Idiotypes expressed early in experimental Schistosoma mansoni infections predict clinical outcomes of chronic disease

Indirect effects of oral tolerance inhibit pulmonary granulomas to Schistosoma mansoni eggs

Parenteral injection of tolerated proteins into orally tolerant mice inhibits the initiation of immunological responses to unrelated proteins and blocks severe chronic inflammatory reactions of immunological origin, such as autoimmune reactions. This inhibitory effect which we have called “indirect effects of oral tolerance” is also known as “bystander suppression.” Herein, we show that i.p. injection of OVA + Al(OH)₃ minutes before i.v. injection of Schistosoma mansoni eggs into OVA tolerant mice blocked the increase of pulmonary granulomas. In addition, the expression of ICAM-1 in lung parenchyma in areas outside the granulomas of OVA-orally tolerant mice was significantly reduced. However, at day 18 after granuloma induction there was no difference in immunofluorescency intensity to CD3, CD4, F4/80, andα-SMA per granuloma area of tolerant and control groups. Reduction of granulomas by reexposure to orally tolerated proteins was not correlated with a shift in Th-1/Th-2 cytokines in serum or lung tissue extract.

Effect of praziquantel treatment of Schistosoma mansoni during pregnancy on immune responses to schistosome antigens among the offspring: results of a randomised, placebo-controlled trial

Background

Offspring of women with schistosomiasis may exhibit immune responsiveness to schistosomes due to in utero sensitisation or trans-placental transfer of antibodies. Praziquantel treatment during pregnancy boosts maternal immune responses to schistosome antigens and reduces worm burden. Effects of praziquantel treatment during pregnancy on responses among offspring are unknown.

Methods

In a trial of anthelminthic treatment during pregnancy in Uganda (ISRCTN32849447; http://www.controlled-trials.com/ISRCTN32849447/elliott), offspring of women with Schistosoma mansoni were examined for cytokine and antibody responses to schistosome worm (SWA) and egg (SEA) antigen, in cord blood and at age one year. Relationships to maternal responses and pre-treatment infection intensities were examined, and responses were compared between the offspring of women who did, or did not receive praziquantel treatment during pregnancy.

Results

Of 388 S. mansoni-infected women studied, samples were obtained at age one year from 215 of their infants. Stool examination for S. mansoni eggs was negative for all infants. Cord and infant samples were characterised by very low cytokine production in response to schistosome antigens with the exception of cord IL-10 responses, which were substantial. Cord and infant cytokine responses showed no association with maternal responses. As expected, cord blood levels of immunoglobulin (Ig) G to SWA and SEA were high and correlated with maternal antibodies. However, by age one year IgG levels had waned and were hardly detectable. Praziquantel treatment during pregnancy showed no effect on cytokine responses or antibodies levels to SWA or SEA either in cord blood or at age one year, except for IgG1 to SWA, which was elevated in infants of treated mothers, reflecting maternal levels. There was some evidence that maternal infection intensity was positively associated with cord blood IL-5 and IL-13 responses to SWA, and IL-5 responses to SEA, and that this association was modified by treatment with praziquantel.

Conclusions

Despite strong effects on maternal infection intensity and maternal immune responses, praziquantel treatment of infected women during pregnancy had no effect on anti-schistosome immune responses among offspring by age one year. Whether the treatment will impact upon the offspring's responses on exposure to primary schistosome infection remains to be elucidated.

Trial registration

ISRCTN: ISRCTN32849447

Idiotype/anti-idiotype immunoregulatory network correlates with an improved clinical outcome of schistosomiasis mansoni in humans

Anti-idiotypes (anti-Ids) have a potential role in the immune modulation of various diseases. To study the correlation of anti-Ids with schistosomiasis mansoni morbidity, ELISA using polyclonal idiotypes (Ids) was used to determine the presence of anti-Ids in sera of 69 patients susceptible and resistant to reinfection. Ids were purified against Soluble Worm Antigen (SWAP) from sera of New Zealand white rabbits immunized with SWAP. The results showed that anti-Ids were detected in 15 (40.5%) of susceptible and 21 (65.6%) of resistant patients. Correlation of intensity of infection with age revealed an inverse relationship in patients positive for anti-Ids (regression coefficient beta = -0.47, p < 0.05) and contrarily, a direct relationship in patients negative for anti-Ids (beta = 0.67, p < 0.001). In addition, there was a direct association between the presence of anti-Ids and the lack of schistosome-related symptoms (chi2 = 3.6, p < 0.05) and hepatomegaly (chi2 = 9.4, p < 0.01). Moreover, comparison of patients positive and negative for anti-Ids revealed that those negative for anti-Ids were more vulnerable to develop symptoms (3.7 times) and hepatomegaly (8.1 times). In conclusion, the study further confirms the role of Id/anti-Id regulatory network as an important participant in the assortment of an improved clinical outcome of schistosomiasis. This may help to formulate a better understanding of the mechanisms of protective immunity in humans and provide perspective for the development of a future vaccine.

Identification of cytokeratin 18 as a biomarker of mouse and human hepatosplenic schistosomiasis

Previously, we demonstrated unique protein expression patterns in 20-week-Schistosoma mansoni-infected CBA/J mice with moderate splenomegaly syndrome (MSS) or hypersplemomegaly syndrome (HSS). To better understand the development of severe pathology, we compared the two-dimensional differential in-gel electrophoresis (2D-DIGE) proteomic signatures of livers from uninfected mice and mice infected for 6, 8, 12, or 20 weeks and found significant changes in collagen isoforms, interleukin-2 (IL-2), cytokeratin 18, hydroxyproline, S. mansoni phosphoenolpyruvate carboxykinase, major urinary protein isoforms, and peroxiredoxin 6. Cytokeratin 18, hydroxyproline, and connective tissue growth factor (CTGF) were chosen for analysis in mouse and human sera using targeted biochemical assays. Consistent with the liver analysis, cytokeratin 18, CTGF, and hydroxyproline were significantly elevated in sera from mice with HSS compared to those from uninfected mice or mice with MSS. Moreover, cytokeratin 18 and CTGF were found to be markers for subjects with hepatosplenic and intestinal schistosomiasis, respectively, while serum hydroxyproline was a strong indicator of fibrosis for severe HS. These findings indicate that schistosome-associated changes to the liver can be detected in the serum and reveal the potential for cytokeratin 18 to be used as a diagnostic marker for early detection of hepatosplenic schistosomiasis.

Coinfection with the intestinal nematode Heligmosomoides polygyrus markedly reduces hepatic egg-induced immunopathology and proinflammatory cytokines in mouse models of severe schistosomiasis

Infection with the trematode helminth Schistosoma mansoni results in a parasite egg-induced, CD4 T-cell-mediated, hepatointestinal granulomatous and fibrosing inflammation that varies greatly in severity, with a higher frequency of milder forms typically occurring in regions where the disease is endemic. One possible explanation for this is that in these regions the degree of inflammation is lessened by widespread concurrent infection with gastrointestinal nematodes. We tested this hypothesis by establishing a murine coinfection model in which mice were infected with the intestinal nematode parasite Heligmosomoides polygyrus prior to infection with S. mansoni. In CBA mice that naturally display a severe form of schistosomiasis, preinfection with H. polygyrus resulted in a marked reduction in schistosome egg-induced hepatic immunopathology, which was associated with significant decreases in the levels of interleukin-17 (IL-17), gamma interferon, tumor necrosis factor alpha, IL-23, IL-6, and IL-1beta and with increases in the levels of IL-4, IL-5, IL-10, and transforming growth factor beta in mesenteric lymph node cells, purified CD4 T cells, and isolated liver granuloma cells. There also were increases in liver Ym1 and forkhead box P3 transcription factor expression. In another model of high-pathology schistosomiasis induced in C57BL/6 mice by immunization with schistosome egg antigens in complete Freund's adjuvant, coinfection with the nematodes also resulted in a marked inhibition of hepatic immunopathology accompanied by similar shifts in cytokine production. These findings demonstrate that intestinal nematodes prevent Th1- and Th17-cell-mediated inflammation by promoting a strong Th2-polarized environment associated with increases in the levels of alternatively activated macrophages and T regulatory cells, which result in significant amelioration of schistosome-induced immunopathology.

Idiotypic networks: toward a renaissance?

Idiotypic networks, after being a dominating paradigm for more than a decade, have fallen out of fashion in parallel with the rapid success of molecular immunobiology. Today signs of a possible renaissance in idiotypic network studies are visible. For system biologists and also for physicists, the network idea remains attractive. Herein, a short account of the historical development of the paradigm is given. The necessary technical and conceptual ingredients for a theoretical description of idiotypic networks are briefly reviewed, and previous approaches are discussed. We also describe a minimalistic model developed in our group that allows for understanding the random evolution toward a highly non-trivial complex architecture. In the network, a connected large cluster of idiotype clones and many disconnected ones coexist, thus resembling the notion of central and peripheral parts proposed in the 'second-generation' version of the paradigm. The connected cluster consists of groups of idiotypic clones with clearly distinct statistical properties. The simplicity of the model allows for calculating the size of the groups and the number of inter- and intragroup links, which define the architecture. Aspects of idiotypic interactions in experimental medicine are discussed, along with the challenges to theory and experimentation.

Early responses associated with chronic pathology in murine schistosomiasis

Inbred male CBA/J mice infected with Schistosoma mansoni develop either hypersplenomegaly syndrome (HSS) or moderate splenomegaly syndrome (MSS) by 20 weeks of infection. Pathologically and immunologically, MSS and HSS closely parallel the intestinal and hepatosplenic clinical forms of schistosomiasis in humans, respectively. By 6 weeks after infection, mice that eventually will become MSS develop T cell-stimulatory, cross-reactive idiotypes (CRI) while HSS mice never produce CRI. Because presence of CRI is useful to predict degree of chronic pathology, we used this measure to investigate what other early immunological events occurred in animals destined to develop severe morbidity. At 8 weeks of infection, there was a strong inverse correlation between CRI and splenomegaly, egg counts, and liver hydroxyproline. Similarly, phorbol myristate acetate (PMA)- and ionomycin-stimulated intracellular cytokine expression of IL-4, IL-5, and GM-CSF in splenic CD4(+) T cells was inversely correlated with serum CRI and directly correlated with spleen size. In contrast, spleen cell intracellular TNF-alpha and peritoneal cell production of nitric oxide demonstrated positive correlations with CRI and inverse correlations with measures of morbidity. Surprisingly, IL-10 and IFN-gamma were not correlated with CRI levels. These studies link chronic pathology to certain immunological responses during the acute phase of schistosomiasis.

Immunopathogenic mechanisms in schistosomiasis: what can be learnt from human studies?

Studies in mice indicate that schistosome egg-induced granuloma formation and hepatic fibrosis depend markedly on cytokine regulation, with interleukin 10 having a central role. There is no clear consensus about the pattern of cytokine production and regulation that causes a minority of chronically exposed patients to develop severe hepatosplenic (HS) disease, which is characterized by periportal fibrosis and portal hypertension. HS disease and the progression of hepatic fibrosis are associated with the production of profibrotic type 2 cytokines in the early stages of infection with Schistosoma mansoni. However, other studies indicate that HS disease is characterized by a predominant T helper 1 profile. Until new tools and approaches are developed to study human disease in endemic areas, investigators must either speculate about indirect evidence from human studies or rely more heavily on findings generated from experimental models of the disease.

PD-L2+ dendritic cells and PD-1+ CD4+ T cells in schistosomiasis correlate with morbidity

Dendritic cells (DC) are critical antigen-presenting cells for the induction and control of immune responses. PD-L2 (B7-DC) is a regulatory ligand on subpopulations of DC, and binds to the co-regulatory receptor PD-1, present on some activated T lymphocytes, leading to down-regulation. We now show that very early during experimental schistosomiasis (by 5 weeks) a significantly higher proportion of splenic CD11c+/B220- DC express PD-L2, and by 6 weeks after infection a higher proportion of splenic CD4 T cells express PD-1. In this CBA/J mouse/Schistosoma mansoni chronic infection model we have shown that most mice develop moderate morbidity (Moderate Splenomegaly Syndrome, MSS), while some parallel-infected mice express different immune characteristics and die or develop severe morbidity (Hypersplenomegaly Syndrome, HSS). We now report a positive correlation between the proportion of splenic CD11c+/B220- DC that express PD-L2 and showing MSS. In contrast, there is an inverse correlation between the proportion of splenic CD3+/CD4+ T lymphocytes that express PD-1 and showing MSS. The data demonstrate that schistosomes can induce sustained elevated percentages of PD-L2-expressing, B220-negative DC. Furthermore, when this potentially immunoregulatory environment occurs chronically, infected mice are most likely to have developed MSS, expressing moderate morbidity.

Immunopathogenesis of schistosomiasis

In schistosomiasis mansoni, the chronic egg-induced granulomatous response in the liver and intestines may eventually cause extensive tissue scarring and development of portal hypertension. Indeed, much of the morbidity and mortality associated with this disease is directly attributable to the deposition of connective tissue elements in affected tissues. Elucidating the mechanisms that regulate the severity of schistosomiasis has been a major research objective over the past several years. Research conducted with DNA microarrays as well as investigations with a variety of gene knock-out mice have been particularly helpful in achieving this goal. A notable accomplishment in the past few years was the identification of interleukin-13 (IL-13) and the IL-13 receptor complex as central regulators of disease progression in schistosomiasis. Liver fibrogenesis is severely decreased in infected IL-13-deficient mice as well as in wildtype animals treated with IL-13 antagonists. In contrast, IL-13 effector function increases dramatically in IL-13 receptor alpha2 (IL-13Ralpha2)-deficient mice. These mice develop severe hepatic fibrosis, fail to downregulate granuloma formation in the chronic phase of S. mansoni infection, and succumb to the disease at an accelerated rate; thus, identifying the 'decoy' IL-13 receptor as a critical life sustaining 'off' switch for tissue damaging egg-induced inflammation.

Immunoregulation and World Health Assembly resolution 54.19: why does treatment control morbidity?

World Health Assembly resolution 54.19, passed in May, 2001, declares the intent of the World Health Organization member States to implement a combined strategy for the control of morbidity caused by schistosomiasis and soil-transmitted helminths. Among other things, the resolution urges ministries to treat all clinical cases and groups at high risk of morbidity such as children, women and those exposed occupationally. The policy is predicated on the evidence that morbidity due to these infections can be controlled by periodic treatment with appropriate chemotherapeutic, anti-helminthic drugs. While it is true that annual or biannual praziquantel treatment for schistosomiasis decreases morbidity, we now question how treatment leads to this beneficial effect. It is clear that treatment kills worms, but we propose that this is only a part of how it leads to reduced morbidity in areas of ongoing transmission and reinfection. By killing worms, we postulate that treatment also effects immunologic changes to the normal host/parasite relationship, and the resulting immune responses lead to both increased resistance (protection against reinfection), and increased immunoregulatory mechanisms that control morbidity upon subsequent reinfections. If the effects of treatment contribute to morbidity control in these ways, a better understanding of how this occurs may allow optimization of these effects of treatment through appropriate periodic treatment regimens, resulting in less reinfection and better morbidity control when reinfection does occur.

Cytokine regulation in experimentally-induced Schistosoma japonicum egg granuloma formation

The formation of granulomas in host tissues in response to trapped Schistosoma japonicum eggs is central to the etiology of schistosomiasis. However, analysis of the host hypersensitivity reactions that result in granuloma formation, in schistosome infection, is not without difficulty. This is due, in part, to the fact that the parasites continuously deposit their eggs as clusters. In order to synchronize host reactions, we established an experimental model of hepatic granuloma formation whereby in vitro laid schistosome eggs are implanted directly into normal and cytokine-deficient mice livers. This model, validated by comparison with an infection model, was used to analyze cytokine regulation of granuloma formation around S. japonicum eggs. Combined models of implantation and cercarial infection were also studied. With special reference to IL-4, IL-13, IFN-gamma and IL-18, our in vitro schistosome egg implantation model has shed new light on the roles of cytokines in both the acute and chronic stages of schistosome egg-induced granuloma formation.

Immune regulation by helminth parasites: cellular and molecular mechanisms

Immunology was founded by studying the body's response to infectious microorganisms, and yet microbial prokaryotes only tell half the story of the immune system. Eukaryotic pathogens--protozoa, helminths, fungi and ectoparasites--have all been powerful selective forces for immune evolution. Often, as with lethal protozoal parasites, the focus has been on acute infections and the inflammatory responses they evoke. Long-lived parasites such as the helminths, however, are more remarkable for their ability to downregulate host immunity, protecting themselves from elimination and minimizing severe pathology in the host.

Parasites and immune responses: memory illusion?

Immunological memory responses to intracellular protozoa and extracellular helminths govern host resistance and susceptibility to reinfection. Humans and livestock living in parasitic disease endemic regions face continuous exposure from a very early age that often leads to asymptomatic chronic infection over their entire lifespan. Fundamental immunological studies suggest that the generation of T-cell memory is driven by tightly coordinated innate and adaptive cellular immune responses rapidly triggered following initial host infection. A key distinguishing feature of immune memory maintenance between the majority of parasitic diseases and most bacterial or viral diseases is long-term antigen persistence. Consequently, functional parasite immune memory is in a continuous, dynamic flux between activation and deactivation producing functional parasite killing or functional memory cell death. In this sense, T-cell immune memory can be regarded as "memory illusion." Furthermore, due to the finite capacity of memory lymphocytes to proliferate, continuous parasite antigen stimulation may exceed a threshold level at some point in the chronically infected host. This may result in suboptimal effector immune memory leading to host susceptibility to reinfection, or immune dysregulation yielding disease reactivation or immune pathology. The goal of this review is to highlight, through numerous examples, what is currently known about T-cell immune memory to parasites and to provide compelling hypotheses on the survival and maintenance of parasite "memory illusion." These novel concepts are discussed in the context of rationale parasite vaccine design strategies.

The immunobiology of schistosomiasis

Schistosomes are parasitic worms that are a prime example of a complex multicellular pathogen that flourishes in the human host despite the development of a pronounced immune response. Understanding how the immune system deals with such pathogens is a daunting challenge. The past decade has seen the use of a wide range of new approaches to determine the nature and function of the immune response to schistosomes. Here, we attempt to summarize advances in our understanding of the immunology of schistosomiasis, with the bulk of the review reflecting the experimental focus on Schistosoma mansoni infection in mice.