Infections and autoimmune thyroid diseases: Parallel detection of antibodies against pathogens with proteomic technology

Infections and autoimmunity--friends or foes?

Autoimmunity can be triggered by many environmental factors, among which infectious agents are pivotal. Here, we summarize current knowledge of the relationship between infection and autoimmunity. An autoimmune disease can be induced or triggered by infectious agents, which can also determine its clinical manifestations. Most infectious agents, such as viruses, bacteria and parasites, can induce autoimmunity via different mechanisms. In many cases, it is not a single infection but rather the 'burden of infections' from childhood that is responsible for the induction of autoimmunity. The development of an autoimmune disease after infection tends to occur in genetically susceptible individuals. By contrast, some infections can protect individuals from specific autoimmune diseases (i.e. the hygiene hypothesis).

In vitro model for the activation of CD4 and CD8 T cell receptors

Previously, most models that sought to explain the misregulation of immune cell function assumed molecular similarities between the disease-causing pathogens and the host's proteins. In recent time several different models have been proposed and in this study, these concepts are compared to a new hypothesis proposing another explanation for this immune dysregulation: the possibility that the mislocalization of proteins may be responsible for autoimmune activity. Based on this hypothesis, proteins are recognized as self or non-self depending on where they appear in sufficiently high concentrations. To examine this new idea, the intracellular human proteins beta-actin, GAPDH, and hemoglobin as well as the extracellular human proteins insulin and albumin, were added to human whole blood samples. After an incubation period, the activation of whole-blood T lymphocytes in the samples was measured. The observed activation pattern of the T lymphocytes fit well with the proposed hypothesis. Therefore, these data suggest that protein mislocalization and/or errors within protein trafficking might be important in the development of autoimmune diseases.

Prevalence of hepatitis C serum antibody in autoimmune diseases

OBJECTIVE

To evaluate the prevalence of serum antibodies against hepatitis C virus and other infectious agents in a large cohort of well-characterized patients with autoimmune diseases (AID).

METHODS

We utilized 1322 sera from patients with 18 different AID and 236 sera from healthy controls from the same countries and with similar age and sex distribution. All sera were tested for the presence of serum anti-hepatitis C virus (HCV) antibodies as well as antibodies directed at other infectious agents and autoantibodies.

RESULTS

Anti-HCV antibody was detected in 115/1322 (8.7%) of patients with AID and 0.4% of matched healthy controls (P < 0.0001). The prevalence of anti-HCV antibody was significantly higher in 7/18 different AID (i.e. cryoglobulinemia, mixed cryoglobulinemia pemphigus vulgaris, vasculitis, secondary anti-phospholipid syndrome, Hashimoto's thyroiditis, and inflammatory bowel disease) compared to controls. Patients with AID and serum anti-HCV positivity had an increased prevalence of antibodies against hepatitis B virus, Toxoplasma gondii and Cytomegalovirus as opposed to a lower frequency of serum autoantibodies.

CONCLUSIONS

The enhanced prevalence of anti-HCV serum antibodies in AID may suggest a role for HCV in tolerance to breakdown, similarly to its established role in mixed cryoglobulinemia. This immune mediated effect does not rule out the role of other infectious agents.

Mathematical analysis of clinical data reveals a homunculus of bacterial mimotopes protecting from autoimmunity via oral tolerance in human

Oral tolerance (OT) means systemic immunological unresponsiveness to harmless antigens present in the gastrointestinal tract. We presumed that tolerance to these antigens may also protect self-proteins that show immunological similarity to the intestinal normal flora. To investigate the existence and in vivo relevance of such a tolerogenic molecular mimicry, we focused our attention to Autoimmune Polyendocrine Syndrome type 1 (APS1) and Hemolysis, Elevated Liver Enzymes, Low Platelet count (HELLP) syndrome. APS1 is a human form of Autoimmune Regulator (AIRE) dysfunction with severely impaired central immunotolerance to a specific set of autoantigens, allowing investigation of tolerogenic mimicry by itself, without a disturbing background. HELLP syndrome is a mediocre manifestation of thrombotic microangiopathy, complicating pregnancy, with platelet-fibrin deposits in small blood vessels and transient development of autoantibodies. Impaired microcirculation in the liver is well described, while intestinal ischemia is possible but has not yet been studied. As the harmless nature of an antigen is essential for OT, ischemia-induced bacterial microinvasion represses this process. In case that oral tolerance to a bacterial homunculus is an existing way of self-protection and has an in vivo relevance when central tolerance is intact, significant intestinal ischemia--if present--is expected to promote autoimmunity in HELLP syndrome. We used an experimentally validated, highly reliable mathematical algorithm to predict the extent of immunological similarity between a certain autoantigen and intestinal bacteria. We found a strong negative correlation between the similarity of autoantigens to intestinal bacteria and the production of specific autoantibodies in APS1 (R=-0.70, P=0.002), while a positive correlation was observed in patients with predominantly the severe/moderately severe form of HELLP syndrome according to Mississippi classification (R=0.94, P=0.005). Autoantigen length inversely correlated with the production of autoantibodies in APS1 (R=-0.68, P=0.004). As a longer chain with more epitopes associates with an increased possibility of mimicry to any proteome, molecular mimicry in general--regarding at least major tissue-specific autoantigens--seems to be rather protective. Our calculations support the hypothesis that OT to an intestinal "bacterial homunculus" is an in vivo relevant mechanism of self-protection in humans, furthermore, HELLP syndrome presumably associates with significant intestinal ischemia and leak, resulting in transient autoimmunity via loss of OT.

Probiotics and immunity

Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host, including the gastrointestinal tract. While this beneficial effect was originally thought to stem from improvements in the intestinal microbial balance, there is now substantial evidence that probiotics can also provide benefits by modulating immune functions. In animal models, probiotic supplementation is able to provide protection from spontaneous and chemically induced colitis by downregulating inflammatory cytokines or inducing regulatory mechanisms in a strain-specific manner. In animal models of allergen sensitization and murine models of asthma and allergic rhinitis, orally administered probiotics can strain-dependently decrease allergen-specific IgE production, in part by modulating systemic cytokine production. Certain probiotics have been shown to decrease airway hyperresponsiveness and inflammation by inducing regulatory mechanisms. Promising results have been obtained with probiotics in the treatment of human inflammatory diseases of the intestine and in the prevention and treatment of atopic eczema in neonates and infants. However, the findings are too variable to allow firm conclusions as to the effectiveness of specific probiotics in these conditions.