A role for antimicrobial peptides in intestinal microsporidiosis. Parasitology. 2009;136:175-181. [PMID: 19079820 DOI: 10.1017/s0031182008005313]

Interactions between microsporidia and other members of the microbiome

The microbiome is the collection of microbes that are associated with a host. Microsporidia are intracellular eukaryotic parasites that can infect most types of animals. In the last decade, there has been much progress to define the relationship between microsporidia and the microbiome. In this review, we cover an increasing number of reports suggesting that microsporidia are common components of the microbiome in both invertebrates and vertebrates. These microsporidia infections can range from mutualistic to pathogenic, causing several physiological phenotypes, including death. Infection with microsporidia often causes a disruption in the normal microbiome, with both increases and decreases of bacterial, fungal, viral, and protozoan species being observed. This impact on the microbiome can occur through upregulation and downregulation of innate immunity as well as morphological changes to tissues that impact interactions with these microbes. Other microbes, particularly bacteria, can inhibit microsporidia and have been exploited to control microsporidia infections. These bacteria can function through regulating immunity, secreting anti-microsporidia compounds, and, in engineered versions, expressing double-stranded RNA targeting microsporidia genes. We end this review by discussing potential future directions to further understand the complex interactions between microsporidia and the other members of the microbiome.

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.

The ins and outs of host-microsporidia interactions during invasion, proliferation and exit

Microsporidia are a large group of fungal-related obligate intracellular parasites. They are responsible for infections in humans as well as in agriculturally and environmentally important animals. Although microsporidia are abundant in nature, many of the molecular mechanisms employed during infection have remained enigmatic. In this review, we highlight recent work showing how microsporidia invade, proliferate and exit from host cells. During invasion, microsporidia use spore wall and polar tube proteins to interact with host receptors and adhere to the host cell surface. In turn, the host has multiple defence mechanisms to prevent and eliminate these infections. Microsporidia encode numerous transporters and steal host nutrients to facilitate proliferation within host cells. They also encode many secreted proteins which may modulate host metabolism and inhibit host cell defence mechanisms. Spores exit the host in a non-lytic manner that is dependent on host actin and endocytic recycling proteins. Together, this work provides a fuller picture of the mechanisms that these fascinating organisms use to infect their hosts.

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.

Expression of α-Defensins, CD20+ B-lymphocytes, and Intraepithelial CD3+ T-lymphocytes in the Intestinal Mucosa of Patients with Liver Cirrhosis: Emerging Mediators of Intestinal Barrier Function

AIM

The present study investigates the role of innate and adaptive immune system of intestinal mucosal barrier function in cirrhosis.

METHODS

Forty patients with decompensated (n = 40, group A), 27 with compensated cirrhosis (n = 27, group B), and 27 controls (n = 27, group C) were subjected to duodenal biopsy. Expression of α-defensins 5 and 6 at the intestinal crypts was evaluated by immunohistochemistry and immunofluorescence. Serum endotoxin, intestinal T-intraepithelial, and lamina propria B-lymphocytes were quantified.

RESULTS

Cirrhotic patients presented higher endotoxin concentrations (p < 0.0001) and diminished HD5 and HD6 expression compared to healthy controls (p = 0.000287, p = 0.000314, respectively). The diminished HD5 and HD6 expressions were also apparent among the decompensated patients compared to compensated group (p = 0.025, p = 0.041, respectively). HD5 and HD6 expressions were correlated with endotoxin levels (r = -0.790, p < 0.0001, r = - 0.777, p < 0.0001, respectively). Although intraepithelial T-lymphocytes were decreased in group A compared to group C (p = 0.002), no notable alterations between groups B and C were observed. The B-lymphocytic infiltrate did not differ among the investigated groups.

CONCLUSIONS

These data demonstrate that decreased expression of antimicrobial peptides may be considered as a potential pathophysiological mechanism of intestinal barrier dysfunction in liver cirrhosis, while remodeling of gut-associated lymphoid tissue as an acquired immune response to bio-pathogens remains an open field to illuminate.

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.

Lactoferrin from Milk: Nutraceutical and Pharmacological Properties

Lactoferrin is an iron-binding protein present in large quantities in colostrum and in breast milk, in external secretions and in polymorphonuclear leukocytes. Lactoferrin's main function is non-immune protection. Among several protective activities shown by lactoferrin, those displayed by orally administered lactoferrin are: (i) antimicrobial activity, which has been presumed due to iron deprivation, but more recently attributed also to a specific interaction with the bacterial cell wall and extended to viruses and parasites; (ii) immunomodulatory activity, with a direct effect on the development of the immune system in the newborn, together with a specific antinflammatory effects; (iii) a more recently discovered anticancer activity. It is worth noting that most of the protective activities of lactoferrin have been found, sometimes to a greater extent, also in peptides derived from limited proteolysis of lactoferrin that could be generated after lactoferrin ingestion. Lactoferrin could therefore be considered an ideal nutraceutic product because of its relatively cheap production from bovine milk and of its widely recognized tolerance after ingestion, along with its well demonstrated protective activities. The most important protective activities shown by orally administered bovine lactoferrin are reviewed in this article.

Contrasting host-pathogen interactions and genome evolution in two generalist and specialist microsporidian pathogens of mosquitoes

Obligate intracellular pathogens depend on their host for growth yet must also evade detection by host defenses. Here we investigate host adaptation in two Microsporidia, the specialist Edhazardia aedis and the generalist Vavraia culicis, pathogens of disease vector mosquitoes. Genomic analysis and deep RNA-Seq across infection time courses reveal fundamental differences between these pathogens. E. aedis retains enhanced cell surface modification and signalling capacity, upregulating protein trafficking and secretion dynamically during infection. V. culicis is less dependent on its host for basic metabolites and retains a subset of spliceosomal components, with a transcriptome broadly focused on growth and replication. Transcriptional profiling of mosquito immune responses reveals that response to infection by E. aedis differs dramatically depending on the mode of infection, and that antimicrobial defensins may play a general role in mosquito defense against Microsporidia. This analysis illuminates fundamentally different evolutionary paths and host interplay of specialist and generalist pathogens.

Effect of bifidobacterium on defensin-5 expression in intestinal injury of preweaning rats

AIM: To investigate the protective effect of bifidobacterium in endotoxin-induced intestinal injury in preweaning rats.

METHODS: Preweaning rats were randomly divided into three groups (n = 40 for each): a control group (group C), a model group (group E) and a treatment group (group T). Both groups E and T were intraperitoneally injected with lipopolysaccharide (LPS) at a dose of 5 mg/kg (5 mg/L in normal saline), and group T was intragastrically administrated with bifidobacterium suspension (2.0 × 10⁹ CFU/mL, 0.5 mL each time, twice a day, until the end of the experiment) 7 d before LPS administration. Group C was intraperitoneally injected with normal saline. After intraperitoneal injection and intragastric administration, the rats were placed back to the initial cage to receive breast feeding. The rats were killed at 2, 6, 12, 24 or 72 h, respectively, after endotoxin or physiological saline injection to collect serum and ileal tissue samples. Myeloperoxidase (MPO) contents in serum and ileum were detected at different times, and expression of ileal defensin-5 mRNA was evaluated by reverse transcription-polymerase chain reaction.

RESULTS: Serum and ileal MPO contents in group E were significantly higher than those in group C (serum contents: 107.50 ± 17.70 vs 157.14 ± 24.67, P < 0.05; ileal contents: 1.03 ± 0.21 vs 1.57 ± 0.33, P < 0.05), which peaked at 12 h and 6 h, respectively. MPO contents in group T were significantly lower than those in group E (serum contents: 114.38 ± 24.56 vs 145.25 ± 23.62, P < 0.05; ileal contents: 1.25 ± 0.24 vs 1.57 ± 0.33, P < 0.05). The expression of defensin-5 mRNA in group E was significantly higher than that in group C (0.953 ± 0.238 vs 0.631 ± 0.146, P < 0.05), which peaked at 2 h, and then decreased gradually. The expression of defensin-5 mRNA in group T was significantly lower than that in group E (0.487 ± 0.149 vs 0.758 ± 0.160, P < 0.05) apparently in 24 h. The expression of defensin-5 mRNA at 2 h in group T was significantly higher than that in group C (0.824 ± 0.158 vs 0.631 ± 0.146, P < 0.05).

CONCLUSION: MPO and defensin-5 mRNA increase in preweaning rats with LPS-induced intestinal injury. Bifidobacterium protects the gut by inhibiting MPO activity, not by increasing defensin-5 secretion.

Potentiated anti-microsporidial activity of Lactobacillus acidophilus CH1 bacteriocin using gold nanoparticles

Through increased awareness and improved diagnostics, microsporidiosis has now been identified in a broader range of human populations; however current therapies are inconsistently effective. Recently, probiotics were determined as means for the control of intestinal parasitic infections through their secretory products; bacteriocins. This is the first study on the effect of bacteriocin produced by Lactobacillus acidophilus CH1 bacteriocin, with or without gold nanoparticles (Au-NPs), against intestinal microsporidiosis in immunosuppressed mice. Fecal and intestinal spore loads, besides viability, extrusion and infectivity of spores from treated animals were assessed. Results showed that the anti-microsporidial effects of bacteriocin were significantly potent. This efficiency was further potentiated upon conjugating bacteriocins with Au-NPs, as it induced a strikingly sustained reduction in fecal spore shedding after cessation of therapy by 1 week (94.26%). Furthermore, reduction in intestinal spore load was highest in bacteriocin/Au-NPs-inoculated mice (89.7%) followed by bacteriocin-inoculated group (73.5%). Spores encountered from stool of bacteriocin/Au-NPs group showed 92.4% viability, versus 93.7% in bacteriocin group. Spore extrusion and infectivity were most inhibited by exposure to bacteriocin/Au-NPs. Safety of bacteriocin/Au-NPs was also verified. Thus, considering the results of the present work, L. acidophilus CH1-derived bacteriocin can present a powerful safe therapy against intestinal microsporidiosis.

Antimicrobial peptides and gut microbiota in homeostasis and pathology

We survive because we adapted to a world of microorganisms. All our epithelial surfaces participate in keeping up an effective barrier against microbes while not initiating ongoing inflammatory processes and risking collateral damage to the host. Major players in this scenario are antimicrobial peptides (AMPs). Such broad-spectrum innate antibiotics are in part produced by specialized cells but also widely sourced from all epithelia as well as circulating inflammatory cells. AMPs belong to an ancient defense system found in all organisms and participated in a preservative co-evolution with a complex microbiome. Particularly interesting interactions between host barrier and microbiota can be found in the gut. The intestinal cell lining not only has to maintain a tightly regulated homeostasis during its high-throughput regeneration, but also a balanced relationship towards an extreme number of mutualistic or commensal inhabitants. Recent research suggests that advancing our understanding of the circumstances of such balanced and sometimes imbalanced interactions between gut microbiota and host AMPs should have therapeutic implications for different intestinal disorders.

Antimicrobial Human β-Defensins in the Colon and Their Role in Infectious and Non-Infectious Diseases

β-defensins are small cationic antimicrobial peptides secreted by diverse cell types including colonic epithelial cells. Human β-defensins form an essential component of the intestinal lumen in innate immunity. The defensive mechanisms of β-defensins include binding to negatively charged microbial membranes that cause cell death and chemoattraction of immune cells. The antimicrobial activity of β-defensin is well reported in vitro against several enteric pathogens and in non-infectious processes such as inflammatory bowel diseases, which alters β-defensin production. However, the role of β-defensin in vivo in its interaction with other immune components in host defense against bacteria, viruses and parasites with more complex membranes is still not well known. This review focuses on the latest findings regarding the role of β-defensin in relevant human infectious and non-infectious diseases of the colonic mucosa. In addition, we summarize the most significant aspects of β-defensin and its antimicrobial role in a variety of disease processes.

Immune response to Encephalitozoon infection review

The microsporidia are emerging agents of infectious disease in both immunocompromised and immunocompetent mammals. Recently, there has been an increased interest in studying the immunobiology of microsporidiosis. This paper discusses the humoral and cell-mediated immune responses to Encephalitozoon spp. The T-cell-mediated responses appear to be most important in conferring resistance. This has become evident by the lethal effects of microsporidiosis in T-cell-deficient hosts. However, much still needs to be learned about the immunobiology of microsporidiosis regarding the specific T-cell responses and the cytokines that provide protective immunity and facilitate the macrophage-mediated killing of microsporidia. Such information will become important in developing immunotherapeutic strategies to control microsporidiosis in the future.

Lactoferricin B inhibits the phosphorylation of the two-component system response regulators BasR and CreB

Natural antimicrobial peptides provide fundamental protection for multicellular organisms from microbes, such as Lactoferricin B (Lfcin B). Many studies have shown that Lfcin B penetrates the cell membrane and has intracellular activities. To elucidate the intracellular behavior of Lfcin B, we first used Escherichia coli K12 proteome chips to identify the intracellular targets of Lfcin B. The results showed that Lfcin B binds to two response regulators, BasR and CreB, of the two-component system. For further analysis, we conducted several in vitro and in vivo experiments and utilized bioinformatics methods. The electrophoretic mobility shift assays and kinase assays indicate that Lfcin B inhibits the phosphorylation of the response regulators (BasR and CreB) and their cognate sensor kinases (BasS and CreC). Antibacterial assays showed that Lfcin B reduced E. coli's tolerance to environmental stimuli, such as excessive ferric ions and minimal medium conditions. This is the first study to show that an antimicrobial peptide inhibits the growth of bacteria by influencing the phosphorylation of a two-component system directly.

Alpha-defensin DEFA1A3 gene copy number elevation in Danish Crohn's disease patients

BACKGROUND AND PURPOSE OF STUDY

Extensive copy number variation is observed for the DEFA1A3 gene encoding alpha-defensins 1-3. The objective of this study was to determine the involvement of alpha-defensins in colonic tissue from Crohn's disease (CD) patients and the possible genetic association of DEFA1A3 with CD.

METHODS

Two-hundred and forty ethnic Danish CD patients were included in the study. Reverse transcriptase PCR assays determined DEFA1A3 expression in colonic tissue from a subset of patients. Immunohistochemical analysis identified alpha-defensin peptides in colonic tissue. Copy number of DEFA1A3 and individual alleles, DEFA1 and DEFA3, were compared with those for controls, by use of combined real-time quantitative PCR and pyrosequencing, and correlated with disease location.

RESULTS

Inflammatory-dependent mRNA expression of DEFA1A3 (P < 0.001), and the presence of alpha-defensin peptides, were observed in colonic tissue samples. Higher DEFA1A3 gene copy number (CD: mean copy number, 7.2 vs. controls 6.7; P < 0.001) and individual DEFA1 alleles (CD mean copy number 5.6 vs. controls 5.1; P < 0.01) were associated with CD, with strong association with colonic location (P < 0.001).

CONCLUSIONS

Alpha-defensins are involved in the inflammation of CD, with local mRNA and peptide expression. In combination with the findings that a high DEFA1A3 copy number is significantly linked to CD, these results suggest that a high DEFA1A3 copy number might be important in hindering the normal inflammatory response in CD, particularly colonic CD.

Latent microsporidial infection in immunocompetent individuals - a longitudinal study

BACKGROUND

Microsporidia (Fungi) have been repeatedly identified as the cause of opportunistic infections predominantly in immunodeficient individuals such as AIDS patients. However, the global epidemiology of human microsporidiosis is poorly understood and the ability of microsporidia to survive and multiply in immunocompetent hosts remains unsolved.

AIMS

To determine the presence of latent microsporidia infections in apparently healthy humans in the Czech Republic, the authors tested sera, urine and stool originating from fifteen persons within a three month period examined on a weekly basis.

METHODS

Sera, stool and urine samples originating from fifteen HIV-negative people at risk with occupational exposure to animals, aged 22-56 years, living in the Czech Republic were tested by indirect immunofluorescence assay (IFA) for the presence of specific anti-microsporidial antibodies, standard Calcofluor M2R staining for the detection of microsporidian spores in all urine sediments and stool smears and molecular methods for the microsporidial species determination.

RESULTS

Specific anti-microsporidial antibodies were detected in fourteen individuals, asymptomatic Encephalitozoon spp. infection was found in thirteen and E. bieneusi infection was detected in seven of those examined. While E. hellem 1A and E. cuniculi II were the major causative agents identified, seven different genotypes of E. bieneusi were recorded.

CONCLUSIONS

These findings clearly show that exposure to microsporidia is common and chronic microsporidiosis is not linked to any clinical manifestation in healthy population. Moreover, our results indicate much higher incidence of microsporidial infections among an apparently healthy population than previously reported. These results open the question about the potential risk of reactivation of latent microsporidiosis in cases of immunosupression causing life-threatening disease.

Defensins in innate immunity

The innate immune system is the first line of defense against many common microorganisms, which can initiate adaptive immune responses to provide increased protection against subsequent re-infection by the same pathogen. As a major family of antimicrobial peptides, defensins are widely expressed in a variety of epithelial cells and sometimes in leukocytes, playing an important role in the innate immune system due to their antimicrobial, chemotactic and regulatory activities. This review introduces their structure, classification, distribution, synthesis, and focuses on their biological activities and mechanisms, as well as clinical relevance. These studies of defensins in the innate immune system have implications for the prevention and treatment of a variety of infectious diseases, including bacterial ocular disease.

Multifunctional host defense peptides: antiparasitic activities

Whereas significant knowledge is accumulating on the antibacterial and antifungal properties of host defense peptides (HDPs) and their synthetic mimics, much less is known of their activities against parasites. A variety of in vitro and in vivo antiparasitic assays suggest that these notorious antimicrobial compounds could represent a powerful tool for the development of novel drugs to fight parasites in the vertebrate host or to complement current therapeutic strategies, albeit the fact that HDPs essentially act by nonspecific mechanisms casts serious doubt on their ability to exert sufficient selectivity to be considered ideal candidates for drug development. This minireview summarizes recent efforts to assess the antiparasitic properties of HDPs and their synthetic derivatives, focusing on two of the most used models - Plasmodium and Leishmania species - for antiparasitic assays against the different development stages.

Innate immune responses to Encephalitozoon species infections

Microsporidia are obligate intracellular, eukaryotic fungi, which have gained recognition as opportunistic parasites in immunocompromised patients. Resistance to lethal microsporidia infections requires a Th1 immune response; how this protection is initiated against Encephalitozoon species is the focus of this review article.