Analysis of antibody responses against coxsackie virus B4 Protein 2C and the diabetes autoantigen GAD65

Clostridia and Enteroviruses as Synergistic Triggers of Type 1 Diabetes Mellitus

What triggers type 1 diabetes mellitus (T1DM)? One common assumption is that triggers are individual microbes that mimic autoantibody targets such as insulin (INS). However, most microbes highly associated with T1DM pathogenesis, such as coxsackieviruses (COX), lack INS mimicry and have failed to induce T1DM in animal models. Using proteomic similarity search techniques, we found that COX actually mimicked the INS receptor (INSR). Clostridia were the best mimics of INS. Clostridia antibodies cross-reacted with INS in ELISA experiments, confirming mimicry. COX antibodies cross-reacted with INSR. Clostridia antibodies further bound to COX antibodies as idiotype-anti-idiotype pairs conserving INS-INSR complementarity. Ultraviolet spectrometry studies demonstrated that INS-like Clostridia peptides bound to INSR-like COX peptides. These complementary peptides were also recognized as antigens by T cell receptor sequences derived from T1DM patients. Finally, most sera from T1DM patients bound strongly to inactivated Clostridium sporogenes, while most sera from healthy individuals did not; T1DM sera also exhibited evidence of anti-idiotype antibodies against idiotypic INS, glutamic acid decarboxylase, and protein tyrosine phosphatase non-receptor (islet antigen-2) antibodies. These results suggest that T1DM is triggered by combined enterovirus-Clostridium (and possibly combined Epstein-Barr-virus-Streptococcal) infections, and the probable rate of such co-infections approximates the rate of new T1DM diagnoses.

Molecular mimicry between virus and host and its implications for dengue disease pathogenesis

Numerous infectious agents may trigger autoimmunity or even result in autoimmune diseases. Several mechanisms have been proposed for pathogen-triggered autoimmunity including molecular mimicry, cryptic antigens, epitope spreading, bystander activation and polyclonal activation. In the case of dengue virus infection which causes serious public health problems, the mechanisms regarding the pathogenesis of dengue hemorrhagic syndrome are not fully resolved. Our previous studies suggest a mechanism of molecular mimicry in which antibodies directed against dengue virus non-structural protein 1 (NS1) cross-react with human platelets and endothelial cells and cause their damage and dysfunction, which may be related to the clinical features of dengue disease. Several cell surface proteins recognized by patient serum samples and anti-NS1 antibodies have been identified. Based on proteomic studies and sequence analysis, the C-terminal region of dengue virus NS1 shows sequence homology with target proteins. In addition, different regions of dengue virus proteins including core, prM, E and NS1 proteins show sequence homology with different coagulatory molecules. As an example, the amino acid sequence 101-106 of E protein (WGNGCG) shows sequence homology with factors XI, X, IX, VII, II (thrombin), plasminogen and tissue plasminogen activator. Furthermore, single chain variable region against NS1 can interfere with fibrin formation, which leads to prolonged thrombin time. We hypothesize that molecular mimicry between dengue virus proteins and coagulatory molecules may induce cross-reactive autoantibodies that can interfere with coagulation activation. A molecular mimicry pathogenesis for dengue disease which involves cross-reactivity of dengue virus with human endothelial cells, platelets and coagulatory molecules is proposed.

Enteroviruses and type 1 diabetes: towards a better understanding of the relationship

Environmental factors, especially viruses, are involved in the initiation or the acceleration of type 1 diabetes (T1D) pathogenesis. Epidemiological data strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), can be associated with T1D. It has been demonstrated that enterovirus infections were significantly more prevalent in at risk individuals, such as siblings of diabetic patients, when they developed anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients strengthened the hypothesis of a relationship between the virus and the disease. Studies performed in vitro and in vivo in animal models helped to discover mechanisms of the infection of pancreas and other tissues, potentially able to play a role in the pathogenesis of T1D. Interestingly, it cannot be excluded that enteroviruses behave as half-devil half-angel since experimental studies suggest that, in certain conditions, these agents would be able to protect individuals against the disease. All of the plausible mechanisms by which enterovirus may be related to T1D will be reviewed here.

The rising incidence of type 1 diabetes mellitus and the role of environmental factors--three decade experience in a primary care health center in Saudi Arabia

BACKGROUND

The incidence of type 1 diabetes has been increasing all over the world including Saudi Arabia and environmental factors have been suggested to play an important role in its etiology.

OBJECTIVE

The aim of this study was to evaluate if there are any contributory roles of various environmental factors in the rising incidence of type 1 diabetes in children in the Eastern Province of Saudi Arabia.

METHODS

We conducted a retrospective study of Saudi Arab subjects (n = 119) diagnosed between 1980 and 2009 with type 1 diabetes and these subjects were classified to six groups on the basis of the onset of diabetes.

RESULTS

119 subjects (61 boys and 58 girls) with confirmed diagnosis of type 1 diabetes met the study eligibility criteria. 89 children (74%) presented with ketoacidosis. The mean age of onset was 4 3/4 years for Group II and age of onset increased to above 8 years on subsequent years. Excessive weight gain was noted in all study groups. No etiological influences of maternal age at birth, birth order, birth weight, early introduction of cow's milk and cereals, infections and vaccines as well as nitrate levels in drinking water were noted in any of the groups. The predicted doubling of diabetes in young children below 5 years as in previous studies was not found in our study.

CONCLUSIONS

The rising incidence of type 1 diabetes over the last 30 years is not proved to have been influenced by various environmental factors.

Autoimmunity in Coxsackievirus B3 induced myocarditis: role of estrogen in suppressing autoimmunity

Picornaviruses are small, non-enveloped, single stranded, positive sense RNA viruses which cause multiple diseases including myocarditis/dilated cardiomyopathy, type 1 diabetes, encephalitis, myositis, orchitis and hepatitis. Although picornaviruses directly kill cells, tissue injury primarily results from autoimmunity to self antigens. Viruses induce autoimmunity by: aborting deletion of self-reactive T cells during T cell ontogeny; reversing anergy of peripheral autoimmune T cells; eliminating T regulatory cells; stimulating self-reactive T cells through antigenic mimicry or cryptic epitopes; and acting as an adjuvant for self molecules released during virus infection. Most autoimmune diseases (SLE, rheumatoid arthritis, Grave's disease) predominate in females, but diseases associated with picornavirus infections predominate in males. T regulatory cells are activated in infected females because of the combined effects of estrogen and innate immunity.

Role of coxsackievirus B4 in the pathogenesis of type 1 diabetes

Environmental factors, especially viruses, are thought to play an important role in the initiation or acceleration of the pathogenesis of type 1 diabetes (T1D). Data from retrospective and prospective epidemiological studies strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), may be associated with the development of T1D. It has also been shown that enterovirus infections are significantly more prevalent in at-risk individuals such as the siblings of diabetic patients, when they develop anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients supports the hypothesis of a relationship between the virus and the disease. Furthermore, studies performed in vitro and in vivo in animal models have increased our knowledge of the role of CV-B4 in T1D by helping to clarify the pathogenic mechanisms of the infection that can lead to beta-cell destruction, including direct virus-induced beta-cell lysis, molecular mimicry, 'bystander activation' and viral persistence. The role of enteroviruses as the sole agents in T1D, and a causal link between these agents and T1D, have not yet been established, although arguments that support such a role for these viruses in the pathogenesis of the disease cannot be ignored.

Autoimmunity in coxsackievirus B3 induced myocarditis

Virus infections are implicated in several autoimmune diseases. Multiple mechanisms of autoimmunity induction have been proposed including antigenic mimicry, production of cryptic epitopes and infection acting as both adjuvant for self-antigens and the mechanism of releasing these cell antigens. Evidence for these mechanisms in coxsackievirus B3 induced myocarditis is discussed.

Enteroviruses and type 1 diabetes

The development of type 1 diabetes mellitus (T1DM) has been linked to exposure to environmental triggers, with Enteroviruses (EV) historically considered the prime suspects. Early serological studies suggested a link between EV infections and the development of T1DM and, though controversial, have been bolstered by more recent studies using more sensitive techniques such as direct detection of the EV genome by RT-PCR in peripheral blood. In this review, we consider the weight of evidence that EV can be considered a candidate trigger of T1DM, using three major criteria: (1) is EV infection associated with clinical T1DM, (2) can EV trigger the development of autoimmunity and (3) what would explain the putative association?

Coxsackievirus-mediated hyperglycemia is enhanced by reinfection and this occurs independent of T cells

The induction of autoimmunity by viruses has been hypothesized to occur by a number of mechanisms. Coxsackievirus B4 (CB4) induces hyperglycemia in SJL mice resembling diabetes in humans. While virus is effectively cleared within 2 weeks, hyperglycemia does not appear until about 8-12 weeks postinfection at a time when replicative virus is no longer detectable. In SJL mice, reinfection with CB4 enhanced the development of hyperglycemia. As predicted, the immune system responded more rapidly to the second infection and virus was cleared more swiftly. However, while infiltrating T cells were found within the pancreas, depletion of the CD4 T cell population prior to secondary infection or use of CD8 knock-out mice had no effect on the development of virus-mediated hyperglycemia. In conclusion, enhanced hyperglycemia induced by CB4 occurs independent of the T cell response.

T-Cell reactivity to the P2C nonstructural protein of a diabetogenic strain of coxsackievirus B4

Enteroviruses are proposed as initiating factors in the etiology of Type 1 diabetes mellitus (Type 1 DM). Molecular mimicry between the autoantigen glutamic acid decarboxylase 65 (GAD65) and the coxsackievirus B4 (CVB4) nonstructural protein P2C is frequently cited as a mechanism by which this virus triggers the disease, but little is known about the immunogenicity of this viral protein in humans, mainly due to the problem of obtaining highly pure preparations of P2C. We generated large amounts of highly pure, soluble P2C protein, coupled to the fusion partner maltose binding protein (MBP-P2C) using the PMAL-c2 bacterial expression plasmid and a two-step purification system comprising amylose resin and ion exchange. Using purified viral protein we show that specific T-cell responses against P2C are detected in the blood of healthy donors and Type 1 DM patients. Proliferation responses to P2C were detected only in subjects also demonstrating T-cell proliferation to CVB4 Vero cell lysates. However, in additional cases T-cell responses to P2C were detectable through the release of interferon-gamma or interleukin-4 in individuals who did not make proliferative responses. Taken together, our data show that the P2C nonstructural protein of CVB4 is targeted by T cells during the antiviral immune response and may trigger the production of T helper 1 and T helper 2 cytokines. The availability of pure, immunogenic P2C should allow the putative role of antiviral responses in the development of autoimmune diabetes to be investigated.