Immune response to Encephalitozoon infection review

CD8 T lymphocytes from B-1 cell-deficient mice down-regulates fungicidal activity of macrophages challenged with E. Cuniculi

BACKGROUND

Encephalitozoon cuniculi is an opportunistic intracellular pathogen that establishes a balanced relationship with immunocompetent individuals depending on the activity of their CD8+ T cells lymphocytes. However, lower resistance to experimental infection with E. cuniculi was found in B-1 deficient mice (Xid), besides increased the number of CD8 T lymphocytes. Here, we evaluated the profile of CD8+ T lymphocytes from Balb/c wild-type (WT) or Balb/c Xid mice (with B-1 cell deficiency) on the microbicidal activity of macrophages challenged with E. cuniculi.

METHODS

Naïve CD8 T lymphocytes from WT or Xid mice uninfected and primed CD8 T lymphocytes from WT or Xid mice infected with E cuniculi were co-cultured with macrophages previously challenged with E. cuniculi. We evaluated macrophages viability and microbicidal activity, and CD8 T lymphocytes viability and presence of activating molecules (CD62L, CD69, and CD107a).

RESULTS

Macrophages co-cultured with naïve CD8 T lymphocytes from WT demonstrated high microbicidal activity. Naïve CD8 T lymphocytes obtained from WT mice had a higher expression of CD69 and LAMP-1-activating molecules compared to Xid CD8+ T lymphocytes. Primed CD8 T lymphocytes from Xid mice proliferated more than those from WT mice, however, when the expression of the activating molecule CD69 associated with the expression of CD62L was kept low. In conclusion, naïve CD8+ T lymphocytes from Xid mice, deficient in B-1 cells, they had reduced expression of activation molecules and cytotoxic activity.

Encephalitozoon spp. as a potential human pathogen

Encephalitzoon spp. are microsporidia, and intracellular opportunistic pathogens. The hosts of these pathogens include vertebrates, invertebrates, and certain protozoa. In people microsporidia may be opportunistic pathogens for immunocompromised patients (with AIDS or after organ transplantation). Infection with these microorganisms was also described in persons with diarrhea and corneal diseases.

The species causing rare infections in humans, Encephalitozooncuniculi, had previously been described from animal hosts. However, several new microsporidial species, including E. intestinalis and E. hellem, have been discovered in humans, raising the question of their natural origin. Vertebrate animals are now identified as hosts for all three microsporidial species infecting humans, implying a zoonotic nature of these microorganisms. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is to present the zoonotic potential of E. intestinalis, E. cuniculi, and E. hellem.

Phagocytosis Is the Sole Arm of Drosophila melanogaster Known Host Defenses That Provides Some Protection Against Microsporidia Infection

Microsporidia are obligate intracellular parasites able to infest specifically a large range of species, including insects. The knowledge about the biology of microsporidial infections remains confined to mostly descriptive studies, including molecular approaches such as transcriptomics or proteomics. Thus, functional data to understand insect host defenses are currently lacking. Here, we have undertaken a genetic analysis of known host defenses of the Drosophila melanogaster using an infection model whereby Tubulinosema ratisbonensis spores are directly injected in this insect. We find that phagocytosis does confer some protection in this infection model. In contrast, the systemic immune response, extracellular reactive oxygen species, thioester proteins, xenophagy, and intracellular antiviral response pathways do not appear to be involved in the resistance against this parasite. Unexpectedly, several genes such as PGRP-LE seem to promote this infection. The prophenol oxidases that mediate melanization have different functions; PPO1 presents a phenotype similar to that of PGRP-LE whereas that of PPO2 suggests a function in the resilience to infection. Similarly, eiger and Unpaired3, which encode two cytokines secreted by hemocytes display a resilience phenotype with a strong susceptibility to T. ratisbonensis.

Mice with genetic and induced B-cell deficiency as a model for disseminated encephalitozoonosis

Encephalitozoon cuniculi, an intracellular pathogen, lives in a balanced relationship with immunocompetent individuals based on the activity of T lymphocytes. We previously highlighted the greater susceptibility of B-1 cell-deficient mice (XID mice) to encephalitozoonosis. This study aimed to develop a model of disseminated and severe encephalitozoonosis in mice with combined immunodeficiency to elucidate the role of B cells. To address this objective, cyclophosphamide (Cy)-treated BALB/c and XID mice were inoculated with E. cuniculi, followed by the evaluation of the immune response and histopathological lesions. Immunosuppressed BALB/c mice manifested no clinical signs with an increase in the populations of T lymphocytes and macrophages in the spleen. Immunosuppressed and infected XID mice revealed elevated T cells, macrophages populations, and pro-inflammatory cytokines levels (IFN-γ, TNF-α, and IL-6) with the presence of abdominal effusion and lesions in multiple organs. These clinical characteristics are associated with extensive and severe encephalitozoonosis. The symptoms and lesion size were reduced, whereas B-2 and CD4+ T cells populations were increased in the spleen by transferring B-2 cells adoptive to XID mice. Moreover, B-1 cells adoptive transfer upregulated the peritoneal populations of B-2 cells and macrophages but not T lymphocytes and decreased the symptoms. Herein, we speculated the consistency in the development of severe and disseminated encephalitozoonosis in mice with genetic deficiency of Bruton's tyrosine kinase (Btk) associated with Cy immunosuppression develop with that of the models with T cell deficiency. Taken together, these data emphasized the crucial role of B cells in the protective immune response against encephalitozoonosis.

Enterocytozoon Bieneusi Infects Children With Inflammatory Bowel Disease Undergoing Immunosuppressive Treatment

Objectives: Patients with inflammatory bowel disease (IBD) are susceptible to intestinal opportunistic infections due to both defective mucosal immunity and altered immune response resulting from immunosuppressive treatment. Microsporidia infecting the gastrointestinal tract and causing diarrhoea can potentially affect the course of IBD.

Methods: Stool samples (90 IBD children and 121 healthy age-matched controls) were screened for Encephalitozoon spp. and Enterocytozoon bieneusi by microscopy and polymerase chain reaction followed by sequencing.

Results:E. bieneusi genotype D was found in seven out of 90 (7.8%) IBD children. No children from the control group were infected, making the pathogen prevalence in the IBD group significant (P = 0.002). Furthermore, infection was confirmed only in patients receiving immunosuppressive treatment (P = 0.013).

Conclusions: Children with IBD are at risk of intestinal E. bieneusi infection, especially when receiving immunosuppressive treatment. Therefore, microsporidia should be considered as a significant infectious agent in this group of patients.

Advancement in our understanding of immune response against Encephalitozoon infection

Microsporidia are a group of obligate, intracellular, spore-forming eukaryotic pathogens, which predominantly infects immunocompromised individuals worldwide. Encephalitozoon spp. is one of the most prevalent microsporidia known to infect humans. Host immune system plays a major role in combating pathogens including Encephalitozoon spp. infecting humans. Both innate and adaptive arms of host immune system work together in combating Encephalitozoon infection. Researchers are conducting studies to elucidate the role of both arms of immune system against Encephalitozoon infection. In addition to cell-mediated adaptive immunity, role of innate immunity is also being highlighted in clearance of Encephalitozoon spp. from host body. Therefore, the current review will give a clear and consolidated update on the role of innate as well as adaptive immunity in protection against Encephalitozoon spp.

Alternatives in Molecular Diagnostics of Encephalitozoon and Enterocytozoon Infections

Microsporidia are obligate intracellular pathogens that are currently considered to be most directly aligned with fungi. These fungal-related microbes cause infections in every major group of animals, both vertebrate and invertebrate, and more recently, because of AIDS, they have been identified as significant opportunistic parasites in man. The Microsporidia are ubiquitous parasites in the animal kingdom but, until recently, they have maintained relative anonymity because of the specialized nature of pathology researchers. Diagnosis of microsporidia infection from stool examination is possible and has replaced biopsy as the initial diagnostic procedure in many laboratories. These staining techniques can be difficult, however, due to the small size of the spores. The specific identification of microsporidian species has classically depended on ultrastructural examination. With the cloning of the rRNA genes from the human pathogenic microsporidia it has been possible to apply polymerase chain reaction (PCR) techniques for the diagnosis of microsporidial infection at the species and genotype level. The absence of genetic techniques for manipulating microsporidia and their complicated diagnosis hampered research. This study should provide basic insights into the development of diagnostics and the pitfalls of molecular identification of these ubiquitous intracellular pathogens that can be integrated into studies aimed at treating or controlling microsporidiosis.

Innate and Adaptive Immune Responses Against Microsporidia Infection in Mammals

Microsporidia are obligate intracellular and eukaryotic pathogens that can infect immunocompromised and immunocompetent mammals, including humans. Both innate and adaptive immune systems play important roles against microsporidian infection. The innate immune system can partially eliminate the infection by immune cells, such as gamma delta T cell, natural killer cells (NKs), macrophages and dendritic cells (DCs), and present the pathogens to lymphocytes. The innate immune cells can also prime and enhance the adaptive immune response via surface molecules and secreted cytokines. The adaptive immune system is critical to eliminate microsporidian infection by activating cytotoxic T lymphocyte (CTL) and humoral immune responses, and feedback regulation of the innate immune mechanism. In this review, we will discuss the cellular and molecular responses and functions of innate and adaptive immune systems against microsporidian infection.

Enterospora nucleophila (Microsporidia) in Gilthead Sea Bream (Sparus aurata): Pathological Effects and Cellular Immune Response in Natural Infections

Enterospora nucleophila is a microsporidian responsible for an emaciative disease in gilthead sea bream (Sparus aurata). Its intranuclear development and the lack of in vitro and in vivo models hinder its research. This study investigated the associated lesions, its detection by quantitative polymerase chain reaction, and the cellular immune response of naturally infected fish. The intensity of infection in the intestine was correlated with stunted growth and reduced body condition. At the beginning of the outbreaks, infection prevalence was highest in intestine and stomach, and in subsequent months, the prevalence decreased in the intestine and increased in hematopoietic organs and stomach. In heavy infections, the intestine had histologic lesions of enterocyte hypercellularity and proliferation of rodlet cells. Infected enterocytes had E. nucleophila spores in the cytoplasm, and a pyknotic nucleus, karyorhexis or karyolysis. Lymphocytes were present at the base of the mucosa, and eosinophilic granule cells were located between the enterocytes. In intestinal submucosa, macrophage aggregates containing spores were surrounded by lymphocytes and granulocytes, with submucosal infiltration of granulocytes. Macrophage aggregates appeared to develop into granulomata with necrotic areas containing parasite remnants. Immunohistochemistry revealed mast cells as the main type of granulocyte involved. Abundant IgM⁺ and IgT⁺ cells were identified by in situ hybridization in the submucosa when intracytoplasmic stages were present. This study describes the lesions of E. nucleophila in gilthead sea bream, an important aquaculture species.

Encephalitozoon cuniculi Genotype III Evinces a Resistance to Albendazole Treatment in both Immunodeficient and Immunocompetent Mice

Of four genotypes of Encephalitozoon cuniculi, E. cuniculi genotype II is considered to represent a parasite that occurs in many host species in a latent asymptomatic form, whereas E. cuniculi genotype III seems to be more aggressive, and infections caused by this strain can lead to the death of even immunocompetent hosts. Although albendazole has been considered suitable for treatment of Encephalitozoon species, its failure in control of E. cuniculi genotype III infection has been reported. This study determined the effect of a 100× recommended daily dose of albendazole on an Encephalitozoon cuniculi genotype III course of infection in immunocompetent and immunodeficient mice and compared the results with those from experiments performed with a lower dose of albendazole and E. cuniculi genotype II. The administration of the regular dose of abendazole during the acute phase of infection reduced the number of affected organs in all strains of mice and absolute counts of spores in screened organs. However, the effect on genotype III was minor. Surprisingly, no substantial effect was recorded after the use of a 100× dose of albendazole, with larger reductions seen only in the number of affected organs and absolute counts of spores in all strains of mice, implying variations in albendazole resistance between these Encephalitozoon cuniculi genotypes. These results imply that differences in the course of infection and the response to treatment depend not only on the immunological status of the host but also on the genotype causing the infection. Understanding how microsporidia survive in hosts despite targeted antimicrosporidial treatment could significantly contribute to research related to human health.

Immunohistochemical localization of TNF-α and IL-4 in granulomas of immunocompetent and immunosuppressed New Zealand white rabbits infected with Encephalitozoon cuniculi

Encephalitozoon cuniculi is a fungi-related, obligate, zoonotic, spore-forming intracellular eukaryotic microorganism. This emerging pathogen causes granulomas to form in the brain and kidneys of infected individuals. The objective of the current study was to detect the distribution of TNF-α- and IL-4-positive cells using immunohistochemistry within these granulomas in both infected immunocompetent (group A) and immunosuppressed (group B) New Zealand white rabbits. In the brain, labeled TNF-α immune cells were mainly located in the granuloma peripheries in group B. Granulomas examined in the kidneys of groups A and B were TNF-α positive, but were significantly different (p < 0.001) when compared with the brain. IL-4-producing immune cells in the brain and kidneys were disseminated within granulomas in groups A and B; however, no significant difference (p > 0.05), was observed. IL-4 positive cells were more numerous in brain sections of group B and differed significantly (p < 0.05) when compared with kidneys. Granulomas were not observed in control animals (groups C and D). In conclusion, we identified TNF-α positive cells in both the brain and kidneys of immunocompetent and immunosuppressed animals; IL-4 positive cells were numerous in the brains of immunosuppressed rabbits; however, in terms of percentage were numerous in the brains of immunocompetent rabbits. Immunosuppression appeared to stimulate a change in the cellular phenotype of Th1- to Th2-like granulomas in the brain and kidneys via an unknown mechanism. Expression of pro- and pre-inflammatory cytokines in microsporidian granulomas suggests a mechanism by which E. cuniculi evades the immune response, causing more severe disease. These results increase our understanding of TNF-α and IL-4-positive cells within the E. cuniculi granuloma microenvironment.

Increased phagocytosis and growth inhibition of Encephalitozoon cuniculi by LPS-activated J774A.1 murine macrophages

Encephalitozoon cuniculi is an obligate macrophage parasite of vertebrates that commonly infects rodents, monkeys, dogs, birds, and humans. In the present study, we aimed to assess the phagocytosis and intracellular survival of E. cuniculi spores using untreated and lipopolysaccharide (LPS)-activated J774A.1 murine macrophages and assess the macrophage viability. The experimental groups comprised untreated spores, spores killed by heat treatment at 90 °C, and spores killed by treatment with 10% formalin. LPS-activated macrophages significantly increased the phagocytosis of spores and reduced their intracellular growth after 24 and 48 h (P < 0.01); however, after 72 h, we observed an increase in spore replication but no detectable microbicidal activity. These results indicate that LPS activation enhanced E. cuniculi phagocytosis between 24 and 48 h of treatment, but the effect was lost after 72 h, enabling parasitic growth. This study contributes to the understanding of the phagocytosis and survival of E. cuniculi in murine macrophages.

Molecular detection and genotyping of Enterocytozoon bieneusi in family pet dogs obtained from different routes in Japan

The present study determined the prevalence of Enterocytozoon (E.) bieneusi infection and genotyped the isolates in family pet dogs obtained from three different routes in Japan. Fresh fecal samples were collected from 597 family pet dogs. A nested polymerase chain reaction (PCR) assay targeting the internal transcribed spacer (ITS) region of ribosomal DNA was employed for detection of E. bieneusi, and the obtained positive PCR amplicons were sequenced for genotyping. The overall prevalence of E. bieneusi in family pet dogs was 4.4%. Significant differences in prevalence were found among the categories of age (<1 year: 8.3% vs. ≥1 year: 3.4%), obtained route (from private owner: 3.2% vs. from pet shop: 3.9% vs. from breeding kennel: 14.3%), and living regions (ranged 0-10.3%). However, no significant differences were observed in the prevalence of living condition (indoor: 4.6% vs. outdoor: 2.0%), and fecal condition (formed: 4.5% vs. soft: 4.7% vs. diarrhea: 0%). Of the 26 sequenced samples, all were identified as genotype PtEb IX, which belongs to the dog-specific genotype. In conclusion, although E. bieneusi infections are relatively common in family pet dogs in Japan, the risk of zoonotic transmission from dogs to humans is likely to be low.

Quantitative analysis of TNF-α, IL-4, and IL-10 expression, nitric oxide response, and apoptosis in Encephalitozoon cuniculi-infected rabbits

The expression of tumor necrosis factor (TNF) -α, interleukin (IL) -4 and IL-10, as well as apoptosis and nitric oxide (NO) levels were measured in the brain and kidneys of immunocompetent and immunosuppressed New Zealand White rabbits infected with Encephalitozoon cuniculi. All of the animals had clinical signs histopathological lesions compatible with encephalitozoonosis and were E. cuniculi-positive by using a carbon immunoassay test. Encephalitozoon cuniculi infection promoted the expression of TNF-α and NO production in the kidneys of infected rabbits, and a synergic effect was observed in animal treated with dexamethasone. The IL-4 expression was similar in the brain and kidneys of infected rabbits, regardless of their immunologic status. The IL-10 mRNA expression in the brain of infected immunosuppressed rabbits was elevated when compared with positive controls. Apoptosis of granuloma mononuclear-like cells was detected in immunocompetent E. cuniculi-infected rabbits, but it was more evident in infected-immunosuppressed animals. Nitric oxide levels were elevated both in immunocompetent and immunosuppressed infected animals, but it was more apparent in the kidneys. These data suggest that modulation of the immune response by E. cuniculi could contribute to the survival of the parasite within phagocytic cells in granulomas via an as yet undetermined mechanism.

Diabetes mellitus increases the susceptibility to encephalitozoonosis in mice

Microsporidiosis are diseases caused by opportunistic intracellular fungi in immunosuppressed individuals, as well as in transplanted patients, the elderly and children, among others. Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and decreased T cell response, neutrophil function, humoral immunity failure, increasing the susceptibility to infections. Here, we investigated the susceptibility of streptozotocin (STZ)-induced type I diabetic and/or immunosuppressed mice to encephalitozoonosis by Encephalitozoon cuniculi. Microscopically, granulomatous hepatitis, interstitial pneumonia and pielonephritis were observed in all infected groups. STZ treatment induced an immunossupressor effect in the populations of B (B-1 and B2) and CD4⁺ T lymphocytes. Moreover, infection decreased CD4⁺ and CD8⁺ T lymphocytes and macrophages of DM mice. Furthermore, infection induced a significant increase of IL-6 and TNF-α cytokine serum levels in DM mice. IFN-γ, the most important cytokine for the resolution of encephalitozoonosis, increased only in infected mice. In addition to the decreased immune response, DM mice were more susceptible to encephalitozoonosis, associated with increased fungal burden, and symptoms. Additionally, cyclophosphamide immunosuppression in DM mice further increased the susceptibility to encephalitozoonosis. Thus, microsporidiosis should be considered in the differential diagnosis of comorbidities in diabetics.

Encephalitozoon cuniculi in rabbits: Serological screening and histopathological findings

Serological prevalence of E. cuniculi infection was assessed in 183 rabbits from central Italy. In seropositive deceased rabbits, histopathological lesions were also evaluated. Sera from 118 rabbits from 6 intensive farms, 10 rabbits from 6 family farms, 16 rabbits from a zoo, 30 rabbits from 5 research laboratories and 9 pet rabbits from 9 different owners, were tested by an enzyme-linked immunosorbent assay. Data were statistically analysed. Tissue samples from brain and kidney of 10 deceased rabbits were formalin-fixed and subsequently analysed by histopathology and immunohistochemistry. Anti-E. cuniculi antibodies were found in 129/183 (70.5%) analysed sera. At statistical analysis, E. cuniculi seropositivity was significantly higher (p<0.05) in industrial and zoo rabbits. At histology, different degrees of pathological lesions were found in serological positive (9) deceased animals. In three rabbits deceased after showing neurological signs, the severity of the lesions was interpreted as a likely cause for their death.

Interferon γ and interleukin 10 responses in immunocompetent and immunosuppressed New Zealand White rabbits naturally infected with Encephalitozoon cuniculi

Levels of interferon (IFN)-γ and interleukin (IL)-10 were measured in the serum of immunocompetent and immunosuppressed New Zealand White rabbits naturally infected with Encephalitozoon cuniculi. IFN-γ levels were elevated in infected rabbits, and a synergic effect was observed in animals treated with the immunosuppressive agent dexamethasone (Dex). The role of IL-10 in infected rabbits remains unclear, as IL-10 levels were similar to those of negative controls. Dex appeared to exhibit a proinflammatory effect, as IFN-γ levels were elevated in infected immunosuppressed rabbits. Similarly, Dex exhibited a synergic effect in infected immunosuppressed rabbits, as evidenced by the elevation in IFN-γ production. These data indicate that the immune response to this glucocorticoid should be considered in the design of future animal model studies of immunosuppression.

Exogenous gene can be integrated into Nosema bombycis genome by mediating with a non-transposon vector

Nosema bombycis, a microsporidium, is a pathogen of pebrine disease of silkworms, and its genomic DNA sequences had been determined. Thus far, the research of gene functions of microsporidium including N. bombycis cannot be performed with gain/loss of function. In the present study, we targeted to construct transgenic N. bombycis. Therefore, hemocytes of the infected silkworm were transfected with a non-transposon vector pIZT/V5-His vector in vivo, and the blood, in which the hemocyte with green fluorescence could be observed, was added to the cultured BmN cells. Furthermore, normal BmN cells were infected with germinated N. bombycis, and the infected cells were transfected with pIZT/V5-His. Continuous fluorescence observations exposed that there were N. bombycis with green fluorescence in some N. bombycis-infected cells, and the extracted genome from the purified N. bombycis spore was used as templates. PCR amplification was carried out with a pair of primers for specifically amplifying the green fluorescence protein (GFP) gene; a specific product representing the gfp gene could be amplified. Expression of the GFP protein through Western blotting also demonstrated that the gfp gene was perfectly inserted into the genome of N. bombysis. These results illustrated that exogenous gene can be integrated into N. bombycis genome by mediating with a non-transposon vector. Our research not only offers a strategy for research on gene function of N. bombycis but also provides an important reference for constructing genetically modified microsporidium utilized for biocontrol of pests.

Encephalitozoon cuniculi: Grading the Histological Lesions in Brain, Kidney, and Liver during Primoinfection Outbreak in Rabbits

This is the first confirmed report of Encephalitozoon cuniculi (E. cuniculi) in farm meat rabbits located in Northern Mexico. Eighty young rabbits exhibited clinical signs of this zoonotic emerging disease, like torticollis, ataxia, paresis, circling, and rolling. Samples of brain, kidney, and liver were examined for histology lesions. For the first time the lesions caused by E. cuniculi were graded according to their severity (I, II, and III) and the size of the granulomas (Types A, B, and C). The main cerebral injuries were Grade III, coinciding with the presence of Type C granulomas. The cerebral lesions were located in the cortex, brain stem, and medulla. The renal lesions were also Grade III distributed throughout cortex and renal medulla, with no granuloma formation. The involvement of hypersensitivity Types III and IV is suggested. All of the rabbits were seropositive to E. cuniculi by CIA testing, suggesting that this zoonotic and emerging pathogen is widely distributed among animals intended for human consumption. We believe this work could be used as a guide when examining E. cuniculi and will provide direction to confirm the diagnosis of this pathogen.

Encephalitozoon cuniculi in pet rabbits: diagnosis and optimal management

Encephalitozoonosis is a significant microsporidial disease of captive pet rabbits (Oryctolagus cuniculus). This article overviews the life cycle, pathogenesis, and host immune response to the parasite. Clinical presentation, differential diagnoses, antemortem diagnostics, and postmortem diagnosis will be discussed. International seroprevalence data and histologic prevalence estimates in the US are presented. A review of current treatment and control recommendations are discussed based on extensive review of controlled studies, which have found fenbendazole to be effective for limiting spread of the disease.

Cerebral microsporidiosis manifesting as progressive multifocal leukoencephalopathy in an HIV-infected individual - a case report

Microsporidia have become increasingly recognized as opportunistic pathogens since the genesis of the AIDS epidemic. The incidence of microsporidiosis has decreased with the advent of combination antiretroviral therapy but it is frequently reported in non-HIV immunosuppressed patients and as a latent infection in immunocompetent individuals. Herein, we describe an HIV-infected male (46 years) with suspected progressive multifocal leukoencephalopathy that has not responded to optimal antiretroviral therapy, steroids, or cidofovir. Post-mortem examination revealed cerebral microsporidiosis. No diagnostic clue however, was found when the patient was alive. This report underscores the need for physicians to consider microsporidiosis (potentially affecting the brain) when no other etiology is established both in HIV, non-HIV immunosuppressed patients and in immunocompetent individuals.

Ubiquitin-mediated response to microsporidia and virus infection in C. elegans

Microsporidia comprise a phylum of over 1400 species of obligate intracellular pathogens that can infect almost all animals, but little is known about the host response to these parasites. Here we use the whole-animal host C. elegans to show an in vivo role for ubiquitin-mediated response to the microsporidian species Nematocida parisii, as well to the Orsay virus, another natural intracellular pathogen of C. elegans. We analyze gene expression of C. elegans in response to N. parisii, and find that it is similar to response to viral infection. Notably, we find an upregulation of SCF ubiquitin ligase components, such as the cullin ortholog cul-6, which we show is important for ubiquitin targeting of N. parisii cells in the intestine. We show that ubiquitylation components, the proteasome, and the autophagy pathway are all important for defense against N. parisii infection. We also find that SCF ligase components like cul-6 promote defense against viral infection, where they have a more robust role than against N. parisii infection. This difference may be due to suppression of the host ubiquitylation system by N. parisii: when N. parisii is crippled by anti-microsporidia drugs, the host can more effectively target pathogen cells for ubiquitylation. Intriguingly, inhibition of the ubiquitin-proteasome system (UPS) increases expression of infection-upregulated SCF ligase components, indicating that a trigger for transcriptional response to intracellular infection by N. parisii and virus may be perturbation of the UPS. Altogether, our results demonstrate an in vivo role for ubiquitin-mediated defense against microsporidian and viral infections in C. elegans.

Latent microsporidiosis caused by Encephalitozoon cuniculi in immunocompetent hosts: a murine model demonstrating the ineffectiveness of the immune system and treatment with albendazole

Background

Microsporidia are obligate intracellular parasites causing severe infections with lethal outcome in immunocompromised hosts. However, these pathogens are more frequently reported as latent infections in immunocompetent individuals and raises questions about the potential risk of reactivation following induced immunosuppression.

Aims

To evaluate the possibility latent microsporidiosis, efficacy or albendazole, and reactivation, the authors monitored the course of E. cuniculi infection in immunocompetent BALB/c mice and immunodeficient SCID mice using molecular methods.

Methods

Mice were per orally infected with 10⁷ spores of E. cuniculi. Selected groups were treated with albendazole, re-infected or chemically immunosuppressed by dexamethasone. The presence of microsporidia in the host’s organs and feces were determined using PCR methods. Changes in numbers of lymphocytes in blood and in spleen after induction of immunosuppression were confirmed using flow cytometry analysis.

Results

Whereas E. cuniculi caused lethal microsporidiosis in SCID mice, the infection in BABL/c mice remained asymptomatic despite parasite dissemination into many organs during the acute infection phase. Albendazole treatment led to microsporidia elimination from organs in BALB/c mice. In SCID mice, however, only a temporary reduction in number of affected organs was observed and infection re-established post-treatment. Dexamethasone treatment resulted in a chronic microsporidia infection disseminating into most organs in BALB/c mice. Although the presence of E. cuniculi in organs of albendazole- treated mice was undetectable by PCR, it was striking that infection was reactivated by immunosuppression treatment.

Conclusion

Our results demonstrated that microsporidia can successfully survive in organs of immunocompetent hosts and are able to reactivate from undetectable levels and spread within these hosts after induction of immunosuppression. These findings stress the danger of latent microsporidiosis as a life-threatening risk factor especially for individuals undergoing chemotherapy and in transplant recipients of organs originating from infected donors.