Infection with Toxocara canis Inhibits the Production of IgE Antibodies to α-Gal in Humans: Towards a Conceptual Framework of the Hygiene Hypothesis?

Tick bites, IgE to galactose-alpha-1,3-galactose and urticarial or anaphylactic reactions to mammalian meat: The alpha-gal syndrome

The recent recognition of a syndrome of tick-acquired mammalian meat allergy has transformed the previously held view that mammalian meat is an uncommon allergen. The syndrome, mediated by IgE antibodies against the oligosaccharide galactose-alpha-1,3-galactose (alpha-gal), can also involve reactions to visceral organs, dairy, gelatin and other products, including medications sourced from non-primate mammals. Thus, fittingly, this allergic disorder is now called the alpha-gal syndrome (AGS). The syndrome is strikingly regional, reflecting the important role of tick bites in sensitization, and is more common in demographic groups at risk of tick exposure. Reactions in AGS are delayed, often by 2-6 h after ingestion of mammalian meat. In addition to classic allergic symptomatology such as urticaria and anaphylaxis, AGS is increasingly recognized as a cause of isolated gastrointestinal morbidity and alpha-gal sensitization has also been linked with cardiovascular disease. The unusual link with tick bites may be explained by the fact that allergic cells and mediators are mobilized to the site of tick bites and play a role in resistance against ticks and tick-borne infections. IgE directed to alpha-gal is likely an incidental consequence of what is otherwise an adaptive immune strategy for host defense against endo- and ectoparasites, including ticks.

Potential roles of Toxocara canis larval excretory secretory molecules in immunomodulation and immune evasion

Toxocara canis larvae invade various tissues of different vertebrate species without developing into adults in paratenic host. The long-term survival of the larvae despite exposure to the well-armed immune response is a notable achievement. The larvae modulate the immune response to help the survival of both the host and the larvae. They skew the immune response to type 2/regulatory phenotype. The outstanding ability of the larvae to modulate the host immune response and to evade the immune arms is attributed to the secretion of Toxocara excretory-secretory products (TESPs). TESPs are complex mixture of differing molecules. The present review deals with the molecular composition of the TESPs, their interaction with the host molecules, their effect on the innate immune response, the receptor recognition, the downstream signals the adaptive immunity and the repair of tissues. This review also addresses the role of TESPs molecules in the immune evasion strategy and the potential effect of the induced immunomodulation in some diseases. Identification of parasite components that influence the nematode-host interactions could enhance understanding the molecular basis of nematode pathogenicity. Furthermore, the identification of helminths molecules with immunomodulatory potential could be used in immunotherapies for some diseases.

The α-Gal Syndrome and Potential Mechanisms

The α-Gal syndrome is a complex allergic disease characterized by the development of specific IgE antibodies against the carbohydrate galactose-α-1,3-galactose (α-Gal), an oligosaccharide present in cells and tissues of non-primate mammals. Individuals with IgE antibodies to α-Gal suffer from a delayed form of anaphylaxis following red meat consumption. There are several features that make the α-Gal syndrome such a unique allergic disease and distinguish it from other food allergies: (1) symptoms causing IgE antibodies are directed against a carbohydrate moiety, (2) the unusual delay between the consumption of the food and the onset of the symptoms, and (3) the fact that primary sensitization to α-Gal occurs via tick bites. This review takes a closer look at the immune response against α-Gal, in healthy and in α-Gal allergic individuals. Furthermore, the similarities and differences between immune response against α-Gal and against the other important glycan moieties associated with allergies, namely cross-reactive carbohydrate determinants (CCDs), are discussed. Then different mechanisms are discussed that could contribute to the delayed onset of symptoms after consumption of mammalian meat. Moreover, our current knowledge on the role of tick bites in the sensitization process is summarized. The tick saliva has been shown to contain proteins carrying α-Gal, but also bioactive molecules, such as prostaglandin E2, which is capable of stimulating an increased expression of anti-inflammatory cytokines while promoting a decrease in the production of proinflammatory mediators. Together these components might promote Th2-related immunity and trigger a class switch to IgE antibodies directed against the oligosaccharide α-Gal. The review also points to open research questions that remain to be answered and proposes future research directions, which will help to get a better understanding and lead to a better management of the disease.

Tick Saliva and the Alpha-Gal Syndrome: Finding a Needle in a Haystack

Ticks and tick-borne diseases are significant public health concerns. Bioactive molecules in tick saliva facilitate prolonged blood-feeding and transmission of tick-borne pathogens to the vertebrate host. Alpha-gal syndrome (AGS), a newly reported food allergy, is believed to be induced by saliva proteins decorated with a sugar molecule, the oligosaccharide galactose-⍺-1,3-galactose (α-gal). This syndrome is characterized by an IgE antibody-directed hypersensitivity against α-gal. The α-gal antigen was discovered in the salivary glands and saliva of various tick species including, the Lone Star tick (Amblyomma americanum). The underlying immune mechanisms linking tick bites with α-gal-specific IgE production are poorly understood and are crucial to identify and establish novel treatments for this disease. This article reviews the current understanding of AGS and its involvement with tick species.

Helminth infection induces non-functional sensitization to house dust mites

BACKGROUND

IgE characterizes the humoral response of allergic sensitization but less is known about what modulates its function and why some patients present clinical symptoms for a given IgE level and others do not. An IgE response also occurs during helminth diseases, independently of allergic symptoms. This response could be a model of non-functional IgE.

OBJECTIVE

To study the IgE response against environmental allergens induced during natural helminth infection.

METHODS

In 28 non allergic subjects from the periphery of Ho Chi Minh city with (H+, n = 18) and without helminth infection (H-, n = 10), we measured IgE and IgG4 against several components of Dermatophagoïdes pteronyssinus (Dpt) and Ascaris (a marker of immunization against nematodes), and determined the IgE component sensitization profile using microarray ISAC biochips. The functional ability of IgE to induce degranulation of cultured mast cells was evaluated in the presence of Dpt.

RESULTS

Non allergic H+ subjects exhibited higher levels of IgE against Dpt compared to H- subjects. Dpt IgE were not functional in vitro and did not recognize usual Dpt major allergens. IgE recognized other component allergens that belong to different protein families, and most were glycosylated. Depletion of IgE recognizing carbohydrate cross-reactive determinant (CCD) did not induce a reduction in Dpt IgE. The Dpt IgG4 were not significantly different.

CONCLUSION

Helminth infections induced IgE against allergens such as Dpt and molecular components that belong to different sources as well as against CCD (such as β-1,2-xylose and/or ⍺-1,3-fucose substituted N-glycans). Dpt IgE were not able to induce degranulation of mast cells and were not explained by sensitization to usual major allergens or N-glycans.

The Potential Contribution of ABO, Lewis and Secretor Histo-Blood Group Carbohydrates in Infection by Toxoplasma gondii

The glycosyltransferases encoded by genes from the human ABO, Lewis, and Secretor histo-blood group systems synthesize part of the carbohydrate antigens in hematopoietic and non-hematopoietic tissues. The combined action of these glycosyltransferases strongly influences cell, tissue, mucosa, and exocrine secretion carbohydrate phenotypes, including those serving as habitat for mutualistic and pathogenic microorganisms. A set of reports investigated associations between Toxoplasma gondii infection and the ABO histo-blood group system, but the results are contradictory. As T. gondii uses the gastrointestinal tract as a route for infection, and in this organ, the expression of ABO, Lewis, and Secretor histo-blood group carbohydrates occurs, it is reasonable to suppose some biological relationship between them. This text reviewed association studies published in recent decades focusing on the potential contribution of the ABO, Lewis, and Secretor histo-blood group carbohydrates and infection by T. gondii.

Tick-human interactions: from allergic klendusity to the α-Gal syndrome

Ticks and the pathogens they transmit, including bacteria, viruses, protozoa, and helminths, constitute a growing burden for human and animal health worldwide. The ability of some animal species to acquire resistance to blood-feeding by ticks after a single or repeated infestation is known as acquired tick resistance (ATR). This resistance has been associated to tick-specific IgE response, the generation of skin-resident memory CD4+ T cells, basophil recruitment, histamine release, and epidermal hyperplasia. ATR has also been associated with protection to tick-borne tularemia through allergic klendusity, a disease-escaping ability produced by the development of hypersensitivity to an allergen. In addition to pathogen transmission, tick infestation in humans is associated with the α-Gal syndrome (AGS), a type of allergy characterized by an IgE response against the carbohydrate Galα1-3Gal (α-Gal). This glycan is present in tick salivary proteins and on the surface of tick-borne pathogens such as Borrelia burgdorferi and Anaplasma phagocytophilum, the causative agents of Lyme disease and granulocytic anaplasmosis. Most α-Gal-sensitized individuals develop IgE specific against this glycan, but only a small fraction develop the AGS. This review summarizes our current understanding of ATR and its impact on the continuum α-Gal sensitization, allergy, and the AGS. We propose that the α-Gal-specific IgE response in humans is an evolutionary adaptation associated with ATR and allergic klendusity with the trade-off of developing AGS.

Characterization of the anti-α-Gal antibody profile in association with Guillain-Barré syndrome, implications for tick-related allergic reactions

Humans evolved by losing the capacity to synthesize the glycan Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal), which resulted in the capacity to develop a protective response mediated by anti-α-Gal IgM/IgG antibodies against pathogens containing this modification on membrane proteins. As an evolutionary trade-off, humans can develop the alpha-Gal syndrome (AGS), a recently diagnosed disease mainly associated with allergic reactions to mammalian meat consumption. The etiology of the AGS is the exposure to tick bites and the IgE antibody response against α-Gal-containing glycoproteins and glycolipids. The objective of this study was to characterize the anti-α-Gal antibody response in association with the immune-mediated peripheral neuropathy, Guillain-Barré syndrome (GBS), and compare it with different factors known to modulate the antibody response to α-Gal such as exposure to tick bites and development of allergic reactions in response to tick bites. The results showed a significant decrease in the IgM/IgG response to α-Gal in GBS patients when compared to healthy individuals. In contrast, the IgM/IgG levels to α-Gal did not change in patients with allergic reactions to tick bites. The IgE response was not affected in GBS patients, but as expected, the IgE levels significantly increased in individuals exposed to tick bites and patients with tick-associated allergies. These results suggest that the immune pathways of anti-α-Gal IgM/IgG and IgE production are independent. Further studies should consider the susceptibility to allergic reactions to tick bites in GBS patients.

The Two Faces of Nematode Infection: Virulence and Immunomodulatory Molecules From Nematode Parasites of Mammals, Insects and Plants

Helminths stage a powerful infection that allows the parasite to damage host tissue through migration and feeding while simultaneously evading the host immune system. This feat is accomplished in part through the release of a diverse set of molecules that contribute to pathogenicity and immune suppression. Many of these molecules have been characterized in terms of their ability to influence the infectious capabilities of helminths across the tree of life. These include nematodes that infect insects, known as entomopathogenic nematodes (EPN) and plants with applications in agriculture and medicine. In this review we will first discuss the nematode virulence factors, which aid parasite colonization or tissue invasion, and cause many of the negative symptoms associated with infection. These include enzymes involved in detoxification, factors essential for parasite development and growth, and highly immunogenic ES proteins. We also explore how these parasites use several classes of molecules (proteins, carbohydrates, and nucleic acids) to evade the host's immune defenses. For example, helminths release immunomodulatory molecules in extracellular vesicles that may be protective in allergy and inflammatory disease. Collectively, these nematode-derived molecules allow parasites to persist for months or even years in a host, avoiding being killed or expelled by the immune system. Here, we evaluate these molecules, for their individual and combined potential as vaccine candidates, targets for anthelminthic drugs, and therapeutics for allergy and inflammatory disease. Last, we evaluate shared virulence and immunomodulatory mechanisms between mammalian and non-mammalian plant parasitic nematodes and EPNs, and discuss the utility of EPNs as a cost-effective model for studying nematode-derived molecules. Better knowledge of the virulence and immunomodulatory molecules from both entomopathogenic nematodes and soil-based helminths will allow for their use as beneficial agents in fighting disease and pests, divorced from their pathogenic consequences.

Anti-Tick Microbiota Vaccine Impacts Ixodes ricinus Performance during Feeding

The tick microbiota is a highly complex ensemble of interacting microorganisms. Keystone taxa, with a central role in the microbial networks, support the stability and fitness of the microbial communities. The keystoneness of taxa in the tick microbiota can be inferred from microbial co-occurrence networks. Microbes with high centrality indexes are highly connected with other taxa of the microbiota and are expected to provide important resources to the microbial community and/or the tick. We reasoned that disturbance of vector microbiota by removal of ubiquitous and abundant keystone bacteria may disrupt the tick-microbiota homeostasis causing harm to the tick host. These observations and reasoning prompted us to test the hypothesis that antibodies targeting keystone bacteria may harm the ticks during feeding on immunized hosts. To this aim, in silico analyses were conducted to identify keystone bacteria in the microbiota of Ixodes nymphs. The family Enterobacteriaceae was among the top keystone taxa identified in Ixodes microbiota. Immunization of α-1,3-galactosyltransferase-deficient-C57BL/6 (α1,3GT KO) mice with a live vaccine containing the Enterobacteriaceae bacterium Escherichia coli strain BL21 revealed that the production of anti-E. coli and anti-α-Gal IgM and IgG was associated with high mortality of I. ricinus nymphs during feeding. However, this effect was absent in two different strains of wild type mice, BALB/c and C57BL/6. This result concurred with a wide distribution of α-1,3-galactosyltransferase genes, and possibly α-Gal, in Enterobacteriaceae and other bacteria of tick microbiota. Interestingly, the weight of I. ricinus nymphs that fed on E. coli-immunized C57BL/6 was significantly higher than the weight of ticks that fed on C57BL/6 immunized with a mock vaccine. Our results suggest that anti-tick microbiota vaccines are a promising tool for the experimental manipulation of vector microbiota, and potentially the control of ticks and tick-borne pathogens.

α-Gal-Based Vaccines: Advances, Opportunities, and Perspectives

Humans and crown catarrhines evolved with the inability to synthesize the oligosaccharide galactose-α-1,3-galactose (α-Gal). In turn, they naturally produce high quantities of the glycan-specific antibodies that can be protective against infectious agents exhibiting the same carbohydrate modification on their surface coat. The protective immunity induced by α-Gal is ensured through an antibody-mediated adaptive and cell-mediated innate immune response. Therefore, the α-Gal antigen represents an attractive and feasible target for developing glycan-based vaccines against multiple diseases. In this review article we provide an insight into our current understanding of the mechanisms involved in the protective immunity to α-Gal and discuss the possibilities and challenges in developing a single-antigen pan-vaccine for prevention and control of parasitic diseases of medical and veterinary concern.

B Cell Responses in the Development of Mammalian Meat Allergy

Studies of meat allergic patients have shown that eating meat poses a serious acute health risk that can induce severe cutaneous, gastrointestinal, and respiratory reactions. Allergic reactions in affected individuals following meat consumption are mediated predominantly by IgE antibodies specific for galactose-α-1,3-galactose (α-gal), a blood group antigen of non-primate mammals and therefore present in dietary meat. α-gal is also found within certain tick species and tick bites are strongly linked to meat allergy. Thus, it is thought that exposure to tick bites promotes cutaneous sensitization to tick antigens such as α-gal, leading to the development of IgE-mediated meat allergy. The underlying immune mechanisms by which skin exposure to ticks leads to the production of α-gal-specific IgE are poorly understood and are key to identifying novel treatments for this disease. In this review, we summarize the evidence of cutaneous exposure to tick bites and the development of mammalian meat allergy. We then provide recent insights into the role of B cells in IgE production in human patients with mammalian meat allergy and in a novel mouse model of meat allergy. Finally, we discuss existing data more generally focused on tick-mediated immunomodulation, and highlight possible mechanisms for how cutaneous exposure to tick bites might affect B cell responses in the skin and gut that contribute to loss of oral tolerance.

Alpha-gal syndrome: challenges to understanding sensitization and clinical reactions to alpha-gal

INTRODUCTION

The α-Gal syndrome (AGS) is a type of allergy characterized by an IgE antibody response against the carbohydrate Galα1-3Galβ1-4GlcNAc-R (α-Gal). Tick bites are recognized as the most important cause of anti-α-Gal IgE antibody increase in humans. Several risk factors have been associated with the development of AGS, but their integration into a standardized disease diagnosis has proven challenging.

AREAS COVERED

Herein we discuss the current AGS diagnosis based on anti-α-Gal IgE titers and propose an algorithm that considers all co-factors in the clinical history of α-Gal-sensitized patients to be incorporated into the AGS diagnosis. The need for identification of host-derived gene markers and tick-derived proteins for the diagnosis of the AGS is also discussed.

EXPERT OPINION

The current AGS diagnosis based on anti-α-Gal IgE titers has limitations because not all patients sensitized to α-Gal and with anti-α-Gal IgE antibodies higher than the cutoff (0.35 IU/ml) develop anaphylaxis to mammalian meat and AGS. The basophil activation test proposed to differentiate between patients with AGS and asymptomatic α-Gal sensitization cannot be easily implemented as a generalized clinical test. In coming years, the algorithm proposed here could be used in a mobile application for easier AGS diagnosis in the clinical practice.

Gut Microbiota Abrogates Anti-α-Gal IgA Response in Lungs and Protects against Experimental Aspergillus Infection in Poultry

Naturally occurring human antibodies (Abs) of the isotypes IgM and IgG and reactive to the galactose-α-1,3-galactose (α-Gal) epitope are associated with protection against infectious diseases, caused by pathogens expressing the glycan. Gut microbiota bacteria expressing α-Gal regulate the immune response to this glycan in animals lacking endogenous α-Gal. Here, we asked whether the production of anti-α-Gal Abs in response to microbiota stimulation in birds, confers protection against infection by Aspergillus fumigatus, a major fungal pathogen that expresses α-Gal in its surface. We demonstrated that the oral administration of Escherichia coli O86:B7 strain, a bacterium with high α-Gal content, reduces the occurrence of granulomas in lungs and protects turkeys from developing acute aspergillosis. Surprisingly, the protective effect of E. coli O86:B7 was not associated with an increase in circulating anti-α-Gal IgY levels, but with a striking reduction of anti-α-Gal IgA in the lungs of infected turkeys. Subcutaneous immunization against α-Gal did not induce a significant reduction of lung anti-α-Gal IgA and failed to protect against an infectious challenge with A. fumigatus. Oral administration of E. coli O86:B7 was not associated with the upregulation of lung cytokines upon A. fumigatus infection. We concluded that the oral administration of bacteria expressing high levels of α-Gal decreases the levels of lung anti-α-Gal IgA, which are mediators of inflammation and lung damage during acute aspergillosis.

Vaccination with Alpha-Gal Protects Against Mycobacterial Infection in the Zebrafish Model of Tuberculosis

The alpha-Gal syndrome (AGS) is associated with tick bites that can induce in humans high levels of IgE antibodies against the carbohydrate Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) present in glycoproteins and glycolipids from tick saliva that mediate primarily delayed anaphylaxis to mammalian meat consumption. It has been proposed that humans evolved by losing the capacity to synthesize α-Gal to increase the protective immune response against pathogens with this modification on their surface. This evolutionary adaptation suggested the possibility of developing vaccines and other interventions to induce the anti-α-Gal IgM/IgG protective response against pathogen infection and multiplication. However, the protective effect of the anti-α-Gal immune response for the control of tuberculosis caused by Mycobacterium spp. has not been explored. To address the possibility of using vaccination with α-Gal for the control of tuberculosis, in this study, we used the zebrafish-Mycobacterium marinum model. The results showed that vaccination with α-Gal protected against mycobacteriosis in the zebrafish model of tuberculosis and provided evidence on the protective mechanisms in response to vaccination with α-Gal. These mechanisms included B-cell maturation, antibody-mediated opsonization of mycobacteria, Fc-receptor (FcR)-mediated phagocytosis, macrophage response, interference with the α-Gal antagonistic effect of the toll-like receptor 2 (TLR2)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB)-mediated immune response, and upregulation of pro-inflammatory cytokines. These results provided additional evidence supporting the role of the α-Gal-induced immune response in the control of infections caused by pathogens with this modification on their surface and the possibility of using this approach for the control of multiple infectious diseases.