[Relationship between parasitic infections and hygiene hypothesis: a review].

Recently, the incidence of infectious diseases continues to decline in many developed countries; however, the incidence of autoimmune diseases and allergic asthma appears a tendency towards a rise over years. "Hygiene hypothesis" provides new insights into the treatment of autoimmune disorders and allergic diseases based on parasitic infections. Increasing evidence shows that parasitic infections may effectively inhibit the development of diabetes, multiple sclerosis, inflammatory bowel disease, rheumatoid arthritis and allergic asthma. There are complex mechanisms underlying the relationship between parasitic infections and "hygiene hypothesis", among which regulatory T (Treg) cells and Th17 cells are becoming a hot topic of research. This paper reviews the progresses in the research on the relationship between parasitic infections and "hygiene hypothesis", and summarizes the roles of Treg cells and Th17 cells in the interplay between parasitic infections and "hygiene hypothesis".

The Potential Role of Schistosome-Associated Factors as Therapeutic Modulators of the Immune System.

The parasites and eggs of helminths, including schistosomes, are associated with factors that can modulate the nature and outcomes of host immune responses, particularly enhancing type 2 immunity and impairing the effects of type 1 and type 17 immunity. The main species of schistosomes that cause infection in humans are capable of generating a microenvironment that allows survival of the parasite by evasion of the immune response. Schistosome infections are associated with beneficial effects on chronic immune disorders, including allergies, autoimmune diseases, and alloimmune responses. Recently, there has been increasing research interest in the role of schistosomes in immunoregulation during human infection, and the mechanisms underlying these roles continue to be investigated. Further studies may identify potential opportunities to develop new treatments for immune disease. In this review, we provide an update on the advances in our understanding of schistosome-associated modulation of the cells of the innate and adaptive immune systems as well as the potential role of schistosome-associated factors as therapeutic modulators of immune disorders, including allergies, autoimmune diseases, and transplant immunopathology. We also discuss potential opportunities for targeting schistosome-induced immunoregulation for future translation to the clinical setting.

Autoimmune Anemia in Malaria.

Severe anemia is a major cause of death by malaria. The loss of uninfected erythrocytes is an important contributor to malarial anemia; however, the mechanisms underlying this pathology are not well understood. Malaria-induced anemia is related to autoimmune antibodies against the membrane lipid phosphatidylserine (PS). In mice, these antibodies induce the clearance of uninfected erythrocytes after binding to PS exposed in their membrane. In human malaria patients there is a strong correlation between anemia and anti-PS antibodies. During malaria, anti-PS antibodies are produced by atypical B cells, whose levels correlate with the development of anemia in patients. Autoimmune responses, which are documented frequently in different infections, contribute to the pathogenesis of malaria by inducing the clearance of uninfected erythrocytes.

Are Viruses and Parasites Linked to Celiac Disease? A Question that Still has no Definite Answer.

Celiac Disease (CD) is a complex autoimmune enteropathy of the small intestine that commonly occurs in genetically predisposed individuals due to intake of gluten and related proteins. Gluten consumption, duration of breast-feeding, various infections, especially frequent intestinal infections, vaccinations and use of antibiotics can be linked to CD. It is predicted that it affects 1% of the global population and its incidence rate is increasing. Most of the people with the HLA-DQ2 or HLADQ8 are at a higher risk of developing this disease. The link between infections and autoimmune diseases has been very much considered in recent years. In several studies, we explained that pathogenic and non-pathogenic microorganisms might have multiple roles in initiation, exacerbation, and development of Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD). In various studies, the relationship between infections caused by viruses, such as Epstein-Barr Virus (EBV), Rotavirus, Hepatitis C (HCV), Hepatitis B virus (HBV), Cytomegalovirus (CMV), and Influenza virus, and parasites including Giardia spp. and Toxoplasma gondii with CD has been raised. However, increasing evidence proposes that some of these microorganisms, especially helminths, can also have protective and even therapeutic roles in the CD process. Therefore, in order to determine the role of microorganisms in the process of this disease, we attempted to summarize the evidence suggesting the role of viral and parasitic agents in pathogenesis of CD.

Tuftsin phosphorylcholine-a novel compound harnessing helminths to fight autoimmunity.

The distinction that in areas where helminthic infections are common, autoimmune diseases are less prevalent, led to the investigation of immune modulatory properties of helminths and their derivatives. Such are phosphorylcholine (PC) moieties which are a component of secreted products of helminths. PC has been broadly studied for its attenuating effects on the human immune system. In an attempt to develop a novel therapeutic small molecule for the treatment of autoimmune conditions, we have conjugated PC with tuftsin, a natural immunomodulatory tetrapeptide, to create TPC. Herein, we review our findings regarding the effects of TPC in murine models of three autoimmune diseases-systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), and rheumatic arthritis (RA), as well as ex-vivo samples from giant cell arteritis (GCA) patients. In all four disease models examined, TPC was shown to attenuate the inflammatory response by reducing expression of pro-inflammatory cytokines and altering the phenotype of T cell expression. In murine models, TPC has further produced a significant improvement in clinical disease scores with no significant side effects noted. Our findings suggest TPC presents promising potential as a novel therapeutic agent for the effective treatment of various autoimmune conditions.

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.

Nodding Syndrome in the Spotlight - Placing Recent Findings in Perspective.

Nodding syndrome (NS) is a debated scientific topic. A recently published study suggests that NS is an autoimmune disorder based on findings of cross-reacting antibodies between neuronal structures and a protein present in Onchocerca volvulus (OV). In our opinion, the proposed causal relationship between OV infection and NS has yet to be demonstrated and, instead, OV infection in NS may be opportunistic.

Regulatory function of parasites in autoimmune disease ­ outcome from experimental model infection

It is estimated that more than half of the nowadays known species are pathogenic parasites. Among macroparasites gastrointestinal nematodes are one of most common and having significant impact on life and health. Those organisms reveal strong, specific immune response in host, involving primary mechanisms associated with regulatory and Th2 cells. Referring to immunomodulatory abilities of helminths, parasite infections started to be considered as a possible therapy for many autoimmune diseases. Clinical trials on 2nd and 3rd stage are conducted in spite that treatment has not been recognized as safe for common use. Despite that the safety of treatment with parasites is still controversial and widely discussed. Our knowledge about mechanisms used by helminth to moderate immune response is still inadequate to predict possible effect of long lasting parasite infection on individual patients.

Nodding syndrome may be an autoimmune reaction to the parasitic worm Onchocerca volvulus.

Nodding syndrome is an epileptic disorder of unknown etiology that occurs in children in East Africa. There is an epidemiological association with Onchocerca volvulus, the parasitic worm that causes onchocerciasis (river blindness), but there is limited evidence that the parasite itself is neuroinvasive. We hypothesized that nodding syndrome may be an autoimmune-mediated disease. Using protein chip methodology, we detected autoantibodies to leiomodin-1 more abundantly in patients with nodding syndrome compared to unaffected controls from the same village. Leiomodin-1 autoantibodies were found in both the sera and cerebrospinal fluid of patients with nodding syndrome. Leiomodin-1 was found to be expressed in mature and developing human neurons in vitro and was localized in mouse brain to the CA3 region of the hippocampus, Purkinje cells in the cerebellum, and cortical neurons, structures that also appear to be affected in patients with nodding syndrome. Antibodies targeting leiomodin-1 were neurotoxic in vitro, and leiomodin-1 antibodies purified from patients with nodding syndrome were cross-reactive with O. volvulus antigens. This study provides initial evidence supporting the hypothesis that nodding syndrome is an autoimmune epileptic disorder caused by molecular mimicry with O. volvulus antigens and suggests that patients may benefit from immunomodulatory therapies.

The Hygiene Hypothesis and Its Inconvenient Truths about Helminth Infections.

Current iterations of the hygiene hypothesis suggest an adaptive role for helminth parasites in shaping the proper maturation of the immune system. However, aspects of this hypothesis are based on assumptions that may not fully account for realities about human helminth infections. Such realities include evidence of causal associations between helminth infections and asthma or inflammatory bowel disease as well as the fact that helminth infections remain widespread in the United States, especially among populations at greatest risk for inflammatory and autoimmune diseases.

Autoimmune pathogenesis of Chagas heart disease: looking back, looking ahead.

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of individuals infected with the protozoan parasite Trypanosoma cruzi. Since the discovery of T. cruzi by Carlos Chagas >100 years ago, much has been learned about Chagas disease pathogenesis; however, the outcome of T. cruzi infection is highly variable and difficult to predict. Many mechanisms have been proposed to promote tissue inflammation, but the determinants and the relative importance of each have yet to be fully elucidated. The notion that some factor other than the parasite significantly contributes to the development of myocarditis was hypothesized by the first physician-scientists who noted the conspicuous absence of parasites in the hearts of those who succumbed to Chagas disease. One of these factors-autoimmunity-has been extensively studied for more than half a century. Although questions regarding the functional role of autoimmunity in the pathogenesis of Chagas disease remain unanswered, the development of autoimmune responses during infection clearly occurs in some individuals, and the implications that this autoimmunity may be pathogenic are significant. In this review, we summarize what is known about the pathogenesis of Chagas heart disease and conclude with a view of the future of Chagas disease diagnosis, pathogenesis, therapy, and prevention, emphasizing recent advances in these areas that aid in the management of Chagas disease.

Reciprocal effects of Schistosoma mansoni infection on spontaneous autoimmune arthritis in IL-1 receptor antagonist-deficient mice.

Schistosome infections have been shown to prevent inflammation in induced-type arthritis models. However, its effects on spontaneous arthritis remain unknown. We here investigated the effects of Schistosoma mansoni (Sm) infection on spontaneous autoimmune arthritis in IL-1 receptor antagonist (IL-1Ra)-deficient mice. Sm infection partially reduced the severity of arthritis in male IL-1Ra-deficient mice. The splenic responses of IL-17 and TNF-α were reduced, while those of IL-4 and IL-10 were enhanced by the infection. However, Sm infection increased IgG rheumatoid factor and anti-dsDNA IgG serum levels. These results suggest that Sm infection has both ameliorating and exacerbating effects on autoimmunity in IL-1Ra-deficient mice.

(Self-) infections with parasites: re-interpretations for the present.

Previously, scientists sometimes resorted to infecting themselves or colleagues with parasites, usually to assess the pathogenicity and obtain insight into the life cycles of the parasites, host specificity, and epidemiology. However, with recent research addressing the possible beneficial impact of intestinal helminths on a range of immune-mediated diseases in humans, these studies offer valuable information, although many are now considered unethical owing to a lack of experimental oversight and informed consent. Here, we critically review cases in which humans were deliberately infected with parasites. Moreover, we summarize the contribution of (self-) infections and propose protist and helminth candidates, chosen on the basis of several criteria, to test as possible therapy for selected human diseases.

The hygiene theory harnessing helminths and their ova to treat autoimmunity.

The incidence of autoimmune diseases is increasing in Western countries, possibly due to the improved sanitary conditions and reduced exposure to infections in childhood (the hygiene hypothesis). There is an ongoing debate whether infection prevents or precipitates autoimmune diseases. Various helminths species used in several animal models were shown to limit inflammatory activity in a variety of diseases including inflammatory bowel disease, multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus. At present the scientific data is based mostly on experimental animal models; however, there is an increasing body of evidence in a number of clinical trials being conducted. Herein we review several clinical trials evaluating the anti-inflammatory effects of helminths and assessing their association with different autoimmune diseases, including inflammatory bowel disease, multiple sclerosis, and autoimmune liver diseases. We also describe the common pathways by which helminths induce immune modulation and the key changes observed in the host immune system following exposure to helminths. These common pathways include the inhibition of IFN-γ and IL-17 production, promotion of IL-4, IL-10 and TGF-ß release, induction of CD4(+) T cell FoxP3(+) expression, and generation of regulatory macrophages, dendritic cells, and B cells. Helminths products are becoming significant candidates for anti-inflammatory agents in this context. However, further research is needed for synthetic analogues of helminths' potent products that mimic the parasite-mediated immunomodulation effect.

Helminth infection in populations undergoing epidemiological transition: a friend or foe?

Helminth infections are highly prevalent in developing countries, especially in rural areas. With gradual development, there is a transition from living conditions that are dominated by infection, poor sanitation, manual labor, and traditional diet to a situation where burden of infections is reduced, infrastructure is improved, sedentary lifestyle dominates, and processed food forms a large proportion of the calorie intake. The combinations of some of the changes in lifestyle and environment are expected to result in alteration of the landscape of diseases, which will become dominated by non-communicable disorders. Here we review how the major helminth infections affect a large proportion of the population in the developing world and discuss their impact on the immune system and the consequences of this for other infections which are co-endemic in the same areas. Furthermore, we address the issue of decreasing helminth infections in many parts of the world within the context of increasing inflammatory, metabolic, and cardiovascular diseases.

An insight into the sialotranscriptome of Triatoma matogrossensis, a kissing bug associated with fogo selvagem in South America.

Triatoma matogrossensis is a Hemiptera that belongs to the oliveirai complex, a vector of Chagas' disease that feeds on vertebrate blood in all life stages. Hematophagous insects' salivary glands (SGs) produce potent pharmacologic compounds that counteract host hemostasis, including anticlotting, antiplatelet, and vasodilatory molecules. Exposure to T. matogrossensis was also found to be a risk factor associated with the endemic form of the autoimmune skin disease pemphigus foliaceus, which is described in the same regions where Chagas' disease is observed in Brazil. To obtain a further insight into the salivary biochemical and pharmacologic diversity of this kissing bug and to identify possible allergens that might be associated with this autoimmune disease, a cDNA library from its SGs was randomly sequenced. We present the analysis of a set of 2,230 (SG) cDNA sequences, 1,182 of which coded for proteins of a putative secretory nature.

Helminthic therapy: improving mucosal barrier function.

The epidemiology of autoimmune diseases and helminth infections led to suggestions that helminths could improve inflammatory conditions, which was then tested using animal models. This has translated to clinical investigations aimed at the safe and controlled reintroduction of helminthic exposure to patients suffering from autoimmune diseases (so-called 'helminthic therapy') in an effort to mitigate the inflammatory response. In this review, we summarize the results of recent clinical trials of helminthic therapy, with particular attention to mechanisms of action. Whereas previous reviews have emphasized immune regulatory mechanisms activated by helminths, we propose that enhancement of mucosal barrier function may have an equally important role in improving conditions of inflammatory bowel diseases.

Reconstitution of the human biome as the most reasonable solution for epidemics of allergic and autoimmune diseases.

A wide range of hyperimmune-associated diseases plague post-industrial society, with a prevalence and impact that is staggering. Strong evidence points towards a loss of helminths from the ecosystem of the human body (the human biome) as the most important factor in this epidemic. Helminths, intestinal worms which are largely eradicated by elements of post-industrial culture including toilets and water treatment facilities, have an otherwise ubiquitous presence in vertebrates, and have co-evolved with the immune system. Not only do helminths discourage allergic and autoimmune reactions by diverting the immune system away from these pathologic processes and stimulating host regulatory networks, helminths release a variety of factors which down-modulate the immune system. A comprehensive view of hyperimmune-related disease based on studies in immunology, parasitology, evolutionary biology, epidemiology, and neurobiology indicates that the effects of biome depletion may not yet be fully realized, and may have an unexpectedly broad impact on many areas of human biology, including cognition. Fortunately, colonization with helminths results in a cure of numerous autoimmune and allergic diseases in laboratory rodents, and clinical studies in humans have indicated their utility for treatment of both multiple sclerosis and inflammatory bowel disease. Based on these considerations, commitment of considerable resources toward understanding the effects of "biome depletion" and systematically evaluating the most effective approach toward biome reconstitution is strongly encouraged.

The impact of parasite infections on the course of multiple sclerosis.

Previously, we demonstrated that helminth-infected MS patients showed significantly lower number of relapses, reduced disability scores, and lower MRI activity compared to uninfected MS subjects. In the current study, 12 patients with diagnosis of relapsing remitting MS presenting parasite infections were prospectively followed during 90 months; due to exacerbation of helminth-infection symptoms after 63 months of follow-up, 4 patients received anti-parasite treatment. Helminth-infection control was associated with significant increase in clinical and radiological MS activities. Moreover, these patients showed significant increase in the number of IFN-γ and IL-12 producing cells, and a fall in the number of TGF-ß and IL-10 secreting cells, as well as CD4+CD25+FoxP3+ Treg cells evident 3 months after anti-helminth treatment began. These new observations on parasite infections associated to MS indicate that parasite regulation of host immunity can alter the course of MS.

[Are parasitic infections advantageous to humans?].

Humans are negatively affected by parasitic infection. However, recent researches revealed that to some extent, parasitic infections are advantageous to humans. Parasitic infections are found to benefit patients of inflammatory bowel disease, diabetes mellitus, autoimmune disease and allergic disorder. Furthermore, they promoted studies on pathogenesis of these diseases, and therefore on safe and effective therapeutic strategy. In addition, by taking the Caenorhabditis elegans as model organism, researchers have made a breakthrough in the area of life science, including signal transduction, functional genomics and drug screening.