Schistosoma mansoni in IL-4-deficient mice

Dynamics of Host Immune Response Development During Schistosoma mansoni Infection

Schistosomiasis is a disease of global significance, with severity and pathology directly related to how the host responds to infection. The immunological narrative of schistosomiasis has been constructed through decades of study, with researchers often focussing on isolated time points, cell types and tissue sites of interest. However, the field currently lacks a comprehensive and up-to-date understanding of the immune trajectory of schistosomiasis over infection and across multiple tissue sites. We have defined schistosome-elicited immune responses at several distinct stages of the parasite lifecycle, in three tissue sites affected by infection: the liver, spleen, and mesenteric lymph nodes. Additionally, by performing RNA-seq on the livers of schistosome infected mice, we have generated novel transcriptomic insight into the development of schistosome-associated liver pathology and fibrosis across the breadth of infection. Through depletion of CD11c+ cells during peak stages of schistosome-driven inflammation, we have revealed a critical role for CD11c+ cells in the co-ordination and regulation of Th2 inflammation during infection. Our data provide an updated and high-resolution account of how host immune responses evolve over the course of murine schistosomiasis, underscoring the significance of CD11c+ cells in dictating host immunopathology against this important helminth infection.

Increased immunogenicity and protection of recombinant Sm14 antigens by heat-killed Cutibacterium acnes in BALB/c mice infected with Schistosoma mansoni

After many years of the excessive use of praziquantel against Schistosoma mansoni (S. mansoni), it has already led to the development of drug resistance. While schistosomiasis is still affecting millions of people every year, vaccination may be one realistic alternative way to control the disease. Currently, S. mansoni 14-kDa fatty acid-binding protein (Sm14) has shown promising results as a vaccine antigen. Yet, the use of an adjuvant may be necessary to further increase the effectiveness of the vaccine. Herein, we investigated the potential of using heat-killed Cutibacterium acnes (C. acnes) as an adjuvant for recombinant Sm14 (rSm14). Immunization of mice with C. acnes-adjuvanted rSm14 showed increased humoral immune responses, compared with mice immunized with rSm14 alone. Additionally, C. acnes-adjuvanted rSm14 vaccination provided higher protection to mice against S. mansoni infection and liver injuries. These results suggest that C. acnes increases the immunogenicity of rSm14, which leads to better protection against S. mansoni infection. Therefore, heat-killed C. acnes may be a promising adjuvant to use with rSm14.

Interleukin-4 Receptor Alpha Expressing B Cells Are Essential to Down-Modulate Host Granulomatous Inflammation During Schistosomasis

Schistosomiasis (bilharzia) is a parasitic helminth disease that can cause severe inflammatory pathology leading to organ damage in humans. Failure of the host to regulate egg-driven granulomatous inflammation causes host morbidity during chronic infection with Schistosoma mansoni. Although the importance of B cells in regulating pathology during chronic infection has been well defined, the specific contribution of IL-4Rα-expressing B cells is still unknown. To address this, we examined B cell-specific IL-4Rα-deficient (mb1^creIL-4Rα^−/lox) mice in three experimental models of schistosomiasis: high-dose (100 cercariae), low dose (30 cercariae), and a synchronous egg challenge. In the high dose model, we found that mice deficient in IL-4Rα-expressing B cells were more susceptible to acute schistosomiasis than B cell-deficient (μMT) mice, succumbing to infection at the acute stage whereas μMT mice survived until the chronic stage. An S. mansoni egg challenge model demonstrated that deleting IL-4Rα expression specifically on B cells resulted in increased lung granulomatous pathology, suggesting a role for this B cell subset in controlling granulomatous pathology. In agreement with this, a low dose model of schistosomiasis—which mimics the course of clinical chronic disease—demonstrated that depleting IL-4Rα-expressing B cells in mb1^creIL-4Rα^−/lox mice considerably impaired the host ability to down-modulate granulomatous inflammation in the liver and gut during chronic schistosomiasis. Taken together, our findings indicate that within the B cell compartment, IL-4Rα-expressing B cells in particular down-modulate the deleterious egg-driven tissue granulomatous inflammation to enable host survival during schistosomiasis in mice.

Low IL-6, IL-10, and TNF-α and High IL-13 Cytokine Levels Are Associated with Severe Hepatic Fibrosis in Schistosoma mansoni Chronically Exposed Individuals

Several studies have attributed the etiopathogenesis of chronic Schistosoma mansoni related hepatic fibrosis to unregulated immune responses against trapped parasite ova in the host. However, there is limited data on immune profiles associated with varying degrees of the disease in a population under chronic exposure to the parasite. We therefore investigated the role of selected T-helper (Th)1, Th2, and Th17 cytokines in relation to hepatic fibrosis severity among individuals resident in a hyper-Schistosoma mansoni endemic region of Western Zambia. Two hundred and forty-four S. mansoni infected individuals with and without fibrosis were analysed for cytokine profiles. Based on hepatic fibrosis stage as determined by ultrasound, participants were categorized into Group 0, Group I, Group II, and Group III. Cytokines were measured in S. mansoni egg stimulated whole blood culture supernatants using the BD Cytometric Bead Array kits. Compared to the nonfibrotic group, participants in the severe hepatic fibrotic group produced less interleukin- (IL-) 6, IL-10, and tumour necrosis factor-alpha (TNF-α). On the other hand, IL-13 was significantly elevated in this group compared to the nonfibrotic group (p < 0.001). Our results suggest that low IL-6, IL-10, and TNF-α and high IL-13 levels may influence S. mansoni disease progression.

The Metabolic Prospective and Redox Regulation of Macrophage Polarization

Macrophage plasticity is an important feature of these innate immune cells. Macrophage phenotypes are divided into two categories, the classically activated macrophages (CAM, M1 phenotype) and the alternatively activated macrophages (AAM, M2 phenotype). M1 macrophages are commonly associated with the generation of proinflammatory cytokines, whereas M2 macrophages are anti-inflammatory and often associated with tumor progression and fibrosis development. Macrophages produce high levels of reactive oxygen species (ROS). Recent evidence suggests ROS can potentially regulate macrophage phenotype. In addition, macrophages phenotypes are closely related to their metabolic patterns, particularly fatty acid/cholesterol metabolism. In this review, we briefly summarize recent advances in macrophage polarization with special attention to their relevance to specific disease conditions and metabolic regulation of polarization. Understanding these metabolic switches can facilitate the development of targeted therapies for various diseases.

Klf4 expression in conventional dendritic cells is required for T helper 2 cell responses

The two major lineages of classical dendritic cells (cDCs) express and require either IRF8 or IRF4 transcription factors for their development and function. IRF8-dependent cDCs promote anti-viral and T-helper 1 (Th1) cell responses, whereas IRF4-expressing cDCs have been implicated in controlling both Th2 and Th17 cell responses. Here, we have provided evidence that Kruppel-like factor 4 (Klf4) is required in IRF4-expressing cDCs to promote Th2, but not Th17, cell responses in vivo. Conditional Klf4 deletion within cDCs impaired Th2 cell responses during Schistosoma mansoni infection, Schistosoma egg antigen (SEA) immunization, and house dust mite (HDM) challenge without affecting cytotoxic T lymphocyte (CTL), Th1 cell, or Th17 cell responses to herpes simplex virus, Toxoplasma gondii, and Citrobacter rodentium infections. Further, Klf4 deletion reduced IRF4 expression in pre-cDCs and resulted in selective loss of IRF4-expressing cDCs subsets in several tissues. These results indicate that Klf4 guides a transcriptional program promoting IRF4-expressing cDCs heterogeneity.

Schistosomiasis-associated pulmonary hypertension

Schistosomiasis, a parasite-borne disease, is highly prevalent in Africa and Asia; it is estimated that close to 20 million people worldwide have a severe form of the disease. The chronic form can affect the gastrointestinal system and lead to hepatosplenic disease, and it may cause cardiopulmonary complications, including pulmonary hypertension. The exact pathogenesis of schistosomiasis-associated pulmonary hypertension (Sch-PH) remains unclear, although several mechanisms, including parasitic arterial embolization, pulmonary arteriopathy, and portopulmonary hypertension-like pathophysiology, have been suggested. The immunopathology of the disease is also unclear, although there are similarities with the immunology of idiopathic pulmonary arterial hypertension (PAH). Finally, the treatment of Sch-PH has not been well studied. There is some evidence on treating the underlying infection, with unclear effect on Sch-PH, and advanced PAH therapies are now being suggested, but more studies are needed to confirm their efficacy.

Beneficial autoimmunity at body surfaces - immune surveillance and rapid type 2 immunity regulate tissue homeostasis and cancer

Epithelial cells (ECs) line body surface tissues and provide a physicochemical barrier to the external environment. Frequent microbial and non-microbial challenges such as those imposed by mechanical disruption, injury or exposure to noxious environmental substances including chemicals, carcinogens, ultraviolet-irradiation, or toxins cause activation of ECs with release of cytokines and chemokines as well as alterations in the expression of cell-surface ligands. Such display of epithelial stress is rapidly sensed by tissue-resident immunocytes, which can directly interact with self-moieties on ECs and initiate both local and systemic immune responses. ECs are thus key drivers of immune surveillance at body surface tissues. However, ECs have a propensity to drive type 2 immunity (rather than type 1) upon non-invasive challenge or stress – a type of immunity whose regulation and function still remain enigmatic. Here, we review the induction and possible role of type 2 immunity in epithelial tissues and propose that rapid immune surveillance and type 2 immunity are key regulators of tissue homeostasis and carcinogenesis.

IL-25 and type 2 innate lymphoid cells induce pulmonary fibrosis

Disease conditions associated with pulmonary fibrosis are progressive and have a poor long-term prognosis with irreversible changes in airway architecture leading to marked morbidity and mortalities. Using murine models we demonstrate a role for interleukin (IL)-25 in the generation of pulmonary fibrosis. Mechanistically, we identify IL-13 release from type 2 innate lymphoid cells (ILC2) as sufficient to drive collagen deposition in the lungs of challenged mice and suggest this as a potential mechanism through which IL-25 is acting. Additionally, we demonstrate that in human idiopathic pulmonary fibrosis there is increased pulmonary expression of IL-25 and also observe a population ILC2 in the lungs of idiopathic pulmonary fibrosis patients. Collectively, we present an innate mechanism for the generation of pulmonary fibrosis, via IL-25 and ILC2, that occurs independently of T-cell-mediated antigen-specific immune responses. These results suggest the potential of therapeutically targeting IL-25 and ILC2 for the treatment of human fibrotic diseases.

Type 2 immunity and wound healing: evolutionary refinement of adaptive immunity by helminths

Helminth-induced type 2 immune responses, which are characterized by the T helper 2 cell-associated cytokines interleukin-4 (IL-4) and IL-13, mediate host protection through enhanced tissue repair, the control of inflammation and worm expulsion. In this Opinion article, we consider type 2 immunity in the context of helminth-mediated tissue damage. We examine the relationship between the control of helminth infection and the mechanisms of wound repair, and we provide a new understanding of the adaptive type 2 immune response and its contribution to both host tolerance and resistance.

Accelerated development of pulmonary fibrosis via Cu,Zn-superoxide dismutase-induced alternative activation of macrophages

Macrophages not only initiate and accentuate inflammation after tissue injury, but they are also involved in resolution and repair. This difference in macrophage activity is the result of a differentiation process to either M1 or M2 phenotypes. M1 macrophages are pro-inflammatory and have microbicidal and tumoricidal activity, whereas the M2 macrophages are involved in tumor progression and tissue remodeling and can be profibrotic in certain conditions. Because mitochondrial Cu,Zn-superoxide dismutase (Cu,Zn-SOD)-mediated H2O2 is crucial for development of pulmonary fibrosis, we hypothesized that Cu,Zn-SOD modulated the macrophage phenotype. In this study, we demonstrate that Cu,Zn-SOD polarized macrophages to an M2 phenotype, and Cu,Zn-SOD-mediated H2O2 levels modulated M2 gene expression at the transcriptional level by redox regulation of a critical cysteine in STAT6. Furthermore, overexpression of Cu,Zn-SOD in mice resulted in a profibrotic environment and accelerated the development of pulmonary fibrosis, whereas polarization of macrophages to the M1 phenotype attenuated pulmonary fibrosis. Taken together, these observations provide a novel mechanism of Cu,Zn-SOD-mediated and Th2-independent M2 polarization and provide a potential therapeutic target for attenuating the accelerated development of pulmonary fibrosis.

IL-13 Signaling in Liver Fibrogenesis

Liver fibrosis is the final common pathway of chronic liver diseases irrespective of etiology. However, etiology deeply impacts progression and characteristics of liver fibrogenesis. IL-13 is the dominant pro-fibrotic cytokine in Schistosomiasis associated liver fibrogenesis. In vitro, IL-13 directly induces expression of fibrosis-associated genes, e.g., collagens or connective tissue growth factor, in hepatic stellate cells. Recently, potential effects of IL-13 in non-Schistosomiasis associated liver fibrosis have been uncovered. This review summarizes the potential roles of IL-13 in chronic liver disease of different etiologies, and the downstream events mediating IL-13 signaling in liver fibrogenesis.

Pulmonary vascular disease associated with parasitic infection--the role of schistosomiasis

Parasitic diseases have been known to cause pulmonary vascular lesions. Schistosomiasis is the most common parasitic disease associated with pulmonary arterial hypertension, although other trematodes have been implicated. Systematic evaluation of and interest in this problem have been rekindled because of the current availability of pulmonary arterial hypertension treatment.

IL-4R{alpha}-responsive smooth muscle cells increase intestinal hypercontractility and contribute to resistance during acute Schistosomiasis

Interleukin-(IL)-4 and IL-13 signal through heterodimeric receptors containing a common IL-4 receptor-alpha (IL-4Ralpha) subunit, which is important for protection against helminth infections, including schistosomiasis. Previous studies demonstrated important roles for IL-4Ralpha-responsive hematopoietic cells, including T cells and macrophages in schistosomiasis. In this study, we examined the role of IL-4Ralpha responsiveness by nonhematopoietic smooth muscle cells during experimental acute murine schistosomiasis. Comparative Schistosoma mansoni infection studies with smooth muscle cell-specific IL-4Ralpha-deficient (SM-MHC(cre)IL-4Ralpha(-/flox)) mice, heterozygous control (IL-4Ralpha(-/flox)) mice, and global IL-4Ralpha-deficient (IL-4Ralpha(-/-)) mice were conducted. S. mansoni-infected SM-MHC(cre)IL-4Ralpha(-/flox) mice showed increased weight loss and earlier mortalities compared with IL-4Ralpha(-/flox) mice, despite comparable T(H)2/type 2 immune responses. In contrast to highly susceptible IL-4Ralpha-deficient mice, increased susceptibility in SM-MHC(cre)IL-4Ralpha(-/flox) mice was not accompanied by intestinal tissue damage and subsequent sepsis. However, both susceptible mutant mouse strains failed to efficiently expel eggs, demonstrated by egg reduction in the feces compared with control mice. Reduced egg expulsion was accompanied by impaired IL-4/IL-13-mediated hypercontractile intestinal responses, which was present in the more resistant control mice. Together, we conclude that IL-4Ralpha responsiveness by smooth muscle cells and subsequent IL-4- and IL-13-mediated hypercontractility are required for host protection during acute schistosomiasis to efficiently expel S. mansoni eggs and to prevent premature mortality.

IL-4(-/-) mice with lethal Mesocestoides corti infections--reduced Th2 cytokines and alternatively activated macrophages

Protection against Mesocestoides corti, a cestode that invades vital organs, is dependent on the production of IL-4, as IL-4(-/-) mice were found to have higher parasite burdens when compared with wild-type mice. The goal of this study was to investigate the role of IL-4 in immunity to M. corti, focusing on the immunological profile and on potential mediators of pathology. IL-4(-/-) mice infected with M. corti showed 100% mortality by 32 days, whereas wild-type mice survived for approximately 1 year. Parasite burdens were significantly increased in the liver, peritoneal, and thoracic cavities of IL-4(-/-) mice, associated with impaired recruitment of inflammatory cells and a reduction in monocytes and macrophages. IL-5 production by splenocytes and expression in liver tissue was decreased in infected IL-4(-/-) mice compared with wild-type mice. In contrast, IL-4(-/-) mice produced increased amounts of IFNgamma and TNFalpha. Alternatively activated macrophages were a major feature of liver granulomas in wild-type mice evidenced by Arginase I expression, while livers from infected IL-4(-/-) mice showed impaired alternative macrophage activation without increased classical macrophage activation. Thus, lethality during M. corti infection of IL-4(-/-) mice is associated with decreased Th2 cytokines, increased Th1 cytokines and impairment of alternatively activated macrophages.

IL-33 induces antigen-specific IL-5+ T cells and promotes allergic-induced airway inflammation independent of IL-4

Type 2 cytokines (IL-4, IL-5, and IL-13) play a pivotal role in helminthic infection and allergic disorders. CD4(+) T cells which produce type 2 cytokines can be generated via IL-4-dependent and -independent pathways. Although the IL-4-dependent pathway is well documented, factors that drive IL-4-independent Th2 cell differentiation remain obscure. We report here that the new cytokine IL-33, in the presence of Ag, polarizes murine and human naive CD4(+) T cells into a population of T cells which produce mainly IL-5 but not IL-4. This polarization requires IL-1R-related molecule and MyD88 but not IL-4 or STAT6. The IL-33-induced T cell differentiation is also dependent on the phosphorylation of MAPKs and NF-kappaB but not the induction of GATA3 or T-bet. In vivo, ST2(-/-) mice developed attenuated airway inflammation and IL-5 production in a murine model of asthma. Conversely, IL-33 administration induced the IL-5-producing T cells and exacerbated allergen-induced airway inflammation in wild-type as well as IL-4(-/-) mice. Finally, adoptive transfer of IL-33-polarized IL-5(+)IL-4(-)T cells triggered airway inflammation in naive IL-4(-/-) mice. Thus, we demonstrate here that, in the presence of Ag, IL-33 induces IL-5-producing T cells and promotes airway inflammation independent of IL-4.

Differential liver protein expression during schistosomiasis

The arrival of eggs in the liver during Schistosoma mansoni infection initiates a protective granulomatous response; however, as the infection progresses, this response results in chronic liver fibrosis. To better understand the impact of schistosomiasis on liver function, we used a proteomic approach to identify proteins whose expression was significantly altered in schistosome-infected mice 8 weeks postinfection. Identification of differentially expressed proteins by mass fingerprinting revealed that schistosome infection markedly reduced the abundance of proteins associated with several normal liver functions (i.e., citric acid cycle, fatty acid cycle, and urea cycle), while proteins associated with stress responses, acute phase reactants, and structural components were all significantly more abundant. The expression patterns of several immunity-related proteins (peroxiredoxin 1, arginase 1, and galectin 1) suggested that different protein forms are associated with schistosome infection. These findings indicate that acute schistosomiasis has a significant impact on specific liver functions and, moreover, that the alterations in specific protein isoforms and upregulation of unique proteins may be valuable as new markers of disease.

The common gamma chain cytokines interleukin (IL)-2 and IL-7 indirectly modulate blood fluke development via effects on CD4+ T cells

The human pathogen Schistosoma mansoni exhibits a highly evolved and intricate relationship with its host, evading immune destruction while co-opting CD4(+) T cell-driven mechanisms to facilitate parasite development and egg excretion. Because the common gamma ( gamma (c)) chain cytokine interleukin (IL)-7 is also implicated in modulating schistosome development, we investigated whether this effect is mediated indirectly through the essential role that IL-7 plays in CD4(+) T cell growth and survival. We demonstrate that attenuated schistosome development in the absence of IL-7 results from dysregulated T cell homeostasis and not from disruption of direct interactions between schistosomes and IL-7. We also identify an indirect role that another gamma (c) chain cytokine plays in schistosome development, demonstrating that IL-2 expression by CD4(+) T cells is essential for normal parasite development. Thus, cytokines critical for CD4(+) T cell survival and function can mediate indirect but potent effects on developing schistosomes and underscore the importance of CD4(+) T cells in facilitating schistosome development.

Tendon healing in interleukin-4 and interleukin-6 knockout mice

Cytokines have been shown to play an important role in tendon and ligament healing by regulating cellular differentiation and activity. The majority of studies that have investigated the role of cytokines in tendon and ligament healing have added them to injured tissue and assessed their effect. Because the efficacy of exogenously applying cytokines is dependent upon many factors such as the correct dosage, timing, and frequency, conflicting results are often reported. To avoid these factors, this study used transgenic mice with knockouts of interleukin-4 (IL4 -/-) and interleukin-6 (IL6 -/-) to investigate their role in tendon healing. Because of the reported roles of both of these cytokines in inflammation and fibroplasia, it was hypothesized that the order of organizational, geometric, and mechanical properties would be (greatest to least) injured IL6 -/-, injured control, and injured IL4 -/- mice. In addition, it was hypothesized that specific cytokines would be upregulated in each knockout group, but not compensate for the lack of IL-4 or IL-6. Mechanical and organizational properties of injured tendons from IL6 -/- mice were inferior to that of control and IL4 -/- mice despite the upregulation of the pro-inflammatory cytokine TNF-alpha. Temporal levels of IL-10 and IL-13 in the IL4 -/- mice resulted in comparable and even superior properties when compared to CTL mice. This study shows that IL-6 could not be compensated for and plays an important role in tendon healing. This study also supports the use of this animal model to further investigate tendon healing.

Opposing roles for IL-13 and IL-13 receptor alpha 2 in health and disease

Interleukin (IL)-13 is a key inducer of several type-2 cytokine-dependent pathologies. It regulates inflammation, mucus production, tissue remodeling, and fibrosis. Consequently, it has become an important therapeutic target for a number of debilitating illnesses, including asthma, idiopathic pulmonary fibrosis, ulcerative colitis, as well as several other diseases in which IL-13 is believed to be overproduced. In the murine model of schistosomiasis, IL-13 has emerged as a central mediator of chronic infection-induced liver pathology. Although IL-4, IL-5, IL-10, and IL-13 each regulate distinct aspects of the granulomatous inflammatory response, IL-13 was identified as the primary mediator of liver fibrosis. Thus, elucidating the mechanisms that regulate the production and function of IL-13 has become an intensive area of research. IL-13 signaling is mediated by the type-2 IL-4 receptor, which consists of the IL-4R alpha and IL-13R alpha 1 chains. However, another IL-13-binding chain, IL-13R alpha 2, appears to strongly inhibit the activity of IL-13. Animals deficient in IL-13R alpha 2 fail to downmodulate granuloma formation in the chronic phase of infection. They also develop severe IL-13-dependent fibrosis and portal hypertension and quickly succumb to the infection. Here, we summarize findings from the schistosomiasis model, which illustrate opposing activities for IL-13 and IL-13R alpha 2 in health and disease.

Effect of IL-4 and IL-13 on collagen production in cultured LI90 human hepatic stellate cells

BACKGROUND

Recently, it has been reported that interleukin 4 (IL-4) and 13 (IL-13) directly activate fibroblasts and promote fibrosis. In the process of hepatic fibrosis, the effects of these cytokines on hepatic stellate cells (HSCs) are not well known.

METHODS

We evaluated the effects of IL-4 and IL-13 on the collagen production and the proliferation of LI90, a hepatic stellate cell line. We also examined whether interferon (IFN) interferes with the expression of collagen, since IFN has been reported to clinically suppress hepatic fibrosis.

RESULTS

The receptor complex for IL-4 and IL-13 was IL-4Ralpha/IL-13Ralpha1 on LI90 cells, and the phosphorylation of Stat6 was induced by IL-4 and IL-13. The treatment of LI90 cells with IL-4 or IL-13 increased the production of collagen I protein levels by nearly three times in comparison with untreated cells. Collagen mRNA levels were increased roughly 10-fold by IL-4 and 100-fold by IL-13. Interestingly, BrdU incorporation in LI90 cells was decreased by IL-4 or IL-13 treatment. Furthermore, induction of collagen I production by these cytokines was blocked by IFNalpha or IFNbeta treatment, although neither treatment alone suppressed collagen production.

CONCLUSIONS

Our data suggested that IL-4 and IL-13 directly affected HSCs by increasing collagen production and suppressing cell proliferation. The anti-fibrogenetic effect of IFN may be due in part to the blockade of IL-4 and IL-13 stimulation of HSCs.

Helminth parasites--masters of regulation

Immune regulation by parasites is a global concept that includes suppression, diversion, and conversion of the host immune response to the benefit of the pathogen. While many microparasites escape immune attack by antigenic variation or sequestration in specialized niches, helminths appear to thrive in exposed extracellular locations, such as the lymphatics, bloodstream, or gastrointestinal tract. We review here the multiple layers of immunoregulation that have now been discovered in helminth infection and discuss both the cellular and the molecular interactions involved. Key events among the host cell population are dominance of the T-helper 2 cell (Th2) phenotype and the selective loss of effector activity, against a background of regulatory T cells, alternatively activated macrophages, and Th2-inducing dendritic cells. Increasingly, there is evidence of important effects on other innate cell types, particularly mast cells and eosinophils. The sum effect of these changes to host reactivity is to create an anti-inflammatory environment, which is most favorable to parasite survival. We hypothesize therefore that parasites have evolved specific molecular strategies to induce this conducive landscape, and we review the foremost candidate immunomodulators released by helminths, including cytokine homologs, protease inhibitors, and an intriguing set of novel products implicated in immune suppression.

Immunopathogenesis of schistosomiasis

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

Absence of interleukin-4 determines less severe pulmonary paracoccidioidomycosis associated with impaired Th2 response

Host resistance to paracoccidiodomycosis, the main deep mycosis in Latin America, is mainly due to cellular immunity and gamma interferon (IFN-gamma) production. To assess the role of interleukin-4 (IL-4), a Th2-inducing cytokine, pulmonary paracoccidioidomycosis was studied in IL-4-deficient (IL-4(-/-)) and wild-type (WT) C57BL/6 mice at the innate and acquired phases of immune response. Forty-eight hours after infection, equivalent numbers of viable Paracoccidioides brasiliensis yeast cells were recovered from the lungs of IL-4(-/-) and WT mice intratracheally infected with one million fungal cells. Alveolar macrophages from infected IL-4(-/-) mice controlled in vitro fungal growth more efficiently than macrophages from WT mice and secreted higher levels of nitric oxide. Compared with WT mice, IL-4(-/-) animals presented increased levels of pulmonary IFN-gamma and augmented polymorphonuclear leukocyte influx to the lungs. Decreased pulmonary fungal loads were characterized in deficient mice at week 2 postinfection, concomitant with diminished presence of IL-10. At week 8, lower numbers of yeasts were recovered from lungs and liver of IL-4(-/-) mice associated with increased production of IFN-gamma but impaired synthesis of IL-5 and IL-10. However, a clear shift to a Th1 pattern was not characterized, since IL-4(-/-) mice did not alter delayed-type hypersensitivity anergy or IL-2 levels. In addition, IL-4 deficiency resulted in significantly reduced levels of pulmonary IL-12, granulocyte-macrophage colony-stimulating factor, IL-3, monocyte chemotactic protein 1, and specific antibody isotypes. In IL-4(-/-) mice, well-organized granulomas restraining fungal cells replaced the more extensive lesions containing high numbers of fungi and inflammatory leukocytes developed by IL-4-sufficient mice. These results clearly showed that genetically determined deficiency of IL-4 can exert a protective role in pulmonary paracoccidioidomycosis.

Cytokine regulation in experimentally-induced Schistosoma japonicum egg granuloma formation

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

P-selectin suppresses hepatic inflammation and fibrosis in mice by regulating interferon gamma and the IL-13 decoy receptor

The selectin family of cell adhesion molecules is widely thought to promote inflammatory reactions by facilitating leukocyte recruitment. However, it was unexpectedly found that mice with targeted deletion of the P-selectin gene (PsKO mice) developed unpolarized type 1/type 2 cytokine responses and severely aggravated liver pathology following infection with the type 2-promoting pathogen Schistosoma mansoni. In fact, liver fibrosis, which is dependent on interleukin 13 (IL-13), increased by a factor of more than 6, despite simultaneous induction of the antifibrotic cytokine interferon gamma (IFN-gamma). Inflammation, as measured by granuloma size, also increased significantly in the absence of P-selectin. When infected PsKO mice were treated with neutralizing anti-IFN-gamma monoclonal antibodies, however, granuloma size was restored to wild-type levels; this finding revealed the potent proinflammatory role of IFN-gamma when expressed concomitantly with IL-13. Untreated PsKO mice also exhibited a significant (sixfold) reduction in decoy IL-13 receptor (IL-13 receptor alpha-2) expression when compared with infected wild-type animals. It is noteworthy, however, that when decoy receptor activity was restored in PsKO mice by treatment with soluble IL-13 receptor alpha-2-Fc, the exacerbated fibrotic response was completely inhibited. Thus, reduced expression of the decoy IL-13 receptor mediated by the elevated type 1 cytokine response probably accounts for the enhanced activity of IL-13 in PsKO mice and for the resultant increase in collagen deposition. In conclusion, the current study has revealed the critical role of P-selectin in the progression of chronic liver disease caused by schistosome parasites. By suppressing IFN-gamma and up-regulating the decoy IL-13 receptor, P-selectin dramatically inhibits the pathologic tissue remodeling that results from chronic type 2 cytokine-mediated inflammation.

Schistosomiasis decreases central nervous system inflammation and alters the progression of experimental autoimmune encephalomyelitis

A preestablished infection with the parasitic helminth, Schistosoma mansoni, significantly reduced the incidence and delayed the onset of experimental autoimmune encephalomyelitis (EAE) in C57BL/6J mice immunized with myelin oligodendrocyte glycoprotein (MOG)(35-55) peptide. The altered disease progression was not solely due to the induction of a strong Th2 response, since intraperitoneal injection of schistosome eggs did not affect disease development. MOG-specific gamma interferon (IFN-gamma), nitric oxide, and tumor necrosis factor alpha production by splenocytes was significantly reduced in schistosome-infected mice compared to uninfected mice. However, similar levels of interleukin-10 (IL-10) were produced in an antigen-specific manner, suggesting that the induction of antigen-specific responses was not inhibited. Analysis of in vivo cytokine production by real-time PCR indicated that IL-12p40, but not IFN-gamma, transcript levels were dramatically reduced in the spinal cords of schistosome-infected, MOG-immunized mice. Furthermore, analysis of the cellular composition of the spinal cords and brains revealed that a preestablished infection with S. mansoni decreased central nervous system (CNS) inflammation, particularly of macrophages and CD4 T cells. These results suggest that schistosomiasis may negatively regulate the onset of EAE by downregulating the production of proinflammatory cytokines and altering CNS inflammation.

IL-13 effector functions

IL-13 was first recognized for its effects on B cells and monocytes, where it upregulated class II expression, promoted IgE class switching and inhibited inflammatory cytokine production. It was also thought to be functionally redundant with IL-4. However, studies conducted with knockout mice, neutralizing antibodies, and novel antagonists demonstrate that IL-13 possesses several unique effector functions that distinguish it from IL-4. Resistance to most gastrointestinal nematodes is mediated by type-2 cytokine responses, in which IL-13 plays a dominant role. By regulating cell-mediated immunity, IL-13 modulates resistance to intracellular organisms including Leishmania major, Leishmania mexicana, and Listeria monocytogenes. In the lung, IL-13 is the central mediator of allergic asthma, where it regulates eosinophilic inflammation, mucus secretion, and airway hyperresponsiveness. Manipulation of IL-13 effector function may also prove useful in the treatment of some cancers like B-cell chronic lymphocytic leukemia and Hodgkin's disease, where IL-13 modulates apoptosis or tumor cell growth. IL-13 can also inhibit tumor immunosurveillance. As such, inhibitors of IL-13 might be effective as cancer immunotherapeutics by boosting type-1-associated anti-tumor defenses. Finally, IL-13 was revealed as a potent mediator of tissue fibrosis in both schistosomiasis and asthma, which indicates that it is a key regulator of the extracellular matrix. The mechanisms that regulate IL-13 production and/or function have also been investigated, and IL-4, IL-12, IL-18, IFN-gamma, IL-10, TGF-beta, TNF-alpha, and the IL-4/IL-13 receptor complex play important roles. This review highlights the effector functions of IL-13 and describes multiple pathways for modulating its activity in vivo.

Factors influencing Leishmania major infection in IL-4-deficient BALB/c mice

The outcome of Leishmania major infection in IL-4-deficient BALB/c mice has been a controversial subject. We have shown that IL-4-deficient BALB/c mice infected with Leishmania major developed progressive lesions and could not contain the replication of the parasites, whereas other studies have reported that IL-4-deficient mice were able to resist infection. Therefore, we examined different factors that can influence the course of Leishmania major infection. We tested different lines of IL-4-deficient BALB/c mice and show that the reported differences in the outcome of infection were not due to the different genetic origin of the embryonic stem cells used to disrupt the IL-4 gene. In addition, we infected IL-4-deficient mice with different isolates of L. major parasites and show that none of the parasite strains tested were cleared, although some of them caused milder pathology. Interestingly, this milder pathology was paralleled by a reduced arginase activity of the parasites. We also tested the influence of age on the course of Leishmania major infection in IL-4-deficient BALB/c mice and show that older mice express a transient resistance. Thus, we conclude that differences in the age of the mice and in the arginase activity of the different isolates of parasites are factors that can influence the non-healing phenotype of IL-4-/- BALB/c mice.

Disruption of the ICOS-B7RP-1 costimulatory pathway leads to enhanced hepatic immunopathology and increased gamma interferon production by CD4 T cells in murine schistosomiasis

Morbidity and mortality in schistosomiasis are largely due to an immune response mediated by CD4 T lymphocytes. Since lymphocyte activation is shaped by costimulatory signals, the specific functions of different costimulatory pathways are of increasing interest. We now examined the role of the inducible costimulatory molecule (ICOS) and its ligand B7-related protein 1 (B7RP-1) in the experimental murine schistosome infection by blocking this costimulatory pathway with monoclonal antibody against ICOS, administered daily by intraperitoneal injection during the patent phase of the disease. The treated mice exhibited enhanced hepatic immunopathology characterized by enlarged egg granulomas and pronounced parenchymal inflammation with hepatocellular necrosis, resulting in elevated liver enzyme levels in serum. Most strikingly, there was a sharp increase in gamma interferon (IFN-gamma) production by schistosome egg antigen-stimulated granuloma cells, bulk mesenteric lymph node (MLN) cells, and purified MLN CD4 T cells, which contrasted with a more discreet change in the Th2-type cytokines interleukin 4 (IL-4) and IL-10. These findings suggest that the ICOS-B7RP-1 costimulatory pathway serves primarily to control IFN-gamma production, thereby promoting a cytokine environment conducive to limited hepatic damage.

Regulation and function of the interleukin 13 receptor alpha 2 during a T helper cell type 2-dominant immune response

Highly polarized type 2 cytokine responses can be harmful and even lethal to the host if they are too vigorous or persist too long. Therefore, it is important to elucidate the mechanisms that down-regulate these reactions. Interleukin (IL)-13 has emerged as a central mediator of T helper cell (Th)2-dominant immune responses, exhibiting a diverse array of functional activities including regulation of airway hyperreactivity, resistance to nematode parasites, and tissue remodeling and fibrosis. Here, we show that IL-13 receptor (R)alpha2 is a critical down-regulatory factor of IL-13-mediated tissue fibrosis induced by the parasitic helminth Schistosoma mansoni. IL-13Ralpha2 expression was induced after the onset of the fibrotic response, IL-10, IL-13, and Stat6 dependent, and inhibited by the Th1-inducing adjuvant IL-12. Strikingly, schistosome-infected C57BL/6 and BALB/c IL-13Ralpha2-deficient mice showed a marked exacerbation in hepatic fibrosis, despite displaying no change in granuloma size, tissue eosinophilia, or mastocytosis. Fibrosis increased despite the fact that IL-13 levels decreased significantly in the liver and serum. Importantly, pathology was prevented when IL-13Ralpha2-deficient mice were treated with a soluble IL-13Ralpha2-Fc construct, formally demonstrating that their exacerbated fibrotic response was due to heightened IL-13 activity. Together, these studies illustrate the central role played by the IL-13Ralpha2 in the down-regulation of a chronic and pathogenic Th2-mediated immune response.

Development of colitis in signal transducers and activators of transcription 6-deficient T-cell receptor alpha-deficient mice: a potential role of signal transducers and activators of transcription 6-independent interleukin-4 signaling for the generation of Th2-biased pathological CD4+ betabetaT cells

Forbidden CD4(+)betabeta T cells, which produce interleukin (IL)-4 predominantly, are a pathological subset in the development of colitis in T-cell receptor alpha chain (TCRalpha)-deficient mice. Stimulation of naive CD4(+) T cells with IL-4 induces Th2 development via the activation of signal transducers and activators of transcription (STAT) 6. In the present study, we had found that IL-4 enhanced the expression of STAT6 in CD4(+)betabeta T cells isolated from TCRalpha(-/-) mice with colitis, suggesting that the IL-4 signal in the CD4(+)betabeta T cells is mediated by STAT6. To further investigate the role of STAT6 in the development of colitis induced by TCRalpha deficiency, we generated double-deficient mice by crossing TCRalpha(-/-) mice and STAT6(-/-) mice. Surprisingly, STAT6 deficiency did not result in decreased severity of colitis in TCRalpha(-/-) mice. STAT6-deficient CD4(+)betabeta T cells produced IL-4 and intraperitoneal injection of anti-IL-4 monoclonal antibody in the nondiseased TCRalpha(-/-) and STAT6 double-deficient mice prevented the colitis formation, thus indicating that the cells differentiated into the Th2 phenotype have the ability to mediate the development of the colitis in the absence of STAT6.

Lack of C3 affects Th2 response development and the sequelae of chemotherapy in schistosomiasis

The role of the third component of complement (C3) during schistosome infection was investigated using mice deficient in C3. While no effect was observed 8 wk after infection on worm development or liver pathology, Ag-specific Th2-associated cytokine production (IL-13, IL-5, IL-6, and IL-10) was significantly reduced, and IFN-gamma production was enhanced in the absence of C3. IgG1 and IgE, but not IgG2a or IgM, Ab responses were also significantly impaired in infected C3(-/-) mice, suggesting that C3 may play a role in IL-4-mediated Th2 response enhancement during schistosome infection. Furthermore, C3-deficient mice could not effectively clear adult worms after praziquantel (PZQ) treatment and suffered increased morbidity due to the overproduction of proinflammatory mediators following drug administration. However, the ischemic liver damage that normally accompanies PZQ administration in infected wild-type mice was substantially reduced in treated C3-deficient mice, probably due to the absence of dead or dying worms in the livers of these animals. Together these results indicate that C3 enhances Th2 responses during schistosome infection, potentiates PZQ-mediated parasite clearance, and reduces chemotherapy-induced proinflammatory mediator production.

Persistence of bronchopulmonary hyper-reactivity and eosinophilic lung inflammation after anti-IL-5 or -IL-13 treatment in allergic BALB/c and IL-4Ralpha knockout mice

BACKGROUND

Antigen-induced bronchopulmonary hyper-reactivity (BHR) is generally associated with eosinophilia. It involves cytokines produced by Th2 lymphocytes, including IL-4, IL-5 and IL-13, which are implicated in IgE production, eosinophil differentiation and attraction, and related events relevant to allergic inflammation, whose mechanisms remain unclear.

OBJECTIVE

To investigate the mechanisms by which Th2 cytokines mediate eosinophilia and subsequent BHR using ovalbumin (OVA)-immunized and OVA-challenged IL-4Ralpha-/- and IL-4-/- mice, which fail to transduce and/or to produce IL-4 and IgE as compared with wild type (WT) mice, and specific neutralizing antibodies.

METHODS

On days 0 and 7, mice were immunized subcutaneously (s.c.) with OVA. At day 14, anti-IL-5 or anti-IL-13 antibodies were administered intranasally and/or intravenously before allergenic challenge. Different functional and cellular parameters were studied in vivo and cytokine production was followed with a newly described ex vivo procedure using lung explants.

RESULTS

IL-4Ralpha-/- and IL-4-/- mice developed BHR and pulmonary eosinophilia, even though eosinophil recruitment to the bronchoalveolar liquid lavage (BALF) was reduced. In vivo, IL-4-/- and IL-4Ralpha-/- mice produced, respectively, no or reduced amounts of IL-5 in the BALF/serum as compared with WT mice, whereas no IL-13 in the BALF was detected. By contrast, ex vivo, surviving lung explants from WT and IL-4-/- or IL-4Ralpha-/- mice produced IL-13 and large amounts of IL-5. The neutralization of IL-5 in vivo (BALF and serum) and ex vivo (from lung explant) in IL-4Ralpha-/- and WT mice failed to suppress BHR and lung eosinophilia, and to modify IL-13 production ex vivo. In addition, neutralization of IL-13 in vivo from lung explant also failed to abrogate BHR and lung eosinophilia, whereas IL-5 was unchanged.

CONCLUSION

Antigen-induced BHR can develop independently from IL-4, IL-5 or IL-13 and from the IL-4alpha receptor chain, suggesting a possible novel IL-4, IL-5 and IL-13-independent pathway for the development of BHR in allergic BALB/c mice. The failure of IL-5 or IL-13 antibodies to prevent BHR in IL-4Ralpha-/- mice suggests that neither is indispensable for BHR but does not exclude a role for lung tissue eosinophilia.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Interleukin-13 fusion cytotoxin arrests Schistosoma mansoni egg-induced pulmonary granuloma formation in mice

Schistosoma mansoni egg-induced lung pathology requires the actions of interleukin (IL)-4 and IL-13. Because receptors for IL-4 and IL-13 share chains, we examined the effect of a fusion protein comprised of IL-13 and Pseudomonas exotoxin (IL13-PE) on the development of pulmonary granulomas in mice. At day 8 after an intravenous injection of live S. mansoni eggs, whole lung samples from IL13-PE-treated mice exhibited significantly lower IL-4 and IL-13 gene expression, smaller granulomas, decreased collagen levels, and increased IL-13 receptor alpha2 gene expression compared to controls. The therapeutic effects of IL13-PE were also observed at day 16 despite the termination of IL13-PE treatment at day 8. These studies demonstrate that targeting IL-4- and IL-13- responsive cells with IL13-PE effectively arrests S. mansoni egg granuloma formation.

Interaction of IL-13 and C10 in the pathogenesis of bleomycin-induced pulmonary fibrosis

The initial stimulus for inflammatory cell recruitment and the mechanisms responsible for the perpetuation and evolution of chronic inflammation, granulation tissue formation, and fibrosis have not been fully elucidated. Although interleukin (IL)-13, a Th2 cytokine, has been shown to have direct effects on fibroblasts that support fibroproliferation, it is also a potent inducer of a novel CC chemokine, C10, which is chemotactic for mononuclear phagocytes. The macrophage/mononuclear phagocyte has been shown to have a role in the pathogenesis of pulmonary fibrosis, serving as an important source of growth factors that regulate extracellular matrix synthesis. In this study we demonstrate that IL-13 and C10 are elevated in the pathogenesis of bleomycin-induced pulmonary fibrosis. Neutralization of IL-13, but not IL-4, attenuated bleomycin-induced pulmonary fibrosis and levels of C10, suggesting that IL-13 has an important role in the development of pulmonary fibrosis. IL-13 is a potent inducer of C10 in vivo, and neutralization of C10 attenuated bleomycin-induced pulmonary fibrosis and intrapulmonary macrophage numbers. This suggests that IL-13 has a role in the development of pulmonary fibrosis that is independent of its direct effect on fibroblasts and is evidence for an interaction between Th2 cytokines and specific CC chemokines.

[Contribution of experimental models to the understanding of immunity to schistosomiasis]

The discovery of a functional division in T helper cells on the basis of their cytokine secretion patterns has changed our vision of immunological responses. This dichotomy has equally shown the complexity of immune responses since there is a well orchestrated cross-regulation of cytokine production induced by viral, bacterial or parasitic pathogens. In the context of type 1-type 2 cytokine pattern, mice has been universally and extensively used to associate an infectious disease according to each category in order to better understand human infections. However, with respect to schistosomiasis, immunological observations in mice have not been confirmed in humans and particularly the nature of the protective immune response. This report will consider the relevance of extrapolating from immunological studies on schistosome in experimentally infected rats to studies on naturally infected humans.

Role of gamma interferon in the pathogenesis of severe schistosomiasis in interleukin-4-deficient mice

In the absence of interleukin-4 (IL-4), infection with Schistosoma mansoni leads to a severe fatal disease rather than the chronic survivable condition that occurs in wild-type (WT) mice. Because the sustained production of NO most closely correlates to weight loss and fatality in infected IL-4(-/-) mice and because gamma interferon (IFN-gamma) is an important inducer of inducible NO synthase, infected IL-4(-/-) mice were treated with anti-IFN-gamma antibodies to determine the role of IFN-gamma during schistosomiasis in WT and IL-4(-/-) animals. When IFN-gamma was neutralized, Th2 responses were enhanced and NO production was reduced in both WT and IL-4(-/-) mice. The decreased NO production correlated with a rescue of proliferation in splenocytes from infected IL-4(-/-) mice. Furthermore, the neutralization of IFN-gamma in vivo improved the gross appearance of the liver and led to a reduction in granuloma size in infected IL-4(-/-) but not WT mice. However, the neutralization of IFN-gamma in vivo did not affect the development of severe disease in infected IL-4(-/-) mice. These results suggest that while the increased production of IFN-gamma does lead to some of the pathology observed in infected IL-4(-/-) mice, it is not ultimately responsible for cachexia and death.

Th1-polarizing immunization with egg antigens correlates with severe exacerbation of immunopathology and death in schistosome infection

In schistosomiasis mansoni, parasite eggs precipitate an intrahepatic granulomatous and fibrosing inflammatory process, which is mediated by, and dependent on, MHC class II-restricted CD4 T helper (Th) lymphocytes specific for schistosome egg antigens (SEA). In the mouse model of the disease, CBA mice develop large granulomas, whereas in C57BL/6 (BL/6) mice these granulomas are significantly smaller. To further investigate how the prevailing cytokine environment influences the development of the egg-induced immunopathology, we immunized the low-pathology BL/6 mice with SEA in complete Freund's adjuvant (CFA) once before, and once again during, the course of a 7-week infection. This immunization caused a pronounced Th1 shift in the SEA-specific CD4 T cell response, which was detected in the mesenteric lymph nodes (MLNs) and spleens, as well as in the granulomatous lesions themselves. The immunized mice displayed a dramatic enhancement of hepatic egg-induced immunopathology manifested by a marked increase in granuloma size and parenchymal inflammation, leading to early death. Control mice immunized with equivalent amounts of SEA or CFA alone displayed the smaller hepatic lesions in a Th2-dominant environment typically seen in the unimmunized BL/6 mice. Analysis of granuloma and MLN lymphocytes from the SEA/CFA-immunized mice revealed that the proportion of CD4 T cells was unchanged in comparison with the control BL/6 groups and remained significantly lower than that seen in the normally high-pathology CBA strain. These results suggest that the shift toward Th1-type cytokine production by a numerically stable population of CD4 T cells correlates with severe exacerbation of immunopathology in schistosomiasis.

Murine schistosomiasis mansoni: coordinate cytokine regulation and differences in cellular immune responses of granuloma cells and splenocytes to endogenous and exogenous schistosome egg antigens

To better understand the cellular immune mechanisms that regulate granulomatous inflammation to Schistosoma mansoni ova, we examined the dynamics of lymphocyte proliferation and cytokine expression by granuloma cells and splenocytes to endogenous and exogenous schistosome egg antigen (SEA) 6-19 weeks postinfection. Compared to splenocytes, granuloma cells (partially CD4+ cells) which are at the site of antigen release were highly activated by endogenous SEA and terminally differentiated as indicated by the more than 10-fold greater frequency of ex vivo interleukin (IL)-4, IL-5 and interferon (IFN)-gamma -secreting cells, greater levels of constitutive cytokine production and failure to proliferate to either endogenous or exogenous SEA. Endogenous cytokine production by granuloma cells was coordinately regulated, enhanced little by exogenous SEA, and temporally correlated with granulomatous inflammation. By contrast, CD4+ splenocytes produced comparatively little cytokine release by endogenous antigen, whereas exogenous SEA strongly induced IL-4, IL-5, IL-10 and IFN-gamma production and lymphocyte proliferation that correlated poorly with the dynamics of granulomatous inflammation. These results show that cytokine responses to endogenous SEA correlated better with granulomatous inflammation than responses to exogenous SEA. Furthermore, granuloma cells and splenocytes demonstrated strikingly different proliferative responses and dynamics of cytokine expression, suggesting that how SEA reactive lymphocytes traffic between lymphoid tissues and the granuloma is critical to a better understanding of the mechanisms of granulomatous inflammation and its modulation.

Therapeutic effect of IL-13 immunoneutralization during chronic experimental fungal asthma

IL-13 and IL-4 are key contributors to the asthmatic phenotype. The temporal role of these cytokines in airway function, inflammation, and remodeling were assessed in a chronic murine model of Asperigillus fumigatus-induced allergic asthma. IL-13 and IL-4 protein levels were significantly elevated by 30 days after conidia challenge in A. fumigatus-sensitized mice. Furthermore, IL-13Ralpha1 mRNA expression was significantly elevated 7 days after conidia challenge and remained elevated until day 21. In contrast, IL-13Ralpha2 mRNA expression, although constitutively expressed in naive lung, was absent in the lungs of A. fumigatus-sensitized mice both before and after conidia challenge. Membrane-bound IL-4R mRNA expression was significantly elevated 7 days after conidia challenge; however, soluble IL-4R mRNA expression was increased 30 days after conidia challenge. Immunoneutralization of IL-13 between days 14 and 30 or days 30 and 38 after fungal sensitization and challenge significantly attenuated airway hyperresponsiveness, collagen deposition, and goblet cell hyperplasia at day 38 after conidia challenge; however, the effects of IL-4 immunoneutralization during the same time periods were not as marked. IFN-gamma and IL-12 release after Aspergillus Ag restimulation was elevated from spleen cells isolated from mice treated with IL-4 anti-serum compared with IL-13 anti-serum or normal rabbit serum-treated mice. This study demonstrates a pronounced therapeutic effect of IL-13-immunoneutralization at extended time points following the induction of chronic asthma. Most importantly, these therapeutic effects were not reversed following cessation of treatment, and IL-13 anti-serum treatment did not alter the systemic immune response to Ag restimulation, unlike IL-4 immunoneutralization. Therefore, IL-13 provides an attractive therapeutic target in allergic asthma.

IL-4 plays a crucial role in regulating oxidative damage in the liver during schistosomiasis

Liver enlargement and hepatocyte proliferation, normal responses in wild-type (WT) mice infected with the parasitic helminth Schistosoma mansoni, were found to be severely impaired in infected IL-4(-/-) mice. Compared with WT mice, increased levels of O(2)(-), NO, and the more highly reactive ONOO(-) were detected in the liver and produced by lesional cells isolated from liver granulomas of infected IL-4(-/-) mice. Concurrently, antioxidant defenses in the liver, specifically catalase levels, diminished dramatically during the course of infection in these animals. This contrasted to the situation in infected WT mice, where catalase levels remained as high as those in normal mice. Actual levels of reactive oxygen and nitrogen intermediates in the livers of infected IL-4(-/-) animals are thus likely to be considerably higher than those in the livers of infected WT mice. To determine whether these changes contributed to the development of the more severe disease that characterizes infection in the IL-4(-/-) animals, we treated infected IL-4(-/-) mice with uric acid, a potent scavenger of ONOO(-). This resulted in significantly increased hepatocyte proliferation, decreased morbidity, and prolonged survival. Taken together, these data indicate that IL-4 is playing a protective role during schistosomiasis by controlling the tight regulation of the generation of reactive oxygen and nitrogen intermediates in the liver.

Signaling via interleukin-4 receptor alpha chain is required for successful vaccination against schistosomiasis in BALB/c mice

Although protective immunity in C57BL/6 mice induced by a single dose of the radiation-attenuated schistosome vaccine is believed to be mediated by Th1-type immune responses, we here report that in BALB/c mice protection can also depend upon signaling via the interleukin-4 (IL-4) receptor which conventionally governs the development of Th2-type immune responses. We show that in BALB/c mice deficient for the IL-4 receptor alpha chain (IL-4Ralpha(-/-)), which are unresponsive to IL-4 and IL-13, vaccine-induced protection is abrogated compared with that in wild-type (WT) mice. In vaccinated IL-4Ralpha(-/-) mice, IL-12p40 production by cells from the skin exposure site was elevated, although gamma interferon (IFN-gamma) production in draining lymphoid tissues was similar in WT and IL-4Ralpha(-/-) mice. Nevertheless, the effector response in IL-4Ralpha(-/-) mice was Th1 biased with elevated IFN-gamma in the lungs and higher immunoglobulin G2a (IgG2a) and IgG2b titers but negligible quantities of Th2-associated IgG1 and IgE. Interestingly, levels of IL-4 were equivalent in WT and IL-4Ralpha(-/-) mice, indicating that Th2 responses were not dependent upon signaling by IL-4 or IL-13. No differences in the phenotype and composition of the pulmonary effector mechanism that might explain the failure to induce protection in IL-4Ralpha(-/-) mice were detected. However, passive transfer of partial protection to naive IL-4Ralpha(-/-) mice, using serum from vaccinated WT mice, indicates that Th2-associated antibodies such as IgG1 have a role in parasite elimination in BALB/c strain mice and that signaling via IL-4R can be an important factor in the generation of protection.

Severe schistosomiasis in the absence of interleukin-4 (IL-4) is IL-12 independent

An interleukin-4 (IL-4)-dependent Th2 response allows wild-type mice to survive infection with the parasite Schistosoma mansoni. In the absence of IL-4, infected mice mount a Th1-like proinflammatory response, develop severe disease, and succumb. Neither the Th1 response nor morbidity is IL-12 dependent in this system.

Role of IgE in primary murine Schistosomiasis mansoni

Schistosoma mansoni infection proceeds in normal mice in the absence of detectable levels of polyclonal or specific immunoglobulin (Ig)E until worms mature and deposit eggs. Hence, the course of a primary S. mansoni infection is not expected to vary appreciably in mice with defects in the IgE production. Experimental increase of IgE production early after infection may, however, influence worm development. In the first approach towards this goal, BALB/c mice were injected with interleukin(IL)4 to raise the level of endogenously synthesized IgE. A significant increase in serum polyclonal IgE and antischistosome IgG1 during the prepatent period was not associated with significant changes in worm and egg burden or liver pathology. During the second approach, mice were injected with IgE which was affinity purified from serum of BALB/c mice infected for 16 weeks with S. mansoni. The purified IgE bound to carbohydrate-independent epitopes of soluble antigens from 3 h larvae, adult worms and eggs and recognized the schistosomular surface membrane. No differences in worm and egg load or granuloma number and size were noted between untreated and exogenous IgE-injected mice. Together, the data demonstrate that by itself IgE does not influence the outcome of infection in primary murine S. mansoni.

The Schistosoma mansoni egg-derived r38 peptide-induced Th1 response affects the synchronous pulmonary but not the asynchronous hepatic granuloma growth

The p38 peptide derived from Schistosoma mansoni egg-antigens (SEA) is a preferential inducer of the Th1 response. In the present study, we investigated whether induction of a p38-specific Th1 or Th2 response can influence granuloma development in infected or sensitized mice. Mice sensitized with SEA/IL-12 3 weeks after infection but before worm oviposition commenced developed Th1 cytokine responses and had significantly reduced hepatic granuloma size. Similar immunization with p38/IL-12 induced a strong peptide-specific Th1, mixed SEA-specific Th1/Th2 responses without effect on hepatic granuloma development. Presentation of p38 with alum or alum/IL-12 mixture enhanced Th2 cytokine responses and hepatic granuloma sizes. In the synchronized pulmonary model, sensitization of naïve mice with p38/IL-12 induced a strong Th1 cytokine production to p38 and SEA, led to a moderate increase in granuloma growth at days 4 and 8 following egg injection and actually promoted the resolution of the lesion by day 16. Sensitization with p38 in alum induced Th2 cytokine production and generated the largest granulomas whereas the p38/alum/IL-12 sensitized group showed intermediate results in cytokine production and granuloma growth. Thus, in infected mice, the p38 induced strong Th1 response was insufficient to cross-regulate the evolving Th2 environment that generated large granulomas.