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

Accelerated clearance of Onchocerca microfilariae and resistance to reinfection in interleukin-4 gene knockout mice

Immunity to Onchocerca microfilariae (mf) in mice is associated with CD4+ Th2 cells and is dependent on IL-5. In view of the role of IL-4 in the development of Th2 cells, we have utilized IL-4 gene knockout mice (IL-4-/-) to investigate microfilarial clearance and resistance to reinfection. Paradoxically, in the absence of IL-4 there is accelerated clearance of microfilariae during a primary infection and unimpeded expression of resistance to reinfection. IL-4-/- mice showed a lack of an IgE response although peripheral eosinophilia was equivalent to wildtype controls. The data presented here suggest that elimination of mf can occur independent of IL-4 and that in this model it may even be detrimental to the host.

Immunoglobulin and cytokine profile in murine secondary hydatidosis

We have investigated specific immune responses in BALB/c mice with experimentally induced secondary hydatidosis. Following intraperitoneal inoculation of brood capsules containing Echinococcus granulosus-protoscoleces, the course of the infection was followed for 513 days. The sera of the mice were screened for the presence of a number of cytokines, and for specific antibodies. During the first 129 days of infection, high levels of cytokines TNF alpha, IL-alpha, IFN gamma, IL-6, and IL-10 and specific IgG1 and IgG3 isotypes were detected, as compared to uninfected controls. The levels of IgM and IgG2a were slightly increased following infection, and remained elevated throughout the period of observation. The levels of IL-1 alpha and specific immunoglobulin of all isotypes except IgM and IgG2a, were significantly decreased 103 days post infection (p.i.), whereas TNF alpha was sharply decreased 129 days p.i. During the period of 129 to 209 days of infection there was an increase in secreted IL-10, and a slow decrease in the levels of IL-6 and IFN gamma. Levels of IgM, IgG, IgG1, and IgG2a plateaued during this period, whereas IgG3 and TNF alpha showed a peak at day 190 p.i. These data suggest the induction of Th2 antibody-mediated immunity with a parallel expansion of Th1-mediated inflammatory responses as important mechanism of host defence against the metacestode.

A major house dust mite allergen disrupts the immunoglobulin E network by selectively cleaving CD23: innate protection by antiproteases

Asthma is a chronic life-threatening disease of worldwide importance. Although allergic asthma and related atopic conditions correlate strongly with immune sensitization to house dust mites, it is unclear why antigens from mites provoke such powerful allergic immune responses. We have characterized the protease activity of Der p I, the group I protease allergen of the house dust mite Dermatophagoides pteronyssinus, and here report that it cleaves the low-affinity immunoglobulin (Ig) E Fc receptor (CD23) from the surface of human B lymphocytes. Der p I selectively cleaves CD23 and has no effect on the expression of any other B cell surface molecules tested. We speculate that this loss of cell surface CD23 from IgE-secreting B cells may promote and enhance IgE immune responses by ablating an important feedback inhibitory mechanism that normally limits IgE synthesis. Furthermore, since soluble CD23 is reported to promote IgE production, fragments of CD23 released by Der p I may directly enhance the synthesis of IgE. alpha 1-Antiprotease, a pulmonary antiprotease, is also shown to inhibit the cleavage of CD23 by Der p I. This may be significant in the etiopathogenesis of asthma, because other indoor pollutants associated with asthma are known to potently inhibit this antiprotease. These data suggest that the proteolytic activity of Der p I, the group I allergen of the house dust mite D. pteronyssinus, is mechanistically linked to the potent allergenicity of house dust mites. Furthermore, inhibition of Der p I by alpha 1-antiprotease suggests a mechanism by which confounding factors, such as tobacco smoke, may act as a risk factor for allergic asthma.

Potentiation of in vitro synthesis of human IgE by cyclosporin A (CsA)

In this study, we investigated the modulatory effects of CsA on in vitro synthesis of IgE, IgG1 and IgG4 by human peripheral blood mononuclear cells (PBMC). In contrast to its known immunosuppressive effect, we have demonstrated that a low dose of CsA (10(-7) M, 120 ng/ml) potentiated IgE production by up to 40-fold (i.e. from 33 +/- 4.5 to 1346 +/- 290 ng/ml). This potentiation was specific for IgE since no such effect was demonstrable with IgG1 and IgG4. Potentiation of IgE synthesis by CsA in the PBMC cultures was partly due to CsA acting on T cells, as demonstrated by the addition of CsA-treated T cells to T cell-depleted cultures. However, potentiation was also demonstrable in a T cell-depleted, anti-CD40-stimulated culture (four-fold increase from 400 +/- 48 to 1606 +/- 127 ng/ml). Our data therefore suggest that there are at least two mechanisms for CsA-induced potentiation of IgE synthesis, one T cell-dependent and the other T cell-independent. The clinical implications of these findings are discussed with regard to the use of CsA in the treatment of Th2-mediated diseases.

Allergic reactivity and IgG subclasses to a proteinase fraction of Setaria digitata in filariasis

A low molecular weight fraction (30 KDa) of the cattle filarial parasite Setaria digitata that was earlier demonstrated to have allergenic activity was characterized to be a zinc-dependent cysteine proteinase. Immediate type hypersensitivity (ITH) reaction to the proteinase was evaluated in lymphatic filariasis patients and in endemic controls from Orissa, India. The extent of ITH positivity to the proteinase in infected individuals ranged from 20% in chronic filariasis (CP) patients group to 56% in asymptomatic microfilaraemic carriers (AS). About 62% of endemic normals (EN) were also ITH positive. The serum levels of IgG subclasses were compared in ITH positive and ITH negative filarial patients (AS and CP) as well as in endemic normals (EN) respectively. IgG4 levels were found to be inversely dependent on ITH reaction only in AS groups. Asymptomatic patients (AS) with positive ITH reactivity had lower IgG4 than ITH negative individuals from the same group. The serum levels of other IgG subclasses except IgG2, did not correlate with ITH reactivity. IgG2 levels were higher in ITH negative EN and CP patients but not in the AS group.

Bancroftian filariasis in Kwale District of Kenya. III. Quantification of the IgE response in selected individuals from an endemic community

One hundred and sixty-two individuals from a community in Kwale District, Kenya, endemic for bancroftian filariasis, were selected for a study on the IgE response to filarial antigen (prepared from adult Brugia pahangi). Following clinical and parasitological examination, the individuals were grouped into different categories, based on the presence/absence of microfilaraemia, the presence/absence of acute or chronic (hydrocele or elephantiasis) clinical manifestations, and age. The total and filarial-specific IgE responses were evaluated in all individuals, and the responses in the various categories were compared with each other and with the responses of control groups of individuals from filariasis-free areas. The majority of individuals from the endemic area had highly elevated serum concentrations of total IgE. Overall and within each clinical category, the concentration of total IgE was higher in those individuals from the endemic area who had microfilaraemias than in those that did not. The majority of individuals from the filariasis endemic area also had significantly elevated levels of filarial-specific IgE. In contrast, the concentration of specific IgE was lower in subjects with microfilariae than in those without, irrespective of their clinical status. Only a small proportion of total IgE was filarial-specific, the mean value varying from 0.4% to 9.8%, depending on category. Among the endemic individuals, the mean proportion of total IgE which was filarial-specific was 3.6 times higher in the microfilaria-negative than in the microfilaria-positive, indicating that much of the filarial-induced IgE in microfilaraemic individuals could be non-specific. No clear relationship was observed between the IgE response and the clinical manifestations or age of the endemic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

IgE regulation by nematodes: the body fluid of Ascaris contains a B-cell mitogen

Nematode infection of human beings or laboratory animals leads to markedly increased levels of circulating IgE, most of which is not specific to worm antigens. This phenomenon is known to be interleukin-4-dependent, but little is known about the mechanism of activation of the response. In an attempt to elucidate this mechanism, we have used a reductive approach with worm products rather than infections. In a previous article we showed that injection of the body fluid of the nematode Ascaris yields a marked increase in circulating IgE. In this study we demonstrate that the body fluid contains a B-cell mitogen. Incubation with purified splenic B cells with 50 micrograms/ml body fluid yields marked proliferation of B cells, as measured by tritiated thymidine uptake. Similarly, Ascaris body fluid stimulates G0 B cells to enter the cell cycle. T cells are unaffected by the mitogen, and the response is dependent on viable accessory cells. Contamination of Ascaris body fluid or reagents by bacterial lipopolysaccharide has been ruled out as a source of artefactual data. A model is proposed, which suggests that the B-cell mitogen in Ascaris body fluid stimulates polyclonal B-cell activity and that other nematode factors either stimulate the release of interleukin-4 or act in an interleukin-4-like manner to cause class switch to IgE.

Immunity in humans to Necator americanus: IgE, parasite weight and fecundity

The effect of the humoral immune response on the weight and fecundity of the hookworm Necator americanus was examined in an endemically-infected human population. There was a highly significant negative correlation between total IgE levels and parasite weight and fecundity, after controlling for any effects of host age and hookworm burden. This correlation was present both at initial treatment and after 2 years' reinfection. There was a similar negative correlation between the number of eosinophils and hookworm weight and fecundity at initial treatment. Correlations with levels of specific antibodies to N. americanus excretory-secretory products were weaker and not significant, although there was a trend towards negative correlations with anti-ES IgE. This is the first field evidence for an effective human immune response to N. americanus. Although the mechanism of this effect is not clear, we suggest that total IgE levels reflected the level of Th2 cell activation.

Studies on the isolation and characterisation of a reaginic antibody in a cat

A reaginic antibody has been demonstrated, by passive cutaneous anaphylaxis (PCA), in the serum of a cat infected with the microfilariae of Brugia pahangi. Recipient cats and pigs were challenged with an extract of Ascaris suum after either a four-hour or a 72-hour period of sensitisation. When the serum was heat treated at 56 degrees C it lost its PCA activity. Gel filtration of the serum revealed a pattern of positive PCA fractions similar to that observed in other species. Attempts to purify the PCA-positive material by Superose gel filtration and ion exchange chromatography by fast protein liquid chromatography (FPLC) were unsuccessful. Affinity chromatography of PCA-positive material by FPLC on protein A demonstrated two bound peaks, the second of which was PCA-positive and eluted as a single peak by ion exchange chromatography. The PCA-positive material from gel filtration did not bind to protein G. The protein A, PCA-positive peak provides a partially purified reaginic antibody for further study.

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

Immunoglobulin (Ig) E is the principal Ig involved in immediate hypersensitivities and chronic allergic diseases such as asthma. Helminths are the most potent infectious agents known for their capacity to stimulate IgE production during the course of infection. In rats, the nematode Trichinella spiralis typically elicits a strong parasite-specific IgE response during infection, and this IgE antibody has been shown to be protective against the parasite in passive transfer experiments. The study reported here analyzed the fate of 125I-labeled myeloma IgE (1R162) in normal and T. spiralis-infected rats after intravenous injection. T. spiralis infection induced a capacity for specific binding to the gut wall of 125I-IgE rather than 125I-IgG1, as well as the transport of IgE, but not IgG1, into the gut lumen. Peak intestinal uptake and transport of 125I-IgE occurred during the first and second weeks after injection but was not elevated in the fourth week, that is, after intestinal adult worms had been expelled. Neither 125I-IgE uptake in the gut wall nor transport to the lumen could be ascribed to tissue damage or vascular leakage. Luminal transport occurred in the small intestine and not the liver, which only transports low molecular weight degraded 125I-IgE. Calculations based on the amount of intact IgE in the lumen suggest that, in a 24-h period, up to 20% of injected 125I-IgE can be transported to the gut lumen during the peak transport period, between 6 and 14 d after infection. The intestinal IgE binding and transport response can be adoptively transferred with T. spiralis immune CD4+ OX22- (CD45RC-) lymphocytes, which are protective, but not the nonprotective sister population CD4+ OX22+ (CD45RC+) of lymphocytes isolated simultaneously from thoracic duct lymph of infected rats. The intravenous infusion of recombinant rat interleukin 4 also elicited significant intestinal uptake of 125I-IgE. We also present evidence for the presence of CD23 on rat intraepithelial lymphocytes. These data provide evidence for a novel, inducible, intestine-specific IgE uptake and transport mechanism.

Immunity and immunoregulation in helminth infections

Parasitic helminths continue to be a major cause of morbidity in human populations, particularly in the tropics and subtropics. The need for effective vaccines that minimize worm burdens, thus reducing associated pathology, is evident. With this goal in mind, an intense research effort is in progress to characterize immune responses to helminths, especially in the context of recent developments in our understanding of the cytokine network. The growing realization that the parasites can themselves subvert host immune responses to their own advantage makes the task of vaccine development that much harder.