Antigen presentation by CD1d contributes to the amplification of Th2 responses to Schistosoma mansoni glycoconjugates in mice

Intra-specific variations in Schistosoma mansoni and their possible contribution to inconsistent virulence and diverse clinical outcomes

BACKGROUND

Schistosoma mansoni was introduced from Africa to the Americas during the transatlantic slave trade and remains a major public health problem in parts of South America and the Caribbean. This study presents a comprehensive comparative analysis of three S. mansoni strains with different geographical origins-from Liberia, Belo Horizonte and Puerto Rico. We demonstrated significant variation in virulence and host-parasite interactions.

METHODS

We investigated the phenotypic characteristics of the parasite and its eggs, as well as the immunopathologic effects on laboratory mouse organ systems.

RESULTS

Our results show significant differences in worm morphology, worm burden, egg size, and pathologic organ changes between these strains. The Puerto Rican strain showed the highest virulence, as evidenced by marked liver and spleen changes and advanced liver fibrosis indicated by increased collagen content. In contrast, the strains from Liberia and Belo Horizonte had a less pathogenic profile with less liver fibrosis. We found further variations in granuloma formation, cytokine expression and T-cell dynamics, indicating different immune responses.

CONCLUSION

Our study emphasizes the importance of considering intra-specific variations of S. mansoni for the development of targeted therapies and public health strategies. The different virulence patterns, host immune responses and organ pathologies observed in these strains provide important insights for future research and could inform region-specific interventions for schistosomiasis control.

Praziquantel Reduces Maternal Mortality and Offspring Morbidity by Enhancing Anti-Helminthic Immune Responses

Alongside the wide distribution throughout sub Saharan Africa of schistosomiasis, the morbidity associated with this chronic parasitic disease in endemic regions is often coupled with infection-driven immunomodulatory processes which modify inflammatory responses. Early life parasite exposure is theorized to drive immune tolerance towards cognate infection as well as bystander immune responses, beginning with in utero exposure to maternal infection. Considering that 40 million women of childbearing-age are at risk of infection worldwide, treatment with Praziquantel during pregnancy as currently recommended by WHO could have significant impact on disease outcomes in these populations. Here, we describe the effects of anthelminthic treatment on parasite-induced changes to fetomaternal cross talk in a murine model of maternal schistosomiasis. Praziquantel administration immediately prior to mating lead to clear re-awakening of maternal anti-parasite immune responses, with persistent maternal immune activation that included enhanced anti-schistosome cytokine responses. Clearance of parasites also improved capacity of dams to endure the additional pressure of pregnancy during infection. Maternal treatment also drove lasting functional alterations to immune system development of exposed offspring. Prenatal anthelminthic treatment skewed offspring immune responses towards parasite clearance and reduced morbidity during cognate infection. Maternal treatment also restored offspring protective IgE antibody responses directed against schistosome antigens, which were otherwise suppressed following exposure to untreated maternal infection. This was further associated with enhanced anti-schistosome cytokine responses from treatment-exposed offspring during infection. In the absence of cognate infection, exposed offspring further demonstrated imprinting across cellular populations. We provide further evidence that maternal treatment can restore a more normalized immune profile to such offspring exposed in utero to parasite infection, particularly in B cell populations, which may underlie improved responsiveness to cognate infection, and support the WHO recommendation of anthelminthic treatment during pregnancy.

Type 2 immunity: a two-edged sword in schistosomiasis immunopathology

Schistosomiasis is the second most debilitating neglected tropical disease globally after malaria, with no available therapy to control disease-driven immunopathology. Although schistosomiasis induces a markedly heterogenous immune response, type 2 immunity is the dominating immune response following oviposition. While type 2 immunity has a crucial role in granuloma formation and host survival during the acute stage of disease, its chronic activation can result in tissue scarring, fibrosis, and organ impairment. Here, we discuss recent advances in schistosomiasis, demonstrating how different immune and non-immune cells and signaling pathways are involved in the induction, maintenance, and regulation of type 2 immunity. A better understanding of these immune responses during schistosomiasis is essential to inform the potential development of candidate therapeutic strategies that fine-tune type 2 immunity to ideally modulate schistosomiasis immunopathology.

Switched phenotypes of macrophages during the different stages of Schistosoma japonicum infection influenced the subsequent trends of immune responses

BACKGROUND

Macrophages play crucial roles in immune responses during the course of schistosomal infections.

METHODS

We currently investigated influence of immunocompetent changes in macrophages via microarray-based analysis, mRNA expression analysis, detection of serum cytokines, and subsequent evaluation of the immune phenotypes following the differentiation of infection-induced lymphocytes in a unique T1/T2 double-transgenic mouse model.

RESULTS

The gradual upregulation of genes encoding YM1, YM2, and interleukin (IL)-4/IL-13 receptors in infected mice indicated the role of type 2 alternatively activated macrophages (M2, AAMφs) in immune responses after Schistosoma japonicum egg production. FACS analysis showed that surface markers MHC class II (IA/IE) and CD8α⁺ of the macrophages also exhibited a dramatic change at the various time points before and after egg-production. The transgenic mouse experiments further demonstrated that the shifting of macrophage phenotypes influenced the percentage of helper T (Th)-2 cells, which was observed to be higher than that of Th1 cells, which increased only at 3 and 5 weeks post-infection. The differentiation of effector B cells showed a similar but more significant trend toward type-2 immunity.

CONCLUSION

These results suggest that the infection of mice with S. japonicum resulted in a final Th2- and Be2-skewed immune response. This may be due to phenotypic changes in the macrophages. The influence of alternatively activated macrophages was also activated by S. japonicum egg production. This study elucidated the existence of variations in immune mechanisms at the schistosome infection stages.

Hygiene hypothesis and autoimmune diseases: A narrative review of clinical evidences and mechanisms

Since the start of the "modern era", characterized by the increase in urbanization, a progressive attention to hygiene and autoimmune conditions has considerably grown. Although these diseases are often multifactorial, it was demonstrated that environment factors such as pollution, diet and lifestyles may play a crucial role together with genetic signature. Our research, based on the newest and most significant literature of this topic, highlights that the progressive depletion of microbes and parasites due to increased socioeconomic improvement, may lead to a derangement of immunoregulatory mechanisms. Moreover, special attention was given to the complex interplay between microbial agents, as gut microbiome, diet and vitamin D supplementation with the aim of identifying promising future therapeutic options. In conclusion, autoimmunity cannot be limited to hygiene-hypothesis, but from the point of view of precision medicine, this theory represents a fundamental element together with the study of genomics, the microbiome and proteomics, in order to understand the complex functioning of the immune system.

Hepatocyte CD1d protects against liver immunopathology in mice with schistosomiasis japonica

Schistosomiasis is a neglected tropical disease with over 250 million people infected worldwide. The main clinically important species Schistosoma mansoni (S. mansoni) and Schistosoma japonicum (S. japonicum) cause inflammatory responses against tissue-trapped eggs, resulting in formation of granulomas mainly in host liver. Persistent granulomatous response results in severe fibrosis in the liver, leading to irreversible impairment of the liver and even death of the host. CD1d, a highly conserved MHC class I-like molecule, is expressed by both haematopoietic and non-haematopoietic cells. CD1d on antigen-presenting cells (APCs) of haematopoietic origin presents pathogen-derived lipid antigens to natural killer T (NKT) cells, which enables them to rapidly produce large amounts of various cytokines and facilitate CD4⁺ T helper (Th) cell differentiation upon invading pathogens. Noteworthy, hepatocytes of non-haematopoietic origin have recently been shown to be involved in maintaining liver NKT cell homeostasis through a CD1d-dependent manner. However, whether hepatocyte CD1d-dependent regulation of NKT cell homeostasis also modulates CD4⁺ Th cell responses and liver immunopathology in murine schistosomiasis remains to be addressed. Here, we show in mice that CD1d expression on hepatocytes was decreased dramatically upon S. japonicum infection, accompanied by increased NKT cells, as well as upregulated Th1 and Th2 responses. Overexpression of CD1d in hepatocytes significantly decreased local NKT numbers and cytokines (IFN-γ, IL-4, IL-13), concomitantly with downregulation of both Th1 and Th2 responses and alleviation in pathological damage in livers of S. japonicum-infected mice. These findings highlight the potential of hepatocyte CD1d-targeted therapies for liver immunopathology control in schistosomiasis.

Toll-like receptor-2 regulates macrophage polarization induced by excretory-secretory antigens from Schistosoma japonicum eggs and promotes liver pathology in murine schistosomiasis

Schistosomiasis is endemic to many regions of the world and affects approximately 200 million people. Conventional adaptive T cell responses are considered to be the primary contributors to the pathogenesis of Schistosoma japonicum infection, leading to liver granuloma and fibrosis. However, the functional polarization of macrophages and the associated underlying molecular mechanisms during the pathogenesis of schistosomiasis remains unknown. In the present study, we found that excretory-secretory (ES) antigens derived from S. japonicum eggs can activate macrophages, which exhibit an M2b polarization. Furthermore, ES antigen-induced M2b polarization was found to be dependent on enhanced NF-κB signaling mediated by the MyD88/MAPK pathway in a TLR2-dependent manner. In addition, the cytokine profile of the liver macrophages from wild-type-infected mice are quite distinct from those found in TLR2 knockout-infected mice by quantitative PCR analysis. More importantly, the size of granuloma and the severity of the fibrosis in the livers of TLR2^-/- mice were significantly reduced compared to that in WT mice. Our findings reveal a novel role for M2b polarization in the pathogenesis of schistosome infection.

Schistosomiasis is a global health concern that affects primarily tropical and subtropical areas. During a schistosome infection, the eggs are trapped in the host liver and products derived from eggs induce a polarized Th2 response, resulting in granuloma formation and eventually fibrosis. Thus, it is important to elucidate the mechanism of granuloma formation and fibrosis development. Here, we show that activated macrophages play a novel role in the promotion of hepatic granuloma formation and liver fibrosis in a Schistosoma japonicum-infected mouse model. In addition, M2b polarization induced by egg products was dependent on enhanced NF-κB signaling mediated by the MyD88/MAPK pathway in a TLR2-dependent manner. Our findings reveal a novel role and mechanism of M2b polarization in the liver pathogenesis in S. japonicum-infected mice.

Type II NKT cells: a distinct CD1d-restricted immune regulatory NKT cell subset

Type II natural killer T cells (NKT) are a subset of the innate-like CD1d-restricted lymphocytes that are reactive to lipid antigens. Unlike the type I NKT cells, which express a semi-invariant TCR, type II NKT cells express a broader TCR repertoire. Additionally, other features, such as their predominance over type I cells in humans versus mice, the nature of their ligands, CD1d/lipid/TCR binding, and modulation of immune responses, distinguish type II NKT cells from type I NKT cells. Interestingly, it is the self-lipid-reactivity of type II NKT cells that has helped define their physiological role in health and in disease. The discovery of sulfatide as one of the major antigens for CD1d-restricted type II NKT cells in mice has been instrumental in the characterization of these cells, including the TCR repertoire, the crystal structure of the CD1d/lipid/TCR complex, and their function. Subsequently, several other glycolipids and phospholipids from both endogenous and microbial sources have been shown to activate type II NKT cells. The activation of a specific subset of type II NKT cells following administration with sulfatide or lysophosphatidylcholine (LPC) leads to engagement of a dominant immunoregulatory pathway associated with the inactivation of type I NKT cells, conventional dendritic cells, and inhibition of the proinflammatory Th1/Th17 cells. Thus, type II NKT cells have been shown to be immunosuppressive in autoimmune diseases, inflammatory liver diseases, and in cancer. Knowing their relatively higher prevalence in human than type I NKT cells, understanding their biology is imperative for health and disease.

Tropheryma whipplei infection and Whipple's disease

Recent advances in medical microbiology, epidemiology, cellular biology, and the availability of an expanded set of diagnostic methods such as histopathology, immunohistochemistry, PCR, and bacterial culture have improved our understanding of the clinical range and natural course of Tropheryma whipplei infection and Whipple's disease. Interdisciplinary and transnational research activities have contributed to the clarification of the pathogenesis of the disorder and have enabled controlled trials of different treatment strategies. We summarise the current knowledge and new findings relating to T whipplei infection and Whipple's disease.

Helminth therapy for organic diseases?

Autoimmune and chronic inflammatory organic diseases represent a "postindustrial revolution epidemics," and their frequency has increased dramatically in the last century. Today, it is assumed that the increase in hygiene standards reduced the interactions with helminth parasites that coevolved with the immune system and are crucial for its proper functioning. Several helminths have been proposed and tested in the search of the ideal therapeutic. In this review, the authors summarize the translational and clinical studies and review the caveats and possible solutions for the optimization of helminth therapies.

The Extended Family of CD1d-Restricted NKT Cells: Sifting through a Mixed Bag of TCRs, Antigens, and Functions

Natural killer T (NKT) cells comprise a family of specialized T cells that recognize lipid antigens presented by CD1d. Based on their T cell receptor (TCR) usage and antigen specificities, CD1d-restricted NKT cells have been divided into two main subsets: type I NKT cells that use a canonical invariant TCR α-chain and recognize α-galactosylceramide (α-GalCer), and type II NKT cells that use a more diverse αβ TCR repertoire and do not recognize α-GalCer. In addition, α-GalCer-reactive NKT cells that use non-canonical αβ TCRs and CD1d-restricted T cells that use γδ or δ/αβ TCRs have recently been identified, revealing further diversity among CD1d-restricted T cells. Importantly, in addition to their distinct antigen specificities, functional differences are beginning to emerge between the different members of the CD1d-restricted T cell family. In this review, while using type I NKT cells as comparison, we will focus on type II NKT cells and the other non-invariant CD1d-restricted T cell subsets, and discuss our current understanding of the antigens they recognize, the formation of stimulatory CD1d/antigen complexes, the modes of TCR-mediated antigen recognition, and the mechanisms and consequences of their activation that underlie their function in antimicrobial responses, anti-tumor immunity, and autoimmunity.

Schistosoma mansoni Soluble Egg Antigens Induce Expression of the Negative Regulators SOCS1 and SHP1 in Human Dendritic Cells via Interaction with the Mannose Receptor

Schistosomiasis is a common debilitating human parasitic disease in (sub)tropical areas, however, schistosome infections can also protect against a variety of inflammatory diseases. This has raised broad interest in the mechanisms by which Schistosoma modulate the immune system into an anti-inflammatory and regulatory state. Human dendritic cells (DCs) show many phenotypic changes upon contact with Schistosoma mansoni soluble egg antigens (SEA). We here show that oxidation of SEA glycans, but not heat-denaturation, abrogates the capacity of SEA to suppress both LPS-induced cytokine secretion and DC proliferation, indicating an important role of SEA glycans in these processes. Remarkably, interaction of SEA glycans with DCs results in a strongly increased expression of Suppressor Of Cytokine Signalling1 (SOCS1) and SH2-containing protein tyrosine Phosphatase-1 (SHP1), important negative regulators of TLR4 signalling. In addition, SEA induces the secretion of transforming growth factor β (TGF-β), and the surface expression of the costimulatory molecules Programmed Death Ligand-1 (PD-L1) and OX40 ligand (OX40L), which are known phenotypic markers for the capacity of DCs to polarize naïve T cells into Th2/Treg cell subsets. Inhibition of mannose receptor (MR)-mediated internalization of SEA into DCs by blocking with allyl α-D-mannoside or anti-MR antibodies, significantly reduced SOCS1 and SHP1 expression. In conclusion, we demonstrate that SEA glycans are essential for induction of enhanced SOCS1 and SHP1 levels in DCs via the MR. Our data provide novel mechanistic evidence for the potential of S. mansoni SEA glycans to modulate human DCs, which may contribute to the capacity of SEA to down-regulate inflammatory responses.

Protective immunity against Schistosoma japonicum infection can be provided by IgG antibodies towards periodate-sensitive or periodate-resistant glycans

BACKGROUND

It has been well accepted that glycans present in schistosomes are highly antigenic. However, it is not clear what kind of worm glycans can affect the infected host to mount IgG responses and whether mounted anti-glycan IgG responses are protective.

METHODS

The contribution of antigenicity by glycans was measured by using competitive ELISA assay in sera from infected mice and humans. Monoclonal antibodies towards soluble Schistosoma japonicum egg antigens (SjEA) were generated from SjEA immunizated mice. The expression of glycans on surfaces of cercaria or young worm and their distributions were examined by immunofluorescence assay. The protective roles of glycans-specific mAbs were assayed by determination of the worm and egg burden in infected mice.

RESULTS

Both periodate-resistant glycans and periodate-sensitive glycans are antigenic in schistosome infections. When monoclonal antibodies against either periodate-sensitive or periodate-resistant glycans were administered prior to schistosome infections in mice, both kinds of anti-glycan antibodies were found to successfully provide protective immunity to infected mice.

CONCLUSIONS

Both periodate-resistant and periodate-sensitive glycans are antigenic, and dominant anti-glycan IgG responses can play important roles in protective immunity in schistosome infected hosts.

Invariant NKT cell response to dengue virus infection in human

BACKGROUND

Dengue viral infection is a global health threat without vaccine or specific treatment. The clinical outcome varies from asymptomatic, mild dengue fever (DF) to severe dengue hemorrhagic fever (DHF). While adaptive immune responses were found to be detrimental in the dengue pathogenesis, the roles of earlier innate events remain largely uninvestigated. Invariant natural killer T (iNKT) cells represent innate-like T cells that could dictate subsequent adaptive response but their role in human dengue virus infection is not known. We hypothesized that iNKT cells play a role in human dengue infection.

METHODS

Blood samples from a well-characterized cohort of children with DF, DHF, in comparison to non-dengue febrile illness (OFI) and healthy controls at various time points were studied. iNKT cells activation were analyzed by the expression of CD69 by flow cytometry. Their cytokine production was then analyzed after α-GalCer stimulation. Further, the CD1d expression on monocytes, and CD69 expression on conventional T cells were measured.

RESULTS

iNKT cells were activated during acute dengue infection. The level of iNKT cell activation associates with the disease severity. Furthermore, these iNKT cells had altered functional response to subsequent ex vivo stimulation with α-GalCer. Moreover, during acute dengue infection, monocytic CD1d expression was also upregulated and conventional T cells also became activated.

CONCLUSION

iNKT cells might play an early and critical role in the pathogenesis of severe dengue viral infection in human. Targeting iNKT cells and CD1d serve as a potential therapeutic strategy for severe dengue infection in the future.

Glycoconjugates in host-helminth interactions

Helminths are multicellular parasitic worms that comprise a major class of human pathogens and cause an immense amount of suffering worldwide. Helminths possess an abundance of complex and unique glycoconjugates that interact with both the innate and adaptive arms of immunity in definitive and intermediate hosts. These glycoconjugates represent a major untapped reservoir of immunomodulatory compounds, which have the potential to treat autoimmune and inflammatory disorders, and antigenic glycans, which could be exploited as vaccines and diagnostics. This review will survey current knowledge of the interactions between helminth glycans and host immunity and highlight the gaps in our understanding which are relevant to advancing therapeutics, vaccine development, and diagnostics.

Chronic schistosome infection leads to modulation of granuloma formation and systemic immune suppression

Schistosome worms have been infecting humans for millennia, but it is only in the last half century that we have begun to understand the complexities of this inter-relationship. As our sophistication about the inner workings of every aspect of the immune system has increased, it has also become obvious that schistosome infections have broad ranging effects on nearly all of the innate and adaptive immune response mechanisms. Selective pressures on both the worms and their hosts, has no doubt led to co-evolution of protective mechanisms, particularly those that favor granuloma formation around schistosome eggs and immune suppression during chronic infection. The immune modulatory effects that chronic schistosome infection and egg deposition elicit have been intensely studied, not only because of their major implications to public health issues, but also due to the emerging evidence that schistosome infection may protect humans from severe allergies and autoimmunity. Mouse models of schistosome infection have been extremely valuable for studying immune modulation and regulation, and in the discovery of novel aspects of immunity. A progression of immune reactions occurs during granuloma formation ranging from innate inflammation, to activation of each branch of adaptive immune response, and culminating in systemic immune suppression and granuloma fibrosis. Although molecular factors from schistosome eggs have been identified as mediators of immune modulation and suppressive functions of T and B cells, much work is still needed to define the mechanisms of the immune alteration and determine whether therapies for asthma or autoimmunity could be developed from these pathways.

How helminths use excretory secretory fractions to modulate dendritic cells

It is well known that helminth parasites have immunomodulatory effects on their hosts. They characteristically cause a skew toward T_H2 immunity, stimulate Treg cells while simultaneously inhibiting T_H1 and T_H17 responses. Additionally, they induce eosinophilia and extensive IgE release. The exact mechanism of how the worms achieve this effect have yet to be fully elucidated; however, parasite-derived secretions and their interaction with antigen presenting cells have been centrally implicated. Herein, we will review the effects of helminth excretory-secretory fractions on dendritic cells and discuss how this interaction is crucial in shaping the host response.

Age-related patterns in human myeloid dendritic cell populations in people exposed to Schistosoma haematobium infection

BACKGROUND

Urogenital schistosomiasis is caused by the helminth parasite Schistosoma haematobium. In high transmission areas, children acquire schistosome infection early in life with infection levels peaking in early childhood and subsequently declining in late childhood. This age-related infection profile is thought to result from the gradual development of protective acquired immunity. Age-related differences in schistosome-specific humoral and cellular responses have been reported from several field studies. However there has not yet been a systematic study of the age-related changes in human dendritic cells, the drivers of T cell polarisation.

METHODS

Peripheral blood mononuclear cells were obtained from a cohort of 61 Zimbabwean aged 5-45 years with a S. haematobium prevalence of 47.5%. Two subsets of dendritic cells, myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry.

FINDINGS

In this population, schistosome infection levels peaked in the youngest age group (5-9 years), and declined in late childhood and adulthood (10+ years). The proportions of both mDCs and pDCs varied with age. However, for mDCs the age profile depended on host infection status. In the youngest age group infected people had enhanced proportions of mDCs as well as lower levels of HLA-DR on mDCs than un-infected people. In the older age groups (10-13 and 14-45 years) infected people had lower proportions of mDCs compared to un-infected individuals, but no infection status-related differences were observed in their levels of HLA-DR. Moreover mDC proportions correlated with levels of schistosome-specific IgG, which can be associated with protective immunity. In contrast proportions of pDCs varied with host age, but not with infection status.

CONCLUSIONS

Our results show that dendritic cell proportions and activation in a human population living in schistosome-endemic areas vary with host age reflecting differences in cumulative history of exposure to schistosome infection.

Helminth infections: therapeutic potential in autoimmune disorders

Knowledge of immunity enables us to predict that the reactions set in response to infection with helminth would prevent concomitant disease driven by an opposing spectrum of immune events. In another way, the immune response generated to combat the helminth infection could counteract the immunopathological reactions that drive autoimmune diseases. Rodent model systems recapitulate many aspects of human autoimmune diseases and have been enormously useful in defining mechanisms of immunopathology after infection. From this theoretical perspective, many researchers have proved that infection with a variety of helminth can ameliorate disease in murine model systems. Thus, helminth-evoked Th2 events were shown to improve disorders in which Th1 events predominated. This raised the question, 'Can this information be translated into therapies for autoimmune diseases in humans via actual infection, cell delivery or drug intervention?' In this review, we will present some experimental trails to treat autoimmune disorders through establishment of some parasitic infections.

Triggering receptor expressed on myeloid cells (TREM)-1 participates in Schistosoma mansoni inflammatory responses

Inflammatory responses to microbial products are amplified by a pathway mediated by triggering a receptor expressed on the myeloid cells (TREM)-1. Relatively a few studies have been performed to investigate the role of TREM-1 in macrophage activation in response to parasitic infection. In this study, we delineate the role of the innate immunoreceptor TREM-1 in the parasite Schistosoma mansoni infection model from early to late (chronic) phases of infection. Flow cytometry analysis revealed gradual increase in the production of TREM-1 protein on CD11b(+) myeloid cells, with maximum production at 5 weeks p.i. Similar results in the pattern of TREM-1 mRNA expressions in splenic CD11b(+) cells from infected mice were obtained by real-time PCR. However, unlike in spleen, the TREM-1 mRNA expression in liver tissue showed no significant increase throughout the infection, including periods of maximum production of parasite eggs. Administration of schistosoma egg homogenate antigen to stimulate J774A.1 cells inhibited TREM-1 expression on the surface, indicating that some substances of the Schistosma eggs may inhibit the expression of TREM-1 on macrophages, lowering the macrophage-mediated inflammatory response of infected hosts.

Schistosoma mansoni egg glycoproteins and C-type lectins of host immune cells: molecular partners that shape immune responses

Schistosome eggs and egg-derived molecules are potent immunomodulatory agents. There is increasing evidence that the interplay between egg glycoproteins and host C-type lectins plays an important role in shaping immune responses during schistosomiasis. As most experiments in this field so far have been performed using complex protein/glycoprotein mixtures or synthetic model glycoconjugates, it is still largely unclear which individual moieties of schistosome eggs are immunologically active. In this review we will discuss molecular aspects of Schistosoma mansoni egg glycoproteins, their interactions with C-type lectins, and the relevance to schistosome egg immunobiology.

Langerhans cells serve as immunoregulatory cells by activating NKT cells

Ultraviolet exposure alters the morphology and function of epidermal Langerhans cells (LCs), which play a role in UV-induced immune suppression. It is generally believed that UV exposure triggers the migration of immature LCs from the skin to the draining lymph nodes (LNs), where they induce tolerance. However, because most of the previous studies employed in vitro UV-irradiated LCs, the data generated may not adequately reflect what is happening in vivo. In this study, we isolated migrating LCs from the LNs of UV-irradiated mice and studied their function. We found prolonged LC survival in the LNs of UV-irradiated mice. LCs were necessary for UV-induced immune suppression because no immune suppression was observed in LC-deficient mice. Transferring LCs from UV-irradiated mice into normal recipient animals transferred immune suppression and induced tolerance. We found that LCs colocalized with LN NKT cells. No immune suppression was observed when LCs were transferred from UV-irradiated mice into NKT cell-deficient mice. NKT cells isolated from the LNs of UV-irradiated mice secreted significantly more IL-4 than NKT cells isolated from nonirradiated controls. Injecting the wild-type mice with anti-IL-4 blocked the induction of immune suppression. Our findings indicate that UV exposure activates the migration of mature LC to the skin draining LNs, where they induce immune regulation in vivo by activating NKT cells.

Invariant natural killer T cells: bridging innate and adaptive immunity

Cells of the innate immune system interact with pathogens via conserved pattern-recognition receptors, whereas cells of the adaptive immune system recognize pathogens through diverse, antigen-specific receptors that are generated by somatic DNA rearrangement. Invariant natural killer T (iNKT) cells are a subset of lymphocytes that bridge the innate and adaptive immune systems. Although iNKT cells express T cell receptors that are generated by somatic DNA rearrangement, these receptors are semi-invariant and interact with a limited set of lipid and glycolipid antigens, thus resembling the pattern-recognition receptors of the innate immune system. Functionally, iNKT cells most closely resemble cells of the innate immune system, as they rapidly elicit their effector functions following activation, and fail to develop immunological memory. iNKT cells can become activated in response to a variety of stimuli and participate in the regulation of various immune responses. Activated iNKT cells produce several cytokines with the capacity to jump-start and modulate an adaptive immune response. A variety of glycolipid antigens that can differentially elicit distinct effector functions in iNKT cells have been identified. These reagents have been employed to test the hypothesis that iNKT cells can be harnessed for therapeutic purposes in human diseases. Here, we review the innate-like properties and functions of iNKT cells and discuss their interactions with other cell types of the immune system.

γδ T lymphocytes kill T regulatory cells through CD1d

Coxsackievirus B3 (CVB3) induces myocarditis, an inflammation of the myocardium, in C57Bl/6 male mice but not in mice lacking γδ+ T cells [γδ knockout (γδKO)]. Suppression of myocarditis in γδKO mice corresponds to an increase in CD4(+) CD25(+) FoxP3(+) T regulatory cells. A subpopulation of the T regulatory cells in infected γδKO mice expressed high levels of CD1d, a non-classical major histocompatibility complex class 1-like molecule. Adoptive transfer of CD1d(+) and CD1d(-) CD4(+) CD25(+) cells into infected C57Bl/6 recipients showed that the CD1d(+) subpopulation is substantially more suppressive than the CD1d(-) subpopulation. T cells expressing the γδ T-cell receptor comprised approximately 30-50% of the infiltrating lymphoid cells in the hearts of myocarditic C57Bl/6 mice and approximately half of the γδ+ cells expressed the Vγ4 T-cell receptor. The Vγ4+ cells lysed T regulatory cells from γδKO mice but not from wild-type (C57Bl/6) animals. Lysis was inhibited by antibody to CD1d and zVAD-fmk, a pan-caspase inhibitor. The Vγ4-γδ+ cells were not lytic to T regulatory cells and did not promote myocarditis. These results demonstrate that Vγ4+ cells selectively abrogate T regulatory cells through recognition of CD1d expressed on the regulatory cells and caspase-dependent apoptosis.

Patients with drug-free long-term graft function display increased numbers of peripheral B cells with a memory and inhibitory phenotype

Several transplant patients maintain stable kidney graft function in the absence of immunosuppression. Here we compared the characteristics of their peripheral B cells to that of others who had stable graft function but were under pharmacologic immunosuppression, to patients with chronic rejection and to healthy volunteers. In drug-free long-term graft function (DF) there was a significant increase in both absolute cell number and frequency of total B cells; particularly activated, memory and early memory B cells. These increased B-cell numbers were associated with a significantly enriched transcriptional B-cell profile. Costimulatory/migratory molecules (B7-2/CD80, CD40, and CD62L) were upregulated in B cells; particularly in memory CD19(+)IgD(-)CD38(+/-)CD27(+) B cells in these patients. Their purified B cells, however, responded normally to a polyclonal stimulation and did not have cytokine polarization. This phenotype was associated with the following specific characteristics which include an inhibitory signal (decreased FcgammaRIIA/FcgammaRIIB ratio); a preventive signal of hyperactive B-cell response (an increase in BANK1, which negatively modulates CD40-mediated AKT activation); an increased number of B cells expressing CD1d and CD5; an increased BAFF-R/BAFF ratio that could explain why these patients have more peripheral B cells; and a specific autoantibody profile. Thus, our findings show that patients with DF have a particular blood B-cell phenotype that may contribute to the maintenance of long-term graft function.

Review series on helminths, immune modulation and the hygiene hypothesis: how might infection modulate the onset of type 1 diabetes?

The development of type 1 diabetes is influenced by both genetic and environmental factors. The current rise in the incidence of diabetes is occurring more rapidly than can be accounted for by genetic change, highlighting the influence of environmental modifiers. Considerable effort has been expended to identify infectious agents that might be responsible for this rise in incidence, but no single infectious agent has been linked to this dramatic increase in type 1 diabetes. There has been increasing interest in the possibility that infections of historical importance that might have shaped our immune systems over evolutionary time may also have played a role in down-modulating some autoimmune and allergic disorders. In this review, some of the ways in which certain organisms might have influenced the onset of autoimmunity are discussed.

V alpha14 i NKT cells are innate lymphocytes that participate in the immune response to diverse microbes

Natural Killer T (NKT) cells constitute a conserved T lymphocyte sublineage that has been implicated in the regulation of various immune responses, including the responses to viruses, bacteria, and parasites. NKT cells recognize self and foreign glycolipids presented by CD1d, a non-classical antigen-presenting molecule, and they rapidly produce various cytokines. Many studies have shown that NKT cells have protective roles following microbial infection through the amplification of innate and adaptive immunity, although NKT cells have detrimental roles in some cases. Recent studies have shed light on the natural antigens recognized by NKT cells and the mechanisms whereby they contribute to host defense, and they suggest that these unique T cells have evolved to jump start the immune response to microbes.

The role of NKT cells in tumor immunity

NKT cells are a relatively newly recognized member of the immune community, with profound effects on the rest of the immune system despite their small numbers. They are true T cells with a T cell receptor (TCR), but unlike conventional T cells that detect peptide antigens presented by conventional major histocompatibility (MHC) molecules, NKT cells recognize lipid antigens presented by CD1d, a nonclassical MHC molecule. As members of both the innate and adaptive immune systems, they bridge the gap between these, and respond rapidly to set the tone for subsequent immune responses. They fill a unique niche in providing the immune system a cellular arm to recognize lipid antigens. They play both effector and regulatory roles in infectious and autoimmune diseases. Furthermore, subsets of NKT cells can play distinct and sometimes opposing roles. In cancer, type I NKT cells, defined by their invariant TCR using Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans, are mostly protective, by producing interferon-gamma to activate NK and CD8(+) T cells and by activating dendritic cells to make IL-12. In contrast, type II NKT cells, characterized by more diverse TCRs recognizing lipids presented by CD1d, primarily inhibit tumor immunity. Moreover, type I and type II NKT cells counter-regulate each other, forming a new immunoregulatory axis. Because NKT cells respond rapidly, the balance along this axis can greatly influence other immune responses that follow. Therefore, learning to manipulate the balance along the NKT regulatory axis may be critical to devising successful immunotherapies for cancer.

In vivo immunomodulatory effects of Antrodia camphorata polysaccharides in a T1/T2 doubly transgenic mouse model for inhibiting infection of Schistosoma mansoni

Antrodia camphorata (A. camphorata) is a fungus commonly used for treatment of viral hepatitis and cancer in Chinese folk medicine. Extract of A. camphorate is reported to possess anti-inflammatory, antihepatitis B virus and anticancer activities. In this study, we tested the in vivo effects of polysaccharides derived from A. camphorata (AC-PS) on immune function by detection of cytokine expression and evaluation of the immune phenotype in a T1/T2 doubly transgenic mouse model. The protective effect of AC-PS in mice was tested by infection with Schistosoma mansoni. The induction of large amounts of IFN-gamma, IL-2 and TNF-alpha mRNA were detected after 2 and 4 weeks of oral AC-PS administration in BALB/c and C57BL/6 mice. In transgenic mice, 3 to 6 weeks of oral AC-PS administration increased the proportion of CD4(+) T cells and B cells within the spleen. More specifically, there was an increase of Th1 CD4(+) T cells and Be1 cells among spleen cells as observed by detection the of Type1/Type2 marker molecules. By using a disease model of parasitic infection, we found that AC-PS treatment inhibited infection with S. mansoni in BALB/C and C57BL/6 mice. AC-PS appears to influence the immune system of mice into developing Th1 responses and have potential for preventing infection with S. mansoni.

Toll-like receptor (TLR)2 and TLR3 sensing is required for dendritic cell activation, but dispensable to control Schistosoma mansoni infection and pathology

Toll-like receptors (TLRs) play an important role in the innate recognition of pathogens by dendritic cells (DCs) and in the induction of immune responses. However, relatively little is known about their functions in innate/acquired responses to complex eukaryotic microorganisms, including helminth parasites. That Schistosoma mansoni eggs activate myeloid DCs through TLR2 and TLR3 has been shown by us and others, but the consequences of this combined activation are still unknown. We show that the engagement of both TLR2 and TLR3 by schistosome eggs is important for the production of inflammatory cytokines and interferon-stimulated genes, such as some chemokines, by DCs. Strikingly, DCs sensitized with ovalbumin in the presence of parasite eggs dramatically reduce the release of Th2-type cytokines by ovalbumin-specific T lymphocytes, an effect that fully depends on TLR3. Finally, although TLR2 and TLR3 have no role in host resistance and in egg-induced granuloma formation in S. mansoni-infected mice, they individually and additionally increase the Th1/Th2 balance of the immune response. Thus, TLR2 and TLR3 sensing is required to shape the immune response during murine schistosomiasis, but is dispensable to control infection and pathology.

Galectin-3 modulates immune and inflammatory responses during helminthic infection: impact of galectin-3 deficiency on the functions of dendritic cells

Galectin-3 (Gal-3) is a multifunctional beta-galactoside-binding lectin that senses self-derived and microbial glycoconjugates. Although Gal-3 is important in immune reactions and host defense in some experimental models, the function of Gal-3 during helminthic diseases (e.g., schistosomiasis) is still elusive. We show that, compared to wild-type Schistosoma mansoni-infected mice, infected Gal-3-/- mice have a reduced number of T and B lymphocytes in the spleen, develop reduced liver granulomas at 7 weeks (acute phase) and 14 weeks (chronic phase) postinfection, and mount a biased cellular and humoral Th1 response. In an attempt to understand this latter phenomenon, we studied the role of endogenous Gal-3 in dendritic cells (DCs), the most potent antigen-presenting cells, both in vitro and in vivo. Although Gal-3 deficiency in DCs does not impact their differentiation and maturation processes, it greatly influences the strength (but not the nature) of the adaptive immune response that they trigger, suggesting that Gal-3 deficiency in some other cell types may be important during murine schistosomiasis. As a whole, this study implies that Gal-3 is a modulator of the immune/inflammatory responses during helminthic infection and reveals for the first time that Gal-3 expression in DCs is pivotal to control the magnitude of T-lymphocyte priming.

CD1-restricted T cells in host defense to infectious diseases

CD1 has been clearly shown to function as a microbial recognition system for activation of T cell responses, but its importance for mammalian protective responses against infections is still uncertain. The function of the group 1 CD1 isoforms, including human CD1a, CDlb, and CDLc, seems closely linked to adaptive immunity. These CD1 molecules control the responses of T cells that are highly specific for particular lipid antigens, the best known of which are abundantly expressed by pathogenic mycobacteria such as Mycobacterium tuberculosis and Mycobacterium leprae. Studies done mainly on human circulating T cells ex vivo support a significant role for group I CD1-restricted T cells in protective immunity to mycobacteria and potentially other pathogens, although supportive data from animal models is currently limited. In contrast, group 2 CD1 molecules, which include human CD1d and its orthologs, have been predominantly associated with the activation of CD1d-restricted NKT cells, which appear to be more appropriately viewed as a facet of the innate immune system. Whereas the recognition of certain self-lipid ligands by CD d-restricted NKT cells is well accepted, the importance of these T cells in mediating adaptive immune recognition of specific microbial lipid antigens remains controversial. Despite continuing uncertainty about the role of CD 1d-restricted NKT cells in natural infections, studies in mouse models demonstrate the potential of these T cells to exert various effects on a wide spectrum of infectious diseases, most likely by serving as a bridge between innate and adaptive immune responses.

The C-type lectin L-SIGN differentially recognizes glycan antigens on egg glycosphingolipids and soluble egg glycoproteins from Schistosoma mansoni

Recognition of pathogen-derived carbohydrate constituents by antigen presenting cells is an important step in the induction of protective immunity. Here we investigated the interaction of L-SIGN (liver/lymph node specific ICAM-3-grabbing nonintegrin), a C-type lectin that functions as antigen receptor on human liver sinusoidal endothelial cells, with egg-derived glycan antigens of the parasitic trematode Schistosoma mansoni. Our data demonstrate that L-SIGN binds both schistosomal soluble egg antigens (SEA) and egg glycosphingolipids, and can mediate internalization of SEA by L-SIGN expressing cells. Binding and internalization of SEA was strongly reduced after treatment of SEA with endoglycosidase H, whereas defucosylation affected neither binding nor internalization. These data indicate that L-SIGN predominantly interacts with oligomannosidic N-glycans of SEA. In contrast, binding to egg glycosphingolipids was completely abolished after defucosylation. Our data show that L-SIGN binds to a glycosphingolipid fraction containing fucosylated species with compositions of Hex(1)HexNAc(5-7)dHex(3-6)Cer, as evidenced by mass spectrometry. The L-SIGN "gain of function" mutant Ser363Val, which binds fucosylated Lewis antigens, did not bind to this fucosylated egg glycosphingolipid fraction, suggesting that L-SIGN displays different modes in binding fucoses of egg glycosphingolipids and Lewis antigens, respectively. Molecular modeling studies indicate that the preferred binding mode of L-SIGN to the respective fucosylated egg glycosphingolipid oligosaccharides involves a Fucalpha1-3GalNAcbeta1-4(Fucalpha1-3)GlcNAc tetrasaccharide at the nonreducing end. In conclusion, our data indicate that L-SIGN recognizes both oligomannosidic N-glycans and multiply fucosylated carbohydrate motifs within Schistosoma egg antigens, which demonstrates that L-SIGN has a broad but specific glycan recognition profile.

The unique role of natural killer T cells in the response to microorganisms

Natural killer T (NKT) cells combine features of the innate and adaptive immune systems. Recently, it has become evident that these T cells have crucial roles in the response to infectious agents. The antigen receptor expressed by NKT cells directly recognizes unusual glycolipids that are part of the membrane of certain Gram-negative bacteria and spirochetes. Moreover, even in the absence of microbial glycolipid antigens, these T cells respond to innate cytokines produced by dendritic cells that have been activated by microbes. This indirect sensing of infection, by responding to cytokines from activated dendritic cells, allows NKT cells to react to a broad range of infectious agents.

Invariant and noninvariant natural killer T cells exert opposite regulatory functions on the immune response during murine schistosomiasis

CD1d-restricted natural killer T (NKT) cells represent a heterogeneous population of innate memory immune cells expressing both NK and T-cell markers distributed into two major subsets, i.e., invariant NKT (iNKT) cells, which express exclusively an invariant T-cell receptor (TCR) alpha chain (Valpha14Jalpha18 in mice), and non-iNKT cells, which express more diverse TCRs. NKT cells quickly produce Th1- and/or Th2-type cytokines following stimulation with glycolipid antigen (Ag) and, through this property, play potent immunoregulatory roles in autoimmune diseases, cancer, and infection. No study has addressed the role of NKT cells in metazoan parasite infections so far. We show that during murine schistosomiasis, the apparent frequency of both iNKT cells and non-iNKT cells decreased in the spleen as early as 3 weeks postinfection (p.i.) and that both populations expressed a greater amount of the activation marker CD69 at 6 weeks p.i., suggesting an activated phenotype. Two different NKT-cell-deficient mouse models, namely, TCR Jalpha18-/- (exclusively deficient in iNKT cells) and CD1d-/- (deficient in both iNKT and non-iNKT cells) mice, were used to explore the implication of these subsets in infection. We show that whereas both iNKT and non-iNKT cells do not have a major impact on the immune response during the early phase (1 and 4 weeks) of infection, they exert important, although opposite, effects on the immune response during the acute phase of the disease (7 and 12 weeks), after schistosome egg production. Indeed, iNKT cells contribute to Th1 cell differentiation whereas non-iNKT cells might be mostly implicated in Th2 cell differentiation in response to parasite Ag. Our findings suggest, for the first time, that helminths activate both iNKT and non-iNKT cells in vivo, enabling them to differentially influence the Th1/Th2 balance of the immune response.

Dendritic cells in the CNS: immune regulators and therapeutic targets for multiple sclerosis treatment

Dendritic cells (DCs) are essential antigen-presenting cells responsible for initiating cellular immune responses. The increasing interest in the mechanisms of DC trafficking has created new and exciting opportunities for bench-to-bedside therapies to treat autoimmune diseases of the central nervous system (CNS). However, tracking the migration of DCs in the CNS has proved to be more problematic owing to their low number in the immunologically privileged environment of the brain and high diversity as a cell population. A significant contributor to immune privilege in the brain is the blood–brain barrier, a unique structure recognized to regulate the entry of immune cells into the brain. Currently, it is hypothesized that the migration of DCs across the blood–brain barrier is critically important for the initiation of immune responses of CNS autoimmunity. This review summarizes the present knowledge on DC trafficking in the CNS and the main functions of these cells in initiating CNS autoimmunity. Selective identification of regulatory molecules and novel therapies to inhibit DC migration and function during CNS autoimmune diseases without affecting normal DC function under physiological conditions will be critical in treatments for neurological inflammatory diseases.

Parasitic worms and inflammatory diseases

The debate on whether infection precipitates or prevents autoimmunity remains a contentious one. Recently the suggestion that some unknown microbe can be at the origin of some chronic inflammatory diseases has been countered by accumulating evidence that decreasing infection rates might have an important role to play in the rising prevalence of autoimmune disorders. The 'Hygiene Hypothesis' was initially postulated to explain the inverse correlation between the incidence of infections and the rise of allergic diseases, particularly in the developed world. Latterly, the Hygiene Hypothesis has been extended to also incorporate autoimmune diseases in general. Amongst the various infectious agents, a particular emphasis has been put on the interaction between parasitic worms and humans. Worm parasites have co-evolved with the mammalian immune system for many millions of years and during this time, they have developed extremely effective strategies to modulate and evade host defences and so maintain their evolutionary fitness. It is therefore reasonable to conclude that the human immune system has been shaped by its relationship with parasitic worms and this may be a necessary requirement for maintaining our immunological health. Fully understanding this relationship may lead to novel and effective treatments for a host of deleterious inflammatory reactions.

Putting the pieces of the puzzle together - a series of hypotheses on the etiology and pathogenesis of type 1 diabetes

This paper presents a series of 10 hypotheses on the etiology of type 1 diabetes. We begin with the hypothesis that wheat gluten is one of the elusive environmental triggers in type 1 diabetes. Habitual consumption of wheat gluten increases the intestinal synthesis of dipeptidyl peptidase IV. This enzyme helps to shape the repertoire of peptides released into the small intestine following the ingestion of wheat gluten by catalyzing the release of X-Pro dipeptides from the N-terminus of the proline-rich glutenins and gliadins in wheat gluten. The release of gluten-derived peptides causes the tight junctions of the small intestine to open through a zonulin-dependent mechanism, which allows these peptides to enter the lamina propria where they get presented as antigens by HLA-DQ, -DR and CD1d molecules. Binding of one or more gluten peptides by CD1d leads to abrogation of oral tolerance, and a marked increase in peripheral immune responses to wheat proteins. Furthermore, it is our contention, that in response to beta cell apoptosis during normal remodeling of the pancreas and CCL19/CCL21 expression within the pancreatic lymph nodes (PLNs), gluten-loaded dendritic cells migrate from the small intestine to the PLNs. These dendritic cells present gluten-derived antigens on the surface of the PLNs, which leads to migration of CD4(-)CD8(-) gammadelta and CD4(-)CD8(+) alphabeta T cells to the pancreas where they mediate Fas and perforin dependent cytotoxicity. We also hypothesize that at least one of the type 1 diabetes associated HLA-DR molecules that bind and present wheat-derived peptide(s) also bind and present an islet cell antigen(s), activating plasma cell synthesis of islet cell autoantibodies and irrevocable, complement-dependent destruction of islet cells. Our final two hypotheses state that type 1 diabetes morbidity is reduced in those areas of globe where genetically susceptible individuals get adequate amounts of vitamin D, in the diet and/or through exposure to sunlight, and in areas where people are exposed to bacterial, viral, or parasitic infections in early childhood.

Induction of interferon-gamma by Taenia crassiceps glycans and Lewis sugars in naive BALB/c spleen and peritoneal exudate cells

Helminth parasites are known to alter host immune responses and the responsible molecules are a potential source of biological immunoadjuvants. Previously, we have reported strong Th-2 type immunomodulatory properties of Taenia crassiceps glycans. In this study, we report interferon-gamma (IFN-gamma) stimulatory activity of fractionated Taenia glycans and Lewis sugars with comparable glycan composition. Our data show that Taenia glycans and Lewis X pentasaccharide are potent stimulators of the Th-1 type cytokine IFN-gamma. We postulate that the terminal beta-(1-4)-galactose residue in Lewis X is associated with IFN-gamma stimulation from naive BALB/c mouse spleen and peritoneal exudate cells. Antibodies to toll-like receptors (TLRs) inhibited the Lewis X-induced IFN-gamma secretion. Lewis X up-regulated the expression of NF-kappaB p65 from naive spleen cells and IFN-gamma transcription in peritoneal exudate cells. These data demonstrate the ability of Lewis type helminth glycans to modulate host responses in a Th-1 direction via NF-kappaB p65, IFN-gamma and macrophage TLRs.

Interleukin-4-dependent innate collaboration between iNKT cells and B-1 B cells controls adaptative contact sensitivity

We showed that hepatic Valpha14+ invariant natural killer T (iNKT) cells, via their rapid interleukin (IL)-4 production, activate B-1 cells to initiate contact sensitivity (CS). This innate collaboration was absent in IL-4(-/-) and signal transducer and activator of transcription (STAT)-6(-/-) mice and was inhibited by anti-IL-4 treatment. These mice have defective CS because they fail to locally recruit the sensitized effector T cells of acquired immunity. Their CS is reconstituted by transfer of downstream-acting 1-day immune B-1 cells from wild-type mice. Responses were not reconstituted with B-1 cells from IL-4 receptor-alpha(-/-) or STAT-6(-/-) mice, nor by IL-4 treatment of B cell-deficient mice at immunization. Finally, IL-4 was preferentially and transiently produced by hepatic iNKT cells within 7 min after sensitization to mediate collaboration between innate-like iNKT cells and the B-1 B cells that participate in the recruitment of effector T cells in vivo.

Dendritic cell activation and function in response to Schistosoma mansoni

Dendritic cells (DC) are uniquely specialised for both antigen acquisition and presentation, linking innate and adaptive immunity. Their central role in the activation of naïve T cells gives DC a strategic position in the control of immune responses. While the mechanisms by which viral, bacterial or protozoal pathogens interact with and activate DC are increasingly understood, much less is known about how these cells react to more complex organisms such as schistosomes. Recent studies have examined the impact on DC of antigens from different life cycle stages of Schistosoma mansoni and have revealed a DC phenotype quite distinct to that of conventional activation. Schistosome antigens elicit little of the cytokine secretion and costimulation that are abundantly triggered in DC by unicellular, proinflammatory pathogens and indeed may even actively inhibit such events. The DC response is not a null one, however, since S. mansoni-exposed DC still act as potent antigen presenting cells capable of generating a powerful Th2 immune response. Understanding the interaction between schistosomes and DC is therefore not only addressing fundamental questions of DC biology and immunity to multicellular parasites but also opens the way to therapeutic manipulation of the immune system.

Activation of Invariant NKT Cells by the Helminth Parasite Schistosoma mansoni

Mouse CD1d-restricted NKT cells, including invariant (i)NKT cells, are innate cells activated by glycolipid Ags and play important roles in the initiation and regulation of immune responses. Through their ability to promptly produce large amounts of Th1 and/or Th2 cytokines upon TCR engagement, iNKT cells exert crucial functions in the immune/inflammatory system during bacterial, protozoan, fungal, and viral infections. However, their roles during metazoan parasite infection, which are generally associated with strong Th2 responses, still remain elusive. In this study, we show that during the course of murine schistosomiasis, iNKT cells exhibit an activated phenotype and that following schistosome egg encounter in the liver, hepatic iNKT cells produce both IFN-gamma and IL-4 in vivo. We also report that schistosome egg-sensitized dendritic cells (DCs) activate, in a CD1d-dependent manner, iNKT cells to secrete IFN-gamma and IL-4 in vitro. Interestingly, transfer of egg-sensitized DCs promotes a strong Th2 response in recipient wild-type mice, but not in mice that lack iNKT cells. Engagement of TLRs in DCs is not necessary for iNKT cell stimulation in response to egg-sensitized DCs, suggesting an alternative pathway of activation. Finally, we propose that self, rather than parasite-derived, CD1d-restricted ligands are implicated in iNKT cell stimulation. Taken together, our data show for the first time that helminths can activate iNKT cells to produce immunoregulatory cytokines in vivo, enabling them to influence the adaptive immune response.

Structural biology of allergens

Major allergens may have special aerobiological properties and allergenic structures. It would also be instructive to consider the properties of nonallergens and nonallergenic responses. In some cases, nonallergenic responses appear to result from a lack of antigenicity and in others from regulation. Proteolytic activity has been proposed as an adjuvant for allergenicity, but lipid binding is far more common and is found for more than 50% of the major allergens. Such structures can enhance allergenicity via Toll-like receptor (TLR) or CD1 pathways. TLR signaling can enhance both Th1 and Th2 responses and be induced by peptides as well as nonproteinaceous ligands.

NKT cells are not critical for HSV‐1 disease resolution

NKT cells are a minor subset of T cells that have important roles in controlling immune responses in disease states including cancer, autoimmunity and pathogenic infections. In contrast to conventional T cells, NKT cells express an invariant TCR and respond to glycolipids presented by CD1d. In this study, we sought to investigate the role of NKT cells in regulating the response to infection with HSV-1, and the mechanism involved, in well-established mouse models. Previous studies of HSV-1 disease in mice have shown clear roles for CD4+ and CD8+ T cells. The role of NKT cells in the resolution of HSV-1 (KOS strain) infection was investigated through flank zosteriform or footpad infection in wild-type versus CD1d-deficient mice, by measurement of viral plaque-forming units at different sites after infection, lesion severity and HSV-1-specific T-cell responses. In contrast to a previous study using a more virulent strain of HSV-1 (SC16 strain), no differences were observed in disease magnitude or resolution, and furthermore, the T-cell response to HSV-1 (KOS strain) was unaltered in the absence of NKT cells. In conclusion, this study shows that NKT cells do not play a general role in controlling the resolution or severity of HSV-1 infection. Instead, the resolution or severity of the infection may depend on the HSV-1 strain under investigation.

Immunoregulation of Autoimmunity by Natural Killer T Cells

Natural killer T (NKT) cells are a conserved subpopulation of lymphocytes that recognize glycolipid antigens in a CD1d context. Upon activation through their semi-invariant T cell receptor, these cells rapidly release large amounts of immunomodulating Th1 and Th2 cytokines. NKT cells have therefore been implicated in immune responses controlling various diseases, including infection, cancer, transplantation, and autoimmunity. Stimulation of the immunoregulatory capacity of NKT cells by the prototypical antigen alpha-galactosylceramide results in amelioration of disease in several animal models. This review will focus on the current knowledge of human NKT cells and their role in autoimmune diseases. The features of these cells and their importance in regulation of autoimmunity suggest that NKT cell-based therapies might be an interesting approach for the treatment of autoimmune diseases.

Schistosomes: the road from host-parasite interactions to vaccines in clinical trials

Insights over recent years into the interactions between helminths, including schistosomes, and the immune system have generated new concepts in immunology and significant advances in vaccine strategies. Here, we report recent advances that substantially increase our understanding of the nature of the host innate and adaptive responses to schistosomes and on strategies elaborated by the parasite to manipulate such responses. We also describe the long road that has allowed us to move from the identification of an anti-schistosome vaccine candidate, a 28kDa glutathione-S-transferase, to its recent evaluation in human clinical trials.

The role of group 1 and group 2 CD1-restricted T cells in microbial immunity

Group 1 and group 2 CD1 present both self and microbial lipid antigens to T cells. While group 1 CD1-restricted T cells are known for their ability to recognize mycobacterial glycolipid antigens, group 2 CD1-restricted T cells are recognized as regulatory T cells that can influence the outcome of innate and adaptive immune responses. The evidence that these T cells contribute to host defense against infectious diseases is reviewed.

Helminth antigens modulate TLR-initiated dendritic cell activation

There is increasing awareness that helminth infections can ameliorate proinflammatory conditions. In part, this is due to their inherent ability to induce Th2 and, perhaps, regulatory T cell responses. However, recent evidence indicates that helminths also have direct anti-inflammatory effects on innate immune responses. In this study, we address this issue and show that soluble molecules from the eggs of the helminth parasite Schistosoma mansoni (SEA) suppress LPS-induced activation of immature murine dendritic cells, including MHC class II, costimulatory molecule expression, and IL-12 production. SEA-augmented LPS-induced production of IL-10 is in part responsible for the observed reduction in LPS-induced IL-12 production. However, analyses of IL-10(-/-) DC revealed distinct IL-10-independent suppressive effects of SEA. IL-10-independent mechanisms are evident in the suppression of TLR ligand-induced MAPK and NF-kappaB signaling pathways. Microarray analyses demonstrate that SEA alone uniquely alters the expression of a small subset of genes that are not up-regulated during conventional TLR-induced DC maturation. In contrast, the effects of SEA on TLR ligand-induced DC activation were striking: when mixed with LPS, SEA significantly affects the expression of >100 LPS-regulated genes. These findings indicate that SEA exerts potent anti-inflammatory effects by directly regulating the ability of DC to respond to TLR ligands.