Effect of helminth-induced immunity on infections with microbial pathogens

Parasitic helminth infections and the control of human allergic and autoimmune disorders

The profile of global health today presents a striking reciprocal distribution between parasitic diseases in many of the world's lower-income countries, and ever-increasing levels of inflammatory disorders such as allergy, autoimmunity and inflammatory bowel diseases in the more affluent societies. Attention is particularly focused on helminth worm parasites, which are associated with protection from allergy and inflammation in both epidemiologic and laboratory settings. One mechanistic explanation of this is that helminths drive the regulatory arm of the immune system, abrogating the ability of the host to expel the parasites, while also dampening reactivity to many bystander specificities. Interest has therefore heightened into whether helminth parasites, or their products, hold therapeutic potential for immunologic disorders of the developed world. In this narrative review, progress across a range of trials is discussed, together with prospects for isolating individual molecular mediators from helminths that may offer defined new therapies for inflammatory conditions.

Lymphotoxin-Dependent B Cell-FRC Crosstalk Promotes De Novo Follicle Formation and Antibody Production following Intestinal Helminth Infection

Secondary lymphoid tissues provide specialized niches for the initiation of adaptive immune responses and undergo a remarkable expansion in response to inflammatory stimuli. Although the formation of B cell follicles was previously thought to be restricted to the postnatal period, we observed that the draining mesenteric lymph nodes (mLN) of helminth-infected mice form an extensive number of new, centrally located, B cell follicles in response to IL-4Rα-dependent inflammation. IL-4Rα signaling promoted LTα1β2 (lymphotoxin) expression by B cells, which then interacted with CCL19 positive stromal cells to promote lymphoid enlargement and the formation of germinal center containing B cell follicles. Importantly, de novo follicle formation functioned to promote both total and parasite-specific antibody production. These data reveal a role for type 2 inflammation in promoting stromal cell remodeling and de novo follicle formation by promoting B cell-stromal cell crosstalk.

Interaction Between Helminths and Toll-Like Receptors: Possibilities and Potentials for Asthma Therapy

Toll-like receptors (TLRs) are essential components of the innate immune system. They play an important role in the pathogenesis of allergic diseases, especially asthma. Since TLRs significantly orchestrate innate and adaptive immune response, their manipulation has widely been considered as a potential approach to control asthma symptoms. It is well established that helminths have immunoregulatory effects on host immune responses, especially innate immunity. They release bioactive molecules such as excretory-secretory (ES) products manipulating TLRs expression and signaling. Thus, given the promising results derived from preclinical studies, harnessing helminth-derived molecules affecting TLRs can be considered as a potential biological therapy for allergic diseases. Prospectively, the data that are available at present suggest that, in the near future, it is possible that helminth antigens will offer new therapeutic strategies and druggable targets for fighting allergic diseases. This review describes the interactions between helminths and TLRs and discusses the potential possibilities for asthma therapy. In this opinion paper, the authors aimed to review the updated literatures on the interplay between helminths, TLRs, and asthma with a view to proposing helminth-based asthma therapy.

Sequential Infection with Common Pathogens Promotes Human-like Immune Gene Expression and Altered Vaccine Response

Immune responses differ between laboratory mice and humans. Chronic infection with viruses and parasites are common in humans, but are absent in laboratory mice, and thus represent potential contributors to inter-species differences in immunity. To test this, we sequentially infected laboratory mice with herpesviruses, influenza, and an intestinal helminth and compared their blood immune signatures to mock-infected mice before and after vaccination against yellow fever virus (YFV-17D). Sequential infection altered pre- and post-vaccination gene expression, cytokines, and antibodies in blood. Sequential pathogen exposure induced gene signatures that recapitulated those seen in blood from pet store-raised versus laboratory mice, and adult versus cord blood in humans. Therefore, basal and vaccine-induced murine immune responses are altered by infection with agents common outside of barrier facilities. This raises the possibility that we can improve mouse models of vaccination and immunity by selective microbial exposure of laboratory animals to mimic that of humans.

Worming Their Way into the Picture: Microbiota Help Helminths Modulate Host Immunity

Parasitic helminths are potent regulators of host immunity, including inhibition of allergic inflammation. In this issue of Immunity, Zaiss et al. (2015) reveal that microbiota compositional shifts during helminth infection contribute to the multifaceted ways that helminths modulate host immunity.

Cohabitation in the Intestine: Interactions among Helminth Parasites, Bacterial Microbiota, and Host Immunity

Both intestinal helminth parasites and certain bacterial microbiota species have been credited with strong immunomodulatory effects. Recent studies reported that the presence of helminth infection alters the composition of the bacterial intestinal microbiota and, conversely, that the presence and composition of the bacterial microbiota affect helminth colonization and persistence within mammalian hosts. This article reviews recent findings on these reciprocal relationships, in both human populations and mouse models, at the level of potential mechanistic pathways and the implications these bear for immunomodulatory effects on allergic and autoimmune disorders. Understanding the multidirectional complex interactions among intestinal microbes, helminth parasites, and the host immune system allows for a more holistic approach when using probiotics, prebiotics, synbiotics, antibiotics, and anthelmintics, as well as when designing treatments for autoimmune and allergic conditions.

Microbiota-Dependent Sequelae of Acute Infection Compromise Tissue-Specific Immunity

Infections have been proposed as initiating factors for inflammatory disorders; however, identifying associations between defined infectious agents and the initiation of chronic disease has remained elusive. Here, we report that a single acute infection can have dramatic and long-term consequences for tissue-specific immunity. Following clearance of Yersinia pseudotuberculosis, sustained inflammation and associated lymphatic leakage in the mesenteric adipose tissue deviates migratory dendritic cells to the adipose compartment, thereby preventing their accumulation in the mesenteric lymph node. As a consequence, canonical mucosal immune functions, including tolerance and protective immunity, are persistently compromised. Post-resolution of infection, signals derived from the microbiota maintain inflammatory mesentery remodeling and consequently, transient ablation of the microbiota restores mucosal immunity. Our results indicate that persistent disruption of communication between tissues and the immune system following clearance of an acute infection represents an inflection point beyond which tissue homeostasis and immunity is compromised for the long-term. VIDEO ABSTRACT.

Mycobacterium tuberculosis-specific CD4+ T-cell response is increased, and Treg cells decreased, in anthelmintic-treated patients with latent TB

In many settings, adults with active or latent tuberculosis will also be coinfected with helminths. Our study aimed to investigate how anthelmintic treatment modulates antimycobacterial immunity, in a setting where helminth reinfection should not occur. We investigated the potential impact of helminth infection on immune responses to Mycobacterium tuberculosis (Mtb) in patients with latent Mtb infection with or without helminth infection (Strongyloides or Schistosoma), and tested T-cell responses before and after anthelmintic treatment. The study was performed in migrants resident in the United Kingdom, where reexposure and reinfection following anthelmintic treatment would not occur. The frequency of CD4(+) IFN-γ(+) T cells was measured following stimulation with Mtb Purified Protein Derivative or ESAT-6/CFP-10 antigen, and concentrations of IFN-γ in culture supernatants measured by ELISA and multiplex bead array. Helminth infection was associated with a lower frequency of CD4(+) IFN-γ(+) T cells, which increased following treatment. Patients with helminth infection showed a significant increase in CD4(+) FoxP3(+) T cells (Treg) compared to those without helminth infection. There was a decrease in the frequency of Treg cells, and an associated increase in CD4(+) IFN-γ(+) T cells after the anthelmintic treatment. Here, we show a potential role of Treg cells in reducing the frequency and function of antimycobacterial CD4(+) IFN-γ(+) T cells, and that these effects are reversed after anthelmintic treatment.

Interactions among bacterial strains and fluke genotypes shape virulence of co-infection

Most studies of virulence of infection focus on pairwise host-parasite interactions. However, hosts are almost universally co-infected by several parasite strains and/or genotypes of the same or different species. While theory predicts that co-infection favours more virulent parasite genotypes through intensified competition for host resources, knowledge of the effects of genotype by genotype (G × G) interactions between unrelated parasite species on virulence of co-infection is limited. Here, we tested such a relationship by challenging rainbow trout with replicated bacterial strains and fluke genotypes both singly and in all possible pairwise combinations. We found that virulence (host mortality) was higher in co-infections compared with single infections. Importantly, we also found that the overall virulence was dependent on the genetic identity of the co-infecting partners so that the outcome of co-infection could not be predicted from the respective virulence of single infections. Our results imply that G × G interactions among co-infecting parasites may significantly affect host health, add to variance in parasite fitness and thus influence evolutionary dynamics and ecology of disease in unexpected ways.

Malaria Parasites in the Asymptomatic: Looking for the Hay in the Haystack

With malaria elimination back on the international agenda, programs face the challenge of targeting all Plasmodium infections, not only symptomatic cases. As asymptomatic individuals are unlikely to seek treatment, they are missed by passive surveillance while remaining infectious to mosquitoes, thus acting as silent reservoirs of transmission. To estimate the risk of asymptomatic infections in various phases of malaria elimination, we need a deeper understanding of the underlying mechanisms favoring carriage over disease, which may involve both pathogen and host factors. Here we review our current knowledge on the determinants leading to Plasmodium falciparum symptomless infections. Understanding the host-pathogen interactions that are most likely to affect transitions between malaria disease states could guide the development of tools to tackle asymptomatic carriers in elimination settings.

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.

Disruptions of Host Immunity and Inflammation by Giardia Duodenalis: Potential Consequences for Co-Infections in the Gastro-Intestinal Tract

Giardia duodenalis (syn. G. intestinalis, or G. lamblia) is a leading cause of waterborne diarrheal disease that infects hundreds of millions of people annually. Research on Giardia has greatly expanded within the last few years, and our understanding of the pathophysiology and immunology on this parasite is ever increasing. At peak infection, Giardia trophozoites induce pathophysiological responses that culminate in the development of diarrheal disease. However, human data has suggested that the intestinal mucosa of Giardia-infected individuals is devoid of signs of overt intestinal inflammation, an observation that is reproduced in animal models. Thus, our understanding of host inflammatory responses to the parasite remain incompletely understood and human studies and experimental data have produced conflicting results. It is now also apparent that certain Giardia infections contain mechanisms capable of modulating their host's immune responses. As the oral route of Giardia infection is shared with many other gastrointestinal (GI) pathogens, co-infections may often occur, especially in places with poor sanitation and/or improper treatment of drinking water. Moreover, Giardia infections may modulate host immune responses and have been found to protect against the development of diarrheal disease in developing countries. The following review summarizes our current understanding of the immunomodulatory mechanisms of Giardia infections and their consequences for the host, and highlights areas for future research. Potential implications of these immunomodulatory effects during GI co-infection are also discussed.

Occurrence of immune cells in the intestinal wall of Squalius cephalus infected with Pomphorhynchus laevis

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.

Modulation of pro- and anti-inflammatory cytokines in active and latent tuberculosis by coexistent Strongyloides stercoralis infection

Helminth infections are known to induce modulation of both innate and adaptive immune responses in active and latent tuberculosis (TB). However, the role of helminth infections in modulating systemic cytokine responses in active and latent tuberculosis (LTB) is not known. To define the systemic cytokine levels in helminth-TB coinfection, we measured the circulating plasma levels of Type 1, Type 2, Type 17, other pro-inflammatory and regulatory cytokines in individuals with active TB (ATB) with or without coexistent Strongyloides stercoralis (Ss) infection by multiplex ELISA. Similarly, we also measured the same cytokine levels in individuals with LTB with or without concomitant Ss infection in a cross-sectional study. Our data reveal that individuals with ATB or LTB and coexistent Ss infection have significantly lower levels of Type 1 (IFNγ, TNFα and IL-2) and Type 17 (IL-17A and IL-17F) cytokines compared to those without Ss infection. In contrast, those with ATB and LTB with Ss infection have significantly higher levels of the regulatory cytokines (IL-10 and TGFβ), and those with LTB and Ss infection also have significantly higher levels of Type 2 cytokines (IL-4, IL-5 and IL-13) as well. Finally, those with LTB (but not ATB) exhibit significantly lower levels of other pro-inflammatory cytokines (IFNα, IFNβ, IL-6, IL-12 and GM-CSF). Our data therefore reveal a profound effect of Ss infection on the systemic cytokine responses in ATB and LTB and indicate that coincident helminth infections might influence pathogenesis of TB infection and disease.

Type 2 immunity-dependent reduction of segmented filamentous bacteria in mice infected with the helminthic parasite Nippostrongylus brasiliensis

BACKGROUND

Dynamic interactions between the host and gastrointestinal microbiota play an important role for local and systemic immune homeostasis. Helminthic parasites modulate the host immune response, resulting in protection against autoimmune disease but also increased susceptibility to pathogen infection. The underlying mechanisms remain largely unknown.

RESULTS

We showed that the type 2 immune response to enteric Nippostrongylus brasiliensis infection in mice was associated with altered intestinal mucin and AMP expression and shifts in microbiota composition. Most strikingly, infection reduced concentrations of intestinal segmented filamentous bacteria (SFB), known inducers of T helper 17 cells, and IL-17-associated gene expression. Infected mice deficient in IL-13 or STAT6 did not reduce SFB or IL-17, and exogenous IL-25 replicated the effects of parasite infection in wild type mice.

CONCLUSIONS

Our data show that parasite infection acts through host type 2 immunity to reduce intestinal SFB and expression of IL-17, providing an example of a microbiota-dependent immune modulation by parasites.

IFNγ and IL-12 Restrict Th2 Responses during Helminth/Plasmodium Co-Infection and Promote IFNγ from Th2 Cells

Parasitic helminths establish chronic infections in mammalian hosts. Helminth/Plasmodium co-infections occur frequently in endemic areas. However, it is unclear whether Plasmodium infections compromise anti-helminth immunity, contributing to the chronicity of infection. Immunity to Plasmodium or helminths requires divergent CD4⁺ T cell-driven responses, dominated by IFNγ or IL-4, respectively. Recent literature has indicated that Th cells, including Th2 cells, have phenotypic plasticity with the ability to produce non-lineage associated cytokines. Whether such plasticity occurs during co-infection is unclear. In this study, we observed reduced anti-helminth Th2 cell responses and compromised anti-helminth immunity during Heligmosomoides polygyrus and Plasmodium chabaudi co-infection. Using newly established triple cytokine reporter mice (Il4^gfpIfng^yfpIl17a^FP635), we demonstrated that Il4^gfp+ Th2 cells purified from in vitro cultures or isolated ex vivo from helminth-infected mice up-regulated IFNγ following adoptive transfer into Rag1^–/– mice infected with P. chabaudi. Functionally, Th2 cells that up-regulated IFNγ were transcriptionally re-wired and protected recipient mice from high parasitemia. Mechanistically, TCR stimulation and responsiveness to IL-12 and IFNγ, but not type I IFN, was required for optimal IFNγ production by Th2 cells. Finally, blockade of IL-12 and IFNγ during co-infection partially preserved anti-helminth Th2 responses. In summary, this study demonstrates that Th2 cells retain substantial plasticity with the ability to produce IFNγ during Plasmodium infection. Consequently, co-infection with Plasmodium spp. may contribute to the chronicity of helminth infection by reducing anti-helminth Th2 cells and converting them into IFNγ-secreting cells.

Approximately a third of the world’s population is burdened with chronic intestinal parasitic helminth infections, causing significant morbidities. Identifying the factors that contribute to the chronicity of infection is therefore essential. Co-infection with other pathogens, which is extremely common in helminth endemic areas, may contribute to the chronicity of helminth infections. In this study, we used a mouse model to test whether the immune responses to an intestinal helminth were impaired following malaria co-infection. These two pathogens induce very different immune responses, which, until recently, were thought to be opposing and non-interchangeable. This study identified that the immune cells required for anti-helminth responses are capable of changing their phenotype and providing protection against malaria. By identifying and blocking the factors that drive this change in phenotype, we can preserve anti-helminth immune responses during co-infection. Our studies provide fresh insight into how immune responses are altered during helminth and malaria co-infection.

A field trial of a PCR-based Mansonella ozzardi diagnosis assay detects high-levels of submicroscopic M. ozzardi infections in both venous blood samples and FTA card dried blood spots

Background

Mansonella ozzardi is a poorly understood human filarial parasite with a broad distribution throughout Latin America. Most of what is known about its parasitism has come from epidemiological studies that have estimated parasite incidence using light microscopy. Light microscopy can, however, miss lighter, submicroscopic, infections. In this study we have compared M. ozzardi incidence estimates made using light microscopy, with estimates made using PCR.

Methods

214 DNA extracts made from Large Volume Venous Blood Samples (LVVBS) were taken from volunteers from two study sites in the Rio Solimões region: Codajás [n = 109] and Tefé [n = 105] and were subsequently assayed for M. ozzardi parasitism using a diagnostic PCR (Mo-dPCR). Peripheral finger-prick blood samples were taken from the same individuals and used for microscopic examination. Finger-prick blood, taken from individuals from Tefé, was also used for the creation of FTA®card dried blood spots (DBS) that were subsequently subjected to Mo-dPCR.

Results

Overall M. ozzardi incidence estimates made with LVVBS PCRs were 1.8 times higher than those made using microscopy (44.9 % [96/214] compared with 24.3 % [52/214]) and 1.5 times higher than the PCR estimates made from FTA®card DBS (48/105 versus 31/105). PCR-based detection of FTA®card DBS proved 1.3 times more sensitive at diagnosing infections from peripheral blood samples than light microscopy did: detecting 24/105 compared with 31/105. PCR of LVVBS reported the fewest number of false negatives, detecting: 44 of 52 (84.6 %) individuals diagnosed by microscopy; 27 of 31 (87.1 %) of those diagnosed positive from DBSs and 17 out of 18 (94.4 %) of those diagnosed as positive by both alternative methodologies.

Conclusions

In this study, Mo-dPCR of LVVBS was by far the most sensitive method of detecting M. ozzardi infections and detected submicroscopic infections. Mo-dPCR FTA®card DBS also provided a more sensitive test for M. ozzardi diagnosis than light microscopy based diagnosis did and thus in settings where only finger-prick assays can be carried-out, it may be a more reliable method of detection. Most existing M. ozzardi incidence estimates, which are often based on light microscope diagnosis, are likely to dramatically underestimate true M. ozzardi parasitism incidence levels.

Beyond mice and men: environmental change, immunity and infections in wild ungulates

In the face of rapid environmental change, anticipating shifts in microparasite and macroparasite dynamics, including emergence events, is an enormous challenge. We argue that immunological studies in natural populations are pivotal to meeting this challenge: many components of environmental change--shifts in biotic assemblages, altered climate patterns and reduced environmental predictability--may affect host immunity. We suggest that wild ungulates can serve as model systems aiding the discovery of immunological mechanisms that link environmental change with parasite transmission dynamics. Our review of eco-immunological studies in wild ungulates reveals progress in understanding how co-infections affect immunity and parasite transmission and how environmental and genetic factors interact to shape immunity. Changes in bioavailability of micronutrients have been linked to immunity and health in wild ungulates. Although physiological stress in response to environmental change has been assessed, downstream effects on immunity have not been studied. Moreover, the taxonomic range of ungulates studied is limited to bovids (bighorn sheep, Soay sheep, chamois, musk oxen, bison, African buffalo) and a few cervids (red deer, black-tailed deer). We discuss areas where future studies in ungulates could lead to significant contributions in understanding the patterns of immunity and infection in natural populations and across species.

Immune antibodies and helminth products drive CXCR2-dependent macrophage-myofibroblast crosstalk to promote intestinal repair

Helminth parasites can cause considerable damage when migrating through host tissues, thus making rapid tissue repair imperative to prevent bleeding and bacterial dissemination particularly during enteric infection. However, how protective type 2 responses targeted against these tissue-disruptive multicellular parasites might contribute to homeostatic wound healing in the intestine has remained unclear. Here, we observed that mice lacking antibodies (Aid^-/-) or activating Fc receptors (Fcrg^-/-) displayed impaired intestinal repair following infection with the murine helminth Heligmosomoides polygyrus bakeri (Hpb), whilst transfer of immune serum could partially restore chemokine production and rescue wound healing in Aid^-/- mice. Impaired healing was associated with a reduced expression of CXCR2 ligands (CXCL2/3) by macrophages (MΦ) and myofibroblasts (MF) within intestinal lesions. Whilst antibodies and helminths together triggered CXCL2 production by MΦ in vitro via surface FcR engagement, chemokine secretion by intestinal MF was elicited by helminths directly via Fcrg-chain/dectin2 signaling. Blockade of CXCR2 during Hpb challenge infection reproduced the delayed wound repair observed in helminth infected Aid^-/- and Fcrg^-/- mice. Finally, conditioned media from human MΦ stimulated with infective larvae of the helminth Ascaris suum together with immune serum, promoted CXCR2-dependent scratch wound closure by human MF in vitro. Collectively our findings suggest that helminths and antibodies instruct a chemokine driven MΦ-MF crosstalk to promote intestinal repair, a capacity that may be harnessed in clinical settings of impaired wound healing.

To complete their lifecycles, helminth parasites have to migrate through tissues such as the skin, lung, liver and intestine. This migration causes severe tissue damage, resulting in the need for rapid repair to restore the integrity and function of damaged tissues. Protective type 2 immune responses against helminths can repair acute lung damage, but they can also promote liver fibrosis. However, how protective immune mechanisms might contribute to wound healing during enteric nematode infection has remained unclear. Here we show that during a protective antibody response, where helminth larvae are trapped in the intestinal mucosa, macrophages and myofibroblasts secrete chemokines, which promote the repair of helminth-caused lesions. Chemokine secretion by macrophages was triggered by antibodies and helminth products, whilst myofibroblasts produced chemokines directly in response to innate recognition of helminth products. The same chemokines that instructed intestinal repair in mice were also secreted by human macrophages, when co-cultured with immune serum and helminths. Finally, human myofibroblasts closed in vitro scratch wounds more rapidly, when stimulated with the chemokine secretions of helminth-antibody activated human macrophages. Thus, our findings reveal a novel mechanism, by which a protective antibody response can promote the repair of intestinal injury during helminth infection.

Epidemiology. Opposite effects of anthelmintic treatment on microbial infection at individual versus population scales

Parasitic worms modulate host immune responses in ways that affect microbial co-infections. For this reason, anthelmintic therapy may be a potent tool for indirectly controlling microbial pathogens. However, the population-level consequences of this type of intervention on co-infecting microbes are unknown. We evaluated the effects of anthelmintic treatment on bovine tuberculosis (BTB) acquisition, mortality after infection, and pathogen fitness in free-ranging African buffalo. We found that treatment had no effect on the probability of BTB infection, but buffalo survival after infection was ninefold higher among treated individuals. These contrasting effects translated into an approximately eightfold increase in the reproductive number of BTB for anthelmintic-treated compared with untreated buffalo. Our results indicate that anthelmintic treatment can enhance the spread of microbial pathogens in some real-world situations.

Chronic filarial infection provides protection against bacterial sepsis by functionally reprogramming macrophages

Helminths immunomodulate their hosts and induce a regulatory, anti-inflammatory milieu that prevents allergies and autoimmune diseases. Helminth immunomodulation may benefit sepsis outcome by preventing exacerbated inflammation and severe pathology, but the influence on bacterial clearance remains unclear. To address this, mice were chronically infected with the filarial nematode Litomosoides sigmodontis (L.s.) and the outcome of acute systemic inflammation caused by i.p. Escherichia coli injection was determined. L.s. infection significantly improved E. coli-induced hypothermia, bacterial clearance and sepsis survival and correlated with reduced concentrations of associated pro-inflammatory cytokines/chemokines and a less pronounced pro-inflammatory macrophage gene expression profile. Improved sepsis outcome in L.s.-infected animals was mediated by macrophages, but independent of the alternatively activated macrophage subset. Endosymbiotic Wolbachia bacteria that are present in most human pathogenic filariae, as well as L.s., signal via TLR2 and modulate macrophage function. Here, gene expression profiles of peritoneal macrophages from L.s.-infected mice revealed a downregulation of genes involved in TLR signaling, and pulsing of macrophages in vitro with L.s. extract reduced LPS-triggered activation. Subsequent transfer improved sepsis outcome in naïve mice in a Wolbachia- and TLR2-dependent manner. In vivo, phagocytosis was increased in macrophages from L.s.-infected wild type, but not TLR2-deficient animals. In association, L.s. infection neither improved bacterial clearance in TLR2-deficient animals nor ameliorated E. coli-induced hypothermia and sepsis survival. These results indicate that chronic L.s. infection has a dual beneficial effect on bacterial sepsis, reducing pro-inflammatory immune responses and improving bacterial control. Thus, helminths and their antigens may not only improve the outcome of autoimmune and allergic diseases, but may also present new therapeutic approaches for acute inflammatory diseases that do not impair bacterial control.

As the human immune system evolved in the presence of helminth infections, it is postulated that improved hygiene and subsequent loss of helminth infections and their immunomodulatory functions contributed to the sharp increase of autoimmune diseases and allergies over the last decades. Accordingly, helminth-induced anti-inflammatory, regulatory immune responses ameliorate allergy and autoimmune diseases and are likely to impact other immunological disorders including sepsis. Sepsis is an exacerbated, systemic inflammatory disease that occurs when pathogens cannot be locally confined and spread via the blood stream. Thus, efficient sepsis therapies should reduce excessive inflammation without impairing protective immune responses. In the present study we demonstrate that chronic filarial infection modulates macrophages to a less pro-inflammatory phenotype with improved phagocytic capacity. This immunomodulation reduces sepsis-induced inflammation and hypothermia and clears bacteria more efficiently thus improving sepsis survival. Moreover, we found that Wolbachia, the endosymbiotic bacteria of filariae, play a crucial role in triggering the correct macrophage response via TLR2. Thus, our observations suggest that helminths and helminth-derived antigens may not only present new treatment options for allergies and autoimmune diseases, but may also allow treatment of sepsis caused inflammation without impairing bacterial control.

Worms and Humans: A Happy Divorce?

Chronic asymptomatic worm infection, often in combination with tuberculosis (TB), is common in low-income countries. Indeed, a life without worm infestation, as is now the case in most high-income countries, is a recent condition for humankind. Worms and Mycobacterium tuberculosis give rise to different immune response patterns (Th2 vs. Th1 driven), and we have studied whether chronic worm infection affects the susceptibility to and control of TB in the low income country of Ethiopia. Our results, as well of those in the general literature, are inconclusive, although we have some rather strong data in support of adult deworming in relation to vaccination with bacillus Calmette-Guérin (BCG) against TB. In addition, we discuss briefly the putative relationship between chronic worm infestation and autoimmunity/allergy.

Antibody-mediated trapping of helminth larvae requires CD11b and Fcγ receptor I

Infections with intestinal helminths severely impact on human and veterinary health, particularly through the damage that these large parasites inflict when migrating through host tissues. Host immunity often targets the motility of tissue-migrating helminth larvae, which ideally should be mimicked by anti-helminth vaccines. However, the mechanisms of larval trapping are still poorly defined. We have recently reported an important role for Abs in the rapid trapping of tissue-migrating larvae of the murine parasite Heligmosomoides polygyrus bakeri. Trapping was mediated by macrophages (MΦ) and involved complement, activating FcRs, and Arginase-1 (Arg1) activity. However, the receptors and Ab isotypes responsible for MΦ adherence and Arg1 induction remained unclear. Using an in vitro coculture assay of H. polygyrus bakeri larvae and bone marrow-derived MΦ, we now identify CD11b as the major complement receptor mediating MΦ adherence to the larval surface. However, larval immobilization was largely independent of CD11b and instead required the activating IgG receptor FcγRI (CD64) both in vitro and during challenge H. polygyrus bakeri infection in vivo. FcγRI signaling also contributed to the upregulation of MΦ Arg1 expression in vitro and in vivo. Finally, IgG2a/c was the major IgG subtype from early immune serum bound by FcγRI on the MΦ surface, and purified IgG2c could trigger larval immobilization and Arg1 expression in MΦ in vitro. Our findings reveal a novel role for IgG2a/c-FcγRI-driven MΦ activation in the efficient trapping of tissue-migrating helminth larvae and thus provide important mechanistic insights vital for anti-helminth vaccine development.

Borrelia burgdorferi promotes the establishment of Babesia microti in the northeastern United States

Babesia microti and Borrelia burgdorferi, the respective causative agents of human babesiosis and Lyme disease, are maintained in their enzootic cycles by the blacklegged tick (Ixodes scapularis) and use the white-footed mouse (Peromyscus leucopus) as primary reservoir host. The geographic range of both pathogens has expanded in the United States, but the spread of babesiosis has lagged behind that of Lyme disease. Several studies have estimated the basic reproduction number (R₀) for B. microti to be below the threshold for persistence (<1), a finding that is inconsistent with the persistence and geographic expansion of this pathogen. We tested the hypothesis that host coinfection with B. burgdorferi increases the likelihood of B. microti transmission and establishment in new areas. We fed I. scapularis larva on P. leucopus mice that had been infected in the laboratory with B. microti and/or B. burgdorferi. We observed that coinfection in mice increases the frequency of B. microti infected ticks. To identify the ecological variables that would increase the probability of B. microti establishment in the field, we integrated our laboratory data with field data on tick burden and feeding activity in an R₀ model. Our model predicts that high prevalence of B. burgdorferi infected mice lowers the ecological threshold for B. microti establishment, especially at sites where larval burden on P. leucopus is lower and where larvae feed simultaneously or soon after nymphs infect mice, when most of the transmission enhancement due to coinfection occurs. Our studies suggest that B. burgdorferi contributes to the emergence and expansion of B. microti and provides a model to predict the ecological factors that are sufficient for emergence of B. microti in the wild.

Enterobiasis and strongyloidiasis and associated co-infections and morbidity markers in infants, preschool- and school-aged children from rural coastal Tanzania: a cross-sectional study

Background

There is a paucity of data pertaining to the epidemiology and public health impact of Enterobius vermicularis and Strongyloides stercoralis infections. We aimed to determine the extent of enterobiasis, strongyloidiasis, and other helminth infections and their association with asymptomatic Plasmodium parasitaemia, anaemia, nutritional status, and blood cell counts in infants, preschool-aged (PSAC), and school-aged children (SAC) from rural coastal Tanzania.

Methods

A total of 1,033 children were included in a cross-sectional study implemented in the Bagamoyo district in 2011/2012. Faecal samples were examined for intestinal helminth infections using a broad set of quality controlled methods. Finger-prick blood samples were subjected to filariasis and Plasmodium parasitaemia testing and full blood cell count examination. Weight, length/height, and/or mid-upper arm circumference were measured and the nutritional status determined in accordance with age.

Results

E. vermicularis infections were found in 4.2% of infants, 16.7%, of PSAC, and 26.3% of SAC. S. stercoralis infections were detected in 5.8%, 7.5%, and 7.1% of infants, PSAC, and SAC, respectively. Multivariable regression analyses revealed higher odds of enterobiasis in children of all age-groups with a reported anthelminthic treatment history over the past six months (odds ratio (OR): 2.15; 95% confidence interval (CI): 1.22 - 3.79) and in SAC with a higher temperature (OR: 2.21; CI: 1.13 - 4.33). Strongyloidiasis was associated with eosinophilia (OR: 2.04; CI: 1.20-3.48) and with Trichuris trichiura infections (OR: 4.13; CI: 1.04-16.52) in children of all age-groups, and with asymptomatic Plasmodium parasitaemia (OR: 13.03; CI: 1.34 - 127.23) in infants. None of the investigated helminthiases impacted significantly on the nutritional status and anaemia, but moderate asymptomatic Plasmodium parasitaemia was a strong predictor for anaemia in children aged older than two years (OR: 2.69; 95% CI: 1.23 – 5.86).

Conclusions

E. vermicularis and S. stercoralis infections were moderately prevalent in children from rural coastal Tanzania. Our data can contribute to inform yet missing global burden of disease and prevalence estimates for strongyloidiasis and enterobiasis. The association between S stercoralis and asymptomatic Plasmodium parasitaemia found here warrants further comprehensive investigations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0644-7) contains supplementary material, which is available to authorized users.

Effects of albendazole on the clinical outcome and immunological responses in helminth co-infected tuberculosis patients: a double blind randomised clinical trial

Despite several review papers and experimental studies concerning the impact of chronic helminth infection on tuberculosis in recent years, there is a scarcity of data from clinical field studies in highly endemic areas for these diseases. We believe this is the first randomised clinical trial investigating the impact of albendazole treatment on the clinical and immunological outcomes of helminth co-infected tuberculosis patients. A randomised, double-blind, placebo-controlled trial of albendazole (400mg per day for 3 days) in helminth-positive tuberculosis patients was conducted in Gondar, Ethiopia. The primary outcome was clinical improvement (ΔTB score) after 2 months. Among secondary outcomes were changes in the levels of eosinophils, CD4+ T cells, regulatory T cells, IFN-γ, IL-5 and IL-10 after 3 months. A total of 140 helminth co-infected tuberculosis patients were included with an HIV co-infection rate of 22.8%. There was no significant effect on the primary outcome (ΔTB score: 5.6±2.9 for albendazole versus 5.9±2.5 for placebo, P=0.59). The albendazole-treated group showed a decline in eosinophil cells (P=0.001) and IL-10 (P=0.017) after 3 months. In an exploratory analysis after 12 weeks, the albendazole treated group showed a trend towards weight gain compared with the placebo group (11.2±8.5 kg versus 8.2±8.7 kg, P=0.08)). The reductions in eosinophil counts and IL-10 show that asymptomatic helminth infection significantly affects host immunity during tuberculosis and can be effectively reversed by albendazole treatment. The clinical effects of helminth infection on chronic infectious diseases such as tuberculosis merit further characterisation.

Health-related quality of life among school children with parasitic infections: findings from a national cross-sectional survey in Côte d'Ivoire

Background

Parasitic infections are still of considerable public health relevance, notably among children in low- and middle-income countries. Measures to assess the magnitude of ill-health in infected individuals, however, are debated and patient-based proxies through generic health-related quality of life (HrQoL) instruments are among the proposed strategies. Disability estimates based on HrQoL are still scarce and conflicting, and hence, there is a need to strengthen the current evidence-base.

Methodology

Between November 2011 and February 2012, a national school-based cross-sectional survey was conducted in Côte d'Ivoire. Children underwent parasitological and clinical examination to assess infection status with Plasmodium and helminth species and clinical parameters, and responded to a questionnaire interview incorporating sociodemographic characteristics, self-reported morbidity, and HrQoL. Validity analysis of the HrQoL instrument was performed, assessing floor and ceiling effects, internal consistency, and correlation with morbidity scores. Multivariate regression models were applied to identify significant associations between HrQoL and children's parasitic infection and clinical status.

Principal Findings

Parasitological examination of 4,848 children aged 5–16 years revealed Plasmodium spp., hookworm, Schistosoma haematobium, Schistosoma mansoni, Ascaris lumbricoides, and Trichuris trichiura prevalences of 75.0%, 17.2%, 5.7%, 3.7%, 1.8%, and 1.3%, respectively. Anemic children showed a significant 1-point reduction in self-rated HrQoL on a scale from 0 to 100, whereas no significant negative association between HrQoL and parasite infection was observed. The 12-item HrQoL questionnaire proofed useful, as floor and ceiling effects were negligible, internally consistent (Cronbach's alpha = 0.71), and valid, as revealed by significant negative correlations and associations with children's self-reported and clinically assessed morbidity.

Conclusions/Significance

Our results suggest that HrQoL tools are not sufficiently sensitive to assess subtle morbidities due to parasitic infection in Ivorian school-aged children. However, more advanced morbid sequelae (e.g., anemia), were measurable by the instrument's health construct. Further investigations on health impacts of parasitic infection among school-aged children and refinement of generic HrQoL questionnaires are warranted.

Infectious diseases like malaria and parasitic worms affect hundreds of millions of people, and impact physical and cognitive development of children in Africa, Asia, and the Americas. Over the past 20 years, it was debated how the magnitude of ill-health due to these conditions should be assessed. One proposed strategy was to include patient-based ratings of wellbeing by administration of health-related quality of life (HrQoL) questionnaires. In order to provide new evidence on disability from parasitic infections, we conducted HrQoL interviews with children aged 5–16 years from 92 schools across Côte d'Ivoire. Children were examined for parasitic infections and clinical signs like anemia, malnutrition, and organ enlargement. We compared the self-rated HrQoL of infected and non-infected children and also considered their sociodemographic background. We could not identify lowered HrQoL in infected children, but we found that children with anemia reported a 1-point lower score on a 100-point HrQoL scale in comparison with their non-anemic counterparts. We consider our HrQoL questionnaire as useful and valid, but would recommend its further testing and development in few purposefully selected settings. Further investigation of disability induced by malaria and parasitic worm infections is warranted.

S. mansoni bolsters anti-viral immunity in the murine respiratory tract

The human intestinal parasite Schistosoma mansoni causes a chronic disease, schistosomiasis or bilharzia. According to the current literature, the parasite induces vigorous immune responses that are controlled by Th2 helper cells at the expense of Th1 helper cells. The latter cell type is, however, indispensable for anti-viral immune responses. Remarkably, there is no reliable literature among 230 million patients worldwide describing defective anti-viral immune responses in the upper respiratory tract, for instance against influenza A virus or against respiratory syncitial virus (RSV). We therefore re-examined the immune response to a human isolate of S. mansoni and challenged mice in the chronic phase of schistosomiasis with influenza A virus, or with pneumonia virus of mice (PVM), a mouse virus to model RSV infections. We found that mice with chronic schistosomiasis had significant, systemic immune responses induced by Th1, Th2, and Th17 helper cells. High serum levels of TNF-α, IFN-γ, IL-5, IL-13, IL-2, IL-17, and GM-CSF were found after mating and oviposition. The lungs of diseased mice showed low-grade inflammation, with goblet cell hyperplasia and excessive mucus secretion, which was alleviated by treatment with an anti-TNF-α agent (Etanercept). Mice with chronic schistosomiasis were to a relative, but significant extent protected from a secondary viral respiratory challenge. The protection correlated with the onset of oviposition and TNF-α-mediated goblet cell hyperplasia and mucus secretion, suggesting that these mechanisms are involved in enhanced immune protection to respiratory viruses during chronic murine schistosomiasis. Indeed, also in a model of allergic airway inflammation mice were protected from a viral respiratory challenge with PVM.

Production and analysis of immunomodulatory excretory-secretory products from the mouse gastrointestinal nematode Heligmosomoides polygyrus bakeri

Heligmosomoides polygyrus bakeri (Hpb) infection in mice is a convenient model for studying the pathophysiology and immunology of gastrointestinal (GI) helminth infection. Hpb infection suppresses immune responses to bystander antigens and unrelated pathogens, and it slows the progression and modifies the outcome of immune-mediated diseases. Hpb-derived excretory-secretory (ES) products potently modulate CD4(+) helper T cell (TH) responses by inducing regulatory T cells, tolerogenic dendritic cells (DCs) and immunoregulatory cytokines. This observation has spiked interest in identifying the immunomodulatory molecules, especially proteins, in ES products from Hpb and other GI nematodes for development as novel therapies to treat individuals with immune-mediated diseases, such as inflammatory bowel diseases (IBDs). In this protocol, we describe how to (i) maintain Hpb in the laboratory for experimental infections, (ii) collect adult worms from infected mice to generate ES products and (iii) evaluate the modulatory effects of ES products on toll-like receptor (TLR) ligand-induced maturation of CD11c(+) DCs. The three major sections of the PROCEDURE can be used independently, and they require ∼6, 10 and 27 h, respectively. Although other methods use a modified Baermann apparatus to collect Hpb adult worms, we describe a method that involves dissection of adult worms from intestinal tissue. The protocol will be useful to investigators studying the host-parasite interface and identifying and analyzing helminth-derived molecules with therapeutic potential.

Coincident helminth infection modulates systemic inflammation and immune activation in active pulmonary tuberculosis

BACKGROUND

Helminth infections are known to modulate innate and adaptive immune responses in active and latent tuberculosis (TB). However, the role of helminth infections in modulating responses associated with inflammation and immune activation (reflecting disease activity and/or severity) in TB is not known.

METHODOLOGY

We measured markers of inflammation and immune activation in active pulmonary TB individuals (ATB) with co-incidental Strongyloides stercoralis (Ss) infection. These included systemic levels of acute phase proteins, matrix metalloproteinases and their endogenous inhibitors and immune activation markers. As a control, we measured the systemic levels of the same molecules in TB-uninfected individuals (NTB) with or without Ss infection.

PRINCIPAL FINDINGS

Our data confirm that ATB is associated with elevated levels of the various measured molecules when compared to those seen in NTB. Our data also reveal that co-incident Ss infection in ATB individuals is associated with significantly decreased circulating levels of acute phase proteins, matrix metalloproteinases, tissue inhibitors of matrix metalloproteinases as well as the systemic immune activation markers, sCD14 and sCD163. These changes are specific to ATB since they are absent in NTB individuals with Ss infection.

CONCLUSIONS

Our data therefore reveal a profound effect of Ss infection on the markers associated with TB disease activity and severity and indicate that co-incidental helminth infections might dampen the severity of TB disease.

Impact of co-infections and BCG immunisation on immune responses among household contacts of tuberculosis patients in a Ugandan cohort

BACKGROUND

Tuberculosis incidence in resource poor countries remains high. We hypothesized that immune modulating co-infections such as helminths, malaria, and HIV increase susceptibility to latent tuberculosis infection (LTBI), thereby contributing to maintaining the tuberculosis epidemic.

METHODS

Adults with sputum-positive tuberculosis (index cases) and their eligible household contacts (HHCs) were recruited to a cohort study between May 2011 and January 2012. HHCs were investigated for helminths, malaria, and HIV at enrolment. HHCs were tested using the QuantiFERON-TB Gold In-Tube (QFN) assay at enrolment and six months later. Overnight whole blood culture supernatants from baseline QFN assays were analyzed for cytokine responses using an 11-plex Luminex assay. Associations between outcomes (LTBI or cytokine responses) and exposures (co-infections and other risk factors) were examined using multivariable logistic and linear regression models.

RESULTS

We enrolled 101 index cases and 291 HHCs. Among HHCs, baseline prevalence of helminths was 9% (25/291), malaria 16% (47/291), HIV 6% (16/291), and LTBI 65% (179/277). Adjusting for other risk factors and household clustering, there was no association between LTBI and any co-infection at baseline or at six months: adjusted odds ratio (95% confidence interval (CI); p-value) at baseline for any helminth, 1.01 (0.39-2.66; 0.96); hookworm, 2.81 (0.56-14.14; 0.20); malaria, 1.06 (0.48-2.35; 0.87); HIV, 0.74 (0.22-2.47; 0.63). HHCs with LTBI had elevated cytokine responses to tuberculosis antigens but co-infections had little effect on cytokine responses. Exploring other risk factors, Th1 cytokines among LTBI-positive HHCs with BCG scars were greatly reduced compared to those without scars: (adjusted geometric mean ratio) IFNγ 0.20 (0.09-0.42), <0.0001; IL-2 0.34 (0.20-0.59), <0.0001; and TNFα 0.36 (0.16-0.79), 0.01.

CONCLUSIONS

We found no evidence that co-infections increase the risk of LTBI, or influence the cytokine response profile among those with LTBI. Prior BCG exposure may reduce Th1 cytokine responses in LTBI.

Macrophage immunoregulatory pathways in tuberculosis

Macrophages, the major host cells harboring Mycobacterium tuberculosis (M.tb), are a heterogeneous cell type depending on their tissue of origin and host they are derived from. Significant discord in macrophage responses to M.tb exists due to differences in M.tb strains and the various types of macrophages used to study tuberculosis (TB). This review will summarize current concepts regarding macrophage responses to M.tb infection, while pointing out relevant differences in experimental outcomes due to the use of divergent model systems. A brief description of the lung environment is included since there is increasing evidence that the alveolar macrophage (AM) has immunoregulatory properties that can delay optimal protective host immune responses. In this context, this review focuses on selected macrophage immunoregulatory pattern recognition receptors (PRRs), cytokines, negative regulators of inflammation, lipid mediators and microRNAs (miRNAs).

Immune modulation by helminth parasites of ruminants: implications for vaccine development and host immune competence

Parasitic helminths reside in immunologically-exposed extracellular locations within their hosts, yet they are capable of surviving for extended periods. To enable this survival, these parasites have developed complex and multifaceted mechanisms to subvert or suppress host immunity. This review summarises current knowledge of immune modulation by helminth parasites of ruminants and the parasite-derived molecules involved in driving this modulation. Such immunomodulatory molecules have considerable promise as vaccine targets, as neutralisation of their function is predicted to enhance anti-parasite immunity and, as such, current knowledge in this area is presented herein. Furthermore, we summarise current evidence that, as well as affecting parasite-specific immunity, immune modulation by these parasites may also affect the ability of ruminant hosts to control concurrent diseases or mount effective responses to vaccination.

Helminth infections coincident with active pulmonary tuberculosis inhibit mono- and multifunctional CD4+ and CD8+ T cell responses in a process dependent on IL-10

Tissue invasive helminth infections and tuberculosis (TB) are co-endemic in many parts of the world and can trigger immune responses that might antagonize each other. We have previously shown that helminth infections modulate the Th1 and Th17 responses to mycobacterial-antigens in latent TB. To determine whether helminth infections modulate antigen-specific and non-specific immune responses in active pulmonary TB, we examined CD4⁺ and CD8⁺ T cell responses as well as the systemic (plasma) cytokine levels in individuals with pulmonary TB with or without two distinct helminth infections—Wuchereria bancrofti and Strongyloides stercoralis infection. By analyzing the frequencies of Th1 and Th17 CD4⁺ and CD8⁺ T cells and their component subsets (including multifunctional cells), we report a significant diminution in the mycobacterial–specific frequencies of mono- and multi–functional CD4⁺ Th1 and (to a lesser extent) Th17 cells when concomitant filarial or Strongyloides infection occurs. The impairment in CD4⁺ and CD8⁺ T cell cytokine responses was antigen-specific as polyclonal activated T cell frequencies were equivalent irrespective of helminth infection status. This diminution in T cell responses was also reflected in diminished circulating levels of Th1 (IFN-γ, TNF-α and IL-2)- and Th17 (IL-17A and IL-17F)-associated cytokines. Finally, we demonstrate that for the filarial co-infections at least, this diminished frequency of multifunctional CD4⁺ T cell responses was partially dependent on IL-10 as IL-10 blockade significantly increased the frequencies of CD4⁺ Th1 cells. Thus, co-existent helminth infection is associated with an IL-10 mediated (for filarial infection) profound inhibition of antigen-specific CD4⁺ T cell responses as well as protective systemic cytokine responses in active pulmonary TB.

While it has long been recognized that helminth infections alter the pathophysiology of allergic and autoimmune disease, data suggest that helminth infections also exert an important immunological effect on concomitant infections and vaccine responses. In particular, helminth coinfection can modulate the severity, pathogenesis and transmission of other infectious diseases. In this study, we examine the mechanism by which helminth infections modulate the immunological responses to tuberculosis antigens in individuals with active pulmonary tuberculosis. Our data suggest that two different helminth infections, with different life cycles, tissue localization and modes of transmission essentially exert very similar effects on the adaptive immune response to tuberculosis antigens in pulmonary tuberculosis. This includes a compromised induction of protective cytokine-expressing T cells as well as inhibitory effects on systemic cytokines that are potentially protective in tuberculosis. The strength of this study lies in the fact that this is the first study to demonstrate that two different helminth infections essentially impair cytokine responses in a similar manner in pulmonary tuberculosis.

Co-infection of long-term carriers of Plasmodium falciparum with Schistosoma haematobium enhances protection from febrile malaria: a prospective cohort study in Mali

Background

Malaria and schistosomiasis often overlap in tropical and subtropical countries and impose tremendous disease burdens; however, the extent to which schistosomiasis modifies the risk of febrile malaria remains unclear.

Methods

We evaluated the effect of baseline S. haematobium mono-infection, baseline P. falciparum mono-infection, and co-infection with both parasites on the risk of febrile malaria in a prospective cohort study of 616 children and adults living in Kalifabougou, Mali. Individuals with S. haematobium were treated with praziquantel within 6 weeks of enrollment. Malaria episodes were detected by weekly physical examination and self-referral for 7 months. The primary outcome was time to first or only malaria episode defined as fever (≥37.5°C) and parasitemia (≥2500 asexual parasites/µl). Secondary definitions of malaria using different parasite densities were also explored.

Results

After adjusting for age, anemia status, sickle cell trait, distance from home to river, residence within a cluster of high S. haematobium transmission, and housing type, baseline P. falciparum mono-infection (n = 254) and co-infection (n = 39) were significantly associated with protection from febrile malaria by Cox regression (hazard ratios 0.71 and 0.44; P = 0.01 and 0.02; reference group: uninfected at baseline). Baseline S. haematobium mono-infection (n = 23) did not associate with malaria protection in the adjusted analysis, but this may be due to lack of statistical power. Anemia significantly interacted with co-infection (P = 0.009), and the malaria-protective effect of co-infection was strongest in non-anemic individuals. Co-infection was an independent negative predictor of lower parasite density at the first febrile malaria episode.

Conclusions

Co-infection with S. haematobium and P. falciparum is significantly associated with reduced risk of febrile malaria in long-term asymptomatic carriers of P. falciparum. Future studies are needed to determine whether co-infection induces immunomodulatory mechanisms that protect against febrile malaria or whether genetic, behavioral, or environmental factors not accounted for here explain these findings.

The parasitic diseases malaria and schistosomiasis are tremendous public health burdens, each affecting over 200 million people worldwide with substantial geographic overlap in sub-Saharan Africa. Understanding how schistosomiasis influences the human immune response to Plasmodium, the agent of malaria, can be important for developing effective malaria vaccines. Past studies have tried to determine if infection with Schistosoma haematobium, which causes urinary schistosomiasis, affects the number of febrile attacks from malaria caused by Plasmodium falciparum in communities where the diseases overlap, but the findings have been inconsistent. Here, we examined 616 healthy people from a village in Mali for symptomless infections with S. haematobium and treated those with infections. We then followed them over a single malaria-transmission season of 7 months during which we diagnosed and treated all febrile malaria attacks. After the season, we examined archived blood collected at enrollment to look for occult P. falciparum infection. The study revealed that people who were infected with both parasites at the beginning of the season were better protected from the malaria attacks than those who were uninfected or infected with either parasite alone. Further studies are needed to confirm these findings and to determine the biological basis for this phenomenon.

Neutrophils prime a long-lived effector macrophage phenotype that mediates accelerated helminth expulsion

We examined the role of innate cells in acquired resistance to the natural murine parasitic nematode, Nippostrongylus brasiliensis. Macrophages obtained from lungs as late as 45 d after N. brasiliensis inoculation were able to transfer accelerated parasite clearance to naive recipients. Primed macrophages adhered to larvae in vitro and triggered increased mortality of parasites. Neutrophil depletion in primed mice abrogated the protective effects of transferred macrophages and inhibited their in vitro binding to larvae. Neutrophils in parasite-infected mice showed a distinct transcriptional profile and promoted alternatively activated M2 macrophage polarization through secretory factors including IL-13. Differentially activated neutrophils in the context of a type 2 immune response therefore prime a long-lived effector macrophage phenotype that directly mediates rapid nematode damage and clearance.

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.

Coinfection. Virus-helminth coinfection reveals a microbiota-independent mechanism of immunomodulation

The mammalian intestine is colonized by beneficial commensal bacteria and is a site of infection by pathogens, including helminth parasites. Helminths induce potent immunomodulatory effects, but whether these effects are mediated by direct regulation of host immunity or indirectly through eliciting changes in the microbiota is unknown. We tested this in the context of virus-helminth coinfection. Helminth coinfection resulted in impaired antiviral immunity and was associated with changes in the microbiota and STAT6-dependent helminth-induced alternative activation of macrophages. Notably, helminth-induced impairment of antiviral immunity was evident in germ-free mice, but neutralization of Ym1, a chitinase-like molecule that is associated with alternatively activated macrophages, could partially restore antiviral immunity. These data indicate that helminth-induced immunomodulation occurs independently of changes in the microbiota but is dependent on Ym1.

Tuberculosis in Papua New Guinea: from yesterday until today

Little is known about the situation of tuberculosis in Papua New Guinea despite its high TB burden, emerging drug resistance and rising HIV co-infection. This review gives an overview on the current situation of TB in PNG and identifies knowledge gaps that should urgently be addressed in the future.

Controversies and challenges in research on urogenital schistosomiasis-associated bladder cancer

Urogenital schistosomiasis, infection with Schistosoma haematobium, is linked to increased risk for the development of bladder cancer, but the importance of various mechanisms responsible for this association remains unclear, in part, owing to lack of sufficient and appropriate animal models. New advances in the study of this parasite, bladder regenerative processes, and human schistosomal bladder cancers may shed new light on the complex biological processes that connect S. haematobium infection to bladder carcinogenesis.

Systemic impact of intestinal helminth infections

In this review, we examine the evidence that intestinal helminths can control harmful inflammatory responses and promote homeostasis by triggering systemic immune responses. Induction of separable components of immunity by helminths, which includes type 2 and immune regulatory responses, can both contribute toward the reduction in harmful type 1 immune responses that drive certain inflammatory diseases. Despite inducing type 2 responses, intestinal helminths may also downregulate harmful type 2 immune responses including allergic responses. We consider the possibility that intestinal helminth infection may indirectly affect inflammation by influencing the composition of the intestinal microbiome. Taken together, the studies reviewed herein suggest that intestinal helminth-induced responses have potent systemic effects on the immune system, raising the possibility that whole parasites or specific molecules produced by these metazoans may be an important resource for the development of future immunotherapies to control inflammatory diseases.

Helminth infection reactivates latent γ-herpesvirus via cytokine competition at a viral promoter

Mammals are coinfected by multiple pathogens that interact through unknown mechanisms. We found that helminth infection, characterized by the induction of the cytokine interleukin-4 (IL-4) and the activation of the transcription factor Stat6, reactivated murine γ-herpesvirus infection in vivo. IL-4 promoted viral replication and blocked the antiviral effects of interferon-γ (IFNγ) by inducing Stat6 binding to the promoter for an important viral transcriptional transactivator. IL-4 also reactivated human Kaposi's sarcoma-associated herpesvirus from latency in cultured cells. Exogenous IL-4 plus blockade of IFNγ reactivated latent murine γ-herpesvirus infection in vivo, suggesting a "two-signal" model for viral reactivation. Thus, chronic herpesvirus infection, a component of the mammalian virome, is regulated by the counterpoised actions of multiple cytokines on viral promoters that have evolved to sense host immune status.

Protection and pathology during parasite infection: IL-10 strikes the balance

The host response to infection requires an immune response to be strong enough to control the pathogen but also restrained, to minimize immune-mediated pathology. The conflicting pressures of immune activation and immune suppression are particularly apparent in parasite infections, where co-evolution of host and pathogen has selected many different compromises between protection and pathology. Cytokine signals are critical determinants of both protective immunity and immunopathology, and, in this review, we focus on the regulatory cytokine IL-10 and its role in protozoan and helminth infections. We discuss the sources and targets of IL-10 during parasite infection, the signals that initiate and reinforce its action, and its impact on the invading parasite, on the host tissue, and on coincident immune responses.

Iron, anemia and hepcidin in malaria

Malaria and iron have a complex but important relationship. Plasmodium proliferation requires iron, both during the clinically silent liver stage of growth and in the disease-associated phase of erythrocyte infection. Precisely how the protozoan acquires its iron from its mammalian host remains unclear, but iron chelators can inhibit pathogen growth in vitro and in animal models. In humans, iron deficiency appears to protect against severe malaria, while iron supplementation increases risks of infection and disease. Malaria itself causes profound disturbances in physiological iron distribution and utilization, through mechanisms that include hemolysis, release of heme, dyserythropoiesis, anemia, deposition of iron in macrophages, and inhibition of dietary iron absorption. These effects have significant consequences. Malarial anemia is a major global health problem, especially in children, that remains incompletely understood and is not straightforward to treat. Furthermore, the changes in iron metabolism during a malaria infection may modulate susceptibility to co-infections. The release of heme and accumulation of iron in granulocytes may explain increased vulnerability to non-typhoidal Salmonella during malaria. The redistribution of iron away from hepatocytes and into macrophages may confer host resistance to superinfection, whereby blood-stage parasitemia prevents the development of a second liver-stage Plasmodium infection in the same organism. Key to understanding the pathophysiology of iron metabolism in malaria is the activity of the iron regulatory hormone hepcidin. Hepcidin is upregulated during blood-stage parasitemia and likely mediates much of the iron redistribution that accompanies disease. Understanding the regulation and role of hepcidin may offer new opportunities to combat malaria and formulate better approaches to treat anemia in the developing world.

Kingdom-agnostic metagenomics and the importance of complete characterization of enteric microbial communities

Advanced sequencing techniques have shown that bacteria are not the only complex and important microbes in the human intestine. Nonbacterial organisms, particularly the virome and the mycobiome, are important regulators of intestinal immunity and inflammation. The virome is mucosal and systemic; it can alter the host response to bacteria and interact with host genes and bacteria to contribute to disease pathogenesis. The human mycobiome is also complex and can contribute to intestinal inflammation. We review what has recently been learned about the nonbacterial and nonarchaeal microbes in the gastrointestinal tract, discussing their potential effects on health and disease and analytical approaches for their study. Studies of associations between the microbiome and intestinal pathology should incorporate kingdom-agnostic approaches if we are to fully understand intestinal health and disease.