Mechanisms of resistance to S. mansoni infection: the rat model

Host genetic backgrounds: the key to determining parasite-host adaptation

Parasitic diseases pose a significant threat to global public health, particularly in developing countries. Host genetic factors play a crucial role in determining susceptibility and resistance to infection. Recent advances in molecular and biological technologies have enabled significant breakthroughs in understanding the impact of host genes on parasite adaptation. In this comprehensive review, we analyze the host genetic factors that influence parasite adaptation, including hormones, nitric oxide, immune cells, cytokine gene polymorphisms, parasite-specific receptors, and metabolites. We also establish an interactive network to better illustrate the complex relationship between host genetic factors and parasite-host adaptation. Additionally, we discuss future directions and collaborative research priorities in the parasite-host adaptation field, including investigating the impact of host genes on the microbiome, developing more sophisticated models, identifying and characterizing parasite-specific receptors, utilizing patient-derived sera as diagnostic and therapeutic tools, and developing novel treatments and management strategies targeting specific host genetic factors. This review highlights the need for a comprehensive and systematic approach to investigating the underlying mechanisms of parasite-host adaptation, which requires interdisciplinary collaborations among biologists, geneticists, immunologists, and clinicians. By deepening our understanding of the complex interactions between host genetics and parasite adaptation, we can develop more effective and targeted interventions to prevent and treat parasitic diseases. Overall, this review provides a valuable resource for researchers and clinicians working in the parasitology field and offers insights into the future directions of this critical research area.

iNOS is essential to maintain a protective Th1/Th2 response and the production of cytokines/chemokines against Schistosoma japonicum infection in rats

Humans and a wide range of mammals are generally susceptible to Schistosoma infection, while some rodents such as Rattus rats and Microtus spp are not. We previously demonstrated that inherent high expression levels of nitric oxide (NO), produced by inducible nitric oxide synthase (iNOS), plays an important role in blocking the growth and development of Schistosoma japonicum in wild-type rats. However, the potential regulatory effects of NO on the immune system and immune response to S. japonicum infection in rats are still unknown. In this study, we used iNOS-knockout (KO) rats to determine the role of iNOS-derived NO in the immune system and immunopathological responses to S. japonicum infection in rats. Our data showed that iNOS deficiency led to weakened immune activity against S. japonicum infection. This was characterized by the impaired T cell responses and a significant decrease in S. japonicum-elicited Th2/Th1 responses and cytokine and chemokine-producing capability in the infected iNOS-KO rats. Unlike iNOS-KO mice, Th1-associated cytokines were also decreased in the absence of iNOS in rats. In addition, a profile of pro-inflammatory and pro-fibrogenic cytokines was detected in serum associated with iNOS deficiency. The alterations in immune responses and cytokine patterns were correlated with a slower clearance of parasites, exacerbated granuloma formation, and fibrosis following S. japonicum infection in iNOS-KO rats. Furthermore, we have provided direct evidence that high levels of NO in rats can promote the development of pulmonary fibrosis induced by egg antigens of S. japonicum, but not inflammation, which was negatively correlated with the expression of TGF-β3. These studies are the first description of the immunological and pathological profiles in iNOS-KO rats infected with S. japonicum and demonstrate key differences between the responses found in mice. Our results significantly enhance our understanding of the immunoregulatory effects of NO on defensive and immunopathological responses in rats and the broader nature of resistance to pathogens such as S. japonicum.

Schistosomiasis is a zoonosis that affects more than 200 million people worldwide. A wide range of mammals, including mice, are permissive hosts of Schistosoma and develop chronic disease characterized by egg-granuloma formation and fibrosis after infection. Rats, on the other hand, are non-permissive hosts and develop efficient immune responses to eliminate the worms. Interestingly, schistosome eggs elicit a dominant Th2 immune response within mouse hosts, whereas rats with schistosomiasis develop a significant Th2 response in the absence of available egg production. The Th2 response in rats seems to play an essential role in the protection of the host against Schistosoma. So far, the factors that lead to the different immune responses to Schistosoma infection in both hosts have not been demonstrated. In this study, our results show that an iNOS-dependent mechanism maintains the function of the immune system in rats by modulating CD4⁺ T cell-mediated Th1/Th2-associated cytokine responses and chemokine production. Additionally, the absence of iNOS led to slow clearance of parasites, increases in the development of worms, and an exacerbation of granuloma formation and fibrosis in rats. Furthermore, high levels of NO in rats can promote the development of fibrosis induced by inflammation (rapid inflammatory repair). Therefore, this study demonstrates that the difference in iNOS levels between mice and rats is responsible for the different immune responses and outcomes induced by schistosome infection in both hosts.

Gene expression changes in mammalian hosts during schistosomiasis: a review

Schistosomiasis affects over 250 million people worldwide with an estimated mortality of more than 200,000 deaths per year in sub-Saharan Africa. Efforts to control schistosomiasis in the affected areas have mainly relied on mass administration of praziquantel, which kills adult but not immature worms of all Schistosoma species. Mammalian hosts respond differently to Schistosoma infection with some being more susceptible than others, which is associated with risk factors such as sociodemographic, epidemiological, immunological and/or genetic. Host genetic factors play a major role in influencing molecular processes in response to schistosomiasis as shown in gene expression studies. These studies highlight gene profiles expressed at different time points of infection using model animals. Immune function related genes; cytokines (Th1 and Th17) are upregulated earlier in infection and Th2 upregulated later indicating a mixed Th1/Th2 response. However, Th1 response has been shown to be sustained in S. japonicum infection. Immune mediators such as matrix metalloproteinases (Mmps) and tissue inhibitors of matrix metalloproteinases (Timps) are expressed later in the infection and these are linked to wound healing and fibrosis. Downregulation of metabolic associated genes is recorded in later stages of infection. Most mammalian host gene expression studies have been done using rodent models, with fewer in larger hosts such as bovines and humans. The majority of these studies have focused on S. japonicum infections and less on S. haematobium and S. mansoni infections (the two species that cause most global infections). The few human schistosomiasis gene expression studies so far have focused on S. japonicum and S. haematobium infections and none on S. mansoni, as far as we are aware. This highlights a paucity of gene expression data in humans, specifically with S. mansoni infection. This data is important to understand the disease pathology, identify biomarkers, diagnostics and possible drug targets.

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.

Loss of natural resistance to schistosome in T cell deficient rat

Schistosomiasis is among the major neglected tropical diseases and effective prevention by boosting the immune system is still not available. T cells are key cellular components governing adaptive immune response to various infections. While common laboratory mice, such as C57BL/6, are highly susceptible to schistosomiasis, the SD rats are extremely resistant. However, whether adaptive immunity is necessary for such natural resistance to schistosomiasis in rats remains to be determined. Therefore, it is necessary to establish genetic model deficient in T cells and adaptive immunity on the resistant SD background, and to characterize liver pathology during schistosomiasis. In this study we compared experimental schistosomiasis in highly susceptible C57BL/6 (B6) mice and in resistant SD rats, using cercariae of Schistosoma japonicum. We observed a marked T cell expansion in the spleen of infected B6 mice, but not resistant SD rats. Interestingly, CD3e^−/− B6 mice in which T cells are completely absent, the infectious burden of adult worms was significantly higher than that in WT mice, suggesting an anti-parasitic role for T cells in B6 mice during schistosome infection. In further experiments, we established Lck deficient SD rats by using CRISPR/Cas9 in which T cell development was completely abolished. Strikingly, we found that such Lck deficiency in SD rats severely impaired their natural resistance to schistosome infection, and fostered parasite growth. Together with an additional genetic model deficient in T cells, the CD3e^−/− SD rats, we confirmed the absence of T cell resulted in loss of natural resistance to schistosome infection, but also mitigated liver immunopathology. Our further experiments showed that regulatory T cell differentiation in infected SD rats was significantly decreased during schistosomiasis, in contrast to significant increase of regulatory T cells in infected B6 mice. These data suggest that T cell mediated immune tolerance facilitates persistent infection in mice but not in SD rats. The demonstration of an important role for T cells in natural resistance of SD rats to schistosomiasis provides experimental evidences supporting the rationale to boost T cell responses in humans to prevent and treat schistosomiasis.

Schistosomiasis is among the major neglected tropical diseases and affects mainly the developing countries. Although the role of the immune system in driving immunopathology in schistosomiasis has been extensively studied, how adaptive immunity contributes to disease resistance during schistosome infection is still not completely understood. Most livestock species as well as humans are susceptible to schistosomiasis, while some mammals are extremely resistant. The common laboratory C57BL/6 mice are highly susceptible to schistosomiasis; however, the SD rats are extremely resistant. In this study, we first used T cell deficient CD3e^−/− C57BL/6 mice and experimental Schistosoma japonicum infection and further established novel T cell deficient models in SD rats to assess anti-parasite roles of T cells. Strikingly, we found that the natural resistance of SD rat to schistosomiasis was abolished in the absence of T cells, despite the fact that the liver pathology was mitigated following infection. Therefore, our study presented experimental support for the rationale to boost T cell function for clearance of schistosome parasites.

Mechanisms of Resistance to Schistosoma japonicum Infection in Microtus fortis, the Natural Non-permissive Host

Human schistosomiasis, which is caused by schistosomes, is a zoonosis that is difficult to control because of the many reservoir hosts. However, Microtus fortis is the only mammal that is naturally resistant to Schistosoma japonicum infection known in China, in which S. japonicum growth and development were arrested on day 12, and the worms eliminated on day 20 post-infection. In this review, we present an overview of the established and purported mechanisms of resistance to S. japonicum infection in M. fortis in comparison to Rattus norvegicus, a semi-permissive host. Clarifying the mechanism of this efficient resistance can help us to better understand host-parasite interaction and to provide better methods to control schistosomiasis.

iTRAQ-Based Comparative Proteomic Analysis of Adult Schistosoma japonicum from Water Buffalo and Yellow Cattle

Schistosomiasis japonicum is one of the most severe zoonotic diseases in China. Water buffalo and yellow cattle are important reservoir hosts and the main transmission sources of Schistosoma japonicum in endemic areas. The susceptibility of these two hosts to schistosome infection is different, as water buffaloes are less susceptible to S. japonicum than yellow cattle. In this study, iTRAQ-coupled LC-MS/MS was applied to compare the protein expression profiles of adult schistosomes recovered from water buffalo with those of yellow cattle. A total of 131 differentially expressed proteins (DEPs) were identified, including 46 upregulated proteins and 85 downregulated proteins. The iTRAQ results were confirmed by Western blotting and quantitative real-time PCR. Further analysis indicated that these DEPs were primarily involved in protein synthesis, transcriptional regulation, protein proteolysis, cytoskeletal structure and oxidative stress response processes. The results revealed that some of the differential expression molecules may affect the development and survival of schistosomes in these two natural hosts. Of note, this study provides useful information for understanding the interplay between schistosomes and their final hosts.

Is arachidonic acid an endoschistosomicide?

Schistosoma mansoni and Schistosoma haematobium are intravascular, parasitic flatworms that infect >250 million people in 70 developing countries, yet not all people of the same community and household are afflicted. Regarding laboratory rodents, mice but not rats are susceptible to infection with S. mansoni and hamsters but not mice are entirely permissive to infection with S. haematobium. A recent Brazilian publication has demonstrated that resistance of the water-rat, Nectomys squamipes to S. mansoni infection might be ascribed to stores of arachidonic acid (ARA)-rich lipids in liver. Several reports have previously shown that ARA is a safe and effective schistosomicide in vitro, and in vivo in mice, hamsters and in children. Schistosoma haematobium appeared more sensitive than S. mansoni to ARA in in vitro and in vivo experiments. Accordingly, it was proposed that ARA increased levels might be predominantly responsible for natural attrition of S. mansoni and S. haematobium in resistant experimental rodents. Therefore, the levels of ARA in serum, lung, and liver of rats (resistant) and mice (susceptible) at 1, 2, 3, 4 and 6 weeks after infection with S. mansoni cercariae and between mice (semi-permissive) and hamster (susceptible) at 1, 2, 3, 4, and 12 weeks after infection with S. haematobium cercariae were compared and contrasted. Neutral triglycerides and ARA levels were assessed in serum using commercially available assays and in liver and lung sections by transmission electron microscopy, Oil Red O staining, and specific anti-ARA antibody-based immunohistochemistry assays. Significant (P < .05), consistent, and reproducible correlation was recorded between ARA content in serum, lung, and liver and rodent resistance to schistosome infection, thereby implicating ARA as an endoschistosomicide.

Nitric oxide blocks the development of the human parasite Schistosoma japonicum

Human schistosomiasis, caused by Schistosoma species, is a major public health problem affecting more than 700 million people in 78 countries, with over 40 mammalian host reservoir species complicating the transmission ecosystem. The primary cause of morbidity is considered to be granulomas induced by fertilized eggs of schistosomes in the liver and intestines. Some host species, like rats (Rattus norvegicus), are naturally intolerant to Schistosoma japonicum infection, and do not produce granulomas or pose a threat to transmission, while others, like mice and hamsters, are highly susceptible. The reasons behind these differences are still a mystery. Using inducible nitric oxide synthase knockout (iNOS^-/-) Sprague-Dawley rats, we found that inherent high expression levels of iNOS in wild-type (WT) rats play an important role in blocking growth, reproductive organ formation, and egg development in S. japonicum, resulting in production of nonfertilized eggs. Granuloma formation, induced by fertilized eggs in the liver, was considerably exacerbated in the iNOS^-/- rats compared with the WT rats. This inhibition by nitric oxide acts by affecting mitochondrial respiration and energy production in the parasite. Our work not only elucidates the innate mechanism that blocks the development and production of fertilized eggs in S. japonicum but also offers insights into a better understanding of host-parasite interactions and drug development strategies against schistosomiasis.

Schistosoma mansoni Infection of Mice, Rats and Humans Elicits a Strong Antibody Response to a Limited Number of Reduction-Sensitive Epitopes on Five Major Tegumental Membrane Proteins

Schistosomiasis is a major disease of the developing world for which no vaccine has been successfully commercialized. While numerous Schistosoma mansoni worm antigens have been identified that elicit antibody responses during natural infections, little is known as to the identities of the schistosome antigens that are most prominently recognized by antibodies generated through natural infection. Non-reducing western blots probed with serum from schistosome-infected mice, rats and humans on total extracts of larval or adult schistosomes revealed that a small number of antigen bands predominate in all cases. Recognition of each of these major bands was lost when the blots were run under reducing condition. We expressed a rationally selected group of schistosome tegumental membrane antigens in insect host cells, and used the membrane extracts of these cells to unambiguously identify the major antigens recognized by S. mansoni infected mouse, rat and human serum. These results revealed that a limited number of dominant, reduction-sensitive conformational epitopes on five major tegumental surface membrane proteins: SmTsp2, Sm23, Sm29, SmLy6B and SmLy6F, are primary targets of mouse, rat and human S. mansoni infection sera antibodies. We conclude that, Schistosoma mansoni infection of both permissive (mouse) and non-permissive (rat) rodent models, as well as humans, elicit a dominant antibody response recognizing a limited number of conformational epitopes on the same five tegumental membrane proteins. Thus it appears that neither infecting schistosomula nor mature adult schistosomes are substantively impacted by the robust circulating anti-tegumental antibody response they elicit to these antigens. Importantly, our data suggest a need to re-evaluate host immune responses to many schistosome antigens and has important implications regarding schistosome immune evasion mechanisms and schistosomiasis vaccine development.

Schistosomiasis is caused by blood flukes residing in the veins of infected individuals and afflicts millions of people in the developing world. The schistosome worms can remain healthy in the bloodstream for more than 10 years, implying an extraordinary ability to evade host immune damage. Scientists are seeking to understand immune evasion so as to find weaknesses in defenses that can be exploited in the development of effective vaccines. Here we investigate the normal antibody response to schistosomes during infection of mice, rats and humans, and show for the first time that this response is highly skewed to the recognition of a small number of proteins present at the worm surface. Surprisingly, these abundant antibodies recognize their targets only when the proteins retain their native conformations, stabilized by the presence of intramolecular disulfide bridges. Because of this conformational-dependence, these antibodies have remained undetected in prior studies in which antibody binding assays were routinely performed in a reducing environment that destroys disulfide bridges. The routine presence of these antibodies within the serum of schistosome infected patients and animals raises new and interesting questions as to their possible role in immune evasion, and has significant implications for schistosomiasis vaccine development.

Local Antiglycan Antibody Responses to Skin Stage and Migratory Schistosomula of Schistosoma japonicum

Schistosomiasis is a tropical disease affecting over 230 million people worldwide. Although effective drug treatment is available, reinfections are common, and development of immunity is slow. Most antibodies raised during schistosome infection are directed against glycans, some of which are thought to be protective. Developing schistosomula are considered most vulnerable to immune attack, and better understanding of local antibody responses raised against glycans expressed by this life stage might reveal possible glycan vaccine candidates for future vaccine research. We used antibody-secreting cell (ASC) probes to characterize local antiglycan antibody responses against migrating Schistosoma japonicum schistosomula in different tissues of rats. Analysis by shotgun Schistosoma glycan microarray resulted in the identification of antiglycan antibody response patterns that reflected the migratory pathway of schistosomula. Antibodies raised by skin lymph node (LN) ASC probes mainly targeted N-glycans with terminal mannose residues, Galβ1-4GlcNAc (LacNAc) and Galβ1-4(Fucα1-3)GlcNAc (LeX). Also, responses to antigenic and schistosome-specific glycosphingolipid (GSL) glycans containing highly fucosylated GalNAcβ1-4(GlcNAcβ1)n stretches that are believed to be present at the parasite's surface constitutively upon transformation were found. Antibody targets recognized by lung LN ASC probes were mainly N-glycans presenting GalNAcβ1-4GlcNAc (LDN) and GlcNAc motifs. Surprisingly, antibodies against highly antigenic multifucosylated motifs of GSL glycans were not observed in lung LN ASC probes, indicating that these antigens are not expressed in lung stage schistosomula or are not appropriately exposed to induce immune responses locally. The local antiglycan responses observed in this study highlight the stage- and tissue-specific expression of antigenic parasite glycans and provide insights into glycan targets possibly involved in resistance to S. japonicum infection.

Specific humoral response of hosts with variable schistosomiasis susceptibility

The schistosome blood flukes are some of the largest global causes of parasitic morbidity. Further study of the specific antibody response during schistosomiasis may yield the vaccines and diagnostics needed to combat this disease. Therefore, for the purposes of antigen discovery, sera and antibody-secreting cell (ASC) probes from semi-permissive rats and sera from susceptible mice were used to screen a schistosome protein microarray. Following Schistosoma japonicum infection, rats had reduced pathology, increased antibody responses and broader antigen recognition profiles compared with mice. With successive infections, rat global serological reactivity and the number of recognized antigens increased. The local antibody response in rat skin and lung, measured with ASC probes, increased after parasite migration and contributed antigen-specific antibodies to the multivalent serological response. In addition, the temporal variation of anti-parasite serum antibodies after infection and reinfection followed patterns that appear related to the antigen driving the response. Among the 29 antigens differentially recognized by the infected hosts were numerous known vaccine candidates, drug targets and several S. japonicum homologs of human schistosomiasis resistance markers-the tegument allergen-like proteins. From this set, we prioritized eight proteins that may prove to be novel schistosome vaccine and diagnostic antigens.

Drug-induced exposure of Schistosoma mansoni antigens SmCD59a and SmKK7

Background

Schistosomiasis is a serious health problem especially in developing countries and affects more than 243 million people. Only few anthelmintic drugs are available up to now. A major obstacle for drug treatment is the different developmental stages and the varying host compartments during worm development. Anthelmintic drugs have been tested mainly on adult schistosomes or freshly transformed cercariae. Knowledge concerning the larval stages is lacking.

Methodology/Principal Findings

In this study, we used in vitro-grown schistosomula (aged between 2 to 14 days) to investigate drug effects of the three anthelmintics praziquantel, artemether, and oxamniquine. Further, we analyzed the antibody accessibility of two exemplary schistosome antigens SmCD59a and SmKK7, before and after drug treatment. Our results demonstrated that praziquantel applied at a concentration of 1 μM inhibited development of all life stages. Application of 10 μM praziquantel led to dramatic morphological changes of all schistosomula. Artemether at 1 and 10 μM had differential effects depending on whether it was applied to 2-day as compared to 7- and 14-day schistosomula. While 2-day schistosomula were not killed but inhibited from further development, severe morphological damage was seen in 7- and 14-day schistosomula. Oxamniquine (1 and 10 μM) led to severe morphological impairment in all life stages. Analyzing the accessibility of the antigens SmCD59a and SmKK7 before drug treatment showed no antibody binding on living intact schistosomula. However, when schistosomula were treated with anthelmintics, both antigens became exposed on the larvae. Oxamniquine turned out to be most effective in promoting antibody binding to all schistosomula stages.

Conclusion

This study has revealed marked differences in anthelmintic drug effects against larvae. Drug treatment increases surface antigen presentation and renders larvae accessible to antibody attack.

Schistosomiasis is one of the major parasitic diseases in developing countries and still causes 200,000 deaths per year. Mass drug administration programs with praziquantel, the drug of choice against schistosomiasis, are currently undertaken in Sub-Saharan Africa. Praziquantel, although efficient against adult worms, fails to cure early infection. The complex developmental stages of schistosomes and migration through varying host compartments with different local drug concentration are a challenge for drug treatment. After infecting their mammalian host, schistosomula traverse through skin and the vasculature of lung, liver and intestines. During their migration, they develop from larvae to paired adults in approximately 4 to 5 weeks. So far, drug effects have been analyzed on adult worms or freshly transformed schistosomula only. Information about the effects on the larval stages is lacking. We were able to transfer the larval development of the first three weeks into the culture dish. This tool can be used for the analysis of drug effects against schistosomula and for investigation of the accessibility, expression and localization of antigens. Rendering the parasite’s larvae vulnerable to the host’s immune system by increasing antigen presentation is an important aspect of drug activity. We demonstrate on in vitro-cultured Schistosoma mansoni larvae, that SmCD59a and SmKK7, as examples for hidden antigens, become accessible to antibodies following drug treatment.

Fundamental factors determining the nature of parasite aggregation in hosts

The distribution of parasites in hosts is typically aggregated: a few hosts harbour many parasites, while the remainder of hosts are virtually parasite free. The origin of this almost universal pattern is central to our understanding of host-parasite interactions; it affects many facets of their ecology and evolution. Despite this, the standard statistical framework used to characterize parasite aggregation does not describe the processes generating such a pattern. In this work, we have developed a mathematical framework for the distribution of parasites in hosts, starting from a simple statistical description in terms of two fundamental processes: the exposure of hosts to parasites and the infection success of parasites. This description allows the level of aggregation of parasites in hosts to be related to the random variation in these two processes and to true host heterogeneity. We show that random variation can generate an aggregated distribution and that the common view, that encounters and success are two equivalent filters, applies to the average parasite burden under neutral assumptions but it does not apply to the variance of the parasite burden, and it is not true when heterogeneity between hosts is incorporated in the model. We find that aggregation decreases linearly with the number of encounters, but it depends non-linearly on parasite success. We also find additional terms in the variance of the parasite burden which contribute to the actual level of aggregation in specific biological systems. We have derived the formal expressions of these contributions, and these provide new opportunities to analyse empirical data and tackle the complexity of the origin of aggregation in various host-parasite associations.

Adjuvant selection for vaccination against murine schistosomiasis

Schistosoma mansoni cercariae penetrate mouse epidermis, detach the glycocalyx and transform into schistosomula, triggering innate immune responses by host keratinocytes and Langerhans cells. Schistosomula leave the dermis and enter blood capillaries, releasing excretory/secretory products (ESP), which induce readily detectable primary adaptive immunity responses, dominated by T helper (Th) 1 and 17 cytokines. Partial protection against murine schistosomiasis may be achieved using subunit antigens and Th1 cytokine-inducing adjuvants. Conversely, resistance to primary and/or secondary schistosomiasis in rats, mice and humans is associated with production of Th2 cytokines. Accordingly, we reasoned that effective vaccination against murine primary schistosomiasis might be achieved provided selection of an adjuvant capable of skewing the S. mansoni larval ESP-mediated Th1/Th17 immune responses towards a Th2 profile. In an aim to select such an adjuvant, we administered the prototypical Th1 and Th2, respectively, C57BL/6 and BALB/c mice with polyinosinic-polycytidylic acid (Poly I/C), peptidoglycan (PGN), or thymic stromal lymphopoietin (TSLP) before exposure to S. mansoni cercariae. Serum antibody reactivity and ex vivo spleen cells (SC) immune responses to larval ESP, in a recombinant or multiple antigen peptide form, were assessed 1 week after infection. Injection with Poly I/C failed to increase interleukin (IL)-4 and led to elevated gamma interferon (IFN-γ) levels released by unstimulated or ESP-stimulated SC. Treatment with PGN triggered hightened amounts of IL-4, IL-17 and IFN-γ released by unstimulated or ESP-stimulated C57BL/6 SC. In contrast, TSLP succeeded in directing the ESP-mediated immune responses towards a Th2-biased profile in prototypical Th1 and Th2 mice.

Strain variation in the susceptibility and immune response to Clonorchis sinensis infection in mice

Mice have shown various susceptibility to infection by Clonorchis sinensis. To compare the intra-specific variation in the host-parasite relationship of C. sinensis, 6 strains of mice (ICR, BALB/c, C57BL/6, DDY, CBA/N, and C3H/HeN) with 3 different haplotypes were evaluated on their susceptibility. The worm recovery rate and immunological responses were observed after 4 and 8 weeks of infection with 30 metacercariae. The highest worm recovery rate was observed as 20.7% in the C3H/HeN strain after 4 weeks of infection along with histopathological changes. The rate was 10.0% in C57BL/6 mice after 8 weeks. ICR, BALB/c, and CBA/N showed elevated levels of IgE at both time points when compared to the rest of the strains. The serum IgG1 and IgG2a levels were elevated in most of the strains; however, the C57BL/6 strain showed a lower level of IgG2a that indicated the IgG1 predominance over IgG2a. The production of IL-4 after concanavalin-A stimulation of splenocytes slightly increased among the mouse strains except C3H/HeN after 4 or 8 weeks of infection, but each strain produced high levels of IFN-γ after 8 weeks, which implied mixed Th1/Th2 responses. ICR, DDY, CBA/N, and C3H/HeN strains showed a significantly increased level of IL-10 after 8 weeks as compared to C57BL/6. All of the strains showed an increased level of IL-13 and suggested fibrotic changes in the mice. In conclusion, mice are insusceptible to infection with C. sinensis; however, the C57BL/6, BALB/c and ICR strains are relatively susceptible after 8 weeks of infection among the six strains. Worm expulsion may be one of the causes of low susceptibility of C3H/HeN mice strain at the 8th week. Elevated IgE, IFN-γ, and IL-13 of infected mice suggest both Th1 and Th2 responses that may be related to the low host susceptibility.

Schistosoma mansoni host-exposed surface antigens characterized by sera and recombinant antibodies from schistosomiasis-resistant rats

Antibodies from Schistosoma mansoni-infected rats, unlike mice, show a higher titer for schistosome apical tegumental antigens compared with non-apical membrane antigens. These antibodies bind to the surface of living lung-stage worms and to formaldehyde-fixed adult worms. We produced a single-chain antibody Fv domain (scFv) phage library displaying the antibody repertoire of rats highly immune to schistosome infection and we selected for scFvs that recognize the host-exposed surface of worms. Five unique rat scFvs (Teg1, Teg4, Teg5, Teg20 and Teg37) were obtained which recognize schistosome surface epitopes. Each of the scFvs recognizes the surface of living schistosomula and lung-stage schistosomules and/or the surface of formaldehyde-fixed adult worms. None of these scFvs reproducibly stained living adult worms. This suggests that a change occurs during the transition from lung schistosomules to 4-week adults such that at least some surface antigens, although remaining on the surface in living adult worms, can no longer be immunologically stained. Teg1 and Teg4 scFvs both recognize specific bands on Western blots. No bands were observed for the other three scFvs, suggesting that these scFvs may recognize non-protein or conformationally-dependent epitopes. Teg1 was unambiguously identified as recognizing the S. mansoni tetraspanin antigen, SmTSP-2, within the large extracellular domain. Teg4 recognizes a 35kDa band tentatively identified as Sm29 by proteomic analysis. These scFvs can now be used to characterize schistosome epitopes at the host-parasite interface, to target worms in vivo, and to study the mechanisms by which these worms naturally evade immune damage to the tegument within permissive hosts.

Ultrastructural and cytochemical aspects of Schistosoma mansoni cercaria

An alternative to identify the critical processes necessary to the parasite establishment of the host is to focus on the evolutionary stage responsible for the primary invasion, i.e. the infection structure. The objective of this study was to ultrastructurally characterize Schistosoma mansoni cercariae, using cytochemical techniques. In order to identify basic proteins, techniques such as ethanolic phosphotungstic acid (EPTA) and ammoniacal silver staining were used. Calcium sites location was achieved using the Hepler technique and to evidence anionic groups, we used cationic ferritin particles and enzyme treatment with trypsin Vibrio cholerae, chondroitinase and neuraminidase. The EPTA technique highlighted the presence of basic tegument proteins, nucleus and nucleolus from subtegumental cells, inclusion bodies and preacetabular glands. After using ammoniacal silver, we observed a strong staining in all infective larvae, particularly in the nuclei of muscle cells, circular muscle tissue and preacetabular glands. Calcium site locations were shown to be uniform, thereby limiting the inner spaces of the larvae, especially muscle cells. Samples treated with cationized ferritin particles presented strong staining at the cuticular level. Neuraminidase treatment did not alter the stained shape of such particles on the trematode surface. However, trypsin or chondroitinase treatment resulted in absence of staining on the larval surface. This information on the biochemical composition of the infecting S. mansoni larvae provides data for a better understanding of the biology of this parasite and background on the intriguing parasite-host relationship.

Augmentation of signaling through BCR containing IgE but not that containing IgA due to lack of CD22-mediated signal regulation

The B cell membrane molecules CD22 and CD72 contain ITIMs in their cytoplasmic portion, and negatively regulate signaling through BCR. Various lines of evidence suggest that ligation of BCR containing IgG (IgG-BCR) transmits augmented signaling due to lack of CD22-mediated signal regulation. However, the signaling capacities of BCR containing IgA and IgE remain largely undefined. In this study, we demonstrate that both IgE-BCR and IgG-BCR, but not IgA-BCR, transmit augmented signaling compared with IgM-BCR. Ligation of IgE-BCR does not induce signaling events required for CD22-mediated signal inhibition, and restoration of these signaling events by coligation of CD22 with BCR abrogates signal augmentation. Furthermore, the cytoplasmic portion of IgE but not that of IgA is sufficient for suppressing CD22-mediated signal inhibition. These findings strongly suggest that the cytoplasmic portion of IgE but not that of IgA reverses CD22-mediated signal inhibition, leading to augmentation of signaling through IgE-BCR but not IgA-BCR. Augmented IgE-BCR signaling appears to play a role in production of large amounts of IgE during helminth infection, whereas regulated signaling through IgA-BCR may be crucial for constitutive production of IgA for mucosal immunity.

Identification of a novel antigen of Schistosoma mansoni shared with Plasmodium falciparum and evaluation of different cross-reactive antibody subclasses induced by human schistosomiasis and malaria

Plasmodium falciparum and Schistosoma mansoni are often found in human coinfections, and cross-reactive antibodies to different components of the two parasites have been detected. In this work, we identified a cross-reactive S. mansoni gene product, referred to as SmLRR, that seems to belong to the leucine-rich repeat protein family. Comparative analysis of SmLRR revealed 57% similarity with a putative gene product encoded in the P. falciparum genome. Antibodies to SmLRR were found in experimental infections and in both S. mansoni- and P. falciparum-infected individuals. Correlative analysis of human anti-SmLRR responses in Kenya and Uganda suggested that malaria and schistosomiasis drive the immunoglobulin G3 (IgG3) and IgG4 isotypes, respectively, against SmLRR, suggesting that there is differential regulation of cross-reactive isotypes depending on the infection. In addition, the levels of anti-SmLRR IgG4, but not the levels of IgG3, correlated positively with the intensity of S. mansoni infection.

Resistance to re-infection after exposure to normal and attenuated schistosome parasites in the baboon model

The baboon model of schistosomiasis has been used extensively to study parasite biology, immune responses and pathological manifestations after natural and experimental infections. The body of knowledge accumulated so far has placed this animal model at the pinnacle in the continuing search for new interventions and might hold the key to the development of new anti-schistosome vaccines. In this review paper, we highlight previous and recent studies that have elevated the baboon to be the model of choice for schistosomiasis research. In particular, the long-term studies of re-infection after chemotherapy as well as the interaction between vaccination, chemotherapy and infection are highlighted.

Phage displaying peptides mimic schistosoma antigenic epitopes selected by rat natural antibodies and protective immunity induced by their immunization in mice

AIM: To obtain the short peptides mimic antigenic epitopes selected by rat natural antibodies to schistosomes, and to explore their immunoprotection against schistosomiasis in mice.

METHODS: Adults worm antigens (AWA) were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and enzyme-linked transferred immunoblotting methods with normal SD rat sera (NRS). The killing effects on schistosomula with fresh and heat-inactivated sera from SD rats were observed. Then the purified IgG from sera of SD rats was used to biopan a phage random peptide library and 20 randomly selected positive clones were detected by ELISA and 2 of them were sequenced. Sixty female mice were immunized thrice with positive phage clones (0, 2^nd, 4^th wk). Each mouse was challenged with 40 cercariae, and all mice were killed 42 d after challenge. The worms and the liver eggs were counted.

RESULTS: NRS could specifically react to the molecules of 75000, 47000, 34500 and 23000 of AWA. Sera from SD rats showed that the mortality rate of schistosomula was 76.2%, and when the sera were heat-inactivated in vitro, the mortality rate was decreased to 41.0% after being cultured for 48 h. The specific phages bound to IgG were enriched about 300-folds after three rounds of biopanning. Twenty clones were detected by ELISA, 19 of them bound to the specific IgG of rat sera. Immunization with these epitopes was carried out in mice. Compared with the control groups, the mixture of two mimic peptides could induce 34.9% (P = 0.000) worm reduction and 67.6% (P = 0.000) total liver egg reduction in mice. Two different mimic peptides could respectively induce 31.0% (P = 0.001), 14.5% (P = 0.074) worm reduction and 61.2% (P = 0.000), 35.7% (P = 0.000) total liver egg reduction. The specific antibody could be induced by immunization of the mimic peptides, and the antibody titer in immunized mice reached more than 1:6400 as detected by ELISA.

CONCLUSION: Specific peptides mimic antigenic molecules can be obtained by biopanning the phage random peptide library and a partially protective immunity against schistosome infection can be stimulated by these phage epitopes in mice.

Development of resistance to reinfection by Clonorchis sinensis in rats

We investigated the induction of resistance to Clonorchis sinensis infection by prior infection in rat and hamster models. Animals were challenged with C. sinensis metacercariae, then treated with praziquantel and reinfected. Worm recovery rate in reinfected animals was used to estimate resistance to reinfection. The determined resistance rates to reinfection in rats and hamsters were 97.7% and 10.3%, respectively. In rats, cure from the primary infection of C. sinensis increased resistant to reinfection, and the greater the worm burden and the longer the duration of primary infection, the higher was the resistance rate. For primary infection doses of 10, 40 and 100 metacercariae per rat, the resistance rates were 87.4%, 93.8% and 98.4%, respectively. The resistance rates in rats after 2 or 8-week primary infection were 78.7% and 95.3%, respectively. All worms recovered from reinfected rats were immature. When cured rats were administered with methylprednisolone, resistance to reinfection became impaired. These findings indicate that rats develop a high degree of resistance to reinfection by C. sinensis after cure. The growths and maturations of reinfected worms were also impaired.

[Alterations in cholesterol, triglyceride and total phospholipid levels in plasma of Callithrix jacchus (sagüi) reinfected by Schistosoma mansoni]

Little information is available on the lipid changes caused by Schistosoma mansoni reinfection. In this work it was evaluated alteration in the plasma lipids due to one reinfection by Schistosoma mansoni in the non human primate Callithrix jacchus (sagüi). Blood samples from C. jacchus, prior and after 60 days infection and reinfection, were collected by intravenous puncture, anticoagulated with EDTA (1mg/mL) and centrifuged at 2,500 xg, in order to obtain the plasma. Total cholesterol, cholesteryl ester, total phospholipid and triglyceride levels were determined by spectrophotometer methods. The results showed that there are significant reduction in cholesterol total, cholesteryl ester, total phospholipid and triglyceride concentrations in plasma of animals reinfected by Schistosoma mansoni, in comparison to the same animals prior and after one infection. This study showed that a second infection of Callithrix jacchus by Schistosoma mansoni causes plasma lipid alterations, which are more significant than after a single infection.

Cytokine production in whole blood cultures from a fishing community in an area of high endemicity for Schistosoma mansoni in Uganda: the differential effect of parasite worm and egg antigens

The human host is continuously exposed to the egg and the adult worm developmental stages of Schistosoma mansoni during chronic infections with the parasite. To assess the cytokine responses induced by these different costimulating stages and how they are influenced by host age and infection intensity, whole blood samples from a cross-sectional cohort of 226 members of a Ugandan fishing community who had been resident in an area with high transmission of S. mansoni for the previous 10 years or from birth were stimulated with S. mansoni egg antigen (SEA) or worm antigen (SWA). SWA-specific gamma interferon (IFN-gamma) production increased with age, and the levels of SWA- and SEA-specific interleukin 3 (IL-3) were weakly correlated with schistosome infection intensity. The production of most cytokines was little affected by age or infection intensity but was either SEA or SWA specific. One hundred thirty-two members of the cohort coproduced IL-5 and IL-13 specifically in response to SWA, whereas only 15 produced these cytokines, and at much lower levels, in response to SEA. IL-10, IL-4, and IFN-gamma were also produced in response to SWA, whereas the response to SEA consisted almost exclusively of IL-10. Our results suggest that, in contrast to what has been described for the murine model of S. mansoni and during acute human infections, chronic intense exposure to and infection with S. mansoni in this cohort resulted in very low levels of response to SEA in vitro in the presence of a vigorous and mixed Th1-Th2 response to SWA.

Altered T helper responses in CD40 and interleukin-12 deficient mice reveal a critical role for Th1 responses in eliminating the helminth parasite Taenia crassiceps

A key feature of helminth infections is the induction of strong Th2-biased immune responses in their hosts. We have previously found that Th2-like responses mediate susceptibility to the helminth parasite Taenia crassiceps, probably by inhibiting Th1 responses required for the development of protective immunity against this parasite. Here we show that mice lacking interleukin-12p35 (IL-12p35-/-) following T. crassiceps infection, failed to mount a Th1 response, but developed a strong Th2-type response, produced higher levels of IgG1, IgE, interleukin-4, interleukin-5 as well as interleukin-13 than wild-type mice, and became highly susceptible to the larval stage of this cestode. In contrast, similarly-infected CD40 deficient BALB/c mice (CD40-/-) displayed impairment of both Th1 and Th2-type responses associated with low levels of interferon-gamma as well as IgE, interleukin-4, interleukin-5 and interleukin-13, but efficiently controlled T. crassiceps infection. Together, these findings suggest a detrimental role for Th2-biased responses during the larval stage of T. crassiceps infection. Furthermore, they also suggest a pivotal role for CD40 in developing Th2-type responses.

Macrophage migration inhibitory factor plays a critical role in mediating protection against the helminth parasite Taenia crassiceps

To determine the role of endogenous migration inhibitory factor (MIF) in regulation of immune response during murine cysticercosis caused by the helminth parasite Taenia crassiceps, we analyzed the course of T. crassiceps infection in MIF(-/-) BALB/c mice. MIF(-/-) mice were highly susceptible to T. crassiceps and developed significantly higher parasite loads compared to similarly infected MIF(+/+) mice. Throughout the course of infection, Taenia crassiceps soluble antigen-stimulated spleen cells from both MIF(+/+) and MIF(-/-) mice produced significant and comparable levels of interleukin-4 (IL-4), but those from MIF(-/-) mice produced significantly more IL-13, as well as gamma interferon (IFN-gamma), suggesting that the susceptibility of MIF(-/-) mice to T. crassiceps was not due to the lack of IFN-gamma production. Interestingly, low levels of both total and specific immunoglobulin G2a were observed in MIF(-/-) cysticercotic mice despite the high IFN-gamma levels; in addition, peritoneal macrophages obtained from T. crassiceps-infected MIF(-/-) mice at different time points failed to respond efficiently to stimulation in vitro with lipopolysaccharide plus IFN-gamma and produced significantly lower levels of IL-12, tumor necrosis factor alpha, and NO compared to those from MIF(+/+) mice. These findings demonstrate that MIF plays a critical role in mediating protection against T. crassiceps in vivo. Moreover, these findings also suggest that impaired macrophage function rather than the lack of Th1 development may be responsible for mediating susceptibility to T. crassiceps.

The LTR72 mutant of heat-labile enterotoxin of Escherichia coli enhances the ability of peptide antigens to elicit CD4(+) T cells and secrete gamma interferon after coapplication onto bare skin

Application of antigens with an adjuvant onto bare skin is a needle-free and pain-free immunization procedure that delivers antigens to the immunocompetent cells of the epidermis. We tested here the immunogenicity and adjuvanticity of two mutants of heat-labile enterotoxin (LT) of Escherichia coli, LTK63 and LTR72. Both mutants were shown to be immunogenic, inducing serum and mucosal antibody responses. The application of LTK63 and LTR72 to bare skin induced significant protection against intraperitoneal challenge with a lethal dose of LT. In addition, both LT mutants enhanced the capacity of peptides TT:830-843 and HA:307-319 (representing T-helper epitopes from tetanus toxin and influenza virus hemagglutinin, respectively) to elicit antigen-specific CD4(+) T cells after coapplication onto bare skin. However, only mutant LTR72 was capable of stimulating the secretion of high levels of gamma interferon. These findings demonstrate that successful skin immunization protocols require the selection of the right adjuvant in order to induce the appropriate type of antigen-specific immune responses in a selective and reliable way. Moreover, the use of adjuvants such the LTK63 and LTR72 mutants, with no or low residual toxicity, holds a lot of promise for the future application of vaccines to the bare skin of humans.

Cutting edge: susceptibility to the larval stage of the helminth parasite Taenia crassiceps is mediated by Th2 response induced via STAT6 signaling

Using STAT6(-/-) BALB/c mice, we analyzed the role of STAT6-induced Th2 response in determining the outcome of murine cysticercosis caused by the helminth parasite Taenia crassiceps. After T. crassiceps infection, wild-type BALB/c mice developed a strong Th2-like response; produced high levels of IgG1, IgE, IL-4, as well as IL-13; and remained susceptible to T. crassiceps. In contrast, similarly infected STAT6(-/-) mice mounted a strong Th1-like response; produced high levels of IgG2a, IL-12, IFN-gamma, as well as nitric oxide; and efficiently controlled T. crassiceps infection. These findings demonstrate that Th2-like response induced via STAT6-mediated signaling pathway mediates susceptibility to T. crassiceps and, furthermore, that unlike the case in most helminths, immunity against T. crassiceps is mediated by a Th1-like rather than Th2-like response.

Efeito de tratamento cirúrgico sobre a atividade da enzima hepática lecitina: colesterol aciltransferase (LCAT) na esquistossomose mansônica

A esquistossomose mansônica é uma doença tropical que constitui um importante problema de saúde pública, na Região Nordeste do Brasil, onde é encontrada em alta endemicidade. Essa parasitose tem o fígado como principal alvo de suas lesões histológicas, alterações fisiopatológicas e manifestações clínicas. Estudos anteriores reportam alterações no metabolismo lipídico associadas à forma hepatoesplênica da esquistosomose.Uma das principais alterações consiste na redução da atividade da enzima hepática LCAT, responsável pela esterificação do colesterol no plasma. Neste trabalho, avaliamos a atividade da LCAT no plasma de pacientes portadores da esquistossomose mansônica hepatoesplênica, os quais foram submetidos a esplenectomia e reimplante de parte de tecido do baço. A atividade enzimática da LCAT foi determinada com substrato radioativo. O [14C]colesterol livre e esterificado, formados por ação da LCAT, foram separados por cromatografia em camada delgada e a radioatividade das amostras foi contada em analisador de cintilação líquida. A atividade da LCAT nos pacientes submetidos a esplenectomia e reimplante de tecido do baço apresentou redução de 32 %, em relação ao grupo controle. Contudo, nos portadores da doença que não foram submetidos ao procedimento cirúrgico a redução na atividade da LCAT foi o dobro (64%) da observada em pacientes esplenectomizados e com reimplante de parte do tecido do baço. Esses resultados sugerem haver uma melhora significativa no efeito da forma grave da esquistossomose mansônica sobre a atividade da LCAT.

Expression of a functional IL-13Ralpha1 by rat B cells

IL-13 mediates its effects through a complex receptor system including IL-4Ralpha and a functional IL-13Ralpha1. IL-13 has been reported to have no effects on mouse B cells due to a lack of receptor expression. However, on human B cells a functional IL-13Ralpha1 has been described. Here, we identified the rat IL-13Ralpha1 in order to analyze its expression and function in rat B cells. The expression of IL-13Ralpha1 has been shown by the presence of mRNA and the corresponding protein in purified rat B cells and in rat hybridoma B cell line. Rat B cells are able to bind IL-13 and to proliferate when cultured with CD40 ligand and IL-13. In vivo experiments showed that administration of IL-13 did enhance IgE production. These results suggest a direct interaction of rat B cells with IL-13 through a functional receptor with an increase of IgE production and provide a relevant model to further study the activity of IL-13 and to better understand its role in human diseases.