A molecular signature for IL-10-producing Th1 cells in protozoan parasitic diseases

Control of visceral leishmaniasis (VL) depends on proinflammatory Th1 cells that activate infected tissue macrophages to kill resident intracellular parasites. However, proinflammatory cytokines produced by Th1 cells can damage tissues and require tight regulation. Th1 cell IL-10 production is an important cell-autologous mechanism to prevent such damage. However, IL-10-producing Th1 (type 1 regulatory; Tr1) cells can also delay control of parasites and the generation of immunity following drug treatment or vaccination. To identify molecules to target in order to alter the balance between Th1 and Tr1 cells for improved antiparasitic immunity, we compared the molecular and phenotypic profiles of Th1 and Tr1 cells in experimental VL caused by Leishmania donovani infection of C57BL/6J mice. We also identified a shared Tr1 cell protozoan signature by comparing the transcriptional profiles of Tr1 cells from mice with experimental VL and malaria. We identified LAG3 as an important coinhibitory receptor in patients with VL and experimental VL, and we reveal tissue-specific heterogeneity of coinhibitory receptor expression by Tr1 cells. We also discovered a role for the transcription factor Pbx1 in suppressing CD4+ T cell cytokine production. This work provides insights into the development and function of CD4+ T cells during protozoan parasitic infections and identifies key immunoregulatory molecules.

Innate immunity and cnidarian-Symbiodiniaceae mutualism

The phylum Cnidaria (sea anemones, corals, hydra, jellyfish) is one the most distantly related animal phyla to humans, and yet cnidarians harbor many of the same cellular pathways involved in innate immunity in mammals. In addition to its role in pathogen recognition, the innate immune system has a role in managing beneficial microbes and supporting mutualistic microbial symbioses. Some corals and sea anemones undergo mutualistic symbioses with photosynthetic algae in the family Symbiodiniaceae. These symbioses can be disrupted by anthropogenic disturbances of ocean environments, which can have devastating consequences for the health of coral reef ecosystems. Several studies of cnidarian-Symbiodiniaceae symbiosis have implicated proteins in the host immune system as playing a role in both symbiont tolerance and loss of symbiosis (i.e., bleaching). In this review, we critically evaluate current knowledge about the role of host immunity in the regulation of symbiosis in cnidarians.

Glycoconjugates of Gram-negative bacteria and parasitic protozoa - are they similar in orchestrating the innate immune response?

Innate immunity is an evolutionarily ancient form of host defense that serves to limit infection. The invading microorganisms are detected by the innate immune system through germline-encoded PRRs. Different classes of PRRs, including TLRs and cytoplasmic receptors, recognize distinct microbial components known collectively as PAMPs. Ligation of PAMPs with receptors triggers intracellular signaling cascades, activating defense mechanisms. Despite the fact that Gram-negative bacteria and parasitic protozoa are phylogenetically distant organisms, they express glycoconjugates, namely bacterial LPS and protozoan GPI-anchored glycolipids, which share many structural and functional similarities. By activating/deactivating MAPK signaling and NF-κB, these ligands trigger general pro-/anti-inflammatory responses depending on the related patterns. They also use conservative strategies to subvert cell-autonomous defense systems of specialized immune cells. Signals triggered by Gram-negative bacteria and parasitic protozoa can interfere with host homeostasis and, depending on the type of microorganism, lead to hypersensitivity or silencing of the immune response. Activation of professional immune cells, through a ligand which triggers the opposite effect (antagonist versus agonist) appears to be a promising solution to restoring the immune balance.

Lipid Droplet, a Key Player in Host-Parasite Interactions

Lipid droplets (lipid bodies, LDs) are dynamic organelles that have important roles in regulating lipid metabolism, energy homeostasis, cell signaling, membrane trafficking, and inflammation. LD biogenesis, composition, and functions are highly regulated and may vary according to the stimuli, cell type, activation state, and inflammatory environment. Increased cytoplasmic LDs are frequently observed in leukocytes and other cells in a number of infectious diseases. Accumulating evidence reveals LDs participation in fundamental mechanisms of host-pathogen interactions, including cell signaling and immunity. LDs are sources of eicosanoid production, and may participate in different aspects of innate signaling and antigen presentation. In addition, intracellular pathogens evolved mechanisms to subvert host metabolism and may use host LDs, as ways of immune evasion and nutrients source. Here, we review mechanisms of LDs biogenesis and their contributions to the infection progress, and discuss the latest discoveries on mechanisms and pathways involving LDs roles as regulators of the immune response to protozoan infection.

Human Intestinal Microbiota: Interaction Between Parasites and the Host Immune Response

The human gut is a highly complex ecosystem with an extensive microbial community, and the influence of the intestinal microbiota reaches the entire host organism. For example, the microbiome regulates fat storage, stimulates or renews epithelial cells, and influences the development and maturation of the brain and the immune system. Intestinal microbes can protect against infection by pathogenic bacteria, viruses, fungi and parasites. Hence, the maintenance of homeostasis between the gut microbiota and the rest of the body is crucial for health, with dysbiosis affecting disease. This review focuses on intestinal protozoa, especially those still representing a public health problem in Mexico, and their interactions with the microbiome and the host. The decrease in prevalence of intestinal helminthes in humans left a vacant ecological niche that was quickly occupied by protozoa. Although the mechanisms governing the interaction between intestinal microbiota and protozoa are poorly understood, it is known that the composition of the intestinal bacterial populations modulates the progression of protozoan infection and the outcome of parasitic disease. Most reports on the complex interactions between intestinal bacteria, protozoa and the immune system emphasize the protective role of the microbiota against protozoan infection. Insights into such protection may facilitate the manipulation of microbiota components to prevent and treat intestinal protozoan infections. Here we discuss recent findings about the immunoregulatory effect of intestinal microbiota with regards to intestinal colonization by protozoa, focusing on infections by Entamoeba histolytica, Blastocystis spp, Giardia duodenalis, Toxoplasma gondii and Cryptosporidium parvum. The possible consequences of the microbiota on parasitic, allergic and autoimmune disorders are also considered.

Dual recognition activity of a rhamnose-binding lectin to pathogenic bacteria and zooxanthellae in stony coral Pocillopora damicornis

Rhamnose-binding lectin (RBL) is a type of Ca²⁺-independent lectin with tandem repeat carbohydrate-recognition domain, and is crucial for the innate immunity in many invertebrates. In this study, the cDNA sequence encoding RBL in coral Pocillopora damicornis (PdRBL-1) was cloned. The PdRBL-1 protein shared highest amino acid sequence similarity (55%) with the polyp of Hydra vulgaris, and contained a signal peptide and two tandem carbohydrate-recognition domains in which all cysteine residues were conserved. Surface plasmon resonance method revealed that the recombinant PdRBL-1 protein bound to LPS and Lipid A, but not to LTA, β-glucan, mannose and Poly (I:C). Results also showed that it bonded with zooxanthellae using western blotting method, and that the bound protein was detectable only at concentrations higher than 10² zooxanthellae cell mL^-1. When recombinant PdRBL-1 protein was preincubated with LPS, lower amounts of protein bound to zooxanthellae compared to cells not preincubated with LPS. Furthermore, PdRBL-1 mRNA expression increased significantly at 12 h, and declined to the baseline at 24 h after heat stress at 31 °C. These results collectively suggest that PdRBL-1 could recognize not only pathogenic bacteria but also symbiotic zooxanthellae, and that the recognition of zooxanthellae by PdRBL-1 could be repressed by pathogenic bacteria through competitive binding. This information allows us to gain new insights in the mechanisms influencing the establishment and maintenance of coral-zooxanthella symbiosis in coral P. damicornis.

Immunity to gastrointestinal microparasites of fish

Fish intestinal parasites cause direct mortalities and also morbidity, poor growth, higher susceptibility to opportunistic pathogens and lower resistance to stress. This review is focused on microscopic parasites (Protozoa and Metazoa) that invade the gastrointestinal tract of fish. Intracellular parasites (mainly Microsporidia and Apicomplexa) evoke almost no host immune reaction while they are concealed in the cytoplasmic and nuclear compartments, and can even use fish cells (macrophages) as Trojan horses to spread in the host. Inflammatory reaction only appears when the parasite bursts infected cells. Immunity against extracellular parasites is depicted for the myxozoans Ceratonova shasta and Enteromyxum spp. The cellular and humoral innate responses and the production of antibodies are crucial for resolving some of these myxozoonoses, but an excessive inflammatory reaction (concerted by cytokines) can become a fatal pathophysiological consequence. The local immune response plays a key role, with numerous genes more strongly regulated in the intestine than at lymphohaematopoietic organs.

Uterine Mast Cells and Immunoglobulin-E Antibody Responses During Clearance of Tritrichomonas foetus

We showed earlier that Tritrichomonas foetus-specific bovine immunoglobulin (Ig)G1 and IgA antibodies in uterine and vaginal secretions are correlated with clearance of this sexually transmitted infection. Eosinophils have been noted in previous studies of bovine trichomoniasis but the role of mast cells and IgE responses have not been reported. The hypothesis that IgE and mast cell degranulation play a role in clearance was tested in 25 virgin heifers inseminated experimentally and infected intravaginally with T. foetus strain D1 at estrus and cultured weekly. Groups were euthanatized at 3, 6, 9, or 12 weeks, when tissues were fixed and secretions were collected for culture and antibody analysis. Immunohistochemistry using a monoclonal antibody to a soluble lipophosphoglycan (LPG)-containing surface antigen (TF1.17) demonstrated antigen uptake by uterine epithelial cells. Lymphoid nodules were detected below antigen-positive epithelium. Little IgG2 antibody was detected but IgG1, IgA, IgM, and IgE T. foetus-specific antibodies increased in uterine secretions at weeks 6 and 9 after infection. This was inversely proportional to subepithelial mast cells numbers and most animals cleared the infection by the sampling time after the lowest mast cell count. Furthermore, soluble antigen was found in uterine epithelium above inductive sites (lymphoid nodules). Cross-linking of IgE on mast cells by antigen and perhaps LPG triggering appears to have resulted in degranulation. Released cytokines may account for production of predominantly Th2 (IgG1 and IgE) and IgA antibody responses, which are related to clearance of the infection.

The Impact of a Successful Anti-Myxosporean Treatment on the Phagocyte Functions of Juvenile and Adult Sparus Aurata L

The aim of the present study was to investigate the impact of a successful anti-myxosporean medication on the innate immune system of fish intensively cultured in the Mediterranean basin. For this purpose, juvenile and adult gilthead seabream ( S. aurata L.) naturally infected with Polysporoplasma sparis in the kidney were used in a small-scale field trial. The infected fish were treated orally with the combination of salinomycin and amprolium, two drugs well known for their anti-coccidial effect in other animals. Drug efficacy and safety was evaluated in terms of changes observed in histopathology, mortality and P. sparis intensity and prevalence rate. Phagocytic functions of head-kidney leucocytes were also investigated at the end as well as one month post the medication. Salinomycin with amprolium exhibited a significant reduction in intensity and prevalence rate in both juvenile and adult fish, and no histopathological evidence for toxic side effects was observed. In addition, the successful treatment was closely correlated with a complete restoration of the diminished phagocytic ability and capacity as well as NO, and lysozyme secretion in a time dependent manner. This data suggests that salilomycin with amprolium can be an alternative treatment for myxosporean infections in warm-water fish, possibly exhibiting their action through the enhancement of host innate functions.

Tuft cells, taste-chemosensory cells, orchestrate parasite type 2 immunity in the gut

The intestinal epithelium forms an essential barrier between a host and its microbiota. Protozoa and helminths are members of the gut microbiota of mammals, including humans, yet the many ways that gut epithelial cells orchestrate responses to these eukaryotes remain unclear. Here we show that tuft cells, which are taste-chemosensory epithelial cells, accumulate during parasite colonization and infection. Disruption of chemosensory signaling through the loss of TRMP5 abrogates the expansion of tuft cells, goblet cells, eosinophils, and type 2 innate lymphoid cells during parasite colonization. Tuft cells are the primary source of the parasite-induced cytokine interleukin-25, which indirectly induces tuft cell expansion by promoting interleukin-13 production by innate lymphoid cells. Our results identify intestinal tuft cells as critical sentinels in the gut epithelium that promote type 2 immunity in response to intestinal parasites.

Antiparasitic DNA vaccines in 21st century

Demands for effective vaccines to control parasitic diseases of humans and livestock have been recently exacerbated by the development of resistance of most pathogenic parasites to anti-parasitic drugs. Novel genomic and proteomic technologies have provided opportunities for the discovery and improvement of DNA vaccines which are relatively easy as well as cheap to fabricate and stable at room temperatures. However, their main limitation is rather poor immunogenicity, which makes it necessary to couple the antigens with adjuvant molecules. This paper review recent advances in the development of DNA vaccines to some pathogenic protozoa and helminths. Numerous studies were conducted over the past 14 years of 21st century, employing various administration techniques, adjuvants and new immunogenic antigens to increase efficacy of DNA vaccines. Unfortunately, the results have not been rewarding. Further research is necessary using more extensive combinations of antigens; alternate delivery systems and more efficient adjuvants based on knowledge of the immunomodulatory capacities of parasitic protozoa and helminths.

A blurring of life-history lines: Immune function, molt and reproduction in a highly stable environment

Rufous-collared sparrows (Zonotrichia capensis peruviensis) from valleys in the Atacama Desert of Chile, live in an extremely stable environment, and exhibit overlap in molt and reproduction, with valley-specific differences in the proportion of birds engaged in both. To better understand the mechanistic pathways underlying the timing of life-history transitions, we examined the relationships among baseline and stress-induced levels of corticosterone (CORT), testosterone, and bacteria-killing ability of the blood plasma (BKA), as well as haemosporidian parasite infections and the genetic structure of two groups of sparrows from separate valleys over the course of a year. Birds neither molting nor breeding had the lowest BKA, but there were no differences among the other three categories of molt-reproductive stage. BKA varied over the year, with birds in May/June exhibiting significantly lower levels of BKA than the rest of the year. We also documented differences in the direction of the relationship between CORT and BKA at different times during the year. The direction of these relationships coincides with some trends in molt and reproductive stage, but differs enough to indicate that these birds exhibit individual-level plasticity, or population-level variability, in coordinating hypothalamo-pituitary-adrenal axis activity with life-history stage. We found weak preliminary evidence for genetic differentiation between the two populations, but not enough to indicate genetic isolation. No birds were infected with haemosporidia, which may be indicative of reduced parasite pressure in deserts. The data suggest that these birds may not trade off among different life-history components, but rather are able to invest in multiple life-history components based on their condition.

De novo transcriptome sequencing of the Octopus vulgaris hemocytes using Illumina RNA-Seq technology: response to the infection by the gastrointestinal parasite Aggregata octopiana

Background

Octopus vulgaris is a highly valuable species of great commercial interest and excellent candidate for aquaculture diversification; however, the octopus’ well-being is impaired by pathogens, of which the gastrointestinal coccidian parasite Aggregata octopiana is one of the most important. The knowledge of the molecular mechanisms of the immune response in cephalopods, especially in octopus is scarce. The transcriptome of the hemocytes of O. vulgaris was de novo sequenced using the high-throughput paired-end Illumina technology to identify genes involved in immune defense and to understand the molecular basis of octopus tolerance/resistance to coccidiosis.

Results

A bi-directional mRNA library was constructed from hemocytes of two groups of octopus according to the infection by A. octopiana, sick octopus, suffering coccidiosis, and healthy octopus, and reads were de novo assembled together. The differential expression of transcripts was analysed using the general assembly as a reference for mapping the reads from each condition. After sequencing, a total of 75,571,280 high quality reads were obtained from the sick octopus group and 74,731,646 from the healthy group. The general transcriptome of the O. vulgaris hemocytes was assembled in 254,506 contigs. A total of 48,225 contigs were successfully identified, and 538 transcripts exhibited differential expression between groups of infection. The general transcriptome revealed genes involved in pathways like NF-kB, TLR and Complement. Differential expression of TLR-2, PGRP, C1q and PRDX genes due to infection was validated using RT-qPCR. In sick octopuses, only TLR-2 was up-regulated in hemocytes, but all of them were up-regulated in caecum and gills.

Conclusion

The transcriptome reported here de novo establishes the first molecular clues to understand how the octopus immune system works and interacts with a highly pathogenic coccidian. The data provided here will contribute to identification of biomarkers for octopus resistance against pathogens, which could improve octopus farming in the near future.

[Progress on IL-27 in immunity to important protozoan parasitic infections]

Parasitic infection can stimulate a series of immune responses and lead to changes in cytokines. This paper focuses on the progress on the role of IL-27 in immunity to some protozoan infection, caused by Toxoplasma gondii, Leishmania, Plasmodium, and Trypanosoma cruzi.

T cell exhaustion in protozoan disease

Protozoan parasites cause severe morbidity and mortality in humans worldwide, especially in developing countries where access to chemotherapeutic agents is limited. Although parasites initially evoke a robust immune response, subsequent immunity fails to clear infection, ultimately leading to the chronic stage. This enigmatic situation was initially addressed in chronic viral models, where T cells lose their function, a phenomenon referred to as 'exhaustion'. However, recent studies demonstrate that this paradigm can be extended to protozoan diseases as well, although with notable differences. These studies have revealed that T cell responses generated against Toxoplasma gondii, Plasmodium sp., and Leishmania sp. can become dysfunctional. This review discusses T cell exhaustion in parasitic infection, mechanisms of development, and a possible role in disease outcome.

[Research advances of interleukin-15 in anti-parasitic infection]

Interleukin-15 (IL-15) is a pro-inflammatory cytokine and also a chemotactic factor for a variety of immune cells, which participates in and regulates the inflammatory response and immune response to organisms. Up to now, the molecular structure and receptor of IL-15 have been widely researched, with important advances in its signal transduction way. However, its application in parasitology is still a relatively new topic. This article summarizes the latest research development of IL-15 in anti-parasitic infection, prospects its mechanism and application.

Pathogens and the placental fortress

Placental infections are major causes of maternal and fetal disease. This review introduces a new paradigm for placental infections based on current knowledge of placental defenses and how this barrier can be breached. Transmission of pathogens from mother to fetus can occur at two sites of direct contact between maternal cells and specialized fetal cells (trophoblasts) in the human placenta: firstly, maternal immune and endothelial cells juxtaposed to extravillous trophoblasts in the uterine implantation site and secondly, maternal blood surrounding the syncytiotrophoblast (SYN). Recent findings suggest that the primary vulnerability is in the implantation site. We explore evidence that the placental SYN evolved as a defense against pathogens, and that inflammation-mediated spontaneous abortion may benefit mother and pathogen.

Proteases as regulators of pathogenesis: examples from the Apicomplexa

The diverse functional roles that proteases play in basic biological processes make them essential for virtually all organisms. Not surprisingly, proteolysis is also a critical process required for many aspects of pathogenesis. In particular, obligate intracellular parasites must precisely coordinate proteolytic events during their highly regulated life cycle inside multiple host cell environments. Advances in chemical, proteomic and genetic tools that can be applied to parasite biology have led to an increased understanding of the complex events centrally regulated by proteases. In this review, we outline recent advances in our knowledge of specific proteolytic enzymes in two medically relevant apicomplexan parasites: Plasmodium falciparum and Toxoplasma gondii. Efforts over the last decade have begun to provide a map of key proteotolyic events that are essential for both parasite survival and propagation inside host cells. These advances in our molecular understanding of proteolytic events involved in parasite pathogenesis provide a foundation for the validation of new networks and enzyme targets that could be exploited for therapeutic purposes. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Combined exposure of carps (Cyprinus carpio L.) to cyanobacterial biomass and white spot disease

OBJECTIVES

Under environmental conditions, fish can be exposed to multiple stressors including natural toxins and infectious agents at the same time. This study brings new knowledge on the effects of controlled exposure to multiple stressors in fish. The aim of this study was to test the hypothesis that influence of cyanobacterial biomass and an infection agent represented by the white spot disease can combine to enhance the effects on fish.

METHODS

Common carps were divided into four groups, each with 40 specimens for 20 days: control group, cyanobacterial biomass exposed group, Ichthyophthirius multifiliis-infected fish (Ich) and cyanobacterial biomass-exposed fish + Ichthyophthirius multifiliis-infected fish. During the experiment we evaluated the clinical signs, mortality, selected haematological parameters, immune parameters and toxin accumulation.

RESULTS

There was no mortality in control fish and cyanobacterial biomass-exposed fish. One specimen died in Ichthyophthirius multifiliis-infected fish and the combined exposure resulted in the death of 13 specimens. The whole leukocyte counts (WBC) of the control group did not show any significant differences. Cyanobacteria alone caused a significant increase of the WBC on day 13 (p≤0.05) and on day 20 (p≤0.01). Also, I. multifiliis caused a significant elevation of WBC (p≤0.01) on day 20. Co-exposition resulted in WBC increased on day 13 and decrease on day 20, but the changes were not significant. It is evident from the differential leukocyte counts that while the increase of WBC in the group exposed to cyanobacteria was caused by elevation of lymphocytes, the increase in the group infected by I. multifiliis was due to the increase of myeloid cells. It well corresponds with the integral of chemiluminescence in the group infected by I. multifiliis, which is significantly elevated on day 20 in comparison with all other groups.

CONCLUSIONS

We can confirm additive action of different agents on the immune system of fish. While single agents seemed to stimulate the immune response, the combination of both caused immunosuppression.

The apicoplast

Parasites like malaria and Toxoplasma possess a vestigial plastid homologous to the chloroplasts of plants. The plastid (known as the apicoplast) is non-photosynthetic but retains many hallmarks of its ancestry including a circular genome that it synthesises proteins from and a suite of biosynthetic pathways of cyanobacterial origin. In this review, the discovery of the apicoplast and its integration, function and purpose are explored. New insights into the apicoplast fatty acid biosynthesis pathway and some novel roles of the apicoplast in vaccine development are reviewed.

First description of naturally acquired Tritrichomonas foetus infection in a Persian cattery in Spain

Tritrichomonas foetus has been identified as the causative agent of feline intestinal trichomonosis, characterized by clinical signs of chronic large bowel diarrhoea. This disease has been reported in cats from the USA, Europe and Australia. However, its epidemiology is still unclear. The aim of the present study was to describe T. foetus infection in a Persian cattery in Spain. T. foetus infection was sequentially diagnosed in 20 cats by direct faecal smear examined under the microscope, specific culture (In Pouch TF medium) and PCR. A standard coprological sedimentation method was also performed in order to screen for other intestinal parasites in all the cats included. In addition, sera were tested for IgG antibodies against Leishmania infantum, Toxoplasma gondii, and for the detection of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). Five out of 20 cats were positive for T. foetus (25%), two of them by microscopy, culture and PCR and three by culture and PCR. No association was found between T. foetus infection and age or sex. L. infantum and T. gondii seroprevalence rates were 15% and 10%, respectively. The prevalence of FeLV p27 antigen and of FIV antibodies in the study population was zero. Cystoisospora spp. oocysts were detected in one cat. These preliminary results show that the transmission of T. foetus infection in cluster conditions may occur between asymptomatic cats and young or immunocompromised animals.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Mice with a selective impairment of IFN-gamma signaling in macrophage lineage cells demonstrate the critical role of IFN-gamma-activated macrophages for the control of protozoan parasitic infections in vivo

IFN-gamma has long been recognized as a cytokine with potent and varied effects in the immune response. Although its effects on specific cell types have been well studied in vitro, its in vivo effects are less clearly understood because of its diverse actions on many different cell types. Although control of multiple protozoan parasites is thought to depend critically on the direct action of IFN-gamma on macrophages, this premise has never been directly proven in vivo. To more directly examine the effects of IFN-gamma on cells of the macrophage lineage in vivo, we generated mice called the "macrophages insensitive to IFN-gamma" (MIIG) mice, which express a dominant negative mutant IFN-gamma receptor in CD68+ cells: monocytes, macrophages, dendritic cells, and mast cells. Macrophage lineage cells and mast cells from these mice are unable to respond to IFN-gamma, whereas other cells are able to produce and respond to this cytokine normally. When challenged in vitro, macrophages from MIIG mice were unable produce NO or kill Trypanosoma cruzi or Leishmania major after priming with IFN-gamma. Furthermore, MIIG mice demonstrated impaired parasite control and heightened mortality after T. cruzi, L. major, and Toxoplasma gondii infection, despite an appropriate IFN-gamma response. In contrast, MIIG mice displayed normal control of lymphocytic choriomeningitis virus, despite persistent insensitivity of macrophages to IFN-gamma. Thus, the MIIG mouse formally demonstrates for the first time in vivo, the specific importance of direct, IFN-gamma mediated activation of macrophages for controlling infection with multiple protozoan parasites.

Clinical significance of enteric protozoa in the immunosuppressed human population

Globally, the number of immunosuppressed people increases each year, with the human immunodeficiency virus (HIV) pandemic continuing to spread unabated in many parts of the world. Immunosuppression may also occur in malnourished persons, patients undergoing chemotherapy for malignancy, and those receiving immunosuppressive therapy. Components of the immune system can be functionally or genetically abnormal as a result of acquired (e.g., caused by HIV infection, lymphoma, or high-dose steroids or other immunosuppressive medications) or congenital illnesses, with more than 120 congenital immunodeficiencies described to date that either affect humoral immunity or compromise T-cell function. All individuals affected by immunosuppression are at risk of infection by opportunistic parasites (such as the microsporidia) as well as those more commonly associated with gastrointestinal disease (such as Giardia). The outcome of infection by enteric protozoan parasites is dependent on absolute CD4(+) cell counts, with lower counts being associated with more severe disease, more atypical disease, and a greater risk of disseminated disease. This review summarizes our current state of knowledge on the significance of enteric parasitic protozoa as a cause of disease in immunosuppressed persons and also provides guidance on recent advances in diagnosis and therapy for the control of these important parasites.

Two-photon microscopy of host-pathogen interactions: acquiring a dynamic picture of infection in vivo

Two-photon (2P) microscopy has become increasingly popular among immunologists for analysing single-cell dynamics in tissues. Researchers are now taking 2P microscopy beyond the study of model antigen systems (e.g. ovalbumin immunization) and are applying the technique to examine infection in vivo. With the appropriate fluorescent probes, 2P imaging can provide high-resolution spatio-temporal information regarding cell behaviour, monitor cell functions and assess various outcomes of infection, such as host cell apoptosis or pathogen proliferation. Imaging of transgenic and knockout mice can be used to probe molecular mechanisms governing the host response to infection. From the microbe side, imaging genetically engineered mutant strains of a pathogen can test the roles of specific virulence factors in pathogenesis. Here, we discuss recent work that has applied 2P microscopy to study models of infection and highlight the tremendous potential that this approach has for investigating host-pathogen interactions.

HLA and infectious diseases

Following their discovery in the early 1970s, classical human leukocyte antigen (HLA) loci have been the prototypical candidates for genetic susceptibility to infectious disease. Indeed, the original hypothesis for the extreme variability observed at HLA loci (H-2 in mice) was the major selective pressure from infectious diseases. Now that both the human genome and the molecular basis of innate and acquired immunity are understood in greater detail, do the classical HLA loci still stand out as major genes that determine susceptibility to infectious disease? This review looks afresh at the evidence supporting a role for classical HLA loci in susceptibility to infectious disease, examines the limitations of data reported to date, and discusses current advances in methodology and technology that will potentially lead to greater understanding of their role in infectious diseases in the future.

HLA and infectious diseases

Following their discovery in the early 1970s, classical human leukocyte antigen (HLA) loci have been the prototypical candidates for genetic susceptibility to infectious disease. Indeed, the original hypothesis for the extreme variability observed at HLA loci (H-2 in mice) was the major selective pressure from infectious diseases. Now that both the human genome and the molecular basis of innate and acquired immunity are understood in greater detail, do the classical HLA loci still stand out as major genes that determine susceptibility to infectious disease? This review looks afresh at the evidence supporting a role for classical HLA loci in susceptibility to infectious disease, examines the limitations of data reported to date, and discusses current advances in methodology and technology that will potentially lead to greater understanding of their role in infectious diseases in the future.

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.

Correlation between CD4 counts of HIV patients and enteric protozoan in different seasons - an experience of a tertiary care hospital in Varanasi (India)

BACKGROUND

Protozoan infections are the most serious among all the superimposed infections in HIV patients and claim a number of lives every year. The line of treatment being different for diverse parasites necessitates a definitive diagnosis of the etiological agents to avoid empirical treatment. Thus, the present study has been aimed to elucidate the associations between diarrhoea and CD4 counts and to study the effect of HAART along with management of diarrhoea in HIV positive patients. This study is the first of its kind in this area where an attempt was made to correlate seasonal variation and intestinal protozoan infestations.

METHODS

The study period was from January 2006 to October 2007 wherein stool samples were collected from 366 HIV positive patients with diarrhea attending the ART centre, inpatient department and ICTC of S.S. hospital, I.M.S., B.H.U., Varanasi. Simultaneously, CD4 counts were recorded to assess the status of HIV infection vis-à-vis parasitic infection. The identification of pathogens was done on the basis of direct microscopy and different staining techniques.

RESULTS

Of the 366 patients, 112 had acute and 254 had chronic diarrhea. The percentages of intestinal protozoa detected were 78.5% in acute and 50.7% in chronic cases respectively. Immune restoration was observed in 36.6% patients after treatment on the basis of clinical observation and CD4 counts. In 39.8% of HIV positive cases Cryptosporidium spp. was detected followed by Microsporidia spp. (26.7%). The highest incidence of intestinal infection was in the rainy season. However, infection with Cyclospora spp. was at its peak in the summer. Patients with chronic diarrhea had lower CD4 cell counts. The maximum parasitic isolation was in the patients whose CD4 cell counts were below 200 cells/microl.

CONCLUSION

There was an inverse relation between the CD4 counts and duration of diarrhea. Cryptosporidium spp. was isolated maximum among all the parasites in the HIV patients. The highest incidence of infection was seen in the rainy season.

[Diagnosis of intestinal-protozoa in patients with immune deficiency]

In our study, we tried to detect gastroenteritis causing intestinal protozoa in patients with immune deficiency and who suffered from diarrhea. We also tried to determine which laboratory methods should be used in detecting intestinal protozoon in these patients. Thirty-six immune deficient patients who had had diarrhea for more than 10 days and 44 immune deficient patients without diarrhea were included in the study. In stool samples taken from all cases, intestinal protozoa were detected using the conventional diagnostic methods including direct wet mount, trichrome and modified acid fast staining as well as serologic diagnostic methods such as ELISA, direct fluorescent antibody (DFA)] and the molecular method of polymerized chain reaction. In our study, we found that intestinal protozoan such as G. intestinalis; C. parvum, B. hominis and E. histolytica could be responsible for the long term diarrhea in patients with immune deficiency. If a pathogen is not detected in the feces by native Lugol (NL), DFA and MAF are suitable techniques for Cryptosporidium spp while ELISA or trichrome staining are suitable methods for E. histolytica. It was concluded in the study that the simple and inexpensive NL method is sufficient in the diagnosis of G. intestinalis and serological or molecular methods are unnecessary. Neutropenia in patients with immune deficiency did not enhance the frequent occurrence of intestinal protozoan infections; and also, in the cases with immune deficiency, it was found that the administration of steroid treatment was not a risk factor in intestinal protozoan disease.

Toll-Like receptors (TLRs) and their ligands

The innate immune system is an evolutionally conserved host defense mechanism against pathogens. Innate immune responses are initiated by pattern recognition receptors (PRRs), which recognize microbial components that are essential for the survival of the microorganism. PRRs are germline-encoded, nonclonal, and expressed constitutively in the host. Different PRRs react with specific ligands and lead to distinct antipathogen responses. Among them, Toll-like receptors (TLRs) are capable of sensing organisms ranging from bacteria to fungi, protozoa, and viruses, and they play a major role in innate immunity. Here, we review the mechanism of pathogen recognition by TLRs.

Shared epigenetic mechanisms control virulence factors in protozoan parasites

Protozoan pathogens have evolved countermeasures to avoid immune clearance and prolong the period of infection in their vertebrate hosts. The type and degree of immune escape strategies depends on the in vivo 'lifestyle' the pathogen has adopted. Here we describe how parasites use different strategies to coordinate their expression of phenotypic variation, which is used in many cases to fool the immune system, or to successfully invade new host cells. Recent insights using modern molecular biology techniques show that this is achieved via a coordinated manner of action of different epigenetic factors such as histone marks, subnuclear localization, or novel unknown mechanism(s). This emerging field may have an enormous impact on disease therapy.

Leishmania amazonensis infection impairs differentiation and function of human dendritic cells

Dendritic cells (DCs) are of utmost importance in initiating an immune response and may also function as targets for pathogens. The presence of pathogens inside DCs is likely to impair their functions and thus, influence immune responses. In the present report, we evaluated the impact of the presence of Leishmania amazonensis during differentiation and maturation of human monocyte-derived DCs. The presence of live L. amazonensis parasites during DC differentiation led to a significant decrease in CD80 (92%) and CD1a (56%) expression and an increase in CD86 (56%) cell surface expression. Phenotypic changes were accompanied by a lower secretion of IL-6, observed after 6 days of DC differentiation in the presence of L. amazonensis. DCs differentiated in the presence of L. amazonensis were used as APC in an autologous coculture, and lower amounts of IFN-gamma were obtained compared with control DCs differentiated in the absence of parasites. The effect of heat-killed parasites, but not of Leishmania antigen, during DC differentiation and maturation was similar to that observed with viable parasites. During maturation, the presence of live L. amazonensis parasites, but not of soluble Leishmania antigen, led to a decrease in IL-6 and IL-10 production. In this way, we observed that the parasite is able to abrogate full DC differentiation, causing a delay in the immune response and likely, favoring its establishment in human hosts.

[Parasites as a cause of urticaria. Helminths and protozoa as triggers of hives?]

Urticaria is one of the most prevalent disorders in dermatological practice. The disease can be incapacitating. There are clear pathophysiological and epidemiological hints that helminths and protozoa are rare but treatable causes of acute and chronic urticaria. Doctors and patients are often not aware that parasitic diseases are increasingly common even in industrialized countries due to a steep rise in migration and international travel. This review presents the most important parasitic causes of urticaria and provides relevant details regarding personal history, clinical presentation, diagnosis and therapy.

Neutrophils and inducible nitric-oxide synthase are critical for early resistance to the establishment of Tritrichomonas foetus infection

Tritrichomonas foetus is the cause of trichomoniasis in cattle. Severe infection is often associated with heavy neutrophil and macrophage accumulation, although it is not known how this response protects during early parasite colonization. The goal of this study was to examine the effects of an early host response upon initial T. foetus colonization within the murine reproductive tract. Mice depleted of neutrophils before T. foetus infection had a significantly higher parasite burden within the reproductive tract compared with mock-depleted control mice. Additionally, gp91(phox-/-)/ iNOS(-/-), and iNOS(-/-) mice had substantially larger parasite burdens than C57BL/6 control mice, whereas gp91l(Phox-/-) mice had similar parasite burden to C57BL/6 control mice. Interestingly, phorbol 12-myristate 13-acetate-stimulated neutrophils and macrophages isolated from all groups of mice were unable to kill T. foetus in vitro. However, macrophages isolated from gp91l(phox-/-) and C57BL/6 mice stimulated with interferon-gamma and lipopolysaccharide were able to kill T. foetus in vitro, whereas macrophages isolated from gp91(phox(-/-)/ iNOS(-/-) and iNOS(-/-) mice were unable to kill T. foetus, suggesting the ability of macrophages to produce reactive nitrogen species but not reactive oxygen species (ROS) is critical for parasite killing during early infection in vivo and in vitro. Additionally, neutrophils seem to control early dissemination of T. foetus throughout the reproductive tract, although production of ROS is not critical for this process.

Alternatively activated macrophages in protozoan infections

A type 1 cytokine-dependent pro-inflammatory response inducing classically activated macrophages is crucial for parasite control during protozoan infections but can also contribute to the development of immunopathological disease symptoms. Accumulating evidence indicates that interleukins 4, 13 and 10, transforming growth factor-beta, immune complexes and apoptotic cells elicited during these infections induce alternative activation states of macrophages, affecting disease outcome by, on the one hand, promoting parasite survival and proliferation and, on the other hand, limiting collateral tissue damage because of excessive type 1 inflammation. Thus, modulation of macrophage activation may be instrumental in allowing parasite persistence and long-term host survival.

Protozoan parasites: programmed cell death as a mechanism of parasitism

Programmed cell death (PCD) is a potent mechanism to remove parasitized cells, but it has also been shown that protozoan parasites can induce or inhibit apoptosis in host cells. In recent years, it has become clear that unicellular parasites can also undergo PCD, meaning that they commit suicide in response to various stimuli. This review focuses on the role of protozoan PCD and on the interaction between protozoan parasites and the host cell death machinery from the perspective of parasite survival strategies.

Use of a live vaccine to modulate Cryptobia salmositica infections in Salmo salar

The vaccine strain of Cryptobia salmositica multiplies in Atlantic salmon Salmo salar and it can modulate the severity of the disease in Cryptobia-infected individuals. Fish injected with the vaccine 3 d post-infection with C. salmositica had lower peak parasitaemias and higher antibody titres than infected fish given the vaccine 7 d post-infection or those infected fish that were not given the vaccine.

Major histocompatibility polymorphism associated with resistance towards amoebic gill disease in Atlantic salmon (Salmo salar L.)

The association between major histocompatibility (MH) polymorphism and the severity of infection by amoebic gill disease (AGD) was investigated across 30 full sibling families of Atlantic salmon. Individuals were challenged with AGD for 19days and then their severity of infection scored by histopathological examination of the gills. Fish were then genotyped for the MH class I (Sasa-UBA) and MH class II alpha (Sasa-DAA) genes using polymorphic repeats embedded within the 3' untranslated regions of the Sasa-UBA and Sasa-DAA genes. High variation in the severity of infection was observed across the sample material, ranging from 0% to 85% gill filaments infected. In total, seven Sasa-DAA-3UTR and ten Sasa-UBA-3UTR marker alleles were identified across the 30 families. A significant association between the marker allele Sasa-DAA-3UTR 239 and a reduction in AGD severity was detected. There was also a significant association found between AGD severity and the presence of two Sasa-DAA-3UTR genotypes. While the associations between MH allele/genotypes and AGD severity reported herein may be statistically significant, the small sample sizes observed for some alleles and genotypes means these associations should be considered as suggestive and future research is required to verify their biological significance.

Enteric opportunistic parasites among HIV infected individuals: associated risk factors and immune status

Data on various etiologic agents causing diarrhea in human immunodeficiency virus type-1 (HIV-1) infected individuals are sparse in Delhi, India. The present study was undertaken to identify various causative agents, the role of associated risk factors and immune status. A case-control study was conducted among 75 HIV-1 infected individuals, 50 with and 25 without diarrheal infection. Fecal samples were screened for coccidian parasites, enteric protozoa, and helminthes by using various staining techniques. The CD4+ T-lymphocyte count was estimated. Enteric parasites were identified among 62.7% individuals, of which Cryptosporidium emerged as the single largest pathogen predominant among 33% of the individuals (P < 0.025). Other parasites diagnosed that were significantly associated with diarrhea were Giardia lamblia (13.3%), microsporidia (6.7%), and Isospora belli (2.7%). Chronic infected diarrheal cases were found to have polyparasitic infections. The mean CD4+ cell count was found to be lower among the diarrheal cases when compared with the non-diarrheal cases (mean, 141 cells/mm(3) versus 390 cells/mm(3)). Similarly, among diarrheal individuals, the chronic diarrheal cases had a comparatively lower CD4+ cell count than the acute cases (mean, 123 cells/mm(3) versus 265 cells/mm(3)). Risk factors found significant during multivariate analysis were: residence in a slum, exposure to pets and animals, use of public toilets, and practice of unsafe homosexual activity. Enteric coccidian parasites were identified as significant agents associated with diarrhea, especially among those with improper hygiene, multiple infections and a lower CD4+ cell count. Thus, this study emphasizes the need for routine screening of enteric parasites as well as education about practicing personal hygiene and taking timely and appropriate prophylactic measures.

Neutrophils, apoptosis and phagocytic clearance: an innate sequence of cellular responses regulating intramacrophagic parasite infections

In complex organisms, apoptosis is a constitutive cell death process that is involved in physiological regulation of cell numbers and that can also be induced in the course of inflammatory and immune responses. Neutrophils are among the first cells recruited during inflammation. Neutrophils constitutively die by apoptosis at inflamed sites, and are ingested by macrophages. Recent studies investigated how phagocytic clearance of senescent neutrophils influences the survival of intracellular protozoan parasites that have been phagocytosed by, or have invaded phagocytes. The results indicate that neutrophil clearance plays an unexpected role in regulation of intramacrophagic protozoan parasite infection.

Cross-talk between apoptosis and cytokines in the regulation of parasitic infection

Parasitic diseases have worldwide medical and economical impact. Host T lymphocytes and the cytokines they produce determine the outcome of parasitic infections. Programmed cell death by apoptosis is induced in the course of parasitic infections, and affects cytokine production by removing activated effector T and B cells. In addition, engulfment of apoptotic cells promotes the secretion of cytokines that regulate intracellular replication of protozoan parasites. In this review, we discuss how the cross-talk between apoptosis and cytokines regulates parasitic infection.

Tritrichomonas foetus: Pathogenesis of acute infection in normal, estradiol-treated, and stressed mice

Environmental stress and endocrine control can affect pathogenesis of sexually transmitted diseases such as trichomoniasis. Acute Tritrichomonas foetus infection was compared in female BALB/c mice to infections in mice treated with high doses of estradiol or housed in constant bright illumination (stressed). In untreated mice, T. foetus readily colonized the reproductive tract, causing minimal epithelial damage and inflammation. Several fold increases of IFN-gamma, TNF-alpha, MCP-1, and IL-6 cytokines were detected after estradiol-treatment of mice, resulting in greatly enhanced inflammation and tissue damage throughout the reproductive tract. Interestingly, estradiol-treatment of mice resulted in reduced T. foetus colonization compared to untreated mice. Infection in stressed mice resulted in increased tissue damage, inflammation, and inflammatory cytokine expression, although parasite colonization within the reproductive tract was similar to that in untreated mice. These results indicate that either estradiol-treatment or stress result in pathogenesis often observed during severe disease. Alternatively, infection in non-treated mice results in chronic colonization, with little inflammation or pathology.

Mixed infection with Trypanoplasma borreli and Trypanosoma carassii induces protection: involvement of cross-reactive antibodies

Mixed infections with Trypanoplasma borreli and Trypanosoma carassii in common carp (Cyprinus carpio L.) are commonly found in nature. So far, in the laboratory, only mono-parasitic infections have been examined in more detail. We studied the influence of mixed rather than mono-parasitic infections on the protective immune response in this naturally occurring host-parasite combination. Mixed infections were established in the laboratory by i.p. injection of fixed numbers of both parasite species and confirmed by species-specific antibody staining. Species-specific parasitaemia was determined by morphological differences and by real-time PCR. T. carassii parasitaemia developed prior to T. borreli. Infections with T. borreli reached higher levels of parasitaemia, compared to T. carassii infections and T. borreli could be lethal. Interestingly, in mixed infections, peak parasitaemia levels were reduced and to a lesser extend survival was increased compared to T. borreli mono-parasitic infections. Cross-reactive antibodies increased earlier and to higher levels in mixed infected fish than in T. borreli mono-parasitic infections. Further, carp that had received a prior T. carassii infection showed increased resistance to re-infection with T. borreli. Our data indicate a protective effect of co-infection with T. carassii on the resistance to T. borreli, possibly mediated via cross-reactive antibodies. We suggest an evolutionary advantage for a co-evolution of T. borreli and T. carassii in carp.