Evaluation of the immune response against Strongyloides venezuelensis in antigen-immunized or previously infected mice

Experimental infection with Schistosoma mansoni isolated from the wild rodent Holochilus sciureus shows a low parasite burden but induces high schistosomiasis severity in BALB/c mice

Wild mammals, especially rodents, can participate in the life cycle of Schistosoma mansoni; however, the impact of these parasite strains on the severity of schistosomiasis remains unclear. The aim of this study was to comparatively evaluate the parasitological and immunopathological alterations induced by an S. mansoni strain isolated from the wild rodent Holochilus sciureus (HS strain) and a parasite strain isolated from a human (LE strain) in experimentally infected mice. Male BALB/c mice were subcutaneously infected with 50 cercariae/mouse of either the HS or the LE strain and were evaluated for 12 weeks. In the experimental groups, the parasite burden was estimated by worm and egg (feces and tissues) count, and immunopathological alterations were evaluated in the liver and intestines. Compared to experimental infection with the LE parasite strain, HS-infected mice showed reduced number of parasite worms but higher fecundity rate, significant reduction in IL-5, IL-10 and IL-13 concentrations, lower EPO-activity in liver homogenate and higher concentrations of TNF-α, IFN-γ, IL-12 and IL-17 in the small intestine homogenate. Moreover, HS infection resulted in higher concentrations of NO end-products in both the liver and intestine, suggesting a predominance of the Th1/Th17 immune response. HS-infected mice also showed higher plasma transaminase levels, formed larger granulomas, and had a higher mortality rate in comparison with LE-infected mice. Data indicate that BALB/c mice infected with the HS strain of S. mansoni showed reduced susceptibility to the parasite but stronger tissue inflammation and high disease severity.

Eosinophils participate in modulation of liver immune response and tissue damage induced by Schistosoma mansoni infection in mice

The severity of chronic schistosomiasis has been mainly associated with the intensity and extension of the inflammatory response induced by egg-secreted antigens in the host tissue, especially in the liver and intestine. During acute schistosomiasis, eosinophils account for approximately 50% of the cells that compose the liver granulomas; however, the role of this cell-type in the pathology of schistosomiasis remains controversial. In the current study, we compared the parasite burden and liver immunopathological changes during experimental schistosomiasis in wild-type (WT) BALB/c mice and BALB/c mice selectively deficient for the differentiation of eosinophils (ΔdblGATA). Our data demonstrated that the absence of eosinophil differentiation did not alter the S. mansoni load or the liver retention of parasite eggs; however, there were significant changes in the liver immune response profile and tissue damage. S. mansoni infection in ΔdblGATA mice resulted in significantly lower liver concentrations of IL-5, IL-13, IL-33, IL-17, IL-10, and TGF-β and higher concentrations of IFN-γ and TNF-α, as compared to WT mice. The changes in liver immune response observed in infected ΔdblGATA mice were accompanied by lower collagen deposition, but higher liver damage and larger granulomas. Moreover, the absence of eosinophils resulted in a higher mortality rate in mice infected with a high parasite load. Therefore, the data indicated that eosinophils participate in the establishment and/or amplification of liver Th-2 and regulatory response induced by S. mansoni, which is necessary for the balance between liver damage and fibrosis, which in turn is essential for modulating disease severity.

Infection by Strongyloides venezuelensis attenuates chronic colitis induced by Dextran Sodium Sulfate ingestion in BALB/c mice

Inflammatory bowel diseases (IBD) are chronic health problems of difficult management and treatment. Epidemiological studies indicate an inverse association between helminth infections and IBD, and experimental data confirm that helminth infections modulate the severity of experimental acute colitis in mice. However, the effects of helminth infections on chronic colitis, which is clinically more relevant, have been poorly explored. Herein, we investigated whether Strongyloides venezuelensis infection in BALB/c mice can ameliorate chronic colitis induced by the ingestion of water containing 2.5% Dextran Sodium Sulfate (DSS) over three seven-day treatment cycles, with an interval of fourteen days between cycles. Infected-only, DSS-exposed-only, and non-exposed/uninfected experimental groups served as controls for comparing the severity of colitis and intestinal inflammation among different groups. Our data showed that S. venezuelensis infection in mice with DSS-induced chronic colitis reduced clinical signs, attenuated colon shortening and inflammation, and prevented mucus ablation. The modulatory effect was accompanied by a low concentration of IFN-γ, high concentrations of TGF-β, IL-22, and IL-33 in the colon, and a significant increase of the percentage of CD4+CD25+Foxp3+ Treg cells in the mesenteric lymph node (MLN). In conclusion, S. venezuelensis infection can reduce the severity of DSS-induced chronic colitis in mice possibly through the stimulation of Treg cells and modulatory cytokines, and induction of mucosal repair mechanisms.

Thymic stromal lymphopoietin contributes to protection of mice from Strongyloides venezuelensis infection by CD4+ T cell-dependent and -independent pathways

When animals are infected with helminthic parasites, resistant hosts mount type II helper T (Th2) immune responses to expel worms. Recent studies have clearly shown that epithelial cell-derived cytokines contribute to the induction of Th2 immune responses. Here we demonstrate the role of endogenous thymic stromal lymphopoietin (TSLP) for protection against Strongyloides venezuelensis (S. venezuelensis) infection, utilizing TSLP receptor-deficient Crlf2-/- mice. The number of eggs per gram of feces (EPG) and worm burden were significantly higher in Crlf2-/- mice than in wild type (WT) mice. S. venezuelensis infection induced Tslp mRNA expression in the skin, lung, and intestine and also facilitated the accumulation of mast cells in the intestine in a TSLP-dependent manner. Furthermore, CD4+ T cells from S. venezuelensis-infected Crlf2-/- mice showed diminished capacity to produce Th2 cytokines in the early stage of infection. Finally, CD4+ cell-depleted Crlf2-/- mice still showed higher EPG counts and worm burden than CD4+ cell-depleted WT mice, indicating that TSLP contributes to protecting mice against S. venezuelensis infection in both CD4+ T cell-dependent and -independent manners.

The IL-33/ST2 pathway is not essential to Th2 stimulation but is key for modulation and survival during chronic infection with Schistosoma mansoni in mice

Morbidity during chronic schistosomiasis has been associated with the induction and modulation of type-2 granulomatous inflammatory response induced by antigens secreted by the eggs, which become trapped in capillary venules of the host tissues, especially in the liver and intestines. IL-33, an alarmin released after cell damage, binds to its ST2 (suppressor of tumorigenicity 2) receptor, expressed in an variety of immune cells, including ILC2 and macrophages, and stimulates the early production of IL-5 and IL-13, which leads to eosinophil infiltration and activation of a Th2 response. However, the role of IL-33/ST2 activation on Schistosoma-induced granuloma formation and modulation is mostly unknown. In the current work, we comparatively evaluated the immune response and granuloma formation in wild-type BALB/c (WT) and BALB/c mice genetically deficient in the IL-33 receptor (ST2^-/-) experimentally infected with Schistosoma mansoni. Mice were infected with 25 or 50 S. mansoni cercariae and followed for up to 14 weeks to assess mortality. Mice from each experimental group were comparatively evaluated for parasite burden, liver immune response, and granuloma appearance during acute and chronic schistosomiasis. Our data showed that the number of circulating worms and eggs retained in the liver and eliminated in the feces was similar in WT and ST2^-/- infected mice, but infected ST2^-/- mice presented an enhanced rate of mortality. Interestingly, the production of type-2 cytokines by soluble egg antigens (SEA)-stimulated spleen cells, the serum concentrations of IL-5 and Immunoglobulin (Ig)-E, and the level of parasite-reactive IgG1 were similar in infected mice of both experimental groups. The concentrations of IL-4, IL-5, IL-13, and IFN-γ in liver homogenate of infected mice also did not differ between the strains at acute schistosomiasis, but there was a significant increase in IL-17 levels in ST2^-/- infected mice at this phase. On the other hand, IL-4, IL-13, IL-10, IL-17, and IFN-γ concentrations were reduced and the ratios of IL-4/IFN-γ and IL-17/IFN-γ were higher in liver homogenate of chronically infected ST2^-/- mice, suggesting unbalanced Th2 and Th17 responses. Moreover, liver granulomas of ST2^-/- mice were larger and disorganized, showing an intense cellular infiltrate, rich in eosinophils and neutrophils. Our results suggest that the absence of the IL-33/ST2 pathway is not essential for the Schistosoma-induced Th2 response, but is necessary to prevent host mortality by modulating granuloma-mediated pathology.

Beneficial effects of Strongyloides venezuelensis antigen extract in acute experimental toxoplasmosis

BACKGROUND

Toxoplasma gondii is a protozoan with worldwide distribution and triggers a strong Th1 immune response in infected susceptible hosts. On the contrary, most helminth infections are characterized by Th2 immune response and the use of helminth-derived antigens to regulate immune response in inflammatory disorders has been broadly investigated.

OBJECTIVES

The aim of this study was to investigate whether treatment with Strongyloides venezuelensis antigen extract (SvAg) would alter immune response against T gondii.

METHODS

C57BL/6 mice were orally infected with T gondii and treated with SvAg, and parasitological, histological and immunological parameters were investigated.

RESULTS

It was observed that SvAg treatment improved survival rates of T gondii-infected mice. At day 7 post-infection, the parasite load was lower in the lung and small intestine of infected SvAg-treated mice than untreated infected mice. Remarkably, SvAg-treated mice infected with T gondii presented reduced inflammatory lesions in the small intestine than infected untreated mice and decreased intestinal and systemic levels of IFN-γ, TNF-α and IL-6. In contrast, SvAg treatment increased T gondii-specific IgA serum levels in infected mice.

CONCLUSIONS

S venezuelensis antigen extract has anti-parasitic and anti-inflammatory properties during T gondii infection suggesting as a possible alternative to parasite and inflammation control.

The effect of maternal Strongyloides venezuelensis infection on mice offspring susceptibility and immune response

Species of Strongyloides infect a wide range of hosts worldwide. Due to their complex life cycle, it is hard to control the transmission of these parasites. Several species show evidence of vertical transmission; however, the impact of this transmission route on the susceptibility of the offspring has been poorly investigated. Herein, we used Strongyloides venezuelensis infected mice to evaluate transplacental and transmammary parasite transmission and their effect on the susceptibility of offspring. Swiss female mice were infected at the end of the gestation or during the breastfeeding period, and their offspring were examined for the presence of the parasite one week after infection of the mother. Our data showed that female mice infected with S. venezuelensis during gestation did not transmit the parasite to their offspring. On the other hand, all newborn mice breastfeeding in S. venezuelensis infected females got infected. To evaluate the effect of early exposure to the parasite on susceptibility and immune response of the hosts, the offspring of each experimental group (non-infected, gestation-infected, and breastfeeding-infected mothers) received anti-helminth treatment after parasite evaluation and were subcutaneously infected with S. venezuelensis upon reaching adulthood. Mice from the group of breastfeeding-infected mothers showed lower susceptibility to S. venezuelensis in adulthood in comparison with mice from non-infected mothers. The low parasite burden was accompanied by earlier eosinophil and neutrophil activation in the gut and higher serum levels of IgE. In contrast, S. venezuelensis infection in adult mice born from gestation-infected mothers presented with more worms in the intestine and lower levels of parasite-reactive IgM in serum in comparison with mice born from non-infected mothers, thus suggesting that early exposure to parasite antigens may modulate the protective immune response. Altogether, our data confirmed transmammary, but not transplacental, transmission of S. venezuelensis in mice and demonstrated that early exposure to the parasite and/or their antigens has an important effect on host susceptibility to a later infection.

Gastrointestinal effects of ivermectin treatment in rats infected with Strongyloides venezuelensis

We aimed to evaluate the effects of ivermectin treatment on gastrointestinal morphology and function after Strongyloides venezuelensis infection. Male rats composed Control (C), Parasitized (Sv), Ivermectin (IVM) and Parasitized and treated with Ivermectin (Sv/IVM) groups. IVM and Sv/IVM groups were subdivided according to IVM: single dose of 200 μg/kg (IVM1 and Sv/IVM1) or three repeated doses of 200 μg/kg at 24 h intervals (IVM3 and Sv/IVM3). First dose of IVM was administered after peak of infection. Eggs per gram (EPG), mean gastric emptying time (MGET), mean cecum arrival time (MCAT) and mean small intestinal transit time (MSITT) were evaluated. Measurements were performed before drug and at peak of infection, first day post peak of infection and 30 days post infection. Same time intervals were simulated for uninfected animals. Number of recovered worms and intestinal morphometry were also rated. Data were analyzed by ANOVA and correlated by Dunnett and Pearson (p < 0.05). Sv/IVM1 and Sv/IVM3 showed reduction of EPG and worms, although only group SV/IVM3 eradicate them. Hastened gastric emptying and slowed intestinal transit provoked by S. venezuelensis infection can be reverted by a single administration of IVM after peak of infection, even without total parasite elimination. Although three consecutive doses of IVM were more efficient to eradicate the parasite, drug administration impaired gastrointestinal function and morphology. IVM alone affected gastrointestinal parameters in uninfected animals for prolonged periods, especially in high doses. In control, there were strong negative correlations between MSITT and muscle layers. Strongyloides venezuelensis infection abolishes such correlations. Longitudinal muscle was thinner in IVM3 and Sv/IVM3 groups and circular thicker in Sv group. Revisiting the action of traditional drugs broadens knowledge in the parasite-host interface and may result in the development of more accurate therapeutic strategies.

Nematode-Infected Mice Acquire Resistance to Subsequent Infection With Unrelated Nematode by Inducing Highly Responsive Group 2 Innate Lymphoid Cells in the Lung

The immune responses against helminths have been investigated individually, and it is well-established that infected hosts develop an immunological memory to resist reinfection by the same pathogen. In contrast, it is poorly understood how the host immune system responds to subsequent infection by unrelated parasites after elimination of the first infection. We previously reported that infection of mice with Strongyloides venezuelensis induces the accumulation of group 2 innate lymphoid cells (ILC2s) in the lung. Here, we demonstrated that S. venezuelensis-experienced (Sv-exp) mice became significantly resistant against infection by Nippostrongylus brasiliensis. N. brasiliensis infection induced enhanced accumulation of ILC2s and eosinophils with increased expressions of mRNA for Th2 cytokines in the lungs of Sv-exp mice. The resistance was dependent on ILC2s, and eosinophils but not on CD4⁺ T cells. Furthermore, pulmonary ILC2s in Sv-exp mice acquired a highly responsive “trained” phenotype; in response to N. brasiliensis infection, they rapidly increased and produced IL-5 and IL-13, which in turn induced the early accumulation of eosinophils in the lungs. IL-33 was required for the accumulation of ILC2s and the resistance of mice against N. brasiliensis infection but insufficient for the induction of trained ILC2s. In conclusion, animals infected with one type of lung-migratory nematodes acquire a specific-antigen-independent resistance to another type of lung-migrating nematodes, providing animals with the capacity to protect against sequential infections with various lung-migratory nematodes.

Acute infection with Strongyloides venezuelensis increases intestine production IL-10, reduces Th1/Th2/Th17 induction in colon and attenuates Dextran Sulfate Sodium-induced colitis in BALB/c mice

Helminth infection can reduce the severity of inflammatory bowel disease. However, the modulatory mechanisms elicited by helminth infection are not yet fully understood and vary depending on the experimental model. Herein we evaluated the effect of acute infection of BALB/c mice with Strongyloides venezuelensis on the clinical course of ulcerative colitis induced by Dextran Sulfate Sodium (DSS) treatment of these animals. For the experiments, S. venezuelensis-infected BALB/c mice were treated orally with 4% DSS solution for seven days. As controls, we used untreated S. venezuelensis infected, DSS-treated uninfected, and untreated/uninfected BALB/c mice. During DSS treatment, mice from the different groups were compared with regards to the clinical signs related to the severity of colitis and intestinal inflammation. Mice acutely infected with S. venezulensis and treated with DSS had reduced clinical score, shortening of the colon, and tissue inflammation. Moreover, DSS-treated and infected mice showed reduced IL-4, INF-γ, and IL-17 levels and increase of IL-10 production in the colon and/or in the supernatant of mesenteric lymph nodes cell cultures that resulted in lower eosinophil peroxidase and myeloperoxidase activity in colon homogenates, when compared with DSS-treated uninfected mice. DSS-treated infected mice also preserved the intestine architecture and had normal differentiation of goblet cells and mucus production in the colon mucosa. In conclusion, the data indicate that the clinical improvement reported in DSS-treated infected mice was accompanied by the lower production of Th1/Th2/Th17 pro-inflammatory cytokines, stimulation of IL-10, and induction of mucosal repair mechanisms.

The role of ILC2 in hookworm infection

Hookworm is a major public health concern, yet still relatively little is known about the immunological responses involved in human infection. Animal studies are mainly confined to using the natural rodent helminth Nippostrongylus brasiliensis as this has been proposed as the most accurate model of hookworm infection in the mouse, with both its life cycle and the immune responses it invokes having been extremely well characterized. In this review, we examine the roles that type 2 innate lymphoid cells (ILC2s) play in immunity and host tolerance to hookworm infection, particularly N. brasiliensis. This includes their role in the initiation and regulation of immune responses, as well as in the resolution and limitation of tissue damage required after an infection with a large organism, such as a helminth.

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

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

Comparative study of cultivation of feces in vermiculite or charcoal to obtain larvae of Strongyloides venezuelensis

INTRODUCTION

We compared feces culturing in charcoal or vermiculite to obtain Strongyloides venezuelensis larvae.

METHODS

Feces (5 g) from infected rats was mixed with vermiculite (10 g) or coal (10 g) in plastic cups and incubated at 28°C for 48 h. Larvae were recovered using Baermann-Moraes method.

RESULTS

Significantly higher number of positive larval cultures were recovered from vermiculite than from charcoal (15/17 and 4/17, respectively; p < 0.001; 990.6 ± 307.5 and 215 ± 78.1 larvae, p = 0.027).

CONCLUSIONS

Vermiculite yields more larvae and provides cleaner pellets, improving larvae identification and facilitating their use for other purposes.

Increased susceptibility to Strongyloides venezuelensis infection is related to the parasite load and absence of major histocompatibility complex (MHC) class II molecules

In human and murine models strongyloidiasis induce a Th2 type response. In the current study we investigated the role of different loads of Strongyloides venezuelensis in the immune response raised against the parasite and the participation of the major histocompatibility complex (MHC) class II molecule in the disease outcome in face of the different parasite burden. The C57BL/6 wild type (WT) and MHC II(-/-) mice were individually inoculated by subcutaneous injection with 500 or 3000 S. venezuelensis L3. The MHC II(-/-) mice infected with 3000L3 were more susceptible to S. venezuelensis infection when compared with WT groups, in which the parasite was completely eliminated. The production of Th2 cytokines and specific IgG1 or IgE antibodies against parasite were significantly lowered in MHC II(-/-) infected mice with different larvae inoculums. The infection of MHC II(-/-) mice with S. venezuelensis induced slight inflammatory alterations in the small intestine, and these lesions were lower when compared with WT mice, irrespective of the parasite load utilized to infect animals. Finally, we concluded that MHC class II molecules are essential in the immune response against S. venezuelensis mainly when infection occurs with high parasite inoculum.

IgG and IgE collaboratively accelerate expulsion of Strongyloides venezuelensis in a primary infection

The host deploys a subset of immune responses to expel helminths, which differs depending on the nature of the helminth. Strongyloides venezuelensis, a counterpart of the human pathogen S. stercoralis, naturally infects rodents and has been used as an experimental model. Here we show that induction of immunoglobulin G (IgG) and IgE is a prerequisite for rapid expulsion of S. venezuelensis during a primary infection. Activation-induced cytidine deaminase-deficient (AID(-/-)) mice, which lack the ability to switch IgM to other isotypes, normally developed T-helper 2 (Th2) cells and intestinal mastocytosis after infection with S. venezuelensis. Although AID(-/-) mice expelled Nippostrongylus brasiliensis normally, they required a much longer period to expel S. venezuelensis than wild-type (WT) mice. Adoptive transfers of immune sera from S. venezuelensis-infected but not N. brasiliensis-infected mice restored the ability of AID(-/-) mice to promptly expel S. venezuelensis. Immune serum-derived IgG and IgE induced worm expulsion via Fc γ receptor III (FcγRIII) and Fc ε receptor I (FcεRI), respectively, and a mixture of IgG and IgE showed collaborative effects. Whereas FcγRIII(-/-) mice or FcεRIα(-/-) mice normally could expel S. venezuelensis, FcγRIII(-/-) mice, when their IgE was neutralized by anti-IgE, or FcεRIα(-/-) mice, when their IgG binding to FcγRIII was blocked by anti-FcγRIII, showed a markedly reduced ability to expel S. venezuelensis. These data reveal that IgG and IgE play redundant roles but act in concert to accelerate S. venezuelensis expulsion. Mast cell-deficient mice, even those equipped with immune serum-derived IgG or IgE, failed to expel S. venezuelensis promptly, suggesting that mast cells are cellular targets of IgG and IgE.

Lower production of IL-17A and increased susceptibility to Mycobacterium bovis in mice coinfected with Strongyloides venezuelensis

The presence of intestinal helminths can down-regulate the immune response required to control mycobacterial infection. BALB/c mice infected with Mycobacterium bovis following an infection with the intestinal helminth Strongyloides venezuelensis showed reduced interleukin-17A production by lung cells and increased bacterial burden. Also, small granulomas and a high accumulation of cells expressing the inhibitory molecule CTLA-4 were observed in the lung. These data suggest that intestinal helminth infection could have a detrimental effect on the control of tuberculosis (TB) and render coinfected individuals more susceptible to the development of TB.

Vaccination with Strongyloides ratti heat shock protein 60 increases susceptibility to challenge infection by induction of Th1 response

The control of strongyloidiasis affecting approximately 100 million people - caused by the gastrointestinal nematode Strongyloides stercoralis - is still based on anti-helminthic treatment. In the current study we analysed the immune response to Strongyloides ratti heat shock protein 60 (srHSP60) as a possible vaccine candidate in the murine system. We show that srHSP60 is a target of both, humoral and cellular response in S. ratti-infected mice. Strikingly, vaccination with srHSP60 without adjuvant or with CFA induced a S. ratti-specific Th1 response in vivo that did not confer protection but slightly increased larval output during challenge infection. Using in vitro T cell stimulation assays we provide further evidence that srHSP60 skewed activated T cells towards a Th1 response that interfered with efficient clearance of S. ratti infection. Vaccination with alum-precipitated srHSP60, in contrast, overruled the Th1-inducing activity intrinsic to srHSP60, induced a Th2 response, and conferred partial protection against a challenge infection. As srHSP60 is actively secreted by S. ratti during all life stages, our findings strongly suggest that srHSP60 induced polarization towards a Th1 response reflects a mechanism of immune evasion by this pathogenic nematode.

Innate and adaptive immunity to the nematode Strongyloides stercoralis in a mouse model

Mice have been used to the study the mechanisms of protective innate and adaptive immunity to larval Strongyloides stercoralis. During primary infection, neutrophils and eosinophils are attracted by parasite components and kill the larvae by release of granule products. Eosinophils also function as antigen-presenting cells for the induction of a Th2 response. B cells produce both IgM and IgG that collaborate with neutrophils to kill worms in the adaptive immune response. Vaccine studies have identified a recombinant diagnostic antigen that induced high levels of immunity to infection with S. stercoralis in mice. These studies demonstrate that there are redundancies in the mechanisms used by the immune response to kill the parasite and that a vaccine with a single antigen may be suitable as a prophylactic vaccine to prevent human strongyloidiasis.

Protection against Nippostrongylus brasiliensis infection in mice is independent of GM-CSF

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a cytokine with the capacity to promote inflammation in a wide variety of infectious and inflammatory diseases. These conditions include allergic airway inflammation, which is driven by T-helper 2 (Th2) cells. Because of the importance of Th2 cells in parasite infections, we have investigated the role of GM-CSF in mice infected with the nematode Nippostrongylus brasiliensis. The effect of primary and secondary infection was investigated in mice lacking functional genes for GM-CSF (CSF2 genes) (ΔGM-CSF mice), and in mice lacking the cytokine receptor common β chain (Δβ mice), the latter being unable to signal in response to GM-CSF and interleukin (IL)-5. ΔGM-CSF mice showed no significant defect in parasite immunity, measured by larval numbers in the lungs, worm numbers in the intestine or egg numbers in the faeces, in either primary or secondary infection. By contrast, the Δβ mice showed increased parasite burden, with higher numbers of lung larvae after secondary infection and higher numbers of intestinal worms and faecal eggs after both primary and secondary infection. Unexpectedly, there were increased numbers of circulating eosinophils in the ΔGM-CSF mice, associated with significantly reduced larval numbers in the lungs. These results indicate that GM-CSF is redundant in protection against N. brasiliensis infection, and that the increased susceptibility of Δβ mice to infection is likely to be attributed to the lack of IL-5 signalling in these mice. The results suggest that clinical use of agents that neutralise GM-CSF may not be associated with increased risk of parasite infection.

Experimental autoimmune encephalomyelitis evolution was not modified by multiple infections with Strongyloides venezuelensis

According to the hygiene hypothesis, the increased incidence of allergic and autoimmune diseases in developed countries is mainly explained by the decreased contact between the human population and certain environmental agents as lactobacillus, mycobacteria and helminths. In this study, we evaluated the effect of multiple infections with Strongyloides venezuelensis on the development of experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Multiple infections before EAE induction were not able to change the evolution of the disease. No alterations were observed in weight loss, clinical score and inflammation intensity at the central nervous system. The presence of significant levels of parasite-specific IgG1 but not IgG2b suggested a Th2 polarization. However, the percentage and absolute number of CD4+CD25+Foxp3+ T cells were not changed, being their levels in the spleen and lymph nodes of infected rats comparable to the ones found in normal animals. These results suggest that a Th2-polarized response without concomitant expansion of Foxp3+ regulatory T cells was not able to modify EAE progression. Even though these results do not threaten the hygiene hypothesis, they suggest that this paradigm might be an oversimplification. They also emphasize the need of a study to compare the immunoregulatory ability associated with different helminth spp.

Update on strongyloidiasis in the immunocompromised host

Immunocompromised persons are the most vulnerable population at risk for developing life-threatening clinical syndromes associated with strongyloidiasis, such as hyperinfection syndrome (HS) or dissemination. This review focuses on describing Strongyloides infection in the immunocompromised host, including immune response against this infection, analyzing the cases with HS published during the past 4 years in the United States, and describing the most sensitive diagnostic tools and the most effective treatment for each clinical syndrome. Strongyloidiasis is becoming an important parasitic disease in the United States, especially in the immunocompromised immigrant population. Because the transplant population is particularly at risk for developing HS, both recipients and donors should be screened for Strongyloides. Clinicians should also be aware that the development of HS can follow unexpectedly a few days after appropriate anthelminthic therapy. Highly sensitive screening tests are still not available in the major tertiary medical centers. Parenteral ivermectin has been used in some severe cases. Further therapy developments and improving diagnostic tools are warranted.

Regulation of immune responses to Strongyloides venezuelensis challenge after primary infection with different larvae doses

Nematode infections are generally followed by high rates of reinfection, leading to elevated prevalence in endemic areas. Therefore, the effective control of nematode infections depends on understanding the induction and regulation of protective mechanisms. However, most experimental models for protective immune response against nematodes use high parasite exposure, not always reflecting what occurs naturally in human populations. In this study, we tested whether infecting mice with different Strongyloides venezuelensis larvae loads would affect protective responses against reinfection. Interestingly, we found that a previous infection with 10-500 larvae conferred high rate of protection against reinfection with S. venezuelensis in mice, by destroying large numbers of migrating larvae. However, low-dose priming did not abolish adult worm maturation, as detected in high-dose primed group. Results also indicated that a previous low-dose infection delayed the development of cellular infiltrate, while a high inoculum rapidly induced these inflammatory features. Cytokine production by splenocyte cultures of challenge infected mice demonstrated that low-dose priming had increased production of IL-4 and IFN-gamma, while high-dose induced IL-4 production but not IFN-gamma. Our data support the hypothesis that low-dose nematode infection does not induce a polarized type-2 immune response, allowing adult worm survival.

Effectiveness of intranasal vaccination against Angiostrongylus costaricensis using a serine/threonine phosphatase 2 A synthetic peptide and recombinant antigens

Intranasal immunization was assayed in C57BL/6 mice against Angiostrongylus costaricensis using a synthetic and a recombinant peptide belonging to the catalytic region of the serine/threonine phosphatase 2 A (PP2A) of the parasite. Immunization was carried out with the synthetic peptide (SP) polymerized either with itself or with the beta fraction of the cholera toxin (CTB) and then enclosed in nanocapsules of phosphatidyl choline, cholesterol and Quil A (ISCOM). Another group of mice was immunized with recombinant peptide. Immunization consisted of two intranasal inoculations at two-week intervals, and the challenge with L3 larvae was made one month after the last vaccination. The effectiveness of immunization was evaluated 30 days after infection by analysis of the number of parasites in the arteries of the immunized mice, as well as by measuring spleen sizes in the experimental groups. The response induced was determined by identifying the isotypes of IgG as well as the IgE and IgA specific antigen response. The interleukins produced by the splenocyte culture of the different groups were assessed after exposing them to the peptide used in the immunization. From our results, 60%, 80%, and 100% protection against the A. costaricensis challenge was achieved in mice immunized with polymerized synthetic peptide in ISCOM, synthetic peptide polymerized with the CTB in ISCOM and inclusion bodies respectively. Splenomegaly was found to be less evident in the immunized mice than in the controls. A significant increase in IFN gamma and IL-17 levels was observed in the group with 100% protection. The results showed that vaccination through the nasal mucosa may constitute a useful method of immunization and result in a protective immune response against A. costaricensis.

Recovery from Strongyloides venezuelensis infection in Lewis rats is associated with a strong Th2 response

In this study, we investigated the characteristics of the infection and subsequent immunity induced by Strongyloides venezuelensis in Lewis rats. Animals were infected with 4000 L3 of S. venezuelensis and number of eggs per gram of faeces indicated an acute phase around day 8 and a recovery phase around day 32 after infection. A strong Th2 polarization during recovery phase was ascertained by a significant increase in IgG1 and IgE compared with that in the acute period. A shift in the cytokine profile confirmed these findings. A predominant production of IFN-gamma during the acute phase was followed by IL-10 production during recovery. Together these findings show that experimental infection of Lewis rats with S. venezuelensis presents a kinetics of parasite establishment and immunity similar to that described in other models of helminthic infection.

Increased susceptibility to Strongyloides venezuelensis in mice due to Mycobacterium bovis co-infection which modulates production of Th2 cytokines

An estimated quarter of the world's population possesses an infection caused by gastrointestinal nematodes, which induce a Th2 type immune response. Concomitant infection of nematodes with Mycobacterium tuberculosis, which induces a predominantly Th1 type response, is very frequent in tropical and subtropical regions. This study examined immune responses of BALB/c mice infected with Strongyloides venezuelensis and then co-infected with Mycobacterium bovis. The number of worms in the intestine, eggs in feces, cytokine production in lungs and intestine and the expression of CD80, CD86, CTLA-4 and CD28 cell markers on pulmonary cells were analysed. Our results indicate that co-infected mice had an increased parasite burden, which correlates with elevated IFN-gamma and IL-10 cytokine production and decreased IL-4 and IL-13. Moreover, decreased expression of CD80 and increased expression of CTLA-4 were observed in co-infected mice. Our data point out that susceptibility to Strongyloides venezuelensis infection is increased by Mycobacterium bovis co-infection, resulting in higher parasite survival.

Major histocompatibility complex (MHC) class II but not MHC class I molecules are required for efficient control of Strongyloides venezuelensis infection in mice

Strongyloides stercoralis is an intestinal nematode capable of chronic, persistent infection and hyperinfection of the host; this can lead to dissemination, mainly in immunosuppressive states, in which the infection can become severe and result in the death of the host. In this study, we investigated the immune response against Strongyloides venezuelensis infection in major histocompatibility complex (MHC) class I or class II deficient mice. We found that MHC II(-/-) animals were more susceptible to S. venezuelensis infection as a result of the presence of an elevated number of eggs in the faeces and a delay in the elimination of adult worms compared with wild-type (WT) and MHC I(-/-) mice. Histopathological analysis revealed that MHC II(-/-) mice had a mild inflammatory infiltration in the small intestine with a reduction in tissue eosinophilia. These mice also presented a significantly lower frequency of eosinophils and mononuclear cells in the blood, together with reduced T helper type 2 (Th2) cytokines in small intestine homogenates and sera compared with WT and MHC I(-/-) animals. Additionally, levels of parasite-specific immunoglobulin M (IgM), IgA, IgE, total IgG and IgG1 were also significantly reduced in the sera of MHC II(-/-) infected mice, while a non-significant increase in the level of IgG2a was found in comparison to WT or MHC I(-/-) infected mice. Together, these data demonstrate that expression of MHC class II but not class I molecules is required to induce a predominantly Th2 response and to achieve efficient control of S. venezuelensis infection in mice.