Evidence for an interleukin 4-inducible immunoglobulin E uptake and transport mechanism in the intestine

CD23-dependent transcytosis of IgE and immune complex across the polarized human respiratory epithelial cells

IgE-mediated allergic inflammation occurs when allergens cross-link IgE on the surface of immune cells, thereby triggering the release of inflammatory mediators as well as enhancing Ag presentations. IgE is frequently present in airway secretions, and its level can be enhanced in human patients with allergic rhinitis and bronchial asthma. However, it remains completely unknown how IgE appears in the airway secretions. In this study, we show that CD23 (FcεRII) is constitutively expressed in established or primary human airway epithelial cells, and its expression is significantly upregulated when airway epithelial cells were subjected to IL-4 stimulation. In a transcytosis assay, human IgE or IgE-derived immune complex (IC) was transported across a polarized Calu-3 monolayer. Exposure of the Calu-3 monolayer to IL-4 stimulation also enhanced the transcytosis of either human IgE or the IC. A CD23-specific Ab or soluble CD23 significantly reduced the efficiency of IgE or IC transcytosis, suggesting a specific receptor-mediated transport by CD23. Transcytosis of both IgE and the IC was further verified in primary human airway epithelial cell monolayers. Furthermore, the transcytosed Ag-IgE complexes were competent in inducing degranulation of the cultured human mast cells. Because airway epithelial cells are the first cell layer to come into contact with inhaled allergens, our study implies CD23-mediated IgE transcytosis in human airway epithelial cells may play a critical role in initiating and contributing to the perpetuation of airway allergic inflammation.

The epithelial gatekeeper against food allergy

The rapid rise of allergic disorders in developed countries has been attributed to the hygiene hypothesis, implicating that increased environmental sanitation in early childhood may be associated with higher incidence of hypersensitivity. Intestinal epithelial barriers play a crucial role in the maintenance of gut homeostasis by limiting penetration of luminal bacteria and dietary allergens, yet allowing antigen sampling via the follicle-associated epithelium for generation of tolerance. However, this intricate balance is upset in allergic intestines, whereby luminal proteins with antigenic properties gain access to the subepithelial compartment and stimulate mast cell degranulation. Recent studies demonstrated that food allergens were protected from lysosomal degradation, and were transported in large quantities across the epithelium by binding to cell surface IgE/CD23 (FcepsilonRII) that prevented the antigenic protein from lysosomal degradation in enterocytes. IL-4 (a Th2-type cytokine) not only increased production of IgE from B cells, but also upregulated the expression of CD23 on intestinal epithelial cells. Further studies indicated that CD23 was responsible for the bidirectional transport of IgE across epithelium. The presence of IgE/CD23 opens a gate for intact dietary allergens to transcytose across the epithelial cells, and thus foments the mast cell-dependent anaphylactic responses. The understanding of the molecular mechanism responsible for epithelial barrier defects may be helpful in designing novel therapies to treat food allergy and other allergic diseases.

The effectors responsible for gastrointestinal nematode parasites, Trichinella spiralis, expulsion in rats

Helper T (Th2) cells type 2 have a central role in host protective responses to gastrointestinal nematode parasite, Trichinella spiralis infection, but the actual effector mechanisms involved in parasite expulsion are still uncertain. Recent evidences suggest that mast cell recruitment and activation may associate with parasite elimination from host intestines in mice. On the other hand, IgE production may induce defensive responses to primary infection with the helminth in rats. The differences of host effector mechanisms to the same experimental infections might disturb our understanding of the host protective mechanisms to gastrointestinal nematode parasite infection. In order to redefine these differences, we investigated in detail the relationship between intestinal immune responses and worm expulsion following T. spiralis infection among several rat strains including mutants. As a result, there were significant correlations of parasite expulsion with mast cell hyperplasia in addition to serum IgE level. Moreover, mast cell-deficient and dysfunction rats showed delayed worm elimination from their gut. Therefore, the present study suggests that mast cells should also be one of the prominent effector cells involved in T. spiralis parasite expulsion in rats as well as mice.

Transcytosis of IgE-antigen complexes by CD23a in human intestinal epithelial cells and its role in food allergy

BACKGROUND & AIMS

Secreted immunoglobulins play an integral role in host defense at mucosal surfaces, and recent evidence shows that IgG can participate in antigen sampling from the intestinal lumen. We examined whether IgE also could facilitate transepithelial antigen sampling.

METHODS

Stool samples from food-allergic patients undergoing oral food challenge were analyzed for CD23 and food-specific IgE. CD23 isoform expression on primary human intestinal epithelial cells (IEC) was analyzed by polymerase chain reaction. The role of CD23 isoforms in transcytosis of antigen and IgE-antigen complexes was assessed using polarized human T84 cells retrovirally transfected with CD23a or CD23b.

RESULTS

CD23 was expressed constitutively on IECs, and food-allergic patients had increased levels of soluble CD23 and food-specific IgE in the stool after challenge. CD23a, but not CD23b, was expressed by primary human IECs. We show in transcytosis assays that CD23a, but not CD23b, acts as a bidirectional transporter of IgE. In addition, specific IgE facilitated the uptake of antigen from the apical surface of an epithelial monolayer by diverting antigen from delivery to lysosomes. Finally, delivery of antigen-IgE complexes across the epithelial barrier could induce the degranulation of rat basophil leukemia cells transfected with the human high-affinity IgE receptor.

CONCLUSIONS

These studies show that CD23a is expressed normally on human IECs, and in the presence of IgE can function as an antigen-sampling mechanism capable of activating subepithelial mast cells. IgE may serve as a secretory immunoglobulin that in concert with CD23 participates in food-induced pathophysiology of the gastrointestinal tract.

Differential Role for CD23 Splice Forms in Apical to Basolateral Transcytosis of IgE/Allergen Complexes

The low affinity receptor for IgE (CD23) was recently implicated in the trans-epithelial transport of IgE-allergen complexes from the luminal side of enterocytes in animal models for intestinal allergy. Here, the respective functions of CD23 splice forms, b and bDelta5, in this apical to basolateral transport event have been investigated. First, the new bDelta5 splice form was further characterized, providing evidence that it binds IgE with high affinity, that its expression is induced by sensitization, and that bDelta5, unlike the classical b, undergoes constitutive internalization through clathrin-coated pits. These results suggested that the two CD23 splice forms were likely involved in different transcytotic events. MDCK cell lines expressing either b or bDelta5 were generated to directly test this hypothesis. In both cell lines, CD23 splice forms were localized at the apical membrane as in enterocytes from sensitized mice. Using mouse monoclonal IgE, we obtained evidence showing that bDelta5 mediates the apical to basolateral transport of free IgE, whereas classical b is much more efficient in mediating the transcytosis of IgE/allergen complexes. The present results shed new light on the role of CD23 species in IgE/allergen transepithelial transport and provide a new powerful physiological tool to study apical to basolateral transcytosis, a process which remains poorly characterized.

Impeded establishment of the infective stage of Trichinella in the intestinal mucosa of mice by passive transfer of an IgA monoclonal antibody

Our previous study showed that the IgA monoclonal antibody (mAb) HUSM-Tb1 forms immunoprecipitates on the cuticular surface of infective larvae of Trichinella britovi, and that intraperitoneal injection of this mAb to mice 5 hr before challenge infection confers a high level of protection against intestinal T. britovi. The same treatment produced a similar effect in BALB/c mice inoculated orally with Trichinella pseudospiralis larvae, indicating that the effects may be seen upon most members of the genus Trichinella. Worms recovered from the intestinal mucosa at 1 hr after challenge infection with T. pseudospiralis was few in mice passively immunized with the mAb, whereas a substantial number of worms were recovered from the mucosa of control groups. These results suggest that the IgA mAb impedes establishment of infective Trichinella worms in the intestinal mucosa. Trichinella worms inoculated orally into BALB/c mice vaccinated with ultraviolet-irradiated muscle larvae 3 weeks earlier were expelled between days 4 and 7 after challenge infection. Although the mAb HUSM-Tb1 originated from the mesenteric lymph node cells of mice vaccinated repeatedly with such irradiated larvae, IgA-mediated expulsion does not seem to play an important role in this vaccination model.

Intestinal epithelial CD23 mediates enhanced antigen transport in allergy: evidence for novel splice forms

We previously demonstrated enhanced transepithelial antigen transport in the intestine of allergic rodents associated with elevated expression of the low-affinity IgE receptor CD23 on enterocytes. Here, we examined the role of CD23 in the transport phenomenon using CD23-/- mice and characterized the isoform of intestinal epithelial CD23. Jejunal segments of sensitized mice were challenged with antigen. Enhanced transepithelial antigen transport and transmucosal antigen flux were found in the intestine of sensitized CD23+/+ but not CD23-/- mice. RT-PCR showed that enterocytes expressed only the isoform b of CD23. Sequencing revealed classic and alternative CD23b transcripts lacking exon 5 (bDelta5) or 6, all of which were translated into functional IgE receptors. The protein encoded by bDelta5 but not the classic b transcript was able to mediate the uptake of anti-CD23 or IgE, whereas both CD23 proteins were internalized after binding to IgE/antigen complexes. Our results suggest that the classic and alternative forms of CD23b display distinct endocytic properties, suggesting that they are likely to play different roles in transepithelial transport of IgE and allergens.

Local allergic reaction in food-hypersensitive adults despite a lack of systemic food-specific IgE

BACKGROUND

Objective tools are lacking for the diagnosis of local gastrointestinal inflammatory reactions in skin prick test (SPT)-negative and serum IgE antibody (s-IgE Ab)-negative patients with suspected food allergy.

OBJECTIVE

The purpose of this investigation was to evaluate the presence of eosinophils, T cells, local IgE-bearing cells, IL-4, and IFN-gamma in small intestinal biopsy specimens from adult SPT-negative/s-IgE Ab-negative patients with food allergy during symptomatic and nonsymptomatic periods.

METHODS

Fourteen patients with food allergy-related gastrointestinal symptoms confirmed by double-blinded, placebo-controlled food challenge (DBPCFC) were investigated. Eleven of the patients were SPT-negative and s-IgE Ab-negative. Sex- and age-matched healthy volunteers were used as controls. Duodenal biopsies were studied with immunostaining through use of a panel of mouse monoclonal antibodies specific for eosinophils, CD3, CD4, CD8, IgE, IL-4, and IFN-gamma.

RESULTS

Significant increases in numbers of MBP+ eosinophils, IgE-bearing cells, and T cells were found in the duodenal mucosa of the patients when they were symptomatic in comparison with when they were asymptomatic and in comparison with healthy controls. Numbers of IL-4+ cells were increased and numbers of IFN-gamma+ cells were reduced in the patients when they were symptomatic in comparison with when they were asymptomatic and in comparison with the controls. There were no differences in total s-IgE levels between any of the groups.

CONCLUSION

A significant correlation was found between the appearance of symptoms of food hypersensitivity and the duodenal presence of IgE-bearing cells, activated eosinophils, and T cells in patients with negative SPT results and negative s-IgE Ab to the offending food. We suggest that a localized IgE-mediated response caused the gastrointestinal symptoms seen in these patients.

Gastrointestinal nematodes, nutrition and immunity: breaking the negative spiral

Nutritionists have long understood that intestinal nematode parasites have deleterious effects on host nutritional status, but only recently has the importance of malnutrition as a predisposing factor to intestinal nematodes been recognized. Here we review experimental and field studies on the effects of protein, energy, zinc, vitamin A, and iron deficiencies on gastrointestinal (GI) nematodes of humans, livestock, and laboratory rodents, and draw certain conclusions about the state of our current understanding. In general, malnutrition promotes the establishment, survival, and fecundity of these parasites, but the magnitude of the effect depends on factors such as host species, parasite species, particular infection protocol used, magnitude of the infection, severity of the nutritional deficiency, and presence of single or multiple infections and single or multiple nutritional deficiencies. We highlight the Th2 arm of the immune system as a component of primary importance in the association between malnutrition and GI nematode infections. We summarize what is known about underlying mechanisms that may account for the observed patterns. Finally, we suggest future research directions.

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.

Enhanced transepithelial antigen transport in intestine of allergic mice is mediated by IgE/CD23 and regulated by interleukin-4

BACKGROUND & AIMS

We previously described a system for enhanced transepithelial transport of antigen in which both the amount of specific antigen and its rate of transport were dramatically increased in intestine of sensitized rats compared with controls. This study investigated the essential components mediating antigen uptake in mice genetically deficient for interleukin (IL)-4 or CD23.

METHODS

Mice were actively or passively sensitized to horseradish peroxidase (HRP). Jejunal segments from control or sensitized mice were mounted in Ussing chambers and challenged with HRP from the luminal side. Tissues were processed for electron microscopy, and photomicrographs were analyzed for antigen uptake (location and area of HRP-containing endosomes). Immunohistochemistry and reverse-transcription polymerase chain reaction were used to detect epithelial CD23 expression.

RESULTS

Actively sensitized IL-4(+/+), but not IL-4(-/-) mice, displayed increased transepithelial antigen transport and CD23 expression on enterocytes. Passively sensitized IL-4(+/+) and IL-4(-/-) mice displayed elevated antigen transport after transfer of immune serum but not if the serum was depleted of immunoglobulin (Ig) E or IL-4. IL-4 added to cultured IEC-4 cells up-regulated expression of CD23 messenger RNA. The augmented antigen uptake was inhibited by anti-CD23 and was absent in sensitized CD23(-/-) mice.

CONCLUSIONS

Our studies indicate that IL-4 regulates IgE/CD23-mediated enhanced transepithelial antigen transport in sensitized mouse intestine.

The immunologic basis for intestinal food allergy

There has been considerable recent broadening of basic concepts of intestinal food allergy, in particular the importance of non-IgE-mediated mechanisms. The traditional emphasis on IgE-mediated allergy now appears inappropriate in light of current studies of the basic mechanisms of oral tolerance to dietary antigen and of increasing recognition of the requirement for early infectious challenge in the prevention of allergic sensitization. This major change in emphasis has been forced both by basic scientific studies and by recognition of novel patterns of food allergic disease within the pediatric population, in which rapid increase in food-allergic sensitization has been noted in the last decade and previously rare phenomena such as multiple food allergies and sensitization of exclusively breast-fed infants to antigens eaten by the mother have become commonplace. It is thus emerging that the possession of exaggerated IgE responses may not be the direct cause of food allergic sensitization but may ensure that such sensitization is clinically obvious. Those without such immediate responses have a complex of symptoms, including diet-responsive eczema and a marked disturbance of intestinal motility. The clear demographic links with socioeconomic privilege and relative protection from gastrointestinal infarctions concord with recent murine data suggesting an obligatory input from innate immune responses to the gut flora in the establishment of oral tolerance.

Enhanced intestinal transepithelial antigen transport in allergic rats is mediated by IgE and CD23 (FcepsilonRII)

We previously reported that active sensitization of rats resulted in the appearance of a unique system for rapid and specific antigen uptake across intestinal epithelial cells. The current studies used rats sensitized to horseradish peroxidase (HRP) to define the essential components of this antigen transport system. Sensitization of rats to HRP stimulated increased HRP uptake into enterocytes (significantly larger area of HRP-containing endosomes) and more rapid transcellular transport compared with rats sensitized to an irrelevant protein or naive control rats. Whole serum but not IgE-depleted serum from sensitized rats was able to transfer the enhanced antigen transport phenomenon. Immunohistochemistry demonstrated that sensitization induced expression of CD23, the low-affinity IgE receptor (FcepsilonRII), on epithelial cells. The number of immunogold-labeled CD23 receptors on the enterocyte microvillous membrane was significantly increased in sensitized rats and was subsequently reduced after antigen challenge when CD23 and HRP were localized within the same endosomes. Finally, pretreatment of tissues with luminally added anti-CD23 antibody significantly inhibited both antigen transport and the hypersensitivity reaction. Our results provide evidence that IgE antibodies bound to low-affinity receptors on epithelial cells are responsible for the specific and rapid nature of this novel antigen transport system.

Suppressed T helper 2 immunity and prolonged survival of a nematode parasite in protein-malnourished mice

Protein malnutrition may increase susceptibility to gastrointestinal parasitic infections, possibly as a result of impaired intestinal and/or systemic T helper 2 (Th2) effector responses induced by down-regulation of Th2 cytokines and/or up-regulation of Th1 cytokines. To test this hypothesis, female BALB/c mice (n = 18/diet) were fed a control (24%), marginal (7%), or deficient (3%) protein diet and given a challenge infection with Heligmosomoides polygyrus. The 3% mice had higher worm burdens at 1, 2, and 4 weeks postchallenge infection (pci), lower increases in serum IgE, reduced intestinal eosinophilia, and depressed mucosal mast cell proliferation and activation at 1-2 weeks pci. To determine whether these suppressed effector responses resulted from altered spleen and mesenteric lymph node (MLN) cytokine production, cells were restimulated in vitro with parasite antigen and cytokine concentrations were measured. Deficient MLN cells secreted significantly less IL-4 and more IFN-gamma at 1-2 weeks pci than did control MLN cells. Deficient spleen cells also secreted more IFN-gamma at 2 weeks pci compared with control spleen cells. From reverse transcription-PCR analyses, the 3% mice also had lower IL-4 mRNA level in spleen and MLN at 1-2 weeks pci. Our study supports the hypothesis that protein malnutrition increases the survival of a nematode parasite by decreasing gut-associated IL-4 (Th2) and increasing IFN-gamma (Th1) within 2 weeks pci, leading to reduced intestinal and systemic Th2 effector responses.

IL-13 in allergy: home at last

The immune response to allergic challenge is thought to include important effects mediated by cytokines. Of considerable interest to immunologists and parasitologists is the distinction between two closely related cytokines, IL-4 and IL-13. Although overlapping functions are inevitable, studies over the past year reveal a distinct role for IL-13 in mediating the physiologic response to a diverse array of allergens and parasites.

Induction and regulation of the IgE response

Immunoglobulin E (IgE) is believed to be one of the major mediators of immediate hypersensitivity reactions that underlie atopic conditions such as urticaria, seasonal allergy, asthma and anaphylaxis. Factors that control IgE production are therefore essential to the pathogenesis of these important afflictions. But a complete understanding of this topic is lacking, while new data have raised questions regarding the precise role of IgE in atopic disease. Evolving concepts of IgE production and elimination are likely to clarify the importance of IgE in health and disease.

Dominance of immunoglobulin G2c in the antiphosphorylcholine response of rats infected with Trichinella spiralis

The antibody response to the L1 stage of Trichinella spiralis has been described as biphasic. Worms resident in the intestine during the first week of infection stimulate an antibody response against a subset of larval proteins. L1 larvae in the muscle at the end stage of infection stimulate a second antibody response against tyvelose-bearing glycoproteins. Antityvelose antibodies protect rats against challenge infection with larvae. The aim of this study was to characterize the rat B-cell response against larval antigens during the intestinal phase of T. spiralis infection and to test the antiparasitic effects of such antibodies. Strain PVG rats were infected orally with 500 larvae. Antibodies specific for phosphorylcholine-bearing proteins of L1 larvae first appeared in serum 9 days postinfection. Absorption experiments showed that the majority of antilarval antibodies produced in rats 16 days after infection with T. spiralis were specific for phosphorylcholine-bearing proteins. A fraction of these antibodies bound to free phosphorylcholine. Immunoglobulin G2c (IgG2c) producing cells in the mesenteric lymph node dominated this early antibody response. IgG2c is associated with T-independent immune responses in the rat; however, a comparison of athymic rats with euthymic controls suggested that only a small fraction of the phosphorylcholine-related antibody response against T. spiralis was T independent. Phosphorylcholine is a common epitope in antigens of bacteria and nematode parasites and has been shown to be a target of protective immunity in certain bacteria. A monoclonal IgG2c antibody was prepared from infected rats and shown to be specific for phosphorylcholine. Monoclonal phosphorylcholine-specific IgG2c failed to protect rats against intestinal infection with T. spiralis. Therefore, our findings do not support a role for phosphorylcholine-bearing antigens in immune defense against T. spiralis; however, the potency of the immune response induced suggests an immunomodulatory role for the lymphocytes involved.

Rapid anti-helminthic response of B lymphocytes in the intestinal mucosal tissues of rats

B cell response to Trichinella spiralis (Ts) adult antigen (Ag) was studied in rats 1-20 days postinfection. B cell recoveries from the mesenteric lymph node (MLN), Peyer's patches (PP), thoracic duct lymph (TDL), and the spleen were determined by FACS analysis and Ag-specific antibody-producing cells (Ab-pc) in these tissues were enumerated using the immunoplaque assay. Total B cell numbers increased 2-70 times from day 3 postinfection in the MLN and TDL obtained from MLN-resected rats (MX) and such proliferation was not found in the PP or the spleen. Ab-pc of all isotypes increased from day 3 in the MLN and from day 2 in the MX-TDL. Among all isotypes, IgE- and IgG1-pc showed the strongest response. Immunofluorescence study revealed that these B cells were activated in the non-PP region of the small intestine. These results indicate an early isotype switch to IgG1 and IgE production in Ts-infected small intestine.

Petechial hemorrhages in the small intestinal Peyer's patches: a new manifestation of systemic anaphylaxis

Systemic anaphylaxis in the rat has major manifestations in the small intestine. In August rats, but not in other strains, intestinal anaphylaxis was accompanied by petechial hemorrhages in Peyer's patches. The occurrence of petechiae was not proportional to the intensity of prostration, cyanosis or gut congestion. No hemorrhages were found in other organs. The petechiae occurred in August rats of either sex after sensitization and challenge with any of several antigens and adjuvants and after passive sensitization with antiserum. The number of Peyer's patches with hemorrhage varied from one to all 20 in individual rats. The occurrence of petechiae was not influenced significantly by the route of sensitization or challenge, by the presence or absence of pinworms in the cecum, or by ancillary treatment at time of challenge with normal serum, normal blood, heparin, pertussis vaccine or lipopolysaccharide. The intestinal mast cells of the susceptible August rats were not different from the mast cells of the resistant strains. Furthermore, mast cells did not reside in the lymphoid follicles of Peyer's patches which was the site of the petechial hemorrhages in anaphylactic August rats. Nor did injections of histamine, serotonin or both cause hemorrhages in Peyer's patches.

Expression of epsilon germ-line gene transcripts and mRNA for the epsilon heavy chain of IgE in nasal B cells and the effects of topical corticosteroid

We have studied the expression of the gene encoding the epsilon heavy chain of IgE in nasal B cells of hayfever patients. We developed probes to detect transcripts of the epsilon germ-line gene and the rearranged gene by in situ hybridization of biopsy sections from the nasal mucosa. We compared tissue from hayfever patients out of season with that of normal controls, and also of hayfever patients treated with topical corticosteroid (fluticasone propionate) or placebo for 6 weeks and then challenged with antigen. epsilon chain mRNA was expressed in an unexpectedly high proportion of nasal B cells of both hayfever patients and normal subjects. However, although similar numbers of B cells were found in both groups, the proportion of cells that express epsilon chain mRNA was several times higher in the hayfever patients. No transcripts of the epsilon germ-line gene were detected in either group before allergen challenge. When hayfever patients were administered antigen locally, early (10-30 min) and late (1-24 h) symptoms ensued. After 24 h, coincident with an increase in the number of cells expressing mRNA for IL-4 in the tissue, epsilon germ-line gene transcripts appeared in the nasal B cells. The induction by allergen of IL-4 mRNA and epsilon germ-line gene transcripts was suppressed by fluticasone propionate treatment. Our results suggest that local IgE synthesis and cytokine regulation of heavy chain switching to IgE occur in the nasal mucosa.

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.

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.

Prospects for the immunological control of ruminant gastrointestinal nematodes: natural immunity, can it be harnessed?

Current understanding of the mucosal immune response to nematode parasites is briefly reviewed with emphasis on the role of the cytokines interleukins-4 and -12 and gamma interferon (IFN gamma) in the development of T-helper responses in rodents. Data from laboratory animals and ruminants indicate that the events associated with a T-helper 2 (Th2) cell response, notably IgE synthesis, eosinophilia and mucosal mastocytosis are protective. Evidence that effector mechanisms may vary for different parasite species is considered. Current gaps in understanding such as the location in the gut and mechanism of antigen processing and presentation as well as the relative contribution of non-immunological effector responses, such as gut motility and mucus secretion, to worm expulsion are discussed.

Effects of maternal ethanol consumption on the subsequent development of immunity to Trichinella spiralis in rat neonates

The immune response of rat pups to the intestinal parasite Trichinella spiralis was studied to determine if maternal pre- and/or postnatal ethanol consumption affected neonatal immune responses. Female rats were fed ethanol-containing (36% of calories) or pair-fed control liquid diets and include groups that were maintained on ethanol as follows: group 1, from day 1 of pregnancy through weaning and whose pups were then placed on ethanol to sacrifice; group 2, from day 1 of pregnancy through lactation; group 3, from day 1 of pregnancy through pup delivery; and group 4, from day 1 of lactation through weaning. A parallel group of animals was pair-fed isocaloric control diet until sacrifice. The pups of all litters were immunized orally with 500 L1 (T. spiralis) larva 5 days after weaning. To examine the effects of maternal ethanol on primary immune responses, one-fourth of the pups from each litter were sacrificed on days 10 and 20 after immunization. To examine the effects on neonatal secondary immune responses, the remaining pups were challenged with 1,000 larva 30 days after the initial immunization and sacrificed either 3 or 8 days after challenge. At the time of sacrifice, blood samples were collected, the intestine removed to determine T. spiralis worm burdens, and suspensions of mesenteric lymph node (MLN) cells prepared. Intestinal worm counts and serum levels of anti-T. spiralis IgM and IgG antibodies, interleukin-2 (IL-2), and tumor necrosis factor (TNF) were determined. In vitro proliferation responses of MLN cells to T. spiralis antigen and to the mitogen concanavalin A (Con A) were also examined. Pups from groups 1 to 3 demonstrated significantly higher intestinal worm counts (decreased immunity) than the pair-fed controls at the day 20 primary immune response sacrifice, and pups from group 1 had significantly higher worm counts at day 3 after a secondary immune challenge. Pups of dams from groups 1, 3, and 4 had significantly lower IgM antibody titers at the day 20 primary immune response sacrifice. All experimental ethanol groups (1 to 4) demonstrated significantly lower IgG antibody titers than that observed in pair-fed control pups at the 20-day sacrifice. IgM antibody titers showed significant reductions for ethanol-treated groups at 3 and 8 days after T. spiralis secondary challenge. In addition, IgG antibody titers were also significantly reduced for all alcohol groups at 3 and 8 days during the secondary immune response. Serum IL-2 and TNF levels were significantly lower in all experimental ethanol groups (1 to 4) relative to pair-fed controls at day 20 during a primary immune response, and IL-2 levels at 3 days postchallenge were lower in groups 2 to 4 after a secondary immune challenge. MLN proliferation responses to antigen and Con A were significantly reduced in ethanol groups 1 to 3 and to Con A in group 4 at day 10 after a primary immune challenge. Ethanol group 3 pups also demonstrated a reduced response to antigen at day 20. For animals undergoing a secondary immune response, ethanol group 2 demonstrated a reduced response to antigen at day 3, whereas groups 2 and 4 showed increased reactivity to antigen at days 3 and 8 postchallenge. These results show that maternal ethanol consumption diminishes the capacity of neonates to respond to T. spiralis antigen and that the depressed immune response involves T- and B-cell-mediated reactions and also affects the production of certain cytokines. These results also suggest that the diminished immune responses are increased with longer periods of maternal and neonatal exposure to ethanol.