Innate immune responses to Encephalitozoon species infections

E. hellem Ser/Thr protein phosphatase PP1 targets the DC MAPK pathway and impairs immune functions

Microsporidia are difficult to be completely eliminated once infected, and the persistence disrupts host cell functions. Here in this study, we aimed to elucidate the impairing effects and consequences of microsporidia on host DCs. Enterocytozoon hellem, one of the most commonly diagnosed zoonotic microsporidia species, was applied. In vivo models demonstrated that E. hellem-infected mice were more susceptible to further pathogenic challenges, and DCs were identified as the most affected groups of cells. In vitro assays revealed that E. hellem infection impaired DCs' immune functions, reflected by down-regulated cytokine expressions, lower extent of maturation, phagocytosis ability, and antigen presentations. E. hellem infection also detained DCs' potencies to prime and stimulate T cells; therefore, host immunities were disrupted. We found that E. hellem Ser/Thr protein phosphatase PP1 directly interacts with host p38α (MAPK14) to manipulate the p38α(MAPK14)/NFAT5 axis of the MAPK pathway. Our study is the first to elucidate the molecular mechanisms of the impairing effects of microsporidia on host DCs' immune functions. The emergence of microsporidiosis may be of great threat to public health.

Characterizing the Proliferation Patterns of Representative Microsporidian Species Enlightens Future Studies of Infection Mechanisms

Background: Microsporidia are a group of pathogens that infect all kinds of animals, such as humans, silkworms, honeybees, and shrimp; they, therefore, pose a severe threat to public health and the economy. There are over 1500 species of microsporidia that have been reported, among which Encephalitozoon hellem and Nosema bombycis are the representative zoonotic and insect-infecting species, respectively. Investigating their cell infection patterns is of great significance for understanding their infection mechanisms. Methods: Specific probes were designed for the ribosomal RNA sequences of microsporidia. Fluorescence in situ hybridization (FISH) was used to trace the proliferation cycle of the pathogens in different cells. Results: Here, two rRNA large subunit gene (LSUrRNA) probes specifically labeling N. bombycis were obtained. The life cycle of N. bombycis in silkworm cells and E. hellem in three kinds of host cells was graphically drawn. N. bombycis meronts were first observed at 30 hours post-infection (hpi), and they began merogony. Sporonts were observed at 42 hpi, and the first entire proliferation cycle was completed at 48 hpi. The proliferation cycle of E. hellem in RK13 and HEK293 epithelial cells was almost the same, completing the first life cycle after 24 hpi, but it was significantly delayed to 32 hpi in RAW264.7. Conclusions: Specific FISH probes were established for labeling microsporidia in multiple host cells. The proliferation characteristics of representative zoonotic and insect-infecting microsporidian species were clarified. This study provides an experimental pattern for future analyses of microsporidian infection mechanisms.

Encephalitozoon hellem Infection Promotes Monocytes Extravasation

Background: Microsporidia are a group of obligated intracellular fungus pathogens. Monocytes and the derivative macrophages are among the most important players in host immunity. The invasion of microsporidia may significantly affect the monocytes maturation and extravasation processes. Methods: We utilized a previously established microsporidia infection murine model to investigate the influences of microsporidia Encephalitozoon hellem (E. hellem) infection on monocyte maturation, releasing into the circulation and extravasation to the inflammation site. Flow cytometry and qPCR analysis were used to compare the monocytes and derivative macrophages isolated from bone marrow, peripheral blood and tissues of E. hellem-infected and control mice. Results: The results showed that the pro-inflammatory group of CD11b⁺Ly-6C⁺ monocytes are promoted in E. hellem-infected mice. Interestingly, the percentage of Ly-6C⁺ monocytes from E. hellem-infected mice are significantly lower in peripheral blood while significantly higher in the inflamed small intestine, together with up-regulated ratio of F4/80 macrophage in small intestine as well. Conclusions: Our findings demonstrated that E. hellem infection leads to promoted monocytes maturation in bone marrow, up-regulation of extravasation from peripheral blood to inflammation site and maturation into macrophages. Our study is the first systematic analysis of monocytes maturation and trafficking during microsporidia infection, and will provide better understanding of the pathogen–host interactions.

Immune Response to Microsporidia

Microsporidia are a group of pathogens, which can pose severe risks to the immunocompromised population, such as HIV-infected individuals or organ transplant recipients. Adaptive immunity has been reported to be critical for protection, and mice depleted of T cells are unable to control these infections. In a mouse model of infection, CD8 T cells have been found to be the primary effector cells and are responsible for protecting the infected host. Also, as infection is acquired via a peroral route, CD8 T cells in the gut compartment act as a first line of defense against these pathogens. Thus, generation of a robust CD8 T-cell response exhibiting polyfunctional ability is critical for host survival. In this chapter, we describe the effector CD8 T cells generated during microsporidia infection and the factors that may be essential for generating protective immunity against these understudied but significant pathogens. Overall, this chapter will highlight the necessity for a better understanding of the development of CD8 T-cell responses in gut-associated lymphoid tissue (GALT) and provide some insights into therapies that may be used to restore defective CD8 T-cell functionality in an immunocompromised situation.

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.

Encephalitozoon cuniculi takes advantage of efferocytosis to evade the immune response

Microsporidia are recognized as opportunistic pathogens in individuals with immunodeficiencies, especially related to T cells. Although the activity of CD8+ T lymphocytes is essential to eliminate these pathogens, earlier studies have shown significant participation of macrophages at the beginning of the infection. Macrophages and other innate immunity cells play a critical role in activating the acquired immunity. After programmed cell death, the cell fragments or apoptotic bodies are cleared by phagocytic cells, a phenomenon known as efferocytosis. This process has been recognized as a way of evading immunity by intracellular pathogens. The present study evaluated the impact of efferocytosis of apoptotic cells either infected or not on macrophages and subsequently challenged with Encephalitozoon cuniculi microsporidia. Macrophages were obtained from the bone marrow monocytes from C57BL mice, pre-incubated with apoptotic Jurkat cells (ACs), and were further challenged with E. cuniculi spores. The same procedures were performed using the previously infected Jurkat cells (IACs) and challenged with E. cuniculi spores before macrophage pre-incubation. The average number of spores internalized by macrophages in phagocytosis was counted. Macrophage expression of CD40, CD206, CD80, CD86, and MHCII, as well as the cytokines released in the culture supernatants, was measured by flow cytometry. The ultrastructural study was performed to analyze the multiplication types of pathogens. Macrophages pre-incubated with ACs and challenged with E. cuniculi showed a higher percentage of phagocytosis and an average number of internalized spores. Moreover, the presence of stages of multiplication of the pathogen inside the macrophages, particularly after efferocytosis of infected apoptotic bodies, was observed. In addition, pre-incubation with ACs or IACs and/or challenge with the pathogen decreased the viability of macrophages, reflected as high percentages of apoptosis. The marked expression of CD206 and the release of large amounts of IL-10 and IL-6 indicated the polarization of macrophages to an M2 profile, compatible with efferocytosis and favorable for pathogen development. We concluded that the pathogen favored efferocytosis and polarized the macrophages to an M2 profile, allowing the survival and multiplication of E. cuniculi inside the macrophages and explaining the possibility of macrophages acting as Trojan horses in microsporidiosis.

Characterization of a Murine Model for Encephalitozoon hellem Infection after Dexamethasone Immunosuppression

BACKGROUND

Encephalitozoon hellem (E. hellem) belongs to a group of opportunistic pathogens called microsporidia. Microsporidia infection symptoms vary and include diarrhea, ocular disorders and systemic inflammations. Traditionally, immunodeficient animals were used to study microsporidia infection. To overcome the difficulties in maintenance and operation using immunodeficient mice, and to better mimic natural occurring microsporidia infection, this study aims to develop a pharmacologically immunosuppressed murine model of E. hellem infection.

METHODS

Wild-type C57BL/6 mice were immunosuppressed with dexamethasone (Dex) and then E. hellem spores were inoculated into the mice intraperitoneally. Control groups were the Dex-immunosuppressed but noninoculated mice, and the Dex-immunosuppressed then lipopolysaccharide (LPS)-treated mice. Mice body weights were monitored and all animals were sacrificed at the 15th day after inoculation. Tissue fragments and immune cells were collected and processed.

RESULTS

Histopathological analysis demonstrated that E. hellem inoculation resulted in a disseminated nonlethal infection. Interestingly, E. hellem infection desensitized the innate immunity of the host, as shown by cytokine expressions and dendritic cell maturation. We also found that E. hellem infection greatly altered the composition of host gut microbiota. (4) Conclusions: Dex-immunosuppressed mice provide a useful tool for study microsporidiosis and the interactions between microsporidia and host immunity.

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.

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.

Hemocytin facilitates host immune responses against Nosema bombycis

Invertebrates lack an adaptive immune response and thus are reliant on their innate immune response for eliminating invading pathogens. The innate immune responses of silkworms against the pathogen Nosema bombycis include: hemocyte aggregation, melanization, antimicrobial peptides, etc. In our current study, we discovered that a silkworm hemostasis-related protein, hemocytin, is up-regulated after Nosema bombycis infection. This novel finding lead to our hypothesis that hemocytin participates in immune responses against N. bombycis. We investigated this hypothesis by analyzing the adhesive effects of hemocytin to invading N. bombycis, and the hemocytin-mediated hemocyte aggregation and hemolymph melanization. We showed that hemocytin can adhere to the surface of N. bombycis, which facilitates the agglutination of N. bombycis and hemocytes as well as the subsequent melanization. Moreover, when we utilize RNAi technology to decrease in vivo hemocytin expression, we found that the proliferation of N. bombycis within the host significantly increased. These results support our hypothesis that hemocytin exerts pro-inflammatory effects by facilitating pathogen agglutination, along with hemocyte aggregation and melanization, to combat N. bombycis. Our study is the first to determine a function of hemocytin in innate immunity against N. bombycis. Moreover, our findings are of great importance to provide potential targets for developing novel strategy against microsporidia infection.

Cyclophosphamide Treatment Mimics Sub-Lethal Infections With Encephalitozoon intestinalis in Immunocompromised Individuals

Microsporidia, including Encephalitozoon intestinalis, are emerging pathogens which cause opportunistic infections in immunocompromised patients, such as those with AIDS, cancer, the elderly and people on immunosuppressive drugs. Intestinal mucosa (IM) is crucial for developing an efficient adaptive immune response against pathogenic micro-organisms, thereby preventing their colonization and subsequent infection. As immunosuppressive drugs affect the intestinal immune response is little known. In the present study, we investigated the immune response to E. intestinalis infection in the IM and gut-associated lymphoid tissue (GALT) in cyclophosphamide (Cy) immunosuppressed mice, to mimic an immunocompromised condition. Histopathology revealed lymphoplasmacytic enteritis at 7 and 14 days-post-infection (dpi) in all infected groups, however, inflammation diminished at 21 and 28 dpi. Cy treatment also led to a higher number of E. intestinalis spores and lesions, which reduced at 28 dpi. In addition, flow cytometry analysis demonstrated CD4⁺ and CD8⁺ T cells to be predominant immune cells, with up-regulation in both Th1 and Th2 cytokines at 7 and 14 dpi, as demonstrated by histopathology. In conclusion, Cy treatment reduced GALT (Peyer’s plaques and mesenteric lymph nodes) and peritoneum populations but increased the T-cell population in the intestinal mucosa and the production of pro-and anti-inflammatory cytokines, which were able to eliminate this opportunistic fungus and reduced the E. intestinalis infection.

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 Phylodiagnosis of Enterocytozoon bieneusi and Encephalitozoon intestinalis in Children with Cancer: Microsporidia in Malignancies as an Emerging Opportunistic Infection

BACKGROUND : Microsporidia may cause infection in both immunocompromised and immunocompetent populations. The best strategy to control microsporidiosis is obtaining thorough knowledge of its outbreak and pathogenicity. PURPOSE : Because of the lack of precise estimation of microsporidia prevalence among Iranian children with cancer, the current study aimed at evaluating the rate of intestinal microsporidia in children undergoing chemotherapy.

METHODS

 Patients with cancer undergoing chemotherapy in a children's hospital in Northwestern Iran were studied; 132 stool samples were collected and stained by the Weber and Ryan-blue modified trichrome staining techniques. The extracted DNA samples were evaluated by the nested polymerase chain reaction (PCR) method. All positive isolates were sequenced for genotyping and phylogenetic analysis.

RESULTS

A total of 17 (12.8%) samples were microscopically positive for microsporidia infection, whereas only 14 (10.6%) cases were positive based on nested PCR results. In the positive samples detected with nested PCR, the frequency of Enterocytozoon bieneusi and Encephalitozoon intestinalis infections was 71.4% (n = 10) and 28.6% (n = 4), respectively. After sequencing and phylogenetic analysis, the genotype of E. bieneusi was type D and the sequences of the isolated species were similar to those of the registered ones.

CONCLUSION

E. bieneusi is a major contributor to microsporidiosis in young immunocompromised patients in Iran. Microsporidia species are well-detected when confirmatory techniques such as molecular methods are in agreement with staining. So, to ensure this, a suggestion has been made to introduce a certain diagnostic test for microsporidiosis.

Encephalitozoon: Tissue Culture, Cryopreservation, and Murine Infection

Microsporidia are eukaryotic unicellular parasites that have been studied for more than 150 years. They are found throughout the world and are capable of infecting various invertebrate and vertebrate hosts. They can cause disease in both immune-compromised and immune-competent humans. In immune-compromised individuals, infections can be severe and often fatal. Microsporidia possess a unique, highly specialized invasion mechanism that involves a structure known as the polar tube as well as the spore wall. During spore germination, the polar tube rapidly discharges from the spore and deliver the sporoplasm into the host cell. Spores are the only stage of microsporidia that can survive outside of host cells. Since the first attempt to culture microsporidia in vitro in 1930s, their cultivation has served a critical role in the study and diagnosis of these parasites. In this chapter, we include methods on the cultivation, isolation, and cryopreservation of Encephalitozoon cuniculi, which can infect humans and provides a useful model for other microsporidia. These methods can also be utilized for the culture of Encephalitozoon hellem or Encephalitozoon intestinalis. © 2018 by John Wiley & Sons, Inc.

Invertebrate host responses to microsporidia infections

Microsporidia are a group of fungi-like intracellular and unicellular parasites, which infect nearly all animals. As "master parasites", over 1400 microsporidian species have been described to date. Microsporidia infections in economical invertebrates (e.g., silkworm, shrimp) cause huge financial losses, while other microsporidia infections in daphnia, nematode, locust, honeybee and mosquito play important roles in the regulation of their population size. Research investigating invertebrate host responses following microsporidia infections has yielded numerous interesting results, especially pertaining to the innate immune response to these pathogens. In this review, we comparatively summarize the invertebrate host responses to various microsporidia infections. We discuss numerous critical events in host responses including ubiquitin-mediated resistance, production of reactive oxygen species, melanization and innate immune pathways, and the increased basic metabolism and the accumulation of juvenile hormone in infected hosts. Recent studies progressing our understanding of microsporidia infection are also highlighted. Collectively, these advances shed more light on general rules of invertebrate host immune responses and pathogenesis mechanisms of microsporidia, and concurrently offer valuable clues for further research on the crosstalk between hosts and intracellular pathogens.

Microsporidia: Obligate Intracellular Pathogens Within the Fungal Kingdom

Microsporidia are obligate intracellular pathogens related to Fungi. These organisms have a unique invasion organelle, the polar tube, which upon appropriate environmental stimulation rapidly discharges out of the spore, pierces a host cell's membrane, and serves as a conduit for sporoplasm passage into the host cell. Phylogenetic analysis suggests that microsporidia are related to the Fungi, being either a basal branch or sister group. Despite the description of microsporidia over 150 years ago, we still lack an understanding of the mechanism of invasion, including the role of various polar tube proteins, spore wall proteins, and host cell proteins in the formation and function of the invasion synapse. Recent advances in ultrastructural techniques are helping to better define the formation and functioning of the invasion synapse. Over the past 2 decades, proteomic approaches have helped define polar tube proteins and spore wall proteins as well as the importance of posttranslational modifications such as glycosylation in the functioning of these proteins, but the absence of genetic techniques for the manipulation of microsporidia has hampered research on the function of these various proteins. The study of the mechanism of invasion should provide fundamental insights into the biology of these ubiquitous intracellular pathogens that can be integrated into studies aimed at treating or controlling microsporidiosis.

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.

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.

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 intestinalis Inhibits Dendritic Cell Differentiation through an IL-6-Dependent Mechanism

Microsporidia are a group of intracellular pathogens causing self-limited and severe diseases in immunocompetent and immunocompromised individuals, respectively. A cellular type 1 adaptive response, mediated by IL-12, IFNγ, CD4+, and CD8+ T cells has been shown to be essential for host resistance, and dendritic cells (DC) play a key role at eliciting anti-microsporidial immunity. We investigated the in vitro response of DC and DC precursors/progenitors to infection with Encephalitozoon intestinalis (Ei), a common agent of human microsporidosis. Ei-exposed DC cultures up-regulated the surface expression of MHC class II and the costimulatory molecules CD86 and CD40, only when high loads of spores were used. A vigorous secretion of IL-6 but not of IL-1β or IL-12p70 was also observed in these cultures. Ei-exposed DC cultures consisted of immature infected and mature bystander DC, as assessed by MHC class II and costimulatory molecules expression, suggesting that intracellular Ei spores deliver inhibitory signals in DC. Moreover, Ei selectively inhibited the secretion of IL-12p70 in LPS-stimulated DC. Whereas Ei-exposed DC promoted allogeneic naïve T cell proliferation and IL-2 and IFNγ secretion in DC-CD4+ T cell co-cultures, separated co-cultures with bystander or infected DCs showed stimulation or inhibition of IFNγ secretion, respectively. When DC precursors/progenitors were exposed to Ei spores, a significant inhibition of DC differentiation was observed without shifting the development toward cells phenotypically or functionally compatible with myeloid-derived suppressor cells. Neutralization experiments demonstrated that this inhibitory effect is IL-6-dependent. Altogether this investigation reveals a novel potential mechanism of immune escape of microsporidian parasites through the modulation of DC differentiation and maturation.

Reactive nitrogen and oxygen species, and iron sequestration contribute to macrophage-mediated control of Encephalitozoon cuniculi (Phylum Microsporidia) infection in vitro and in vivo

Encephalitozoon cuniculi (Phylum Microsporidia) infects a wide range of mammals, and replicates within resting macrophages. Activated macrophages, conversely, inhibit replication and destroy intracellular organisms. These studies were performed to assess mechanisms of innate immune responses expressed by macrophages to control E. cuniculi infection. Addition of reactive oxygen and nitrogen species inhibitors to activated murine peritoneal macrophages statistically significantly, rescued E. cuniculi infection ex vivo. Mice deficient in reactive oxygen species, reactive nitrogen species, or both survived ip inoculation of E. cuniculi, but carried significantly higher peritoneal parasite burdens than wild-type mice at 1 and 2 weeks post inoculation. Infected peritoneal macrophages could still be identified 4 weeks post inoculation in mice deficient in reactive nitrogen species. L-tryptophan supplementation of activated murine peritoneal macrophage cultures ex vivo failed to rescue microsporidia infection. Addition of ferric citrate to supplement iron, however, did significantly rescue E. cuniculi infection in activated macrophages and further increased parasite replication in non-activated macrophages over non-treated resting control macrophages. These results demonstrate the contribution of reactive oxygen and nitrogen species, as well as iron sequestration, to innate immune responses expressed by macrophages to control E. cuniculi infection.