Immunity to helminths: is too much IgE parasite--rather than host-protective?

Endocannabinoid modulation of allergic responses: Focus on the control of FcεRI-mediated mast cell activation

Allergic reactions are highly prevalent pathologies initiated by the production of IgE antibodies against harmless antigens (allergens) and the activation of the high-affinity IgE receptor (FcεRI) expressed in the surface of basophils and mast cells (MCs). Research on the mechanisms of negative control of those exacerbated inflammatory reactions has been intense in recent years. Endocannabinoids (eCBs) show important regulatory effects on MC-mediated immune responses, mainly inhibiting the production of pro-inflammatory mediators. However, the description of the molecular mechanisms involved in eCB control of MC activation is far from complete. In this review, we aim to summarize the available information regarding the role of eCBs in the modulation of FcεRI-dependent activation of that cell type, emphasizing the description of the eCB system and the existence of some of its elements in MCs. Unique characteristics of the eCB system and cannabinoid receptors (CBRs) localization and signaling in MCs are mentioned. The described and putative points of cross-talk between CBRs and FcεRI signaling cascades are also presented. Finally, we discuss some important considerations in the study of the effects of eCBs in MCs and the perspectives in the field.

The interaction of host and nematode galectins influences the outcome of gastrointestinal nematode infections

Galectins are a family of proteins that bind β-galactosides and play key roles in a variety of cellular processes including host defence. They have been well studied in hosts but less so in gastrointestinal nematodes. Both host and parasite galectins are present in the gastrointestinal tract following infection. Parasite galectins can both bind antibody, especially highly glycosylated IgE and be bound by antibody. Parasite galectins may act as molecular sponges that soak up antibody. Host galectins promote mast cell degranulation while parasite galectins inhibit degranulation. Host and parasite galectins can also bind mucins and influence mucus viscosity. As the protective response against gastrointestinal nematode infection is partly dependent on IgE mediated mast cell degranulation and mucus, the interactions between host and parasite galectins play key roles in determining the outcome of infection.

Allergen skin test reactivity and asthma are inversely associated with ratios of IgG4/IgE and total IgE/allergen-specific IgE in Ugandan communities

Background

Serum inhibition of allergen‐specific IgE has been associated with competing IgG4 and non‐specific polyclonal IgE. In allergen immunotherapy, beneficial responses have been associated with high IgG4/IgE ratios. Helminths potentiate antibody class switching to IgG4 and stimulate polyclonal IgE synthesis; therefore, we hypothesized a role for helminth‐associated IgG4 and total IgE in protection against atopic sensitization and clinical allergy (asthma) in tropical low‐income countries.

Methods

Among community residents of Ugandan rural Schistosoma mansoni (Sm)–endemic islands and a mainland urban setting with lower helminth exposure, and among urban asthmatic schoolchildren and non‐asthmatic controls, we measured total, Schistosoma adult worm antigen (SWA)–specific, Schistosoma egg antigen (SEA)–specific and allergen (house dust mite [HDM] and German cockroach)–specific IgE and IgG4 by ImmunoCAP^® and/or ELISA. We assessed associations between these antibody profiles and current Sm infection, the rural‐urban environment, HDM and cockroach skin prick test (SPT) reactivity, and asthma.

Results

Total IgE, total IgG4 and SWA‐, SEA‐ and allergen‐specific IgE and IgG4 levels were significantly higher in the rural, compared to the urban setting. In both community settings, both Sm infection and SPT reactivity were positively associated with allergen‐specific and total IgE responses. SPT reactivity was inversely associated with Schistosoma‐specific IgG4, allergen‐specific IgG4/IgE ratios and total IgE/allergen‐specific IgE ratios. Asthmatic schoolchildren, compared with non‐asthmatic controls, had significantly higher levels of total and allergen‐specific IgE, but lower ratios of allergen‐specific IgG4/IgE and total IgE/allergen‐specific IgE.

Conclusions and clinical relevance

Our immuno‐epidemiological data support the hypothesis that the IgG4–IgE balance and the total IgE–allergen‐specific IgE balance are more important than absolute total, helminth‐ or allergen‐specific antibody levels in inhibition of allergies in the tropics.

Cellular and molecular changes and immune response in the intestinal mucosa during Trichinella spiralis early infection in rats

Background:

The main targets of the host’s immune system in Trichinella spiralis infection are the adult worms (AW), at the gut level, and the migrant or newborn larvae (NBL), at systemic and pulmonary levels. Most of the studies carried out in the gut mucosa have been performed on the Payer’s patches and/or the mesenteric lymph nodes but not on the lamina propria, therefore, knowledge on the gut immune response against T. spiralis remains incomplete.

Methods

This study aimed at characterizing the early mucosal immune response against T. spiralis, particularly, the events taking place between 1 and 13 dpi. For this purpose, Wistar rats were orally infected with muscle larvae of T. spiralis and the humoral and cellular parameters of the gut immunity were analysed, including the evaluation of the ADCC mechanism exerted by lamina propria cells.

Results

A marked inflammation and structural alteration of the mucosa was found. The changes involved an increase in goblet cells, eosinophils and mast cells, and B and T lymphocytes, initially displaying a Th1 profile, characterised by the secretion of IFN-γ and IL-12, followed by a polarization towards a Th2 profile, with a marked increase in IgE, IgG1, IL-4, IL-5 and IL-13 levels, which occurred once the infection was established. In addition, the helminthotoxic activity of lamina propria cells demonstrated the role of the intestine as a place of migrant larvae destruction, indicating that not all the NBLs released in the gut will be able to reach the muscles.

Conclusions

The characterization of the immune response triggered in the gut mucosa during T. spiralis infection showed that not only an effector mechanism is directed toward the AW but also towards the NBL as a cytotoxic activity was observed against NBL exerted by lamina propria cells.

Clinical pathology of larval toxocariasis

Human toxocariasis is a worldwide helminth zoonosis caused by roundworms of the genus Toxocara. Toxocariasis is the most common helminth infection in many countries. Disease caused by Toxocara can be classified into five clinical forms: generalised, neurological, ocular, covert, and asymptomatic. The clinical pathology of toxocariasis largely depends on the form of infection, the intensity of the infection, the larvae localisation, and the age of the host. Because histological and molecular examination of toxocariasis is limited by difficulties in obtaining material to analyse, clinical diagnosis is often based on nonspecific tests, such as the detection of eosinophilia and hyperimmunoglobulinemia E (Hyper-IgE). Specific analysis uses an initial ELISA test to detect anti-Toxocara IgG and requires confirmation for all positive results via Western blot. This strategy does not distinguish between actual and recent infections, making the monitoring of disease a challenge for clinicians. Additional research will be required to distinguish active disease from the presence of recent infection.

Differences in the Importance of Mast Cells, Basophils, IgE, and IgG versus That of CD4+ T Cells and ILC2 Cells in Primary and Secondary Immunity to Strongyloides venezuelensis

There is evidence that mast cells, basophils, and IgE can contribute to immune responses to parasites; however, the relative levels of importance of these effector elements in parasite immunity are not fully understood. Previous work in Il3-deficient and c-kit mutant Kit^W/W-v mice indicated that interleukin-3 and c-Kit contribute to expulsion of the intestinal nematode Strongyloides venezuelensis during primary infection. Our findings in mast cell-deficient Kit^W-sh/W-sh mice and two types of mast cell-deficient mice that have normal c-kit ("Hello Kitty" and MasTRECK mice) confirmed prior work in Kit^W/W-v mice that suggested that mast cells play an important role in S. venezuelensis egg clearance in primary infections. We also assessed a possible contribution of basophils in immune responses to S. venezuelensis By immunohistochemistry, we found that numbers of basophils and mast cells were markedly increased in the jejunal mucosa during primary infections with S. venezuelensis Studies in basophil-deficient Mcpt8^DTR mice revealed a small but significant contribution of basophils to S. venezuelensis egg clearance in primary infections. Studies in mice deficient in various components of immune responses showed that CD4⁺ T cells and ILC2 cells, IgG, FcRγ, and, to a lesser extent, IgE and FcεRI contribute to effective immunity in primary S. venezuelensis infections. These findings support the conclusion that the hierarchy of importance of immune effector mechanisms in primary S. venezuelensis infection is as follows: CD4⁺ T cells/ILC2 cells, IgG, and FcRγ>mast cells>IgE and FcεRI>basophils. In contrast, in secondary S. venezuelensis infection, our evidence indicates that the presence of CD4⁺ T cells is of critical importance but mast cells, antibodies, and basophils have few or no nonredundant roles.

IgE and mast cells in host defense against parasites and venoms

IgE-dependent mast cell activation is a major effector mechanism underlying the pathology associated with allergic disorders. The most dramatic of these IgE-associated disorders is the fatal anaphylaxis which can occur in some people who have developed IgE antibodies to otherwise innocuous antigens, such as those contained in certain foods and medicines. Why would such a highly "maladaptive" immune response develop in evolution and be retained to the present day? Host defense against parasites has long been considered the only beneficial function that might be conferred by IgE and mast cells. However, recent studies have provided evidence that, in addition to participating in host resistance to certain parasites, mast cells and IgE are critical components of innate (mast cells) and adaptive (mast cells and IgE) immune responses that can enhance host defense against the toxicity of certain arthropod and animal venoms, including enhancing the survival of mice injected with such venoms. Yet, in some people, developing IgE antibodies to insect or snake venoms puts them at risk for having a potentially fatal anaphylactic reaction upon subsequent exposure to such venoms. Delineating the mechanisms underlying beneficial versus detrimental innate and adaptive immune responses associated with mast cell activation and IgE is likely to enhance our ability to identify potential therapeutic targets in such settings, not only for reducing the pathology associated with allergic disorders but perhaps also for enhancing immune protection against pathogens and animal venoms.

Potential effector and immunoregulatory functions of mast cells in mucosal immunity

Mast cells (MCs) are cells of hematopoietic origin that normally reside in mucosal tissues, often near epithelial cells, glands, smooth muscle cells, and nerves. Best known for their contributions to pathology during IgE-associated disorders such as food allergy, asthma, and anaphylaxis, MCs are also thought to mediate IgE-associated effector functions during certain parasite infections. However, various MC populations also can be activated to express functional programs--such as secreting preformed and/or newly synthesized biologically active products--in response to encounters with products derived from diverse pathogens, other host cells (including leukocytes and structural cells), damaged tissue, or the activation of the complement or coagulation systems, as well as by signals derived from the external environment (including animal toxins, plant products, and physical agents). In this review, we will discuss evidence suggesting that MCs can perform diverse effector and immunoregulatory roles that contribute to homeostasis or pathology in mucosal tissues.

Fish immune responses to parasitic copepod (namely sea lice) infection

Parasitic copepods, in particular sea lice, have considerable impacts upon global freshwater and marine fisheries, with major economic consequences recognized primarily in aquaculture. Sea lice have been a contentious issue with regards to interactions between farmed and wild populations of fish, in particular salmonids, and their potential for detrimental effects at a population level. The following discussion will pertain to aquatic parasitic copepod species for which we have significant information on the host-parasite interaction and host response to infection (Orders Cyclopoida, Poecilostomatoida and Siphonostomatoida). This review evaluates prior research in terms of contributions to understanding parasite stage specific responses by the host, and in many cases draws upon model organisms like Lepeophtheirus salmonis and Atlantic salmon to convey important concepts in fish responses to parasitic copepod infection. The article discusses TH1 and TH2-like host responses in light of parasite immunomodulation of the host, current methods of immunological stimulation and where the current and future work in this field is heading.

Impaired protection against Trichinella spiralis in mice with high levels of IgE

Helminth infection induces production of a large amount of immunoglobulin E (IgE) to nonhelminth antigens. Although such "irrelevant" IgE is a major proportion of total IgE in the host, its biological significance remains unclear. Therefore, I examined protective activity against Trichinella spiralis in mice with high levels of IgE by repeated injections of anti-dansyl IgE monoclonal antibody or Nippostrongylus brasiliensis infection. Injected anti-dansyl IgE occupied IgE receptors on mast cells in naive mice. Protective activity against T. spiralis, determined with number of muscle larvae 5weeks after infection, was impaired in mice treated with anti-dansyl IgE. The impaired protection was found in mice treated with anti-dansy IgE 7 and 14days after infection, but not 21 and 28days after infection, indicating that IgE-dependent protection operates at an early stage after infection. In the next experiments, mice were infected with N. brasiliensis 4weeks before T. spiralis infection to obtain high levels of IgE. The protective activity against T. spiralis was decreased by N. brasiliensis infection. On the other hand, protection against T. spiralis was comparable in IgE-deficient SJA/9 mice and in anti-IgE-treated BALB/c mice with or without N. brasiliensis infection, suggesting that impairment of protection is dependent on IgE. These results indicate that the high levels of irrelevant IgE are beneficial for helminths and, alternatively, that anti-helminth IgE antibodies are protective for hosts. In addition, the impaired protection was found in IgE high-responder mice but not in low-responder mice, suggesting that protection against T. spiralis is controlled by IgE responsiveness in the host.

Sequential class switching is required for the generation of high affinity IgE antibodies

Generation of anaphylaxis-inducing high affinity IgE requires sequential class switching.

IgE antibodies with high affinity for their antigens can be stably cross-linked at low concentrations by trace amounts of antigen, whereas IgE antibodies with low affinity bind their antigens weakly. In this study, we find that there are two distinct pathways to generate high and low affinity IgE. High affinity IgE is generated through sequential class switching (μ→γ→ε) in which an intermediary IgG phase is necessary for the affinity maturation of the IgE response, where the IgE inherits somatic hypermutations and high affinity from the IgG1 phase. In contrast, low affinity IgE is generated through direct class switching (μ→ε) and is much less mutated. Mice deficient in IgG1 production cannot produce high affinity IgE, even after repeated immunizations. We demonstrate that a small amount of high affinity IgE can cause anaphylaxis and is pathogenic. Low affinity IgE competes with high affinity IgE for binding to Fcε receptors and prevents anaphylaxis and is thus beneficial.

Total IgE in urban Black South African teenagers: the influence of atopy and helminth infection

Total IgE levels are usually elevated in allergic diseases, being highest in atopic eczema, followed by atopic asthma and allergic rhinitis. Genetic factors are believed to play a role in total IgE levels, with higher levels seen in Black African subjects. Total IgE is also raised in parasite infection. Thus, the higher total IgE levels in Black Africans could be because of environmental rather than genetic factors. Few studies have investigated the usefulness of total IgE levels in the evaluation of atopy in Black Africans. The objective of this study was to determine the total IgE levels in unselected urban Black African high school children and to correlate this with atopy and ascaris sensitization. Atopic status was assessed by means of specific allergen sensitization (skin prick tests to eight inhalant and four food allergens), self-reported asthma and bronchial hyper-responsiveness measured by methacholine challenge. Ascaris sensitization was assessed by means of ascaris IgE measured by CAP-RAST. Total IgE levels were markedly skewed toward the left and were not distributed in a Gaussian or a log-normal distribution. Skin prick tests were positive for aeroallergens in 32.3% of subjects. Thirty four percent had elevated ascaris IgE. Total IgE was higher in atopic vs. non-atopic subjects and correlated with the number of positive skin prick tests, self-reported asthma and bronchial hyper-responsiveness. Subjects without allergy (or) atopy had a median total IgE of 80-90 kU/I. In addition total IgE correlated with ascaris IgE. Subjects with no ascaris sensitization had median total IgE of 77.1 kU/l. Subjects with neither atopy/asthma nor ascaris sensitisation had a median total IgE of 69.9 kU/I, similar to the levels seen in people of other genetic origins. This study suggests that helminthic infection rather than genetic differences, may be the major determining factor of IgE levels in certain populations.

Geohelminth infections: a review of the role of IgE and assessment of potential risks of anti-IgE treatment

Geohelminth infections are major parasitic infections with a worldwide distribution. Immunoglobulin E (IgE) is considered to play a central role in protective immunity against these parasites although the evidence from experimental animal models infected with helminth parasites and treated with anti-IgE antibodies and from observational studies in human populations of the immunologic correlates of protective immunity against helminths do not support a critical role for IgE in mediating protection against helminths. Anti-IgE treatment of human allergic disorders using a humanized monoclonal IgE antibody (omalizumab, Xolair) has been approved for clinical use in the USA and Europe and there is concern that this treatment may be associated with increased morbidity in populations exposed to helminth infections. A recently published randomized controlled trial investigating the risk of geohelminth infections in allergic patients receiving omalizumab in Brazil has provided some evidence that omalizumab may not be associated with increased morbidity attributable to these parasites. This review examines the evidence for a role of IgE in protective immunity against helminth parasites, discusses the findings of the randomized controlled trial, assesses the potential risks and provides recommendations for anti-IgE treatment in groups of allergic patients with different exposure risks for helminth infections.

Anti-IgE antibodies for the treatment of IgE-mediated allergic diseases

The pharmacological purposes of the anti-IgE therapy are to neutralize IgE and to inhibit its production to attenuate type I hypersensitivity reactions. The therapy is based on humanized IgG1 antibodies that bind to free IgE and to membrane-bound IgE on B cells, but not to IgE bound by the high-affinity IgE.Fc receptors on basophils and mast cells or by the low-affinity IgE.Fc receptors on B cells. After nearly 20 years since inception, therapeutic anti-IgE antibodies (anti-IgE) have been studied in about 30 Phase II and III clinical trials in many allergy indications, and a lead antibody, omalizumab, has been approved for treating patients (12 years and older) with moderate-to-severe allergic asthma. Anti-IgE has confirmed the roles of IgE in the pathogenesis of asthma and helped define the concept "allergic asthma" in clinical practice. It has been shown to be safe and efficacious in treating pediatric allergic asthma and treating allergic rhinitis and is being investigated for treating peanut allergy, atopic dermatitis, latex allergy, and others. It has potential for use to combine with specific and rush immunotherapy for increased safety and efficacy. Anti-IgE thus appears to provide a prophylactic and therapeutic option for moderate to severe cases of many allergic diseases and conditions in which IgE plays a significant role. This chapter reviews the evolution of the anti-IgE concept and the clinical studies of anti-IgE on various disease indications, and presents a comprehensive analysis on the multiple intricate immunoregulatory pharmacological effects of anti-IgE. Finally, it reviews other approaches that target IgE or IgE-expressing B cells.

Identification and characterization of a novel antigen from the nematodeNippostrongylus brasiliensis recognized by specific IgE

Identification and characterization of IgE-inducing antigens are important for elucidating the mechanisms involved in IgE-mediated immune responses in allergic diseases and parasite infections. While many allergens have been characterized, little is known about parasite antigens inducing specific IgE following infection. In order to identify antigens from the nematode Nippostrongylus brasiliensis, we generated an IgE-producing B cell hybridoma from N. brasiliensis-infected C57BL/6 mice and constructed a cDNA phage display library from N. brasiliensis. We successfully cloned and expressed an N. brasiliensis antigen (Nb-Ag1) that showed specific binding to anti-N. brasiliensis IgE. Nb-Ag1 localized to the pharynx of adult N. brasiliensis, suggesting that Nb-Ag1 is a potential pharyngeal gland antigen. Nb-Ag1-specific IgE could be detected in the serum of N. brasiliensis-infected mice, but only for a short time and only following a challenge infection. In contrast, local administration of Nb-Ag1 during primary, secondary and tertiary infections induced Nb-Ag1-specific IgE-mediated active cutaneous anaphylaxis. Therefore, amongst the high amounts of polyclonal total IgE, low levels of parasite-specific IgE responses are induced during primary helminth infections. Here, we show that even such low levels of parasite-specific IgE are sufficient to prime mast cells in vivo and mediate degranulation.

Induction of IgE and allergic-type responses in fur mite-infested mice

High serum IgE levels are characteristic of allergic diseases and immune responses to nematode parasites. A murine allergy model based on infestation with the fur mites Myocoptes musculinus and Myobia musculi was investigated. Analysis of mite infestation in various knockout mice revealed that IgE production in response to these ectoparasites was dependent on T cells, IL-4, and CD40L. Secretion of IL-4 by CD4+ T cells obtained from peripheral LN draining mite-infested skin sites was increased with progressing mite infestation and correlated with the serum IgE induction. A time course analysis of the mRNA expression of switched IgE, activation-induced cytidine deaminase (AID), and epsilon germ-line transcripts (epsilonGLT) suggested that switching to IgE in response to fur mites occurred initially in skin-draining LN. In addition, mite infestation induced mast cell degranulation in the skin as well as mast cell infiltration into skin-draining LN. Analysis of the immune response generated in mite-infested mice is a valuable model for the investigation of allergic disorders and provides information for better understanding of mechanisms involved in IgE induction and regulation in a physiological way of allergen-exposure resembling atopic sensitization in humans.

Human hookworm infection in the 21st century

The scientific study of human hookworm infection began at the dawn of the twentieth century. In recent years, there have been dramatic improvements in our understanding of many aspects of this globally widespread parasite. This chapter reviews recent advances in our understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century. Advances in molecular biology has lead to the identification of a variety of new molecules from hookworms, which have importance either in the molecular pathogenesis of hookworm infection or in the host-parasite relationship; some are also promising vaccine targets. At present, relatively little is known about the immune responses to hookworm infection, although it has recently been speculated that hookworm and other helminths may modulate specific immune responses to other pathogens and vaccines. Our epidemiological understanding of hookworm has improved through the development of mathematical models of transmission dynamics, which coupled with decades of field research across multiple epidemiological settings, have shown that certain population characteristics can now be recognised as common to the epidemiology, population biology and control of hookworm and other helminth species. Recent recognition of the subtle, but significant, impact of hookworm on health and education, together with the simplicity, safety, low cost and efficacy of chemotherapy has spurred international efforts to control the morbidity due to infection. Large-scale treatment programmes are currently underway, ideally supported by health education and integrated with the provision of improved water and sanitation. There are also on-going efforts to develop novel anthelmintic drugs and anti-hookworm vaccines.

Various types of Dirofilaria immitis polyproteins selectively induce a Th2-Type immune response

Dirofilaria immitis polyproteins (DiAgs) are found as 15-kDa monomeric and 30-kDa dimeric forms in excretory-secretory products of the adult worm. We evaluated the ability of various types of recombinant DiAg (rDiAg; V1 and V2 as monomers and V1V2, V2V1, V1V1, and V2V2 as dimers) to influence Th1/Th2 immune responses. V1-, V1Vx- and V2-, V2Vx-driven nonspecific immunoglobulin E (IgE) production peaked at 21 and 14 days after administration, respectively. Dimer-induced IgE response was an interesting biphasic pattern with the second peaks on days 35 (V2Vx) or 42 (V1Vx). Absolute amounts of nonspecific IgE production induced with monomers were larger than those observed with dimers at the first peak. The magnitude of cell expansion and interleukin-10 (IL-10) production in mesenteric lymph node (MLN) B-cell induced with rDiAgs was linked to the levels of the first IgE peak in vivo and IgE produced by rDiAg plus IL-4-stimulated B cells in vitro. All rDiAgs failed to augment IgG2c production. V2 and V2Vx elicited IL-4 production by MLN cells more rapidly than V1 and V1Vx. The inhibitory effect of rDiAg on gamma interferon (IFN-gamma) production was stronger in monomers than in dimers. Neutralization of IL-10 restored IFN-gamma production, whereas the expression of IL-4 and IgE was partly prevented by depletion of IL-10. These results indicate that monomer rather than dimer is an efficient form of DiAg and suggest that the difference of IgE-inducing capacity among these DiAgs is closely associated with the pattern of both B-cell activation and IL-4 production.

Is there a common mechanism of gastrointestinal nematode expulsion?

Parasitic gastrointestinal (GI) nematodes are one of the most commonly acquired infections in the world. Although they cause relatively little mortality, infections result in high levels of morbidity that can result in developmental consequences in infected children and cause significant economic loss in infected animals. Over the last 30 years there has been extensive research into the mechanisms controlling the expulsion of gastrointestinal nematodes. Although many of the effector mechanisms that contribute to the loss of the parasite have been defined, we still appear to be some way from understanding the actual cause of parasite loss. Part of this stems from the different responses induced by different gastrointestinal parasites. It is clear that a Th2 response is essential for the expulsion of GI helminths; however, each of the characteristic immunological effector mechanisms induced following infection with these parasites may not be required or may be insufficient in isolation, but together they operate to expel GI helminths. These responses then succeed more efficiently in some cases than in others to induce parasite expulsion. The contribution made by various effector mechanisms to the expulsion of these parasites may therefore be a reflection of both the niche which the parasite inhabits as well as possible evasive/suppressive mechanisms employed by the parasites. In this review the various aspects of parasite expulsion will be described and the controversial issues in the field will be discussed.

Augmentation by Bursaphelenchus xylophilus, a pine wood nematode, of polyclonal IgE production induced by lipopolysaccharide plus interleukin-4 in murine splenocytes

Bursaphelenchus xylophilus (B. xylophilus) is a pine wood nematode that is known to cause pine wilt disease. We report here that B. xylophilus extracts augmented the polyclonal immunoglobulin E (IgE) production induced by lipopolysaccharide (LPS) plus interleukin-4 (IL-4) both in murine splenocytes and purified B cells as determined by ELISA and ELIspot assays, but they did not cause such a promotion in the absence of either LPS or IL-4. We also observed that the antigen-nonspecific IgE levels were increased in sera of mice treated with B. xylophilus extracts, which were comparable to those of Ascaris suum extracts. These findings suggest that administration of B. xylophilus extracts could suppress allergic diseases via a saturation of mast cell Fcepsilon receptors or/and an inhibition of antigen-specific IgE synthesis to the allergen by a polyclonal response.

Atopy, helminths, and cancer

There are two hypotheses for the primary function of the T(H)/IgE system: protection against helminths that 'spills over' into inappropriate allergic responses in the modern environment, or protection from a variety of environmental carcinogens and infectious diseases that is adaptive even today. We suggest that rather than being alternatives, these two hypotheses fit into a single causal framework. Atopic responses to helminths kill, inhibit, or expel the parasites, thereby reducing their debilitating effects, the most serious of which is bladder cancer. The ultimate (evolutionary) reason for the T(H)2/IgE system may be minimizing chances that multiple biotic and abiotic hazards and carcinogens will enter the body; in some tropical areas, helminths are the major proximate (immediate) triggers of this response.

Differences in prevalence, intensity of infection and parasite-specific antibody levels do not predict different age-infection profiles

Acquired immunity is believed to influence the age-infection profile of Schistosoma infections. We compared antibody responses against Schistosoma mansoni adult worm antigen (AWA) and soluble egg antigen (SEA) in 164 residents of two communities with different levels of infection. IgG, IgA, IgM, IgE, and IgG subclass 1 to 4 antibodies were determined by ELISA. Seventy-five of the subjects were from Harbu, an area with a prevalence of 39% and an intensity of infection of 116 eggs per gram of stool (EPG), whereas 89 subjects were from Bati, with a prevalence of 66% and intensity of infection of 256 EPG. In both communities the prevalence and the intensity of infection were highest in the age group 10-14 years, although both were significantly higher in Bati than in Harbu. Mean levels of AWA-specific IgA, IgM, IgG, IgG1 and IgG2, and of SEA-specific IgG, IgM, IgG2 and IgG3 were significantly higher in Bati than in Harbu. However, mean levels of IgE against worm and egg antigens were significantly higher in Harbu than in Bati. Significant differences were detected in the levels of IgA, IgE, IgG, IgM, IgG1 and IgG2 against AWA, and in IgE, IgM, IgG2 and IgG3 against SEA according to the place of residence. The levels of anti-AWA IgG, IgG1 and IgG2 and anti-SEA IgG, IgG1 and IgG4 were significantly associated with the intensity of infection. Anti-AWA IgM levels were associated with age, whereas sex and age had interacting effects on the levels of AWA-specific IgG1 and SEA-specific IgG and IgM. Antibody responses exhibited different age-related patterns in the two communities. This may indicate that differences in history of exposure influence the evolution of immune responses. However, the study did not support the view that differences in antibody levels between communities subject to different levels of infection result in a systematic deviation in age-infection profile (the "peak shift").

Omalizumab and the immune system: an overview of preclinical and clinical data

OBJECTIVE

This review discusses the role of immunoglobulin (Ig)E in allergic disease, inhibition of IgE with omalizumab, and the consequences of IgE inhibition (both clinically and in terms of the effect on the immune system).

DATA SOURCES

Relevant publications obtained from a literature review.

STUDY SELECTION

Relevant publications on IgE, allergic disease, and anti-IgE were critically evaluated.

RESULTS

IgE plays a key role in allergic diseases such as allergic asthma and allergic rhinitis. Its role in healthy individuals is less well defined. Treatment of allergic asthma and rhinitis with omalizumab, a humanized monoclonal anti-IgE antibody, causes a marked reduction in circulating free IgE levels. This has been shown to reduce symptoms and decrease the need for other medication in patients with these allergic diseases. Anti-IgE treatment with omalizumab did not cause any of the complications that might, in theory, be expected to result from reduction in circulating free IgE, such as adverse effects upon the immune system or other body systems.

CONCLUSIONS

The limited clinical data currently available suggest that this novel method of treatment for allergic asthma and rhinitis seems to be both effective and well tolerated in clinical use.

Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status. II. Humoral responses

The filarial-specific humoral responses (IgG1, IgG2, IgG3, IgG4 and IgE) to a Brugia pahangi antigen was assessed in 9 groups of adult individuals from a Wuchereria bancrofti-endemic area in north-east Tanzania. In 5 of the groups, individuals were negative for microfilariae (mf) and circulating filarial antigen (CFA) and had leg lymphoedema of varying severity ranging from early to more advanced grades. A 6th group had mixed grades of lymphoedema and were actively infected with mf and/or CFA. Three groups of asymptomatic individuals with different infection status (mf+CFA+; mf-CFA+; mf-CFA-) were also included. No differences in the antibody levels were observed between the 5 uninfected pathology groups. However, groups with advanced lymphoedema had a significantly higher level of IgG3 as compared to groups with early lymphoedema. A decline in the IgG4/IgE ratios were observed when moving from groups with early to groups with more advanced lymphoedema, which could indicate that increasing levels of IgE relatively to IgG4 are associated with progression of pathology. When all study groups were compared, higher IgG4/IgE ratios were observed in infected groups than in uninfected groups. This could suggest that high levels of IgG4 relative to IgE protect the parasite, whereas the opposite may play a role in parasite killing. When relating IgG4/IgE ratios to levels of gamma interferon (IFN gamma), a clear inverse relationship was observed. Thus, high levels of IFN gamma were found in groups with low IgG4/IgE ratios (uninfected groups) and low levels of IFN gamma were found in groups with high IgG4/IgE ratios (infected groups). The relationship between cellular (IFN gamma) and humoral (IgG4/IgE ratios) responses and their possible role in parasite protection and killing, and in development of early lymphoedema, are discussed.

Gastro-allergic anisakiasis as a consequence of simultaneous primary and secondary immune response

Gastro-allergic anisakiasis has been reported as an entity in which an acute parasitism by Anisakis simplex is accompanied by an immunoglobulin (Ig)E-mediated systemic allergic reaction. Serum samples were obtained from 24 patients within 24 h after the onset of symptoms (day 0) and after 1 month (day 30) and in 13 patients after 6 months. Total IgE was assessed by the Imx method. Specific IgE was assessed by CAP-FEIA. Specific IgM, IgG, IgG4 and IgA antibodies were assessed by enzyme-linked immunosorbent assay against crude extract (CE) and excretory-secretory products (ESP). IgE immunoblotting (IB) was directed against CE or ESP (day 0 and day 30). We found a rise of total IgE, specific IgE, number of bands in IgE-IB, IgG and IgG4 between day 0 and day 30 with a fall to near basal levels after 6 months. IgM levels were highest at day 0, falling over the next 6 months and IgA levels remained almost unchanged. Correlation studies revealed a parallel stimulation of nearly all Ig isotypes, except IgM anti-ESP, whose antibody levels correlated negatively with specific IgG levels. We found an extension of the IgE antibody repertoire in IB. We conclude that the allergic IgE-mediated reaction in the course of gastro-allergic anisakiasis involves a parallel secondary Th2 type memory response and a primary immunologic stimulation of both Th2 and Th1 lymphocyte subsets against previously unrecognized antigens.

Recombinant Dirofilaria immitis polyprotein that stimulates murine B cells to produce nonspecific polyclonal immunoglobulin E antibody

Nonspecific immunoglobulin E (IgE) production is an event characteristically observed in parasitic helminth infections, but its mechanisms are still unclear. To define these mechanisms, we prepared a recombinant Dirofilaria immitis protein (rDiAg) and assessed its effect on nonspecific IgE production. rDiAg preferentially induced nonspecific IgE production, without eliciting specific IgE production, as well as a Th2-type cytokine profile (high interleukin-4 [IL-4] and IL-10 production but low gamma interferon production) in BALB/c mice. rDiAg significantly elicited the proliferative response of naive B cells. This response was not abolished by polymyxin B, an inhibitor of lipopolysaccharide (LPS), and rDiAg normally expanded splenic B cells from LPS nonresponder C3H/HeJ mice. Thus, the mitogenic effect of rDiAg was not due to LPS contamination. rDiAg also enhanced levels of CD23 expression on splenic B cells. Splenic B cells produced marked levels of IgE when cultured with the combination of rDiAg and IL-4 (rDiAg-IL-4), whereas peritoneal B cells produced negligible levels of IgE. rDiAg-IL-4-induced IgE production by splenic B cells was synergistically increased by coculture with peritoneal B cells. rDiAg-driven IL-10 secretion was higher in peritoneal B cells than in splenic B cells. IgE production by splenic B cells cocultured with peritoneal B cells was decreased to a level comparable to that by splenic B cells in the presence of a neutralizing anti-IL-10 monoclonal antibody. Collectively, these results suggest that rDiAg-induced polyclonal expansion and IgE class switching of splenic B cells contribute to nonspecific IgE production and that these responses are enhanced by peritoneal B-cell-derived IL-10.

A factor of inducing IgE from a filarial parasite is an agonist of human CD40

Immune responses to parasitic helminth are usually characterized by quite mysterious phenomena: dominance of Th2-like immunity and antigen-nonspecific IgE secretion. We previously purified a factor from Dirofilaria immitis that induces antigen-nonspecific IgE in rats and named it DiAg. In the presence of IL-4, DiAg induces mouse B cells to secrete IgE, which is antigen-nonspecific polyclonal antibody. We investigated the biochemical characteristics of DiAg as a factor of inducing IgE in this study. Recombinant DiAg (rDiAg) with interleukin (IL)-4 induced IgE synthesis in highly purified human normal B cells in vitro cell culture systems. The addition of recombinant human soluble CD40 IgG fusion protein (rsCD40-Ig) inhibited induction of IgE synthesis by rDiAg with IL-4. Monocyte cells were stimulated with rDiAg and recombinant human soluble CD40L (rsCD40L); IL-12 and TNF-alpha were induced. The addition of rsCD40-Ig to THP-1 cells activated with rDiAg and rsCD40L inhibited the production of IL-12. rDiAg bound to the monocyte cell membrane fraction and recombinant human soluble CD40; this binding of rDiAg was competitively inhibited by addition of rsCD40L. Moreover, in CD40-deficient mice, IgE production and MLN-B cell proliferation by rDiAg were completely absent. Based on these results, we concluded that DiAg is an agonist of CD40.

Immune responses in hookworm infections

Hookworms infect perhaps one-fifth of the entire human population, yet little is known about their interaction with our immune system. The two major species are Necator americanus, which is adapted to tropical conditions, and Ancylostoma duodenale, which predominates in more temperate zones. While having many common features, they also differ in several key aspects of their biology. Host immune responses are triggered by larval invasion of the skin, larval migration through the circulation and lungs, and worm establishment in the intestine, where adult worms feed on blood and mucosa while injecting various molecules that facilitate feeding and modulate host protective responses. Despite repeated exposure, protective immunity does not seem to develop in humans, so that infections occur in all age groups (depending on exposure patterns) and tend to be prolonged. Responses to both larval and adult worms have a characteristic T-helper type 2 profile, with activated mast cells in the gut mucosa, elevated levels of circulating immunoglobulin E, and eosinophilia in the peripheral blood and local tissues, features also characteristic of type I hypersensitivity reactions. The longevity of adult hookworms is determined probably more by parasite genetics than by host immunity. However, many of the proteins released by the parasites seem to have immunomodulatory activity, presumably for self-protection. Advances in molecular biotechnology enable the identification and characterization of increasing numbers of these parasite molecules and should enhance our detailed understanding of the protective and pathogenetic mechanisms in hookworm infections.

Serum CD23 is not altered in gastroallergic anisakiasis, but correlates with the production of specific IgE and the amount of polyclonal stimulation

BACKGROUND

Previous studies have shown elevated serum levels of the cytokines IL-4 and sCD23 in atopic patients and parasitic disease. Gastroallergic anisakiasis is an acute parasitic disease, accompanied by IgE-mediated clinical symptoms and an important increase of specific and total IgE.

METHODS

Sixteen patients with acute urticaria/angioedema due to parasitism by Anisakis simplex after intake of raw or undercooked fish were selected, and serum samples were taken in the emergency room within 24 h (day 0; n=16), after 1 month (n=16), and after 6 months (n=10). Serum samples were studied for specific IgE against A. simplex, total IgE, sCD23, and IL-4.

RESULTS

Mean values for sCD23 did not change in the observation period. Only 4/16 serum samples showed measurable IL-4 levels. Specific IgE and total IgE levels were found to be elevated after 1 month; after 6 months, they fell to nearly basal values. There was a positive correlation between sCD23 and specific IgE at day 0 and follow-up (r=0.55-0.69, P<0.026); a positive correlation between sCD23 and total IgE (r=0.54-0.62, P<0.056). Basal sCD23 could moderately predict the percentual increment of total IgE in the first month (r=0.56, P<0.038).

CONCLUSION

Thus, it seems that interindividual variability of sCD23 is an important factor, with higher values predisposing to more production of unrelated IgE, independently of the parasite's action.

A factor of inducing IgE from a filarial parasite prevents insulin-dependent diabetes mellitus in nonobese diabetic mice

Parasitic helminth infections are characterized by eosinophilia and markedly elevated levels of circulating antigen-nonspecific immunoglobulin E (IgE), responses from which concern helminth protection. We previously purified a factor from Dirofilaria immitis that induces antigen-nonspecific IgE in mice and rats. Recombinant DiAg (rDiAg) has various biological activities. It is also known that parasitic helminth infection generates tremendous Th2 responses. The nonobese diabetic (NOD) mouse spontaneously develops Th1 cell-dependent autoimmune diabetes. Here we investigated the effects of rDiAg on the initiation and progression of this disease. rDiAg treatment of 6-week-old NOD females (the age at which insulitis typically begins) completely prevented insulitis and diabetes. Thus, rDiAg impaired the islet Ag-specific Th1 cell response in vivo, and the prevention of diabetes by rDiAg was associated with switching of the response from a Th1 to a Th2 profile. Since rDiAg clearly prevented insulitis by inhibiting the development and further accumulation of pathogenic Th1 cells to islets of Langerhans, we conclude that DiAg is a native Th2 inducer in filarial helminth and that Th1 responses are required for early events in the development of spontaneous autoimmune diabetes. In conclusion, the presence of parasitic helminth infections may play an important role as an immunomodulator in some autoimmune diseases or allergies.

Importance of immunoglobulin E (IgE) in the protective mechanism against gastrointestinal nematode infection: looking at the intestinal mucosae

This review discusses experimental evidences that indicate the IgE participation on the effector mechanisms that leads to gastrointestinal nematode elimination. Data discussed here showed that, for most experimental models, the immune response involved in nematode elimination is regulated by Th-2 type cytokines (especially IL-4). However, the mechanism(s) that result in worm elimination is not clear and might be distinct in different nematode species. Parasite specific IgE production, especially the IgE produced by the intestinal mucosae or associated lymphoid organs could participate in the intestinal elimination of Trichinella spiralis from infected rats. Intestinal IgE may also be important to the protective mechanism developed against other gastrointestinal nematodes that penetrate the murine duodenum mucosa tissue, such as Strongyloides venezuelensis and Heligmosomoides polygyrus. At least in Trichinella spiralis infected rats, the results indicated that intestinal IgE might work independently from mast cell degranulation for worm elimination.

Role of IgE in primary murine Schistosomiasis mansoni

Schistosoma mansoni infection proceeds in normal mice in the absence of detectable levels of polyclonal or specific immunoglobulin (Ig)E until worms mature and deposit eggs. Hence, the course of a primary S. mansoni infection is not expected to vary appreciably in mice with defects in the IgE production. Experimental increase of IgE production early after infection may, however, influence worm development. In the first approach towards this goal, BALB/c mice were injected with interleukin(IL)4 to raise the level of endogenously synthesized IgE. A significant increase in serum polyclonal IgE and antischistosome IgG1 during the prepatent period was not associated with significant changes in worm and egg burden or liver pathology. During the second approach, mice were injected with IgE which was affinity purified from serum of BALB/c mice infected for 16 weeks with S. mansoni. The purified IgE bound to carbohydrate-independent epitopes of soluble antigens from 3 h larvae, adult worms and eggs and recognized the schistosomular surface membrane. No differences in worm and egg load or granuloma number and size were noted between untreated and exogenous IgE-injected mice. Together, the data demonstrate that by itself IgE does not influence the outcome of infection in primary murine S. mansoni.

Immunology and biochemistry of Hymenolepis diminuta

This review is an account of modern research into the immunology and biochemistry of the rat tapeworm, Hymenolepis diminuta. The first half of the review is devoted to the immunological responses of the host to the parasite. It describes the specific responses that occur when the host is exposed to a primary infection, and the changes that occur when further infections are superimposed on the primary one. The aquisition of immunity to the tapeworm and its persistence in the absence of the infection are also discussed, as well as the non-specific responses of the host to the parasite. The second half of the review is concerned with biochemistry, summarizing the early biochemical work that has been carried out on the tapeworm and describing the metabolic pathways now thought to be characteristic of the parasite. What little information that exists on intermediary metabolism in eggs and larvae is summarized here. Much of this section is concerned with the role of mitochondria in H. diminuta, especially the control of the critical branchpoint (PK/PEPCK), which partitions carbon into either the cytosol or the mitochondrion. The role of 5-hydroxytryptamine in controlling both worm behaviour and metabolism is discussed, followed by a brief look at some other effectors that may prove in the future to have great significance in regulating the parasite. Finally, there is a detailed consideration of strain variation within H. diminuta and of the impact on the tapeworm of components of the immune system, formerly described as the 'crowding effect'. The review concludes with a brief discussion of evolutionary aspects of the rat-tapeworm relationship and a comprehensive bibliography.

Natural immunity to Ascaris lumbricoides associated with immunoglobulin E antibody to ABA-1 allergen and inflammation indicators in children

Children putatively immune to the large roundworm Ascaris lumbricoides were identified in an area of Nigeria where infection is hyperendemic. Immunity was associated with higher levels of serum ferritin, C-reactive protein, and eosinophil cationic protein, indicating ongoing acute phase or inflammatory processes. In contrast, children who were susceptible to the infection had little serological evidence of inflammation despite their high parasite burdens. Immunoglobulin G (IgG) antibody activity in all subclasses was present in high titer in most children but appeared to have no protective function. Despite exceptionally high total IgE levels, there was no evidence that atopic responses to local common allergens was associated with natural immunity to Ascaris. Among those individuals who produced IgG antibody to recombinant ABA-1 allergen of Ascaris, the naturally immune group had significantly more IgE antibody to the allergen than did those susceptible to the infection. IgE antibody responses in conjunction with innate inflammatory processes therefore appear to associate with natural immunity to ascariasis.

IgE and tumor necrosis factor in malaria infection

IgE, the immunoglobulin instrumental in atopic diseases is also elevated in many infections. This paper reports on the occurrence and possible pathogenic role of IgE in human Plasmodium falciparum malaria, one of the most widely spread and severe infectious diseases world wide. Plasmodial infections induce IgE elevation in the blood of the majority of people living in malaria endemic areas and up to 5% of this IgE constitutes anti-malaria antibodies. Production of IgE is controlled by T cells and elevated IgE concentrations in the blood of malaria patients are the result of an increased ratio of T-helper 2 (Th2) over T-helper 1 (Th1) cells. The underlying Th1 to Th2 switch is controlled by a variety of environmental and genetic factors. The importance of the latter is demonstrated by the IgE levels occurring in monozygotic or dizygotic twins originating from malarious areas of Africa. While these levels were indistinguishable within monozygotic twin pairs, they were different within the dizygotic pairs. Comparison of the levels of total IgE or IgE anti-malaria antibodies in patients with uncomplicated malaria with those in patients with the severe form of the disease (cerebral malaria or severe malaria without cerebral involvement) indicate that these levels are significantly higher in the cases with severe disease. This is the reverse with IgG and suggests that IgE plays a role in malaria pathogenesis. An important pathogenic mediator causing malaria fever and tissue lesions is tumor necrosis factor (TNF), generally believed to be induced by toxins released from the parasite. However, sera from malaria patients can also cause TNF release from monocytes in a reaction dependent on the presence of IgE containing immune complexes or aggregates. This results in induction and cross-linking of Fcepsilon receptor II (CD23) and by binding to and activating these cells, IgE will contribute to a local over-production of TNF in capillaries and post-capillary venules where P. falciparum parasites or their products accumulate in the severe forms of this disease.

IgE antibody during infection with the ovine abomasal nematode, Teladorsagia circumcincta: primary and secondary responses in serum and gastric lymph of sheep

A monoclonal antibody to ovine IgE was employed in an ELISA to investigate the IgE antibody responses in serum and gastric lymph to a primary infection of Teladorsagia circumcincta, and following challenge in previously infected sheep. During a primary response, IgE antibody to antigens derived from the infective third stage (L3) and adult (L5) worms were negligible, with low levels of IgE antibody detected in serum and lymph. In contrast, there was a pronounced IgE antibody response in 2/4 sheep to L3 antigens during 2-8 days after challenge of previously infected animals but low levels of IgE antibody to L5 antigens. This response was confirmed in a second but similar experiment, where relatively high levels of IgE antibody was detected to antigens from L3. Antibody levels were higher in lymph than in serum from the same animals, and Western blots of L3 antigen following SDS-PAGE under reducing conditions revealed several bands of MW26-96KD which reacted with the IgE antibody from gastric lymph. Immunohistochemical staining indicated that these IgE antibodies may be reacting with allergens associated with the surface cuticle of the worms.

The pro-allergic influences of helminth parasites

Parasitic infection is highly allergenic, and the present paper illustrates how parasites might disrupt the regulation of IgE synthesis, resulting in heightened Th-2 responses. The study of parasites, and dysregulation of the IgE network, could in turn provide information relating to the aetiology of allergic diseases such as asthma and atopic dermatitis.

Intestinal nematode parasites, cytokines and effector mechanisms

Laboratory models of intestinal nematode infection have played an important role in developing our understanding of the immune mechanisms that operate against infectious agents. The type of helper T cell response that develops following infection with intestinal nematode parasites is critical to the outcome of infection. The early events that mediate polarisation of the helper T cell subsets towards either Th1 or Th2 during intestinal nematode infection are not well characterised, but it is likely that multiple factors influence the induction of a Th1 or Th2 type response, just as multiple effector mechanisms are involved in worm expulsion. Costimulatory molecules have been shown to be important in driving T helper cell development down a specific pathway as has the immediate cytokine environment during T cell activation. If helper T cells of the Th2 type gain ascendancy then a protective immune response ensues, mediated by Th2 type cytokines and the effector mechanisms they control. In contrast, if an inappropriate Th1 type response predominates the ability to expel infection is compromised. Equally important is the observation that multiple potential effector mechanisms are stimulated by nematode infection, with a unique combination operating against the parasite depending on nematode species and its life cycle stage. Despite the close association between intestinal nematode infection and the generation of eosinophilia, mastocytosis and IgE it has been difficult to consistently demonstrate a role for these effector cells/molecules in resistance to nematode parasites, although mast cells are clearly important in some cases. It therefore seems that, in general, less classical Th2 controlled effector mechanisms, which remain poorly defined, are probably important in resistance to nematode parasites. Thus, our understanding of both the induction and effector phases remains incomplete and will remain an intense area of interest in the coming years.

Tropomyosin implicated in host protective responses to microfilariae in onchocerciasis

A cDNA from adult female Onchocerca volvulus encoding the C-terminal portion of a tropomyosin isoform (termed MOv-14) has been shown previously to confer protective immunity in rodent models of onchocerciasis. The full-length sequence (designated Ov-tmy-1) obtained by PCR amplification, codes for a protein of 33 kDa and shares 91% identity with tropomyosins from other nematodes, falling to 57% identity with human alpha-tropomyosin. Ov-TMY-1 migrates with an apparent molecular mass of 42 kDa on SDS/PAGE and is present in all life-cycle stages, as determined by immunoblotting. Immunogold electron microscopy identified antigenic sites within muscle blocks and the cuticle of microfilariae and infective larvae. Anti-MOv14 antibodies were abundant in mice exhibiting serum-transferable protection against microfilariae conferred by vaccination with a PBS-soluble parasite extract. In contrast, little or no MOv14-specific antibody was present in mice inoculated with live microfilariae, in which resistance is mediated by antibody-independent mechanisms. In human infections, there was an inverse correlation between anti-tropomyosin IgG levels and densities of microfilariae in the skin. Seropositivity varied with the relative endemicity of infection. An immunodominant B cell epitope within Ov-TMY-1 (AQLLAEEADRKYD) was mapped to the N terminus of the MOv14 protein by using sera from protectively vaccinated mice. Intriguingly, the sequence coincides with an IgE-binding epitope within shrimp tropomyosin, believed to be responsible for hypersensitivity in individuals exhibiting allergy to shellfish. IgG and IgE antibodies reacting with the O. volvulus epitope were detected in human infections. It is concluded that antibody responses to tropomyosin may be important in limiting microfilarial densities in a proportion of individuals with onchocerciasis and have the potential to mediate hypersensitivity reactions to dead microfilariae, raising the possibility of a link with the immunopathology of infection.

Protection against Schistosoma mansoni infection with a recombinant baculovirus-expressed subunit of calpain

Infections by human schistosomes, in particular Schistosoma mansoni, account for significant morbidity and mortality every year in tropical and sub-tropical areas. The eggs of the parasite induce pathological changes in the infected host; in chronic and heavy infections, these changes may lead to death. A well-designed anti-schistosomal vaccine, alone or in concert with existing control measures such as chemotherapy, may prove to be a safe, inexpensive, and effective means of reducing the occurrence of severe disease and death in S. mansoni infection. Previous studies have demonstrated the importance of the syncytial layer containing the apical plasma membrane (APM) of S. mansoni in both the survival of the parasite in the mammalian host and as a potential source of immunogens which may be utilized as vaccine candidates. In this paper, we present evidence for the protective capacity of several schistosomal antigen preparations, including a calcium binding protein of the APM, S. mansoni calpain (GenBank accession no. M74233). We have constructed and characterized expression of a recombinant baculovirus expressing the large subunit of S. mansoni calpain, Sm-p80. This recombinant Sm-p80 is recognized by IgA, IgM, IgG1, and IgG3 isotype antibodies found in S. mansoni-infected human sera and partially-purified recombinant Sm-p80 provided a 29-39% reduction in worm burden in immunized mice challenged with S. mansoni. Our data indicate that Sm-p80 may be a useful vaccine antigen for the reduction of the morbidity associated with S. mansoni infections of mammalian hosts.

Th2-mediated host protective immunity to intestinal nematode infections

Despite many years of study, relatively little is known about the effector mechanisms that operate against intestine-dwelling nematodes. Most of the current understanding comes from studies of laboratory model systems in rodents. It is clear that when an intestinal helminth infection takes place the immune system generates a strong Th2-mediated response, which regulates a variety of responses characteristic of helminth infections such as eosinophilia, intestinal mastocytosis and elevated IgE production. The ability to modulate the host's immune response in vivo with cytokine-specific monoclonal antibodies and recombinant cytokines, together with the use of animals with disruption of key genes involved in the immune response, have provided powerful tools with which to dissect the potential effector mechanisms operating. In the absence of a T-cell compartment the host is unable to expel the parasite. If a Th1-dominated response is generated, protective immunity is almost universally compromised. Thus, it it would appear that some aspect of a Th2-mediated response controls effector mechanisms. Although it is clear that for some infections the mast cell appears to be involved in protection, probably through the generation of a non-specific inflammatory response, how these cells become activated remains unclear. Data from infections in transgenic animals suggest that activation is not through the high-affinity receptor for IgE. Such studies also call into doubt the importance of conventional interactions between effector leucocytes and antibody. There is little evidence to support a protective role for eosinophilia in any system. New data also imply that, although interleukin 4 (IL-4) is generally important (and can exert effects independent of an adaptive immune response), it is not always sufficient to mediate protection; other Th2 cytokines (e.g. IL-13) may warrant closer investigation. It is apparent that a number of potential Th2-controlled effector mechanisms (some of which may be particularly important at mucosal surfaces) remain to be explored. Overall, it is likely that worm expulsion is the result of a combination of multiple mechanisms, some of which are more critical to some species of parasite than to others.

Effects of anti-IgE mAb on serum IgE, Fc epsilon RII/CD23 expression on splenic B cells and worm burden in mice infected with Paragonimus westermani

It is generally accepted that parasite-specific IgE plays a crucial role in host defense against helminthic parasites. However, the role of high levels of nonspecific IgE in helminthic infections is still controversial. To investigate the role of nonspecific IgE in primary infections with P. westermani, the effect of anti-IgE mAb treatment on serum IgE, Fc epsilon RII/CD23 expression and worm burden in Paragonimus-infected mice were examined. In mice treated with anti-IgE antibody, the total IgE levels were not detectable (1 microgram/ml) throughout the experiment compared with untreated infected mice. The mean percentages of Fc epsilon RII/CD23 positive splenic B cells in anti-IgE treated mice (range: 20.3 - 30.5) were also decreased throughout the experiment compared with untreated infected mice (range: 35.7 - 44.4). Reduction of the total IgE and expression of Fc epsilon RII/CD23 on splenic B cells resulted in decreased worm burden six weeks post infection. These results suggest that high levels of nonspecific IgE in mice with primary infections of P. westermani play a harmful, rather than beneficial, role for the host, perhaps by interfering with CD23-dependent cellular pathways.

Intragastric immunization of rats with Entamoeba histolytica trophozoites induces cecal mucosal IgE, eosinophilic infiltration, and type I hypersensitivity

We have investigated the role of IgE in the local immunity of intestinal amebiasis, a parasitic infection known to induce specific antibody-forming cells (AFC) and IgA antibodies in rodents and humans. We found that intragastric immunization of rats with glutaraldehyde-fixed Entamoeba histolytica trophozoites significantly increased antiameba AFC in the Peyer's patches and spleen and that the lamina propria of the cecum from immunized animals was infiltrated by eosinophils armed with IgE antibodies. Morphometric analysis showed that IgE-containing cells and eosinophils were nearly three times more abundant in the cecum of immunized rats. Antigenic challenge with amebal lysates provoked an increase in the short-circuit current and in the transepithelial potential difference in Ussing-chambered cecum preparations from immunized rats. Although eosinophilia and the increase of IgE are common consequences of infection by parasitic worms, our results indicate that local immunity in intestinal amebiasis also involves IgE deposition, eosinophil infiltration, and type I hypersensitivity, which may explain some symptoms of amebic dysentery such as colic, abdominal tension, tenesmus, and bloody stools.

Immunoglobulin E, a pathogenic factor in Plasmodium falciparum malaria

Most children and adults living in areas where the endemicity of Plasmodium falciparum malaria is high have significantly elevated levels of both total immunoglobulin E (IgE) and IgE antimalarial antibodies in blood. This elevation is highest in patients with cerebral malaria, suggesting a pathogenic role for this immunoglobulin isotype. In this study, we show that IgE elevation may also be seen in severe malaria without cerebral involvement and parallels an elevation of tumor necrosis factor alpha (TNF). IgE-containing serum from malaria immune donors was added to tissue culture plates coated with rabbit anti-human IgE antibodies or with P. falciparum antigen. IgE-anti-IgE complexes as well as antigen-binding IgE antibodies induced TNF release from peripheral blood mononuclear cells (PBMC). Nonmalaria control sera with no IgE elevation induced significantly less of this cytokine, and the TNF-inducing capacity of malaria sera was also strongly reduced by passing them over anti-IgE Sepharose columns. The cells giving rise to TNF were adherent PBMC. The release of this cytokine probably reflects cross-linking of their low-affinity receptors for IgE (CD23) by IgE-containing immune complexes known to give rise to monocyte activation via the NO transduction pathway. In line with this, adherent monocytic cells exposed to IgE complexes displayed increased expression of CD23. As the malaria sera contained IgG anti-IgE antibodies, such complexes probably also play a role in the induction of TNF in vivo. Overproduction of TNF is considered a major pathogenic mechanism responsible for fever and tissue lesions in P. falciparum malaria. This overproduction is generally assumed to reflect a direct stimulation of effector cells by certain parasite-derived toxins. Our results suggest that IgE elevation constitutes yet another important mechanism involved in excessive TNF induction in this disease.

IgE, allergies and helminth parasites: a new perspective on an old conundrum

This paper analyses the association between infection with helminth parasites, the elevated production of IgE and the expression of allergies. Interpretations of this interaction have taken place in a scientific environment whose most secure element is the immunochemistry of allergic reactions resulting in a substantial body of literature that has sought a biological role for allergic reactivity in protective immunity directed against helminth parasites. While the association between helminth infections and elevated levels of IgE, mast cells and eosinophils is well established, a functional role for allergic reactions in protection against helminths has eluded experimental proof. Instead of this hypothesis, it is proposed that allergic reactivity is rarely present in helminth-infected individuals because allergic reactions do not function to regulate helminth infections. Data from many sources are used to establish that the 'normal' state of all mammals is to be infected with helminth parasites from shortly after birth until well into adulthood. Only in the last 100 years or so have people living in areas of high development with sophisticated water and sewage systems been able to escape helminth infection. Allergies are as conspicuously present in these human populations as they are absent in populations that are still regularly exposed to helminths. Furthermore, in populations with endemic helminthoses there is little overt expression of allergic pathology that could be connected to the acquisition or elimination of helminth parasites. Based on these observations, it is suggested that endemic helminthoses activate the Th2 system, particularly at mucosal surfaces, to provide a different level of immunological homeostasis than currently occurs in developed societies. Under these conditions, mast cells, eosinophils and IgE rarely participate in reactions that we would recognize as 'allergic', although their participation in the control of helminth infections is still envisaged. Allergic reactions are considered to be a purely pathologic consequence of the disruption of this homeostatic mechanism and are not protective at all for the individual expressing them. This interpretation is derived from the immunobiology of the host-parasite interaction rather than the biology of allergies and should lead to new concepts regarding both allergic disease and the role of helminth infections in human and animal populations.