Animal Models of Human Disease

The use of animal models of human disease is critical for furthering our understanding of disease mechanisms, for the discovery of novel targets for treatment, and for translational research. This Special Topic entitled "Animal Models of Human Disease" aimed to collect state-of-the-art primary research studies and review articles from international experts and leading groups using animal models to study human diseases. Submissions were welcomed on a wide range of animal models and pathologies, including infectious disease, acute injury, regeneration, cancer, autoimmunity, degenerative and chronic disease. Seven participating MDPI journals supported the Special Topic, namely: Biomedicines, Cells, Current Issues in Molecular Biology, Diagnostics, Genes, the International Journal of Molecular Sciences, and the International Journal of Translational Medicine. In total, 46 papers were published in this Special Topic, with 37 full length original research papers, 2 research communications and 7 reviews. These contributions cover a wide range of clinically relevant, translatable, and comparative animal models, as well as furthering understanding of fundamental sciences, covering topics on physiological processes, on degenerative, inflammatory, infectious, autoimmune, neurological, metabolic, heamatological, hormonal and mitochondrial disorders, developmental processes and diseases, cardiology, cancer, trauma, stress, and ageing.

A Pilot Study on Peptidylarginine Deiminases and Protein Deimination in Animal Cancers across Vertebrate Species

PADs are a group of calcium-dependent enzymes that play key roles in inflammatory pathologies and have diverse roles in cancers. PADs cause irreversible post-translational modification of arginine to citrulline, leading to changes in protein function in different cellular compartments. PAD isozyme diversity differs throughout phylogeny in chordates, with five PAD isozymes in mammals, three in birds, and one in fish. While the roles for PADs in various human cancers are mounting (both in regards to cancer progression and epigenetic regulation), investigations into animal cancers are scarce. The current pilot-study therefore aimed at assessing PAD isozymes in a range of animal cancers across the phylogeny tree. In addition, the tissue samples were assessed for total protein deimination and histone H3 deimination (CitH3), which is strongly associated with human cancers and also indicative of gene regulatory changes and neutrophil extracellular trap formation (NETosis). Cancers were selected from a range of vertebrate species: horse, cow, reindeer, sheep, pig, dog, cat, rabbit, mink, hamster, parrot, and duck. The cancers chosen included lymphoma, kidney, lung, testicular, neuroendocrine, anaplastic, papilloma, and granulosa cell tumour. Immunohistochemical analysis revealed that CitH3 was strongly detected in all of the cancers assessed, while pan-deimination detection was overall low. Both PAD2 and PAD3 were the most predominantly expressed PADs across all of the cancers assessed, while PAD1, PAD4, and PAD6 were overall expressed at lower, albeit varying, levels. The findings from this pilot study provide novel insights into PAD-mediated roles in different cancers across a range of vertebrate species and may aid in the understanding of cancer heterogeneity and cancer evolution.

Prostate cancer and microfluids

Microfluidic systems aim to detect sample matter quickly with high sensitivity and resolution, on a small scale. With its increased use in medicine, the field is showing significant promise in prostate cancer diagnosis and management due, in part, to its ability to offer point-of-care testing. This review highlights some of the research that has been undertaken in respect of prostate cancer and microfluidics. Firstly, this review considers the diagnosis of prostate cancer through use of microfluidic systems and analyses the detection of prostate specific antigen, proteins, and circulating tumor cells to highlight the scope of current advancements. Secondly, this review analyses progressions in the understanding of prostate cancer physiology and considers techniques used to aid treatment of prostate cancer, such as the creation of a micro-environment. Finally, this review highlights potential future roles of microfluidics in assisting prostate cancer, such as in exosomal analysis. In conclusion, this review shows the vast scope and application of microfluidic systems and how these systems will ensure advancements to future prostate cancer management.

Peptidylarginine Deiminase Isozyme-Specific PAD2, PAD3 and PAD4 Inhibitors Differentially Modulate Extracellular Vesicle Signatures and Cell Invasion in Two Glioblastoma Multiforme Cell Lines

Glioblastoma multiforme (GBM) is an aggressive adult brain tumour with poor prognosis. Roles for peptidylarginine deiminases (PADs) in GBM have recently been highlighted. Here, two GBM cell lines were treated with PAD2, PAD3 and PAD4 isozyme-specific inhibitors. Effects were assessed on extracellular vesicle (EV) signatures, including EV-microRNA cargo (miR21, miR126 and miR210), and on changes in cellular protein expression relevant for mitochondrial housekeeping (prohibitin (PHB)) and cancer progression (stromal interaction molecule 1 (STIM-1) and moesin), as well as assessing cell invasion. Overall, GBM cell-line specific differences for the three PAD isozyme-specific inhibitors were observed on modulation of EV-signatures, PHB, STIM-1 and moesin protein levels, as well as on cell invasion. The PAD3 inhibitor was most effective in modulating EVs to anti-oncogenic signatures (reduced miR21 and miR210, and elevated miR126), to reduce cell invasion and to modulate protein expression of pro-GBM proteins in LN229 cells, while the PAD2 and PAD4 inhibitors were more effective in LN18 cells. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for deiminated proteins relating to cancer, metabolism and inflammation differed between the two GBM cell lines. Our findings highlight roles for the different PAD isozymes in the heterogeneity of GBM tumours and the potential for tailored PAD-isozyme specific treatment.

Cannabidiol Is a Novel Modulator of Bacterial Membrane Vesicles

Membrane vesicles (MVs) released from bacteria participate in cell communication and host-pathogen interactions. Roles for MVs in antibiotic resistance are gaining increased attention and in this study we investigated if known anti-bacterial effects of cannabidiol (CBD), a phytocannabinoid from Cannabis sativa, could be in part attributed to effects on bacterial MV profile and MV release. We found that CBD is a strong inhibitor of MV release from Gram-negative bacteria (E. coli VCS257), while inhibitory effect on MV release from Gram-positive bacteria (S. aureus subsp. aureus Rosenbach) was negligible. When used in combination with selected antibiotics, CBD significantly increased the bactericidal action of several antibiotics in the Gram-negative bacteria. In addition, CBD increased antibiotic effects of kanamycin in the Gram-positive bacteria, without affecting MV release. CBD furthermore changed protein profiles of MVs released from E. coli after 1 h CBD treatment. Our findings indicate that CBD may pose as a putative adjuvant agent for tailored co-application with selected antibiotics, depending on bacterial species, to increase antibiotic activity, including via MV inhibition, and help reduce antibiotic resistance.

Peptidylarginine Deiminase Inhibitors Reduce Bacterial Membrane Vesicle Release and Sensitize Bacteria to Antibiotic Treatment

Outer membrane and membrane vesicles (OMV/MV) are released from bacteria and participate in cell communication, biofilm formation and host-pathogen interactions. Peptidylarginine deiminases (PADs) are phylogenetically conserved enzymes that catalyze post-translational deimination/citrullination of proteins, causing structural and functional changes in target proteins. PADs also play major roles in the regulation of eukaryotic extracellular vesicle release. Here we show phylogenetically conserved pathways of PAD-mediated OMV/MV release in bacteria and describe deiminated/citrullinated proteins in E. coli and their derived OMV/MVs. Furthermore, we show that PAD inhibitors can be used to effectively reduce OMV/MV release, both in Gram-negative and Gram-positive bacteria. Importantly, this resulted in enhanced antibiotic sensitivity of both E. coli and S. aureus to a range of antibiotics tested. Our findings reveal novel strategies for applying pharmacological OMV/MV-inhibition to reduce antibiotic resistance.

Mesenchymal Stromal Cell Derived Extracellular Vesicles Reduce Hypoxia-Ischaemia Induced Perinatal Brain Injury

Background

Neonatal hypoxic-ischemic (HI) insult is a leading cause of disability and death in newborns, with therapeutic hypothermia being the only currently available clinical intervention. Thus there is a great need for adjunct and novel treatments for enhanced or alternative post-HI neuroprotection. Extracellular vesicles (EVs) derived from mesenchymal stromal/stem cells (MSCs) have recently been shown to exhibit regenerative effects in various injury models. Here we present findings showing neuroprotective effects of MSC-derived EVs in the Rice–Vannucci model of severe HI-induced neonatal brain insult.

Methods

Mesenchymal stromal/stem cell-derived EVs were applied intranasally immediately post HI-insult and behavioral outcomes were observed 48 h following MSC-EV treatment, as assessed by negative geotaxis. Brains were thereafter excised and assessed for changes in glial responses, cell death, and neuronal loss as markers of damage at 48 h post HI-insult.

Results

Brains of the MSC-EV treated group showed a significant decrease in microglial activation, cell death, and percentage tissue volume loss in multiple brain regions, compared to the control-treated groups. Furthermore, negative geotaxis test showed improved behavioral outcomes at 48 h following MSC-EV treatment.

Conclusion

Our findings highlight the clinical potential of using MSC-derived EVs following neonatal hypoxia-ischaemia.

Cannabidiol Affects Extracellular Vesicle Release, miR21 and miR126, and Reduces Prohibitin Protein in Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is the most common and aggressive form of primary malignant brain tumor in adults, with poor prognosis. Extracellular vesicles (EVs) are key-mediators for cellular communication through transfer of proteins and genetic material. Cancers, such as GBM, use EV release for drug-efflux, pro-oncogenic signaling, invasion and immunosuppression; thus the modulation of EV release and cargo is of considerable clinical relevance. As EV-inhibitors have been shown to increase sensitivity of cancer cells to chemotherapy, and we recently showed that cannabidiol (CBD) is such an EV-modulator, we investigated whether CBD affects EV profile in GBM cells in the presence and absence of temozolomide (TMZ). Compared to controls, CBD-treated cells released EVs containing lower levels of pro-oncogenic miR21 and increased levels of anti-oncogenic miR126; these effects were greater than with TMZ alone. In addition, prohibitin (PHB), a multifunctional protein with mitochondrial protective properties and chemoresistant functions, was reduced in GBM cells following 1 h CBD treatment. This data suggests that CBD may, via modulation of EVs and PHB, act as an adjunct to enhance treatment efficacy in GBM, supporting evidence for efficacy of cannabinoids in GBM.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Cannabidiol (CBD) Is a Novel Inhibitor for Exosome and Microvesicle (EMV) Release in Cancer

Exosomes and microvesicles (EMV) are lipid bilayer-enclosed structures, released by cells and involved in intercellular communication through transfer of proteins and genetic material. EMV release is also associated with various pathologies, including cancer, where increased EMV release is amongst other associated with chemo-resistance and active transfer of pro-oncogenic factors. Recent studies show that EMV-inhibiting agents can sensitize cancer cells to chemotherapeutic agents and reduce cancer growth in vivo. Cannabidiol (CBD), a phytocannabinoid derived from Cannabis sativa, has anti-inflammatory and anti-oxidant properties, and displays anti-proliferative activity. Here we report a novel role for CBD as a potent inhibitor of EMV release from three cancer cell lines: prostate cancer (PC3), hepatocellular carcinoma (HEPG2) and breast adenocarcinoma (MDA-MB-231). CBD significantly reduced exosome release in all three cancer cell lines, and also significantly, albeit more variably, inhibited microvesicle release. The EMV modulating effects of CBD were found to be dose dependent (1 and 5 μM) and cancer cell type specific. Moreover, we provide evidence that this may be associated with changes in mitochondrial function, including modulation of STAT3 and prohibitin expression, and that CBD can be used to sensitize cancer cells to chemotherapy. We suggest that the known anti-cancer effects of CBD may partly be due to the regulatory effects on EMV biogenesis, and thus CBD poses as a novel and safe modulator of EMV-mediated pathological events.

Peptidylarginine Deiminases-Roles in Cancer and Neurodegeneration and Possible Avenues for Therapeutic Intervention via Modulation of Exosome and Microvesicle (EMV) Release?

Exosomes and microvesicles (EMVs) are lipid bilayer-enclosed structures released from cells and participate in cell-to-cell communication via transport of biological molecules. EMVs play important roles in various pathologies, including cancer and neurodegeneration. The regulation of EMV biogenesis is thus of great importance and novel ways for manipulating their release from cells have recently been highlighted. One of the pathways involved in EMV shedding is driven by peptidylarginine deiminase (PAD) mediated post-translational protein deimination, which is calcium-dependent and affects cytoskeletal rearrangement amongst other things. Increased PAD expression is observed in various cancers and neurodegeneration and may contribute to increased EMV shedding and disease progression. Here, we review the roles of PADs and EMVs in cancer and neurodegeneration.

Exosomes serve as tumour markers for personalized diagnostics owing to their important role in cancer metastasis

Exosomes, membrane vesicles of 40–100 nm in diameter, are derived from endosomes in various cells. The bioactive molecules specifically packed into exosomes can be horizontally transferred into recipient cells changing their biological properties, by which tumour cells continuously modify their surrounding microenvironment and distant target cells favouring cancer metastasis. It has been suspected for a long time that exosomes participate in the whole process of tumour metastasis. Although there is much unknown and many controversies in the role of cancer exosome, the major contribution of tumour-associated exosomes to different steps of cancer metastasis are demonstrated in this review. Mainly because these exosomes are easily accessible and capable of representing their parental cells, exosomes draw much attention as a promising biomarker for tumour screening, diagnosis and prognosis. Currently, researchers have found numerous biomarkers in exosomes with great potential to be utilized in personalized medicine. In this article, we summarize the roles of biomarkers, which are validated by clinical samples. Even though many conundrums remain, such as exosome extraction, large multicentre validation of biomarkers and data interpretation, exosomes are certain to be used in clinical practice in the near future as the field rapidly expands.

A novel role for peptidylarginine deiminases in microvesicle release reveals therapeutic potential of PAD inhibition in sensitizing prostate cancer cells to chemotherapy

INTRODUCTION

Protein deimination, defined as the post-translational conversion of protein-bound arginine to citrulline, is carried out by a family of 5 calcium-dependent enzymes, the peptidylarginine deiminases (PADs) and has been linked to various cancers. Cellular microvesicle (MV) release, which is involved in cancer progression, and deimination have not been associated before. We hypothesize that elevated PAD expression, observed in cancers, causes increased MV release in cancer cells and contributes to cancer progression.

BACKGROUND

We have previously reported that inhibition of MV release sensitizes cancer cells to chemotherapeutic drugs. PAD2 and PAD4, the isozymes expressed in patients with malignant tumours, can be inhibited with the pan-PAD-inhibitor chloramidine (Cl-am). We sought to investigate whether Cl-am can inhibit MV release and whether this pathway could be utilized to further increase the sensitivity of cancer cells to drug-directed treatment.

METHODS

Prostate cancer cells (PC3) were induced to release high levels of MVs upon BzATP stimulation of P2X7 receptors. Western blotting with the pan-protein deimination antibody F95 was used to detect a range of deiminated proteins in cells stimulated to microvesiculate. Changes in deiminated proteins during microvesiculation were revealed by immunoprecipitation and immunoblotting, and mass spectrometry identified deiminated target proteins with putative roles in microvesiculation.

CONCLUSION

We report for the first time a novel function of PADs in the biogenesis of MVs in cancer cells. Our results reveal that during the stimulation of prostate cancer cells (PC3) to microvesiculate, PAD2 and PAD4 expression levels and the deimination of cytoskeletal actin are increased. Pharmacological inhibition of PAD enzyme activity using Cl-am significantly reduced MV release and abrogated the deimination of cytoskeletal actin. We demonstrated that combined Cl-am and methotrexate (MTX) treatment of prostate cancer cells increased the cytotoxic effect of MTX synergistically. Refined PAD inhibitors may form part of a novel combination therapy in cancer treatment.

Blood/plasma secretome and microvesicles

A major but hitherto overseen component of the blood/plasma secretome is that of extracellular vesicles (EVs) which are shed from all blood cell types. These EVs are made up of microvesicles (MVs) and exosomes. MVs, 100nm-1μm in diameter, are released from the cell surface, and are a rich source of non-conventionally secreted proteins lacking a conventional signal peptide, and thus not secreted by the classical secretory pathways. Exosomes are smaller vesicles (≤100nm) having an endocytic origin and released upon multivesicular body fusion with the plasma membrane. Both vesicle types play major roles in intercellular cross talk and constitute an important component of the secretome especially in the area of biomarkers for cancer. The release of EVs, which are found in all the bodily fluids, is enhanced in cancer and a major focus of cancer proteomics is therefore targeted at EVs. The blood/plasma secretome is also a source of EVs, potentially diagnostic of infectious disease, whether from EVs released from infected cells or from the pathogens themselves. Despite the great excitement in this field, as is stated here and in other parts of this Special issue entitled: An Updated Secretome, much of the EV research, whether proteomic or functional in nature, urgently needs standardisation both in terms of nomenclature and isolation protocols. This article is part of a Special Issue entitled: An Updated Secretome.

Vesiclepedia: a compendium for extracellular vesicles with continuous community annotation

Extracellular vesicles (EVs) are membraneous vesicles released by a variety of cells into their microenvironment. Recent studies have elucidated the role of EVs in intercellular communication, pathogenesis, drug, vaccine and gene-vector delivery, and as possible reservoirs of biomarkers. These findings have generated immense interest, along with an exponential increase in molecular data pertaining to EVs. Here, we describe Vesiclepedia, a manually curated compendium of molecular data (lipid, RNA, and protein) identified in different classes of EVs from more than 300 independent studies published over the past several years. Even though databases are indispensable resources for the scientific community, recent studies have shown that more than 50% of the databases are not regularly updated. In addition, more than 20% of the database links are inactive. To prevent such database and link decay, we have initiated a continuous community annotation project with the active involvement of EV researchers. The EV research community can set a gold standard in data sharing with Vesiclepedia, which could evolve as a primary resource for the field.

Pulsed extremely low-frequency magnetic fields stimulate microvesicle release from human monocytic leukaemia cells

Microvesicles are released from cell surfaces constitutively during early apoptosis or upon activation with various stimuli including sublytic membrane attack complex (MAC). This study shows that an alternating current, pulsed, extremely low-frequency electromagnetic field (0.3 μT at 10 Hz, 6V AC) induced transient plasma membrane damage that allowed calcium influx. This in turn caused a release of stimulated microvesicles (sMV). When extracellular calcium was chelated with EGTA, sMV biogenesis initiated by ELFMF was markedly reduced and the reduction was less than when the stimulation was the deposition of sublytic MAC. This suggested that pulsed ELFMF resulted in transcellular membrane pores causing organelles to leak additional calcium into the cytoplasm (which EGTA would not chelate) which itself can lead to sMV release.

Microvesicles in health and disease

Microvesicles (or MVs) are plasma membrane-derived vesicles released from most eukaryotic cells constitutively during early apoptosis or at higher levels after chemical or physical stress conditions. This review looks at some of the functions of MVs in terms of intercellular communication and ensuant signal transduction, including the transport of proteins (unconventional protein export) as well as of mRNA and microRNA. MVs also have roles in membrane repair, the removal of misfolded proteins, and in the control of apoptosis. We also discuss the role MVs have been shown to have in invasive growth and metastasis as well as in hypoxia in tumours and cerebral ischaemia. The association of MVs in infectious and autoimmune disease is also summarised together with their possible use as therapeutic agents.

Trypanosoma cruzi immune evasion mediated by host cell-derived microvesicles

The innate immune system is the first mechanism of vertebrate defense against pathogen infection. In this study, we present evidence for a novel immune evasion mechanism of Trypanosoma cruzi, mediated by host cell plasma membrane-derived vesicles. We found that T. cruzi metacyclic trypomastigotes induced microvesicle release from blood cells early in infection. Upon their release, microvesicles formed a complex on the T. cruzi surface with the complement C3 convertase, leading to its stabilization and inhibition, and ultimately resulting in increased parasite survival. Furthermore, we found that TGF-β-bearing microvesicles released from monocytes and lymphocytes promoted rapid cell invasion by T. cruzi, which also contributed to parasites escaping the complement attack. In addition, in vivo infection with T. cruzi showed a rapid increase of microvesicle levels in mouse plasma, and infection with exogenous microvesicles resulted in increased T. cruzi parasitemia. Altogether, these data support a role for microvesicles contributing to T. cruzi evasion of innate immunity.

Human plasma membrane-derived vesicles halt proliferation and induce differentiation of THP-1 acute monocytic leukemia cells

Plasma membrane-derived vesicles (PMVs) are small intact vesicles released from the cell surface that play a role in intercellular communication. We have examined the role of PMVs in the terminal differentiation of monocytes. The myeloid-differentiating agents all-trans retinoic acid/PMA and histamine, the inflammatory mediator that inhibits promonocyte proliferation, induced an intracellular Ca(2+)-mediated PMV (as opposed to exosome) release from THP-1 promonocytes. These PMVs cause THP-1 cells to enter G(0)-G(1) cell cycle arrest and induce terminal monocyte-to-macrophage differentiation. Use of the TGF-β receptor antagonist SB-431542 and anti-TGF-β1 Ab showed that this was due to TGF-β1 carried on PMVs. Although TGF-β1 levels have been shown to increase in cell culture supernatants during macrophage differentiation and dendritic cell maturation, the presence of TGF-β1 in PMVs is yet to be reported. In this study, to our knowledge we show for the first time that TGF-β1 is carried on the surface of PMVs, and we confirm the presence within PMVs of certain leaderless proteins, with reported roles in myeloid cell differentiation. Our in vitro findings support a model in which TGF-β1-bearing PMVs, released from promonocytic leukemia cells (THP-1) or primary peripheral blood monocytes on exposure to sublytic complement or after treatment with a differentiation therapy agent, such as all-trans retinoic acid, significantly reduce proliferation of THP-1 cells. Such PMVs also induce the terminal differentiation of primary peripheral blood monocytes as well as THP-1 monocytes.

Human plasma membrane-derived vesicles inhibit the phagocytosis of apoptotic cells--possible role in SLE

Plasma membrane-derived vesicles (PMVs) also known as microparticles, are small membrane-bound vesicles released from the cell membrane via blebbing and shedding. PMVs have been linked with various physiological functions as well as pathological conditions such as inflammation, autoimmune disease and cardiovascular disease. PMVs are characterised by the expression of phosphatidylserine (PS) on the plasma membrane. PS, also expressed on apoptotic cells (ACs) enables macrophages to phagocytose ACs. As it is widely known that PMV production is increased during apoptosis, we were able to show that PMVs could compete dose dependently with ACs for the PS receptor on macrophages, so reducing phagocytosis of ACs. In a clinical setting this may result in secondary necrosis and further pathological conditions. In SLE in which there are raised PMV levels, there is an anti-phospholipid-mediated increase in PMV release, which can be abrogated by depletion of IgG. Our work provides an insight into how PMVs may play a role in the aetiology of autoimmune disease, in particular SLE.

Involvement of lectin pathway activation in the complement killing of Giardia intestinalis

Giardia intestinalis (syn. G. lamblia, G. duodenalis) is a flagellated unicellular eukaryotic microorganism that commonly causes diarrheal disease throughout the world. In humans, the clinical effects of Giardia infection range from the asymptomatic carrier state to a severe malabsorption syndrome possibly due to different virulence of the Giardia strain, the number of cysts ingested, the age of the host, and the state of the host immune system at the time of infection. The question about how G. intestinalis is controlled by the organism remains unanswered. Here, we investigated the role of the complement system and in particular, the lectin pathway during Giardia infections. We present the first evidence that G. intestinalis activate the complement lectin pathway and in doing so participate in eradication of the parasite. We detected rapid binding of mannan-binding lectin, H-ficolin and L-ficolin to the surface of G. intestinalis trophozoites and normal human serum depleted of these molecules failed to kill the parasites. Our finding provides insight into the role of lectin pathway in the control of G. intestinalis and about the nature of surface components of parasite.

Role of early lectin pathway activation in the complement-mediated killing of Trypanosoma cruzi

The complement system is the first line of defence against pathogen infection and can be activated by the classic, alternative and lectin pathways. Trypanosoma cruzi, the causative agent of Chagas disease, has to evade complement system killing and invade the host cells to progress in infection. T. cruzi infectious stages resist complement-mediated killing by expressing surface receptors, which dissociate or prevent C3 convertase formation. Here, we present the first evidence that T. cruzi activates the complement lectin pathway. We detected rapid binding of mannan-binding lectin, H-ficolin, and L-ficolin to the surface of T. cruzi, and found that serum depleted of these molecules failed to kill parasites. Furthermore, lectin pathway activation by T. cruzi required the MBL-associated serine protease 2 (MASP2) activity resulting in C2 factor cleavage. In addition, we demonstrate that the infectious stage of T. cruzi inhibits the lectin pathway activation and complement killing expressing the complement C2 receptor inhibitor trispanning (CRIT) protein. Transgenic parasites overexpressing CRIT were highly resistant to complement-mediated killing. CRIT-derived peptides inhibited both C2 binding to the surface of T. cruzi and parasite killing. Biochemical studies revealed that the CRIT extracellular domain 1 inhibits MASP2 cleavage of C2 factor and thereby impairs C3 convertase formation. Our findings establish that the complement lectin pathway recognizes T. cruzi and provide molecular insights into how the infectious stage inhibits this activation to resist complement system killing.

Monocytic THP-1 cells stimulated by normal human serum (NHS) release cytokine-bearing plasma membrane-derived vesicles (PMVs), and can be inhibited by methyl-beta-cyclodextrin, calpeptin and Rho-kinase inhibitor, Y-27632 (98.27)

Stimulation of human acute monocytic cells with sublytic complement leads to an increase of intracellular calcium resulting in the release of two forms of microvesicles, one derived from the surface membrane (between 0.1-1 μm), which we term plasma membrane-derived vesicles (PMVs) and exosomes (50-100nm) released by exocytosis. Much work has been documented on the release of PMVs, using various stimuli, and the roles they play in disease, but comparatively little is available on inhibition of PMV release. Although upon stimulation cells release exosomes in addition to PMVs, little has been reported on ways of differentiating between these two microvesicle types. Our aim was therefore to identify inhibitors of PMV release and to effectively differentiate between PMVs and exosomes. Methyl-β -cyclodextrin, an inhibitor of lipid rafts, calpeptin, which inhibits calpain and Rho-kinase inhibitor, Y-27632 were found to inhibit effectively the release of PMVs. Exosomes separated from PMVs by sucrose gradient were confirmed by electron microscopy and compared to PMVs were found to express less phosphatidylserine, but more CD63. Of the various cytokines carried by PMVs and exosomes, macrophage migration inhibition factor was found at a four-fold higher level in PMVs.

Source of Research Support: Royal Society, London.

Complement C2 receptor inhibitor trispanning confers an increased ability to resist complement-mediated lysis in Trypanosoma cruzi

The ability to resist complement differs between the Y and Colombiana Trypanosoma cruzi strains. We found that the Y strain of T. cruzi was more able to resist the classical and lectin pathways of complement activation than the Colombiana strain. The complement C2 receptor inhibitor trispanning gene (CRIT) is highly conserved in both strains. At the protein level, CRIT is expressed only in stationary-phase epimastigotes of the Y but not the Colombiana strain and is expressed in infectious metacyclic trypomastigotes of both strains. Y strain epimastigotes with an overexpressed CRIT gene (pTEX-CRIT) had higher survival in normal human serum (NHS). Overexpression of the Y strain CRIT gene in Colombiana epimastigote forms increased the parasite's resistance to lysis mediated by the classical and lectin pathways but not to lysis mediated by alternative pathways. CRIT involvement on the parasite surface was confirmed by showing that the lytic activity of NHS against epimastigotes could be restored by adding excess C2.

CRIT is expressed on podocytes in normal human kidney and upregulated in membranous nephropathy

Complement C2 receptor inhibitor trispanning (CRIT) is a novel human complement regulatory cell surface receptor. It binds the human complement protein C2 and blocks the classical pathway of complement activation, thus protecting the cell against complement attack. CRIT expression in the kidney was analyzed by immunohistochemistry and in situ hybridization. Normal kidney and renal biopsies of patients with different nephropathies were studied. In glomeruli, CRIT protein was expressed only in podocytes. CRIT was also detected in endothelial cells of arterioles and arteries, but not of veins and peritubular and glomerular capillaries. A homogeneous and marked upregulation of CRIT was observed in podocytes in membranous nephropathy (MN). In focal and segmental glomerulosclerosis (FSGS) and minimal change disease, CRIT was downregulated in glomeruli with a loss of the staining in sclerotic lesions of FSGS. No specific changes were observed in the other nephropathies studied. However, podocytes showed in all pathologies a redistribution of CRIT in the cell bodies of 'activated' podocytes. The intensity of mRNA transcription correlated directly with the protein staining in the normal kidney and in MN. These data indicate that CRIT is expressed in the normal human kidney essentially by glomerular podocytes and arterial endothelial cells. The podocyte CRIT expression is upregulated in MN, which is in strong contrast with the known loss of podocyte complement receptor 1. CRIT might represent the last line of defense against complement aggression in MN, and the upregulation of CRIT in 'activated' podocytes might represent a similar self-defense mechanism.

CRIT peptide interacts with factor B and interferes with alternative pathway activation

Complement C2 receptor inhibitor trispanning (CRIT) inhibits the classical pathway (CP) C3 convertase formation by competing with C4b for the binding of C2. The C-terminal 11-amino-acid of the first CRIT-extracellular domain (CRIT-H17) has a strong homology with a sequence in the C4beta chain, which is responsible for the binding of C2. Since the CP and alternative pathway (AP) C3 convertases have many functional and structural similarities, we further investigated the effects of CRIT-H17 on the AP. The factor D-mediated cleavage of factor B (FB) was blocked by CRIT-H17. By ELISA and immunoblot, CRIT-H17 was shown to bind FB. CRIT-H17 had no decay activity on the C3bBb complex as compared to decay-accelerating factor. Binding of CRIT-H17 to FB did not interfere with the assembly of C3bB complex. In a haemolytic assay using C2-deficient serum, CRIT-H17 interfered with AP complement activation.

Complement C2 receptor inhibitor trispanning: from man to schistosome

Horizontal gene transfer (HGT), in relation to genetic transfer between hosts and parasites, is a little described mechanism. Since the complement inhibitor CRIT was first discovered in the human Schistosoma parasite (the causative agent of Bilharzia) and in Trypanosoma cruzi (a parasite causing Chagas' disease), it has been found to be distributed amongst various species, ranging from the early teleost cod to rats and humans. In terms of evolutionary distance, as measured in a phylogenetic analysis of these CRIT genes at nucleotide level, the parasitic species are as removed from their human host as is the rat sequence, suggesting HGT. The hypotheses that CRIT in humans and schistosomes is orthologous and that the presence of CRIT in schistosomes occurs as a result of host-to-parasite HGT are presented in the light of empirical data and the growing body of data on mobile genetic elements in human and schistosome genomes. In summary, these data indicate phylogenetic proximity between Schistosoma and human CRIT, identity of function, high nucleotide/amino acid identity and secondary protein structure, as well as identical genomic organization.

Complement C2 receptor inhibitor trispanning: a novel human complement inhibitory receptor

The complement system presents a powerful defense against infection and is tightly regulated to prevent damage to self by functionally equivalent soluble and membrane regulators. We describe complement C2 receptor inhibitor trispanning (CRIT), a novel human complement regulatory receptor, expressed on hemopoietic cells and a wide range of tissues throughout the body. CRIT is present in human parasites through horizontal transmission. Serum complement component C2 binds to the N-terminal extracellular domain 1 of CRIT, which, in peptide form, blocks C3 convertase formation and complement-mediated inflammation. Unlike C1 inhibitor, which inhibits the cleavage of C4 and C2, CRIT only blocks C2 cleavage but, in so doing, shares with C1 inhibitor the same functional effect, of preventing classical pathway C3 convertase formation. Ab blockage of cellular CRIT reduces inhibition of cytolysis, indicating that CRIT is a novel complement regulator protecting autologous cells.

Parasite interaction with host complement: beyond attack regulation

Many orthologous proteins of known mammalian receptors have been discovered in parasites. Besides disguising the parasite as self in terms of the host immune system, evidence is accumulating that these receptors link to signalling pathways in parasites that appear to be involved in their growth or development. Recently, several proteins of the host complement system, which forms part of the innate defence against invading microorganisms, have been shown to possess alternative functions. These complement proteins interact with signalling pathways involved in early development and differentiation, as well as organ and tissue regeneration. By altering cellular interactions and responses, complement is being shown to have novel roles besides the originally described inflammatory role. The possibility exists that, as for other host factors interacting with parasites and affecting their growth or development, host complement proteins could also have such an influence.

Complement Mediates the Binding of HIV to Erythrocytes

A fraction of HIV is associated with erythrocytes even when the virus becomes undetectable in plasma under antiretroviral therapy. The aim of the present work was to further characterize this association in vitro. We developed an in vitro model to study the factors involved in the adherence of HIV-1 to erythrocytes. Radiolabeled HIV-1 (HIV) and preformed HIV-1/anti-HIV immune complexes (HIV-IC) were opsonized in various human sera, purified using sucrose density gradient ultracentrifugation, and incubated with human erythrocytes. We observed that, when opsonized in normal human serum, not only HIV-IC, but also HIV, bound to erythrocytes, although the adherence of HIV was lower than that of HIV-IC. The adherence was abolished when the complement system was blocked, but was maintained in hypogammaglobulinemic sera. Complement-deficient sera indicated that both pathways of complement were important for optimal adherence. No adherence was seen in C1q-deficient serum, and the adherence of HIV was reduced when the alternative pathway was blocked using anti-factor D Abs. The adherence could be inhibited by an mAb against complement receptor 1. At supraphysiological concentrations, purified C1q mediated the binding of a small fraction of HIV and HIV-IC to erythrocytes. In conclusion, HIV-IC bound to erythrocytes as other types of IC do when exposed to complement. Of particular interest was that HIV alone bound also to erythrocytes in a complement/complement receptor 1-dependent manner. Thus, erythrocytes may not only deliver HIV-IC to organs susceptible to infection, but free HIV as well. This may play a crucial role in the progression of the primary infection.

Phage therapy: a reappraisal of bacteriophages as antibiotics

The concept of phage therapy to treat bacterial infections was born with the discovery of the bacteriophage almost a century ago. After a chequered history, its current renaissance is fueled by the dangerous appearance of antibiotic-resistant bacteria on a global scale. As a mark of this renewed interest, the unanswered problems of phage therapy are now being addressed, especially for human use. Phage therapy in the agricultural, food-processing and fishery industries is already being successfully applied, and this review, whilst being aware of the potential drawbacks, emphasizes the need for further carefully controlled empirical data on its efficacy and safety in treating human and animal disease, especially in view of its numerous advantages over antibiotics. Finally the potential of phage therapy against bioterrorism and the emergence of second generation phage antibacterials based on phage-derived single-protein lysis systems are addressed.

A peptide derived from the parasite receptor, complement C2 receptor inhibitor trispanning, suppresses immune complex-mediated inflammation in mice

Complement C2 receptor inhibitor trispanning (CRIT) is a Schistosoma protein that binds the human complement protein, C2. We recently showed that peptides based on the ligand binding region of CRIT inhibit the classical pathway (CP) of complement activation in human serum, using hemolytic assays and so speculated that on the parasite surface CRIT has the function of evading human complement. We now show that in vitro the C2-binding 11-aa C terminus of the first extracellular domain of CRIT, a 1.3-kDa peptide termed CRIT-H17, inhibits CP activation in a species-specific manner, inhibiting mouse and rat complement but not that from guinea pig. Hitherto, the ability of CRIT to regulate complement in vivo has not been assessed. In this study we show that by inhibiting the CP, CRIT-H17 is able to reduce immune complex-mediated inflammation (dermal reversed passive Arthus reaction) in BALB/c mice. Upon intradermal injection of CRIT-H17, and similarly with recombinant soluble complement receptor type 1, there was a 41% reduction in edema and hemorrhage, a 72% reduction in neutrophil influx, and a reduced C3 deposition. Furthermore, when H17 was administered i.v. at a 1 mg/kg dose, inflammation was reduced by 31%. We propose that CRIT-H17 is a potential therapeutic agent against CP complement-mediated inflammatory tissue destruction.

Complement C2 receptor inhibitor trispanning and the beta-chain of C4 share a binding site for complement C2

Complement C2 receptor inhibitor trispanning (CRIT) of the Schistosoma parasite binds human C2 via the C2a segment. The receptor in vivo functions as C2 decoy receptor by directly competing with C4b for binding to C2. As a result, CRIT is able to limit the extent of classical pathway (CP) C3 convertase formation. We report that the CRIT-extracellular domain 1 (ed1) peptide inhibits CP-mediated complement activation with an ICH(50) of approximately 0.1 microM, the C-terminal 11 aa of CRIT-ed1, named H17, even more effectively. The beta-chain region F222-Y232 of C4 shares 55% identity and 73% similarity with H17. Peptides based on this region also inhibit CP in a dose-dependent manner. As further evidence of C2 binding we showed CRIT-ed1 peptides and homologous C4 beta-chain peptides to inhibit complement in C2 hemolytic assays. We have predicted C4 beta-c F222-Y232 as a C2 binding site which we have termed the CRIT-ed1 domain, and the sequence [F/H]EVKX(4/5)P as a consensus C2-binding sequence. Anti-CRIT-ed1 cross-reacts with the C4 beta-chain and F222EVKITPGKPY232 appears to be the key epitope recognized by this Ab. Furthermore, anti-CRIT-ed1 was found to inhibit CP activation in a total hemolytic assay. We believe that Schistosoma CRIT-ed1, as well as C4 beta-chain peptides based on the CRIT-ed1 domain, function as interface peptides. These peptides, based on C2-binding sequences in CRIT, or C4, competitively inhibit the binding of C2 to C4b and thus limit the activation of C. The C4 peptides, unlike CRIT-ed1, did not inhibit the cleavage of C2 by C1s.

A Schistosoma protein, Sh-TOR, is a novel inhibitor of complement which binds human C2

Human complement regulatory (also called inhibitory) proteins control misdirected attack of complement against autologous cells. Trypanosome and schistosome parasites which survive in the host vascular system also possess regulators of human complement. We have shown Sh-TOR, a protein with three predicted transmembrane domains, located on the Schistosoma parasite surface, to be a novel complement regulatory receptor. The N-terminal extracellular domain, Sh-TOR-ed1, binds the complement protein C2 from human serum and specifically interacts with the C2a fragment. As a result Sh-TOR-ed1 pre-incubated with C2 inhibits classical pathway (CP)-mediated haemolysis of sheep erythrocytes in a dose-dependent manner. In CP-mediated complement activation, C2 normally binds to C4b to form the CP C3 convertase and Sh-TOR-ed1 has short regions of sequence identity with a segment of human C4b. We propose the more appropriate name for TOR of CRIT (complement C2 receptor inhibitory trispanning).

Schistosoma TOR (trispanning orphan receptor), a novel, antigenic surface receptor of the blood-dwelling, Schistosoma parasite

Sh-TOR is a novel, putative three transmembrane domain receptor of Schistosoma haematobium, which has no extensive homology to any other known protein. The 0.86 kb open reading frame was found to encode a novel protein, 286 amino acids long and of 32 kDa. It was shown that Sh-TOR can be phosphorylated on tyrosine and the protein sequence reveals a long cytoplasmic tail with several consensus phosphorylation sites for enzymes which characteristically associate with membrane receptors. The proposed topology of Sh-TOR, based on antibody recognition of transfected Sh-TOR, predicts that the amino terminus is extracellular and the carboxyl terminus intracellular. Sh-TOR is a non-glycosylated protein found in the surface tegumental plasma membrane, and tegumental surface pits of adult schistosomes. The 1.35 kb transcript was most highly expressed in the larval stage, which is more susceptible to immune attack. A TOR homologue from Schistosoma mansoni is also described. A homologue from Trypanosoma cruzi, another human parasite was also isolated, but not from the free-living nematode Caenorhabditis elegans. Recombinant Sh-TOR is specifically recognised by a passively protective serum, from baboons vaccinated with irradiated Schistosoma parasite. Together with its surface location, this means that Sh-TOR is also a potential vaccine candidate molecule.

phi 20, a temperate bacteriophage isolated from Bacillus anthracis exists as a plasmidial prophage

This study describes the isolation of temperate B. anthracis phages, from 4 out of 20 B. anthracis strains screened, by use of the inducing agents mitomycin C and UV light. Phage phi 20 isolated from B. anthracis Sterne 34F2 (pXO1+ pXO2-) was shown to have double-stranded DNA of size 48756 bp and a restriction site map showing nine sites for enzymes BamHI, BglII, and SstI is included. The phi 20 genome was found to exist as a plasmidial prophage and the phage itself to have a polyhedral head of diameter 65 nm and tail 217 nm long and 15 nm wide.