Epitopes of the Onchocerca volvulus RAL1 antigen, a member of the calreticulin family of proteins, recognized by sera from patients with onchocerciasis

Proteomic Analysis Reveals Differential Protein Expression Induced by Inhibition of Prolyl Oligopeptidase in Filarial Parasites

Prolyl oligopeptidase (POP) plays a crucial role in the processing and degradation of neuropeptides and regulates inositol trisphosphate (IP3) signaling in mammals. We have reported that POP inhibition leads to IP3-mediated calcium efflux leading to mitochondrial-mediated apoptosis in the filarial parasite Setaria cervi. This study further elucidates the effect of altered calcium homeostasis on the proteome of filarial parasites. Adult parasites were treated with POP's specific inhibitor, Z-Pro-prolinal (ZPP), for 7 h. Cytosolic and mitochondrial proteome was analyzed using 2D gel electrophoresis coupled with MALDI-MS/MS. Phosphoproteins were also analyzed in the cytosolic fraction of the parasites. The phosphoprotein analysis revealed 7, and 9 spots in the cytosolic fraction of control and ZPP-treated parasites, respectively. The two identified protein spots in the treated set were found to be involved in G protein signaling. In cytosolic fraction, 109 and 112 protein spots were observed in control and treated parasites, respectively. Of these, 56 upregulated and 32 downregulated protein spots were observed in the treated set. On the other hand, 50 and 47 protein spots were detected in the mitochondrial fraction of control and treated parasites, respectively. Of these spots, 18 upregulated and 12 down-regulated protein spots were found in treated parasites. In silico analysis showed that the identified proteins were involved in energy metabolism, calcium signaling, stress response, and cytoskeleton organization. These findings correlate with our previous results suggesting the important regulatory role of POP in signaling and different metabolic pathways of filarial parasites.

The Functional Parasitic Worm Secretome: Mapping the Place of Onchocerca volvulus Excretory Secretory Products

Nematodes constitute a very successful phylum, especially in terms of parasitism. Inside their mammalian hosts, parasitic nematodes mainly dwell in the digestive tract (geohelminths) or in the vascular system (filariae). One of their main characteristics is their long sojourn inside the body where they are accessible to the immune system. Several strategies are used by parasites in order to counteract the immune attacks. One of them is the expression of molecules interfering with the function of the immune system. Excretory-secretory products (ESPs) pertain to this category. This is, however, not their only biological function, as they seem also involved in other mechanisms such as pathogenicity or parasitic cycle (molting, for example). We will mainly focus on filariae ESPs with an emphasis on data available regarding Onchocerca volvulus, but we will also refer to a few relevant/illustrative examples related to other worm categories when necessary (geohelminth nematodes, trematodes or cestodes). We first present Onchocerca volvulus, mainly focusing on the aspects of this organism that seem relevant when it comes to ESPs: life cycle, manifestations of the sickness, immunosuppression, diagnosis and treatment. We then elaborate on the function and use of ESPs in these aspects.

Trypanosoma cruzi Calreticulin: Immune Evasion, Infectivity, and Tumorigenesis

To successfully infect, Trypanosoma cruzi evades and modulates the host immune response. T. cruzi calreticulin (TcCalr) is a multifunctional, endoplasmic reticulum (ER)-resident chaperone that, translocated to the external microenvironment, mediates crucial host-parasite interactions. TcCalr binds and inactivates C1 and mannose-binding lectin (MBL)/ficolins, important pattern- recognition receptors (PRRs) of the complement system. Using an apoptotic mimicry strategy, the C1-TcCalr association facilitates the infection of target cells. T. cruzi infection also seems to confer protection against tumorigenesis. Thus, recombinant TcCalr has important antiangiogenic properties, detected in vitro, ex vivo, and in ovum, most likely contributing at least in part, to its antitumor properties. Consequently, TcCalr is useful for investigating key issues of host-parasite interactions and possible new immunological/pharmacological interventions in the areas of Chagas' disease and experimental cancer.

Evaluation of Opisthorchis viverrini calreticulin for potential host modulation

The multifunctional calreticulin (CALR) was identified as a major calcium-binding protein of the endoplasmic reticulum before being recognized as a chaperone in the same place. Only later were activities of calreticulin outside the endoplasmic reticulum described that for example affect cell proliferation and the innate immune system. In the present work we have investigated those extracellular activities of CALR from the cancerogenic human liver fluke Opisthorchis viverrini (OvCALR), as they might be important in host/parasite interaction. We first demonstrate that OvCALR is released from the parasite and stimulates a specific humoral immune response. Recombinant OvCALR is then shown to suppress proliferation of primary endothelial cells, their motility and sprouting activities. The potential of OvCALR to interfere with the complement system is established, firstly by demonstrating its direct binding to C1q and, secondly by suppression of hemolysis of sensitized red blood cells. These findings suggest that OvCALR is an important parasite antigen that could modulate diverse host functions and support parasite survival.

Entamoeba histolytica Calreticulin Induces the Expression of Cytokines in Peripheral Blood Mononuclear Cells Isolated From Patients With Amebic Liver Abscess

Calreticulin (CRT) is a highly conserved protein in the endoplasmic reticulum that plays important roles in the regulation of key cellular functions. Little is known about the participation of E. histolytica CRT (EhCRT) in the processes of pathogenicity or in the modulation of the host immune response. The aim of this study was to evaluate the role of CRT in the proliferation and the cytokine profile in peripheral blood mononuclear cells (PBMCs) from patients with amebic liver abscess (ALA) during the acute phase (AP-ALA) of the disease compared to patients during the resolution phase (R-ALA). The PBMCs from each participant were cocultured with EhCRT and tested by the colorimetric method to evaluate their proliferation index (PI). The supernatants were subjected to an enzyme-linked immunosorbent assay (ELISA) to evaluate the concentration of cytokines. The mean values of all groups were compared using the independent t-test. When the PIs of individuals without diagnosis of liver abscess (NEG) were compared, there were no statistically significant differences in the proliferation of PBMCs between patients with AP-ALA and R-ALA when stimulated with EhCRT or concanavalin A (ConA). However, the levels of interleukins [IL-6, IL-10, granulocyte colony stimulating factor (GCSF), and transforming growth factor β1 (TGFβ1)] were higher in patients with AP-ALA, whereas in patients with R-ALA, higher levels of interferon gamma (IFNγ) were detected. These results suggest that EhCRT acts as a mitogen very similar to the activity of ConA. In addition, EhCRT is an excellent immunogen for the specific activation of PBMCs, inducing the differential expression of ILs depending on the outcome of disease, determining the type of immune response: a Th2 cytokine profile during the acute phase and a Th1 profile during the resolution phase.

O-5S quantitative real-time PCR: a new diagnostic tool for laboratory confirmation of human onchocerciasis

Background

Onchocerciasis is a parasitic disease caused by the filarial nematode Onchocerca volvulus. In endemic areas, the diagnosis is commonly confirmed by microscopic examination of skin snip samples, though this technique is considered to have low sensitivity. The available melting-curve based quantitative real-time PCR (qPCR) using degenerated primers targeting the O-150 repeat of O. volvulus was considered insufficient for confirming the individual diagnosis, especially in elimination studies. This study aimed to improve detection of O. volvulus DNA in clinical samples through the development of a highly sensitive qPCR assay.

Methods

A novel hydrolysis probe based qPCR assay was designed targeting the specific sequence of the O. volvulus O-5S rRNA gene. A total of 200 clinically suspected onchocerciasis cases were included from Goma district in South-west Ethiopia, from October 2012 through May 2013. Skin snip samples were collected and subjected to microscopy, O-150 qPCR, and the novel O-5S qPCR.

Results

Among the 200 individuals, 133 patients tested positive (positivity rate of 66.5%) and 67 negative by O-5S qPCR, 74 tested positive by microscopy (37.0%) and 78 tested positive by O-150 qPCR (39.0%). Among the 133 O-5S qPCR positive individuals, microscopy and O-150 qPCR detected 55.6 and 59.4% patients, respectively, implying a higher sensitivity of O-5S qPCR than microscopy and O-150 qPCR. None of the 67 individuals who tested negative by O-5S qPCR tested positive by microscopy or O-150 qPCR, implying 100% specificity of the newly designed O-5S qPCR assay.

Conclusions

The novel O-5S qPCR assay is more sensitive than both microscopic examination and the existing O-150 qPCR for the detection of O. volvulus from skin snip samples. The newly designed assay is an important step towards appropriate individual diagnosis and control of onchocerciasis.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2382-3) contains supplementary material, which is available to authorized users.

Evaluation of the immunodiagnostic potential of a recombinant surface protein domain from Acanthamoeba castellanii

Acanthamoeba spp. are free-living protists widely distributed in environment, able to cause keratitis, encephalitis and skin lesions in humans and animals. Acanthamoeba spp. exist in two forms: an infective trophozoite and a dormant cyst. Several factors contribute to the pathogenesis of Acanthamoeba spp. The parasite adhesion to the host cell is the primary step for infection and is mediated by a mannose binding-protein, expressed in the surface and considered the main pathogenicity factor in Acanthamoeba spp. So far, there was no evidence of another surface protein of Acanthamoeba spp. relevant for host invasion or infection by these organisms. The aims of this study were to identify and characterize an Acanthamoeba castellanii surface protein and to evaluate its diagnostic potential. In silico predictions of surface proteins allowed to identify the A. castellanii calreticulin as a possible surface antigen. The coding sequence of a predicted extracellular domain of A. castellanii calreticulin was cloned by in vivo homologous recombination and the recombinant polypeptide (AcCRT29-130) was produced. Its immunodiagnostic potential was assessed in a recombinant antigen-based ELISA with sera from experimentally infected rats that developed keratitis and encephalitis, and sera from patients with encephalitis. The AcCRT29-130 was significantly more recognized by sera from encephalitis infected rats in comparison with the non-infected controls. Human sera from encephalitis patients, however presented no significant response. These results showed the AcCRT29-130 potential for A. castellanii infection immunodiagnosis in animals, with further studies being required for assessment of its use for human infections.

Is the Antitumor Property of Trypanosoma cruzi Infection Mediated by Its Calreticulin?

Eight to 10 million people in 21 endemic countries are infected with Trypanosoma cruzi. However, only 30% of those infected develop symptoms of Chagas' disease, a chronic, neglected tropical disease worldwide. Similar to other pathogens, T. cruzi has evolved to resist the host immune response. Studies, performed 80 years ago in the Soviet Union, proposed that T. cruzi infects tumor cells with similar capacity to that displayed for target tissues such as cardiac, aortic, or digestive. An antagonistic relationship between T. cruzi infection and cancer development was also proposed, but the molecular mechanisms involved have remained largely unknown. Probably, a variety of T. cruzi molecules is involved. This review focuses on how T. cruzi calreticulin (TcCRT), exteriorized from the endoplasmic reticulum, targets the first classical complement component C1 and negatively regulates the classical complement activation cascade, promoting parasite infectivity. We propose that this C1-dependent TcCRT-mediated virulence is critical to explain, at least an important part, of the parasite capacity to inhibit tumor development. We will discuss how TcCRT, by directly interacting with venous and arterial endothelial cells, inhibits angiogenesis and tumor growth. Thus, these TcCRT functions not only illustrate T. cruzi interactions with the host immune defensive strategies, but also illustrate a possible co-evolutionary adaptation to privilege a prolonged interaction with its host.

Is it all That Bad When Living with an Intracellular Protozoan? The Role of Trypanosoma cruzi Calreticulin in Angiogenesis and Tumor Growth

The immune system protects against disease, but may aberrantly silence immunity against "altered self," with consequent development of malignancies. Among the components of the endoplasmic reticulum (ER), important in immunity, is calreticulin (CRT) that, in spite of its residence in the ER, can be translocated to the exterior. Trypanosoma cruzi is the agent of Chagas disease, one of the most important global neglected infections, affecting several hundred thousand people. The syndrome, mainly digestive and circulatory, affects only one-third of those infected. The anti-tumor effects of the infection are known for several decades, but advances in the identification of responsible T. cruzi molecules are scarce. We have shown that T. cruzi CRT (TcCRT) better executes the antiangiogenic and anti-tumor effects of mammal CRT and its N-terminus vasostatin. In this regard, recombinant TcCRT (rTcCRT) and/or its N-terminus inhibit angiogenesis in vitro, ex vivo, and in vivo. TcCRT also inhibits the growth of murine adenocarcinomas and melanomas. Finally, rTcCRT fully reproduces the anti-tumor effect of T. cruzi infection in mice. Thus, we hypothesize that, the long reported anti-tumor effect of T. cruzi infection is mediated at least in part by TcCRT.

Immunological activity difference between native calreticulin monomers and oligomers

We have recently demonstrated that the greatly increased immunological activities of recombinant murine calreticulin (rCRT) are largely attributed to its self-oligomerization. Although native CRT (nCRT) can also oligomerize under stress conditions in vitro, whether this phenomenon could occur inside cells and the immunological activity difference between nCRT monomers and oligomers remained unclear. In this study, we illustrated the formation of CRT oligomers in tranfectant cells under “heat & low pH” (42°C/pH 6.5) condition. The mixture of nCRT oligomers and monomers (OnCRT) was obtained after 3 hr treatment of murine monomeric nCRT (MnCRT) under similar condition (42°C/pH 5.0) in vitro. The OnCRT thus obtained was better recognized by 2 monoclonal Abs from mice that had been immunized with oligomeric rCRT. Unlike MnCRT, OnCRT was able to elicit CRT-specific IgG production in mice. OnCRT also stimulated bone-marrow derived dendritic cells (BMDCs) to secrete significantly higher levels of TNF-α, IL-6 and IL-12p40 than did MnCRT in vitro. We postulate that oligomerization of soluble CRT may occur under certain pathophysiological conditions (e.g. ultrahyperpyrexia) and the resultant oligomers may exhibit exaggerated immunostimulating activities, thereby affiliating the inflammatory responses in vivo.

Entamoeba histolytica and E. dispar Calreticulin: inhibition of classical complement pathway and differences in the level of expression in amoebic liver abscess

The role of calreticulin (CRT) in host-parasite interactions has recently become an important area of research. Information about the functions of calreticulin and its relevance to the physiology of Entamoeba parasites is limited. The present work demonstrates that CRT of both pathogenic E. histolytica and nonpathogenic E. dispar species specifically interacted with human C1q inhibiting the activation of the classical complement pathway. Using recombinant EhCRT protein, we demonstrate that CRT interaction site and human C1q is located at the N-terminal region of EhCRT. The immunofluorescence and confocal microscopy experiments show that CRT and human C1q colocalize in the cytoplasmic vesicles and near to the surface membrane of previously permeabilized trophozoites or are incubated with normal human serum which is known to destroy trophozoites. In the presence of peripheral mononuclear blood cells, the distribution of EhCRT and C1q is clearly over the surface membrane of trophozoites. Nevertheless, the level of expression of CRT in situ in lesions of amoebic liver abscess (ALA) in the hamster model is different in both Entamoeba species; this molecule is expressed in higher levels in E. histolytica than in E. dispar. This result suggests that EhCRT may modulate some functions during the early moments of the host-parasite relationship.

Immunological mechanisms involved in the protection against intestinal taeniosis elicited by oral immunization with Taenia solium calreticulin

Oral immunization with functional recombinant Taenia solium calreticulin (rTsCRT) induces 37% reduction in tapeworm burden in the experimental model of intestinal taeniosis in hamsters. Furthermore, tapeworms recovered from vaccinated animals exhibit diminished length, being frequently found in more posterior parts of the small intestine. The aim of this study was to analyze the immunological mechanisms involved in protection in response to rTsCRT oral immunization. Hamsters were orally immunized with rTsCRT using cholera toxin (CT) as adjuvant, weekly for 4 weeks. Fifteen days after the last boost animals were challenged with four T. solium cysticerci. Reduction in the adult worm recovery and increased transcription of mRNA for IL-4 and IFN-γ in the mucosa of rTsCRT+CT immunized animals were observed. Immunization also induced goblet cell hyperplasia in the mucosa surrounding the implantation site of the parasite. Specific IgG and IgA antibodies in serum and fecal supernatants were detected after the second immunization, being more pronounced after challenge. Our data suggest that oral vaccination with rTsCRT+CT regulates a local expression of IL-4 and IFN-γ, stimulating secretion of IgA that, together with the increase of goblet cells and mucin production, could result in an unfavorable environment for T. solium promoting an impaired tapeworm development.

Roles of Trypanosoma cruzi calreticulin in parasite-host interactions and in tumor growth

In Latin America, there are about 10-12 million people infected with Trypanosoma cruzi, the agent of Chagas' disease, one of the most important neglected tropical parasitism. Identification of molecular targets, specific for the aggressor or host cells or both, may be useful in the development of pharmacological and/or immunological therapeutic tools. Classic efforts in Chagas' disease explore those strategies. Although the immune system frequently controls parasite aggressions, sterile immunity is seldom achieved and chronic interactions are thus established. However, laboratory-modified immunologic probes aimed at selected parasite targets, may be more effective than their unmodified counterparts. Calreticulin (CRT) from vertebrates is a calcium binding protein, present mainly in the endoplasmic reticulum (ER), where it directs the conformation of proteins and controls calcium levels. We have isolated, gene-cloned, expressed and characterized T. cruzi calreticulin (TcCRT). Upon infection, the parasite can translocate this molecule from the ER to the surface, where it inhibits both the classical and lectin complement pathways. Moreover, by virtue of its capacity to bind and inactivate first complement component C1, it promotes parasite infectivity. These two related properties reside in the central domain of this molecule. A different domain, amino terminal, binds to endothelial cells, thus inhibiting their angiogenic capacity. Since tumor growth depends, to a large extent on angiogenesis, their growth is also inhibited.

Entamoeba histolytica calreticulin: an endoplasmic reticulum protein expressed by trophozoites into experimentally induced amoebic liver abscesses

Entamoeba histolytica calreticulin (EhCRT) is remarkably immunogenic in humans (90-100% of invasive amoebiasis patients). Nevertheless, the study of calreticulin in this protozoan is still in its early stages. The exact location, biological functions, and its role in pathogenesis are yet to be fully understood. The aim of the present work is to determine the location of EhCRT in virulent trophozoites in vivo and the expression of the Ehcrt gene during the development of experimentally induced amoebic liver abscesses (ALA) in hamsters. Antibodies against recombinant EhCRT were used for the immunolocalization of EhCRT in trophozoites through confocal microscopy; immunohistochemical assays were also performed on tissue sections of ALAs at different times after intrahepatic inoculation. The expression of the Ehcrt gene during the development of ALA was estimated through both in situ RT-PCR and real-time RT-PCR. Confocal assays of virulent trophozoites showed a distribution of EhCRT in the cytoplasmic vesicles of different sizes. Apparently, EhCRT is not exported into the hepatic tissue. Real-time RT-PCR demonstrated an over-expression of the Ehcrt gene at 30 min after trophozoite inoculation, reaching a peak at 1-2 h; thereafter, the expression fell sharply to its original levels. These results demonstrate for the first time in an in vivo model of ALA, the expression of Ehcrt gene in E. histolytica trophozoites and add evidence that support CRT as a resident protein of the ER in E. histolytica species. The in vivo experiments suggest that CRT may play an important role during the early stages of the host-parasite relationship, when the parasite is adapting to a new environment, although the protein seems to be constitutively synthesized. Moreover, trophozoites apparently do not export EhCRT into the hepatic tissue in ALA.

Excreted/secreted proteins from trypanosome procyclic strains

Trypanosoma secretome was shown to be involved in parasite virulence and is suspected of interfering in parasite life-cycle steps such as establishment in the Glossina midgut, metacyclogenesis. Therefore, we attempted to identify the proteins secreted by procyclic strains of T. brucei gambiense and T. brucei brucei, responsible for human and animal trypanosomiasis, respectively. Using mass spectrometry, 427 and 483 nonredundant proteins were characterized in T. brucei brucei and T. brucei gambiense secretomes, respectively; 35% and 42% of the corresponding secretome proteins were specifically secreted by T. brucei brucei and T. brucei gambiense, respectively, while 279 proteins were common to both subspecies. The proteins were assigned to 12 functional classes. Special attention was paid to the most abundant proteases (14 families) because of their potential implication in the infection process and nutrient supply. The presence of proteins usually secreted via an exosome pathway suggests that this type of process is involved in trypanosome ESP secretion. The overall results provide leads for further research to develop novel tools for blocking trypanosome transmission.

Taenia solium: current understanding of laboratory animal models of taeniosis

Neurocysticercosis is a public health problem in many developing countries and is the most frequent parasitic disease of the brain. The human tapeworm carrier is the main risk factor for acquiring neurocysticercosis. Since the parasite lodges only in the human intestine, experimental models ofTaenia soliumtaeniosis have been explored. Macaques, pigs, dogs, cats and rabbits are unsuccessful hosts even in immunodepressed status. By contrast, rodents are adequate hosts since tapeworms with mature, pregravid and, in some cases, gravid proglottids develop after infection. In this review, information that has been generated with experimental models of taeniosis due toT. soliumis discussed. Initially, the use of the model for immunodiagnosis of human taeniosis and evaluation of intervention measures is summarized. Next, descriptions of tapeworms and comparison of hamsters, gerbils and other mammals as experimental models are discussed, as well as data on the humoral immune response, the inflammatory reaction and the production of cytokines associated to Th1 and Th2 responses in the intestinal mucosa. Finally, evaluation of protection induced against the development of tapeworms by recombinantT. soliumcalreticulin in hamsters is summarized and compared to other studies.

Exocytosis and protein secretion in Trypanosoma

Background

Human African trypanosomiasis is a lethal disease caused by the extracellular parasite Trypanosoma brucei. The proteins secreted by T. brucei inhibit the maturation of dendritic cells and their ability to induce lymphocytic allogenic responses. To better understand the pathogenic process, we combined different approaches to characterize these secreted proteins.

Results

Overall, 444 proteins were identified using mass spectrometry, the largest parasite secretome described to date. Functional analysis of these proteins revealed a strong bias toward folding and degradation processes and to a lesser extent toward nucleotide metabolism. These features were shared by different strains of T. brucei, but distinguished the secretome from published T. brucei whole proteome or glycosome. In addition, several proteins had not been previously described in Trypanosoma and some constitute novel potential therapeutic targets or diagnostic markers. Interestingly, a high proportion of these secreted proteins are known to have alternative roles once secreted. Furthermore, bioinformatic analysis showed that a significant proportion of proteins in the secretome lack transit peptide and are probably not secreted through the classical sorting pathway. Membrane vesicles from secretion buffer and infested rat serum were purified on sucrose gradient and electron microscopy pictures have shown 50- to 100-nm vesicles budding from the coated plasma membrane. Mass spectrometry confirmed the presence of Trypanosoma proteins in these microvesicles, showing that an active exocytosis might occur beyond the flagellar pocket.

Conclusions

This study brings out several unexpected features of the secreted proteins and opens novel perspectives concerning the survival strategy of Trypanosoma as well as possible ways to control the disease. In addition, concordant lines of evidence support the original hypothesis of the involvement of microvesicle-like bodies in the survival strategy allowing Trypanosoma to exchange proteins at least between parasites and/or to manipulate the host immune system.

Mapping the complement C1q binding site in Haemonchus contortus calreticulin

Haemonchus contortus is an economically important gastrointestinal parasite of domestic animals. The parasite secretes calreticulin (CalR), a Ca(++) binding protein which modulates the host immune response. One way by which this protein acts is by inhibiting the classical complement pathway by binding to complement C1q protein. Understanding CalR-C1q interaction is important to develop methods to enhance host immune response. In this study, we have mapped the regions in the N-domain of CalR that facilitates C1q binding by generating small recombinant fragments of the domain and using synthetic peptides. In addition to already identified C1q binding motifs in human CalR, two additional sites in the N-domain of H. contortus were revealed with the following sequences-GKYYDDAKRD and the AKFPKKFT. The significance of multiple C1q binding motifs in CalR is discussed in relation to host-parasite interactions.

The endoplasmic reticulum chaperone calreticulin is recruited to the uropod during capping of surface receptors in Entamoeba histolytica

Calreticulin (CRT), an intracellular chaperone protein, is crucial for proper folding and transport of proteins through the endoplasmic reticulum (ER). It has recently been identified as a critical regulator of some several different cellular functions such as migration, phagocytosis of apoptotic cells and cytotoxic T lymphocyte- or natural killer cell-mediated lysis. Characterization of CRT isolated from parasites may thus help to decipher the contribution of this protein in the parasites' biology and host-parasite interactions. Here, we report descriptive data on the localization of Entamoeba histolytica's CRT at rest and following cap formation by Concanavalin A. As expected, CRT from E. histolytica localizes in the ER. However, the protein was surprisingly found to localize to the parasite surface and, furthermore, to concentrate in the uropod following activation of surface receptors by capping with Concanavalin A.

Anti-calreticulin antibodies in patients with inflammatory bowel disease

PURPOSE

Although the pathogenesis of inflammatory bowel disease (IBD) is unclear, autoimmune processes seem to play roles in IBD because several types of autoantibodies have been found in it. Calreticulin (CRT) is a soluble Ca2+ binding protein which is present in a wide variety of cells. CRT is localized mainly in the endoplasmic reticulum and is often a target for autoantibodies. The aim of this study was to evaluate the clinical significance of anti-CRT antibodies measured by enzyme-linked immunosorbent assay (ELISA) using the sera of patients with ulcerative colitis (UC) and Crohn's disease (CD).

METHODS

We measured the serum anti-CRT antibodies of 31 Japanese patients with UC and 24 with CD by ELISA. The controls were 105 subjects: 30 healthy persons, 44 patients with primary biliary cirrhosis (PBC), 21 with systemic lupus erythematosus (SLE) and 10 with acute colitis (AC).

RESULTS

The mean titer of anti-CRT antibodies was significantly higher in patients with UC than in healthy individuals (p <0.05). The prevalence of anti-CRT antibodies in these patients was significantly higher during the initial phase than during the passing phase (p <0.05). In patients with CD, the mean titer of anti-CRT antibodies was not significantly higher than in healthy individuals. The positivity for anti-CRT antibodies, however, was about 30% in those patients, which was as high as in patients with UC, SLE and PBC. In patients with AC, anti-CRT antibodies were all negative.

CONCLUSIONS

The positivity of anti-CRT antibodies may have a diagnostic value for IBD, especially in the initial phase of UC.

Screening for immunomodulatory proteins of the intestinal parasitic nematode Heligmosomoides polygyrus

Parasitic nematodes are constantly exposed to the immune effector mechanisms of their hosts. One strategy of the worms to cope with these defence reactions is the secretion of modulatory proteins that down-regulate cell-mediated immune responses. We analysed the proliferation of mesenteric lymph node cells of mice infected with Heligmosomoides polygyrus and showed that cellular proliferation was strongly suppressed in the chronic phase of infection. To identify proteins of H. polygyrus that are involved in parasite-induced immunomodulation, worm extract and culture supernatant of adult H. polygyrus were fractionated by gel chromatography and activity of each fraction was determined. One of the fractions (fraction 9) of worm extract as well as worm secretory products inhibited the antigen-specific cellular proliferation by about 40%. This reduced cellular reactivity coincided with a down-regulation of inducible nitric oxide production of mouse macrophages by 57%. Furthermore, fraction 9 contained antigens that were recognized by IgE antibodies of H. polygyrus-infected mice and induced degranulation of an IgE-sensitized basophil cell line. Single proteins of fraction 9 were analysed by mass spectrometry. These data suggest that antigens that are recognised by IgE antibodies might play an important role in immunomodulation exerted by nematode infections.

Hard tick calreticulin (CRT) gene coding regions have only one intron with conserved positions and variable sizes

Calreticulin (CRT) is a unique eukaryotic gene. The CRT gene product, calreticulin, was first identified as a calcium binding protein in 1974, but further investigations have indicated that CRT protein performs many functions in cells, including involvement in evading the host's immune system by parasites. Many studies of CRT have been published since the molecule was first discovered; however, the CRT gene exon-intron structure is only known for a limited number of ectoparasite species. In this study, we compared tick CRT genomic sequences to the corresponding cDNA from 28 species and found that 2 exons and 1 intron are present in the tick CRT gene. The intron position is conserved in 28 hard ticks, but intron size and nucleotide sequences vary. Three tick introns possess duplicated fragments and are twice as long as other introns. All tick CRT introns obey the GT-AG rule in the splice-site junctions and are phase 1 introns. By comparing tick CRT introns to those of fruit fly, mouse, and human, we conclude that tick CRT introns belong to the intron-late type. The number and size of CRT introns have increased through the evolution of eukaryotes.

Characterization of Haemonchus contortus calreticulin suggests its role in feeding and immune evasion by the parasite

Haemonchus contortus, a gastrointestinal parasite of sheep and goat feeds on the blood of its host and causes bleeding at the biting site. In this report, we demonstrate that the Ca2+ binding protein, calreticulin (CalR), is present in excretory/secretory products of adult worms. The secreted CalR enhanced plasma coagulation time. Using recombinant fragments, this property has been mapped to C-terminal part of the molecule which has binding sites for Ca2+ as well as clotting factors. Complement protein C1q bound to immobilized CalR and C1q dependent lysis of sensitized sheep erythrocytes was inhibited by CalR, a function mapped to N-domain of the protein. Factor X and a 24 kDa polypeptide derived from prothrombin but not prothrombin bound to immobilized CalR. The binding site for 24 kDa polypeptide in the CalR molecule has been localized in the P-domain. Our results suggest at least two functions for secreted CalR: first, to prevent blood clotting by binding to Ca2+ and clotting factors thus enabling parasite to feed on the host blood and second to modulate the host immune response by binding to complement C1q thereby facilitating parasite's survival within the host.

Epitopes of calreticulin recognised by IgA autoantibodies from patients with hepatic and coeliac disease

Calreticulin (CRT) was identified as a frequent target of serum autoantibodies (Ab) in various diseases, but anti-CRT Ab of IgA isotype were described only in coeliac (CLD) and some hepatic diseases. Employing ELISA with recombinant CRT we found significantly higher (P<0.001) levels of IgA anti-CRT Ab in sera of patients with primary biliary cirrhosis (PBC) (77.6+/-8.9 AU/mean+/-SE), autoimmune hepatitis (AIH) (105.1+/-9.2 AU) and alcoholic liver cirrhosis (ALC) (193.5+/-21.0 AU) relative to healthy controls (38.6+/-2.0 AU). The levels of IgG anti-CRT Ab in sera of patients with PBC (59.5+/-3.4 AU), AIH (89.7+/-7.9 AU) and ALC (86.4+/-6.2 AU) were also significantly increased (P<0.001) when compared with controls (38.5+/-2.1 AU). Pepscan technique with decapeptides of CRT (each overlapping by eight amino acids) revealed antigenic epitopes of this molecule recognised by IgA Ab of almost all tested patients-KGKNVLINKD and QVKSGTIFDNFL. We also identified disease specific antigenic epitopes on CRT molecule, predominantly recognised by IgA Ab of patients suffering from a particular disease: GGYVKLFPNS and YVKLFPNSLD in AIH (83%, 92% of patients), GLQTSQDARF and EQRLKEEEED in CLD (both 75%) and ASKPEDWDER in ALC (67%). Identification of disease specific CRT epitopes contributes to clarification of autoreactivity against this molecule.

Association of autoantibodies against small nuclear ribonucleoproteins (snRNPs) with symptomatic Toxocara canis infestation

Several studies have demonstrated the occurrence of autoantibodies in the course of infestations with helminth parasites and a number of target proteins have been identified. Sera from patients suffering from toxocarosis, a disease caused by the parasitic roundworm Toxocara canis, and from healthy individuals were tested for autoantibodies by immunofluorescence and immunoblot assays using HEp-2 cells as antigen. A considerable proportion of the sera from patients with toxocarosis-associated symptoms were autoantibody-positive, with a speckled staining pattern in the immunofluorescence test (62%) and with anti-snRNP reactivity in the immunoblot assay (98%). In contrast, significantly fewer sera from asymptomatic individuals scored positive in these assays (18% in the immunofluorescence test, P < 0.005; 24% in the immunoblot, P < 0.005). Although the causative link between Toxocara infestation and the occurrence of autoantibodies is still unclear, our results show that increased amounts of autoantibodies are associated with clinical symptoms of inflammation. Thus a serum test for autoantibodies in toxocarosis patients might be a valuable gatekeeper assay for the decision for or against anti-inflammatory treatment.

Cloning, Characterization, and Functional Expression of Taenia Solium Calreticulin

Calreticulin is an endoplasmic reticulum protein involved in the homeostasis of intracellular Ca++ and other physiological processes. A complementary DNA clone containing the complete coding sequence of Taenia solium calreticulin (TsCRT) was isolated and characterized. Recombinant TsCRT was expressed in bacteria as a 50-kDa protein that specifically bound calcium when tested in a radioassay. The deduced amino acid sequence has 47-50% identity with other reported calreticulins. Poor recognition of TsCRT by human and pig sera with confirmed cysticercosis discourages its use for diagnosis of the disease. However, further characterization and localization studies could provide insights into the role of TsCRT in T. solium physiology and host-parasite interactions.

Comparative genomics of gene expression in the parasitic and free-living nematodes Strongyloides stercoralis and Caenorhabditis elegans

Although developmental timing of gene expression is used to infer potential gene function, studies have yet to correlate this information between species. We analyzed 10,921 ESTs in 3311 clusters from first- and infective third-stage larva (L1, L3i) of the parasitic nematode Strongyloides stercoralis and compared the results to Caenorhabditis elegans, a species that has an L3i-like dauer stage. In the comparison of S. stercoralis clusters with stage-specific expression to C. elegans homologs expressed in either dauer or nondauer stages, matches between S. stercoralis L1 and C. elegans nondauer-expressed genes dominated, suggesting conservation in the repertoire of genes expressed during growth in nutrient-rich conditions. For example, S. stercoralis collagen transcripts were abundant in L1 but not L3i, a pattern consistent with C. elegans collagens. Although a greater proportion of S. stercoralis L3i than L1 genes have homologs among the C. elegans dauer-specific transcripts, we did not uncover evidence of a robust conserved L3i/dauer 'expression signature.' Strikingly, in comparisons of S. stercoralis clusters to C. elegans homologs with RNAi knockouts, those with significant L1-specific expression were more than twice as likely as L3i-specific clusters to match genes with phenotypes. We also provide functional classifications of S. stercoralis clusters.

Role of calreticulin from parasites in its interaction with vertebrate hosts

Although parasites range from protozoan to complex, evolutionary advanced arthropods, in general, a hallmark of parasite life cycles is their ability to adapt to changes in temperature, pH and host defense strategies. Calreticulin, a calcium-binding protein, highly conserved and multifunctional, is present in every cell of higher organisms, except erythrocytes. The surprising array of calreticulin-associated functions include lectin-like chaperoning, calcium storage and signaling, modulation of gene expression, cell adhesion, enhancement of phagocytosis of C1q or collectin opsonized apoptotic cells, inhibition of angiogenesis and tumoral growth, inhibition of perforin pore formation in T and NK cells, and inhibition of C1q-dependent complement activation. Likewise, calreticulin is present in a wide spectrum of sub cellular compartments. Parasite calreticulin shows a surprisingly high degree of conservation within the framework of its functional domains. Its role within the parasite/host relationship needs to be assessed further, in particular with regard to its impact on parasite infectivity, by helping to evade from its hosts' immune response. With special emphasis on calreticulin from Trypanosoma cruzi, the intracellular protozoan agent of American trypanosomiasis (Chagas' disease), we wish to exemplify and highlight the various implications of parasite calreticulin, within the pathophysiology of parasite-mediated human and animal disease.

Cloning and partial characterization of a Boophilus microplus (Acari: Ixodidae) calreticulin

We report the cloning, sequence characterization and expression analysis of a calreticulin (CRT) coding cDNA of Boophilus microplus. CRT is a calcium-binding protein involved in multiple cell functions and possibly implicated in parasites host immune system evasion. The CRT cDNA sequence and its molecular characterization are described. Sequence similarity and phylogenetic analyses indicate a close relationship to other arthropod CRT sequences. The CRT cDNA was also expressed in a procariotic system and the recombinant protein (rBmCRT) was used to raise antibodies in a rabbit. Expression analyses of the corresponding gene in different developmental stages and tissues were performed by RT-PCR and Western-blot, which indicated a ubiquitous expression of the B. microplus calreticulin gene and demonstrated its presence in saliva. Sera of tick-infested bovines suggested that this protein may not be able to induce an IgG-based humoral response in its natural host.

A Schistosoma mansoni 62-kDa band is identified as an irradiated vaccine T-cell antigen and characterized as calreticulin

The Schistosoma mansoni soluble adult worm antigen (SAWA) bands of 62/60 kDa were found to contain immunodominant T-cell immunogen(s) in irradiated cercariae-immunized Swiss and C57BL/6 mice. In the present study, spleen T cells of BALB/c mice immunized twice with ultraviolet light-irradiated cercariae proliferated and produced interleukin 4 in response to the 62/60-kDa SAWA bands in T-cell western assays. To characterize the 62/60-kDa bands, an adult S. mansoni worm cDNA expression library constructed in lambdagt11 was immunoscreened with serum of mice immunized with the 62/60-kDa antigens, and the immunoreactive cDNA inserts were sequenced. Purified 62- and 60-kDa proteins were used for amino acid microsequencing and for immunization studies in Swiss, C57BL/6, and BALB/c mice and rabbits. Taken together, the data indicated that the 60-kDa molecules are poorly immunogenic in mice and rabbits, whereas the 62-kDa species identified as S. mansoni calreticulin, is a good T- and B-cell antigen and represents a potential vaccine candidate.

Fine specificity of autoantibodies to calreticulin: epitope mapping and characterization

Extracellular calreticulin (CRT) as well as anti-CRT antibodies have been reported in patients with various autoimmune disorders and CRT has been implicated in 'epitope spreading' to other autoantigens such as the Ro/SS-A complex. In addition, antibodies against parasite forms of the endoplasmic reticulum chaperone, CRT, have been found in patients suffering from onchocerciasis and schistosomiasis. In this study, we screened sera for anti-CRT antibodies from patients with active and inactive systemic lupus ertythematosus (SLE) and primary or secondary Sjögren's syndrome. Approximately 40% of all SLE patients were positive for anti-CRT antibodies. The antigenic regions of CRT were determined using full length CRT and fragments of CRT prepared in yeast and Escherichia coli, respectively. Synthetic 15mer peptides corresponding to the major autoantigenic region of CRT (amino acids 1-289), each one overlapping by 12 amino acids, were used to map the B cell epitopes on the CRT protein recognized by autoimmune sera. Major antigenic epitopes were found to be associated with the N-terminal half of the protein in 69% of the SLE sera from active disease patients, while the C-domain was not antigenic. Major epitopes were found to be reactive with antibodies in sera from SLE patients with both active and inactive disease, spanning different regions of the N and P-domains. Sera from both healthy and disease controls and primary Sjögren's syndrome patients were non-reactive to these sequences. Limited proteolysis of CRT with two major leucocyte serine proteases, elastase and cathepsin G, demonstrated that an N-terminal region of CRT is resistant to digestion. Interestingly, some of the epitopes with the highest reactivity belong to the fragments of the protein which bind to C1q and inhibit complement activation. Whether C1q association with CRT is a pathological or protective interaction between these two proteins is currently under investigation.

Onchocerca volvulus: limited heterogeneity in the nuclear and mitochondrial genomes

West African populations of Onchocerca volvulus endemic to the rain forest and savanna bioclimes of West Africa differ in their ability to induce ocular disease in infected individuals. In recent years, both clinical- and animal-model-based studies have implicated particular parasite antigens in the development of ocular onchocerciasis. To test the hypothesis that the difference in pathogenic potential of blinding and nonblinding parasites might be reflected in qualitative differences in antigens that have been implicated in the development of ocular onchocerciasis, we compared the sequences of two parasite antigens implicated in the development of ocular disease in blinding- and nonblinding-strain parasites. The results demonstrated a high level of homogeneity between the parasite strains in these genes. The study was extended to include additional nuclear genes encoding antigens that are commonly recognized by individuals infected with O. volvulus and to the mitochondrial genome of the parasite. The results demonstrate a high degree of homogeneity in both the nuclear and the mitochondrial genomes among O. volvulus isolates collected from several different sites in Africa and in the Americas. This high degree of genetic homogeneity may reflect the passage of the parasite through a recent genetic bottleneck.

KDEL proteins are found on the surface of NG108-15 cells

Although KDEL proteins are primarily localized to the endoplasmic reticulum (ER), we have employed surface biotinylation method to demonstrate that the KDEL proteins calreticulin (Crt), protein disulfide isomerase (PDI) and the 78-kDa glucose regulated protein (GRP78) are found on the surface of the NG108-15 cell line. In contrast, the 94-kDa glucose regulated protein (GRP94), another KDEL protein, is not found on the cell surface. Calnexin (Cnx), a type-1 integral transmembrane ER protein which is partially homologous to Crt but lacks the KDEL sequence, is not detected on the cell surface either. While only small amounts of the total GRP78, PDI and Crt molecules exist on the cell surface at steady state, a significant fraction of the newly synthesized molecules are transported to the cell surface and transport of these proteins is inhibited by treatment with brefeldin A. The surface GRP78 contains the KDEL sequence. On the cell surface, GRP78, PDI and Crt associate with other proteins and form complexes of different sizes. Surface Crt is found to be essential for the neurite formation when NG108-15 cells are induced to differentiate using dibutyryl cAMP.

Mutagenic analysis of the 3' cis-acting elements of the rubella virus genome

Thermodynamically predicted secondary structure analysis of the 3'-terminal 305 nucleotides (nt) of the rubella virus (RUB) genome, a region conserved in all RUB defective interfering RNAs, revealed four stem-loop (SL) structures; SL1 and SL2 are both located in the E1 coding region, while SL3 and SL4 are within the 59-nt 3' untranslated region (UTR) preceding the poly(A) tract. SL2 is a structure shown to interact with human calreticulin (CAL), an autoantigen potentially involved in RUB RNA replication and pathogenesis. RNase mapping indicated that SL2 and SL3 are in equilibrium between two conformations, in the second of which the previously proposed CAL binding site in SL2, a U-U bulge, is not formed. Site-directed mutagenesis of the 3' UTR with a RUB infectious clone, Robo302, revealed that most of the 3' UTR is required for viral viability except for the 3'-terminal 5 nt and the poly(A) tract, although poly(A) was rapidly regenerated during subsequent replication. Maintenance of the overall SL3 structure, the 11-nt single-stranded sequence between SL3 and SL4, and the sequences forming SL4 were all important for viral viability. Studies on the interaction between host factors and the 3' UTR showed the formation of three RNA-protein complexes by gel mobility shift assay, and UV-induced cross-linking detected six host protein species, with molecular masses of 120, 80, 66, 55, 48, and 36 kDa, interacting with the 3' UTR. Site-directed mutagenesis of SL2 by nucleotide substitutions showed that maintenance of SL2 stem rather than the U-U bulge was critical in CAL binding since mutants having the U-U bulge base paired had a similar binding activity for CAL as the native structure whereas mutants having the SL2 stem destabilized had much lower binding activity. However, all of these mutations gave rise to viable viruses when introduced into Robo302, indicating that binding of CAL to SL2 is independent of viral viability.

Molecular characterization of a calcium-binding protein from the filarial parasite Dirofilaria immitis

A full length D. immitis cDNA (nDiCal) encoding a protein with significant similarity to the calreticulin protein family was isolated from a 6-day fourth-stage larval cDNA expression library by immunoscreening, using serum from a rabbit immunized by repeated injection of small numbers of third-stage larvae. nDiCal is 1538 bp long and contains the 21 bp nematode splice leader sequence SL1 at the 5' end. nDiCal encodes for a protein (pDiCal) with a predicted molecular mass of 46 kDa. pDiCal sequence analysis revealed similarities with calreticulin, a protein that typically resides in the endoplasmic reticulum. pDiCal possesses three consensus sequences of the calreticulin family of proteins: a neutral N-terminal region with a putative signal sequence; a proline- and tryptophan-rich P region; and a highly acidic C-terminal region. A 45Ca2+-overlay assay showed that recombinant pDiCal (rDiCal) is a Ca2+-binding protein. Antibodies to rDiCal identified a 56 kDa native antigen in all developmental stages including the excretory-secretory products derived from larvae and adult worms. Localization studies demonstrated the ubiquitous presence of pDiCal with intense expression in the hypodermis and syncitial muscle cells in both male and female adult worms. Labeling was also seen in the developing embryos within the uterus of the female worms. Sera from immune as well as chronically-infected microfilaremic dogs contained antibodies that bind rDiCal. In addition, immunoblot analysis showed that serum from a rabbit immunized with L3 cuticles reacted with rDiCal.

Implications of Calreticulin Function in Parasite Biology

Calreticulin (CR) is a Ca(2+)-binding, multifunctional protein. The amazing array of CR-associated functions range from intracellular activities in secondary messenger release, protein folding and the modulation of gene expression to potential interactions with host receptors and signaling machinery and recognition by the host immune system. The multifunctional nature of CR may impact upon the ability of cells to recognize extracellular stimuli and coordinate appropriate responses. Identification of CR isolated from parasites and the conservation of its functions suggests that investigations into the contributions of CR to various aspects of parasite biology should be undertaken because it may reveal information regarding parasite interaction with the host and how the parasite may modulate its response to the host.

Identification of an epitope of a recombinant Onchocerca volvulus protein that induces corneal pathology

Ocular onchocerciasis results from immune recognition of parasite proteins released into the eye by degenerating microfilariae. Previous studies have shown that pathology similar to human ocular onchocerciasis can be induced in sensitized mice by intracorneal injection with Onchocerca volvulus antigens. In the current study, we used this murine model to map the segments of O. volvulus protein disulfide isomerase (OvPDI) associated with the development of corneal pathology. Subclones of OvPDI were constructed encompassing one or more predicted T cell epitopes. Keratitis was induced in BALB/c mice after subcutaneous immunizations with OvPDI, followed by intracorneal challenge of OvPDI constructs. Truncated OvPDI proteins containing amino acids 450-481 of OvPDI were found to induce keratitis, whereas constructs that did not include this region did not induce corneal pathology. Consistent with this observation, two peptides derived from the 450-481 region stimulated T cell proliferation to a greater degree than control carrier protein. DNA sequence analysis of cDNAs encoding OvPDI from blinding and non-blinding strains of O. volvulus indicated no differences in the primary amino acid sequence of the 450-481 domain. Immunization of animals with OvPDI induced antibodies recognizing a 55 kDa host protein, identical to the predicted molecular weight of the mouse PDI homologue. Together, these data implicate specific antigenic epitopes of OvPDI in the development of O. volvulus mediated corneal pathology.

The Schizosaccharomyces pombe homologue of the chaperone calnexin is essential for viability

We have cloned a Schizosaccharomyces pombe gene, here designated cnx1, encoding the homologue of the endoplasmic reticulum molecular chaperone calnexin. Disruption of the cnx1 gene was lethal, demonstrating that it has an essential cellular function. Transcription of cnx1 mRNA is initiated at multiple sites, and it can be induced by various stress treatments that lead to the accumulation of unfolded and/or misfolded proteins in the endoplasmic reticulum. The encoded Cnx1p protein more closely resembles its plant and animal calnexin homologues than that of Saccharomyces cerevisiae. Cnx1p is acidic and migrates aberrantly on SDS-polyacrylamide gel electrophoresis, similar to its mammalian counterparts. Cnx1p contains the hallmark KPEDWD motifs that are found in all members of the calnexin/calreticulin family of proteins. Using an in vitro translation-processing system, we have shown that Cnx1p has the characteristic type I topology of calnexin proteins. Unlike its higher eukaryotic homologues, Cnx1p has a site for N-glycosylation that was modified in an in vitro translation-processing assay.

Characterization of genes encoding members of the nuclear hormone receptor superfamily from Onchocerca volvulus

Several lines of evidence suggest that molting in parasitic nematodes is controlled through the action of steroid molting hormones, or ecdysones. In other organisms, the central mediator of steroid hormone action is the hormone receptor. These receptor molecules are members of a superfamily of proteins called the nuclear hormone receptor family. Using an oligonucleotide derived from the amino-acid sequence of the Drosophila melanogaster ecdysone receptor, genes encoding homologues of the nuclear hormone receptor family were identified in the genome of the human filarial parasite Onchocerca volvulus. The O. volvulus genome contains at least three genes that encode putative members of the nuclear hormone receptor superfamily. A complete cDNA for one of these genes, designated OvNHR-1, has been isolated and characterized. The OvNHR-1 cDNA was 2378 bp in length, and contained a single open reading frame of 1104 bp. The open reading frame encoded a peptide with all of the features characteristic of a member of the nuclear hormone receptor superfamily of proteins. OVNHR-1 appeared to be encoded by a single-copy gene. Expression of the mRNA corresponding to OvNHR-1 was developmentally regulated, with maximal expression occurring during early embryogenesis. The polypeptide encoded by the OvNHR-1 open reading frame is antigenic in a minority of individuals exposed to O. volvulus.