. polygyrus-induced T1D protection, nor did anti-IL-10 receptor blocking antibody. These findings suggest that infection with H. polygyrus significantly inhibits T1D in NOD mice through CD25- and IL-10-independent mechanisms and also reduces the severity of T1D when administered late after the onset of insulitis.

Helminths as governors of immune-mediated inflammation.

Immune-mediated diseases (e.g. inflammatory bowel disease, asthma, multiple sclerosis and autoimmune diabetes) are increasing in prevalence and emerge as populations adopt meticulously hygienic lifestyles. This change in lifestyles precludes exposure to helminths (parasitic worms). Loss of natural helminth exposure removes a previously universal Th2 and regulatory immune biasing imparted by these organisms. Helminths protect animals from developing immune-mediated diseases (colitis, reactive airway disease, encephalitis and diabetes). Clinical trials show that exposure to helminths can reduce disease activity in patients with ulcerative colitis or Crohn's disease. This paper summarises work by multiple groups demonstrating that colonization with helminths alters immune reactivity and protects against disease from dysregulated inflammation.

Infection with Schistosoma mansoni prevents insulin dependent diabetes mellitus in non-obese diabetic mice.

The spontaneous development of insulin dependent diabetes mellitus in non-obese diabetic (NOD) mice has been shown to be mediated by a Th1 response against beta cell antigens. It is known that in murine models of Schistosoma mansoni infection, egg production is associated with a switch from a Th1 to Th2 response. This subsequent dominance of a Th2 response in S.mansoni infected mice has been shown to influence the response to other infectious agents or antigens. We therefore determined whether infection with S.mansoni could influence the spontaneous incidence of insulin dependent diabetes mellitus (IDDM) in NOD mice. Infection with this helminth significantly reduced the spontaneous incidence of IDDM. IDDM was also prevented by injecting parasite eggs alone. Because until relatively recently humans might expect to succumb to a variety of infectious agents, the current freedom from infection might permit the expression of a genetic predisposition to autoimmune pathology and be responsible for the increased incidence of IDDM.

IL-1 receptor antagonist inhibits recurrence of disease after syngeneic pancreatic islet transplantation to spontaneously diabetic non-obese diabetic (NOD) mice.

The effect of an IL-1 receptor antagonist on recurrence of hyperglycaemia after syngeneic pancreatic islet transplantation to spontaneously diabetic female NOD mice was investigated. The transplanted animals were treated with either the receptor antagonist (8.0 mg/kg body weight per day for 12-14 days) or PBS, delivered by subcutaneously implanted osmotic pumps. In the control animals, a transient normoglycaemia was achieved, but hyperglycaemia was generally observed 6 days after islet transplantation. Administration of IL-1 receptor antagonist had a clear protective effect against recurrence of hyperglycaemia until day 14, but after cessation of drug delivery hyperglycaemia re-appeared. The results indicate that continuous administration of the IL-1 receptor antagonist can prevent recurrence of the diabetogenic process in NOD mice. IL-1 receptor antagonist may therefore become a useful adjuvant immunomodulating therapy after human islet transplantation in insulin-dependent diabetes mellitus.