Toxoplasma gondii Matrix Antigen 1 Is a Secreted Immunomodulatory Effector

Our studies on novel cyst wall proteins serendipitously led us to the discovery that cyst wall and vacuolar matrix protein MAG1, first identified a quarter of a century ago, functions as a secreted immunomodulatory effector. MAG1 is a dense granular protein that is found in the parasitophorous vacuolar matrix in tachyzoite vacuoles and the cyst wall and matrix in bradyzoite vacuoles. In the current study, we demonstrated that MAG1 is secreted beyond the parasitophorous vacuole into the host cytosol in both tachyzoites and bradyzoites. Secretion of MAG1 gradually decreases as the parasitophorous vacuole matures, but prominent MAG1 puncta are present inside host cells even at 4 and 6 days following infection. During acute murine infection, Δmag1 parasites displayed significantly reduced virulence and dissemination. In the chronic stage of infection, Δmag1 parasites generated almost no brain cysts. To identify the mechanism behind the attenuated pathology seen with Δmag1 parasites, various immune responses were screened in vitro using bone marrow-derived macrophages (BMDM). Infection of BMDM with Δmag1 parasites induced a significant increase in interleukin 1β (IL-1β) secretion, which is a hallmark of inflammasome activation. Heterologous complementation of MAG1 in BMDM cells prevented this Δmag1 parasite-induced IL-1β release, indicating that secreted MAG1 in host cytosol dampens inflammasome activation. Furthermore, knocking out GRA15 (an inducer of IL-1β release) in Δmag1 parasites completely inhibited all IL-1β release by host cells following infection. These data suggest that MAG1 has a role as an immunomodulatory molecule and that by suppressing inflammasome activation, it would favor survival of the parasite and the establishment of latent infection.IMPORTANCEToxoplasma gondii is an Apicomplexan that infects a third of humans, causing encephalitis in AIDS patients and intellectual disabilities in congenitally infected patients. We determined that one of the cyst matrix proteins, MAG1, which had been thought to be an innate structural protein, can be secreted into the host cell and suppress the host immune reaction. This particular immune reaction is initiated by another parasite-secreted protein, GRA15. The intricate balance of inflammasome activation by GRA15 and suppression by MAG1 protects mice from acute death while enabling parasites to disseminate and establish chronic cysts. Our finding contributes to our understanding of how parasites persist in the host and how T. gondii modulates the host immune system.

Validation of ELISA with recombinant antigens in serological diagnosis of canine Leishmania infantum infection

BACKGROUND

Dogs are the main peridomiciliary reservoir of Leishmania infantum thus the correct diagnosis of infection is essential for the control of the transmission and treatment as well. However, the diagnosis is based on serological assays that are not fully effective.

OBJECTIVE

We aimed to establish an effective serological assay for the diagnosis of L. infantum infected dogs using Leishmania-derived recombinant antigens.

METHODS

Leishmania derived rK39-, rK28-, rKR95-based enzyme-linked immunosorbent assay (ELISA) was standardized using symptomatic and asymptomatic L. infantum-infected dogs. Then 2,530 samples from inquiry in endemic areas for VL were evaluated and the results compared with recommended assays by the Brazilian Ministry of Health (MH algorithm). Further samples from a cohort of 30 dogs were searched.

FINDINGS

For rK39-, rK28- and rKR95-ELISA the sensitivity was around 97% and specificity 100%. The positivity of these three ELISA in the inquiry samples was 27-28%, around 10% higher than the assays currently in use. When cohort samples were searched, we observed likely false-negative results (> 65%) with supposedly negative samples that turned positive six months later with the assays in use (MH algorithm).

MAIN CONCLUSIONS

For the diagnosis of L. infantum-infected dogs, rK39-based ELISA showed better diagnostic performance than other assays in use in Brazil and worldwide.

Antigenicity assessment of the Theileria equi merozoite antigen (EMA-2) expressed in Pichia pastoris in mice and horses

Equine theileriosis is a severe equine disease caused by the protozoan Theileria equi, which is prevalent in tropical and subtropical areas. In this study, a recombinant equi merozoite antigen-2 (rEMA-2) of T. equi was used as an immunogen. Two groups of 10 mice each were divided into control and vaccinated groups. Sixty mares seronegative for theileriosis were divided in two groups, one vaccinated and another group as a control animal. Mice and mares of the vaccinated groups were inoculated with 150 μL of the vaccine containing 50 μg of rEMA-2 and 2 mL of the vaccine containing 200 μg of rEMA-2, respectively, at days 0 and 21. The immunogenicity of rEMA-2 was evaluated by ELISA and fluorescent antibody test (IFAT) using serum from vaccinated mice, mares and antigenicity in naturally infected horse. At every point throughout the ELISA study, there were significant differences between the vaccinated and control groups (p < 0.05). The vaccine induced 3- and 4-fold IgG increases in mice at the 14th and 28th day, respectively, compared to the control group. The horses' IgG dynamics showed a significant (p < 0.05) increase in the total IgG titer as early as day 7, which increased until day 28 at which time a more significant (p < 0.001) IgG titer was observed. In evaluating the isotypes, we observed a trend similar to that of total IgG, where IgG(T) (IgG3-5) were significantly (p < 0.05) more elevated than the other isotypes analyzed, followed by IgGb (IgG4-7) and IgGa (IgG1). Positive fluorescence was detected by IFAT, suggesting that the protein is immunogenic and conserves some epitopes identical to the native T. equi antigens present in the equine blood smear. Thus, our results suggest that rEMA-2 can be a promising vaccinal antigen.

Expression of full-length Plasmodium falciparum P48/45 in P. berghei blood stages: A method to express and evaluate vaccine antigens

The transmission-blocking vaccine candidate Pfs48/45 from the human malaria parasite Plasmodium falciparum is known to be difficult to express in heterologous systems, either as full-length protein or as correctly folded protein fragments that retain conformational epitopes. In this study we express full-length Pfs48/45 in the rodent parasite P. berghei. Pfs48/45 is expressed as a transgene under control of the strong P. berghei schizont-specific msp1 gene promoter (Pfs48/45@PbMSP1). Pfs48/45@PbMSP1 schizont-infected red blood cells produced full-length Pfs48/45 and the structural integrity of Pfs48/45 was confirmed using a panel of conformation-specific monoclonal antibodies that bind to different Pfs48/45 epitopes. Sera from mice immunized with transgenic Pfs48/45@PbMSP1 schizonts showed strong transmission-reducing activity in mosquitoes infected with P. falciparum using standard membrane feeding. These results demonstrate that transgenic rodent malaria parasites expressing human malaria antigens may be used as means to evaluate immunogenicity and functionality of difficult to express malaria vaccine candidate antigens.

Assessment and optimization of Theileria parva sporozoite full-length p67 antigen expression in mammalian cells

Delivery of various forms of recombinant Theileria parva sporozoite antigen (p67) has been shown to elicit antibody responses in cattle capable of providing protection against East Coast fever, the clinical disease caused by T. parva. Previous formulations of full-length and shorter recombinant versions of p67 derived from bacteria, insect, and mammalian cell systems are expressed in non-native and highly unstable forms. The stable expression of full-length recombinant p67 in mammalian cells has never been described and has remained especially elusive. In this study, p67 was expressed in human-derived cells as a full-length, membrane-linked protein and as a secreted form by omission of the putative transmembrane domain. The recombinant protein expressed in this system yielded primarily two products based on Western immunoblot analysis, including one at the expected size of 67 kDa, and one with a higher than expected molecular weight. Through treatment with PNGase F, our data indicate that the larger product of this mammalian cell-expressed recombinant p67 cannot be attributed to glycosylation. By increasing the denaturing conditions, we determined that the larger sized mammalian cell-expressed recombinant p67 product is likely a dimeric aggregate of the protein. Both forms of this recombinant p67 reacted with a monoclonal antibody to the p67 molecule, which reacts with the native sporozoite. Additionally, through this work we developed multiple mammalian cell lines, including both human and bovine-derived cell lines, transduced by a lentiviral vector, that are constitutively able to express a stable, secreted form of p67 for use in immunization, diagnostics, or in vitro assays. The recombinant p67 developed in this system is immunogenic in goats and cattle based on ELISA and flow cytometric analysis. The development of a mammalian cell system that expresses full-length p67 in a stable form as described here is expected to optimize p67-based immunization.

East Coast fever, caused by the tick-borne protozoan parasite Theileria parva, is a disease that results in significant bovine morbidity, mortality, and production losses in regions of sub-Saharan Africa. Susceptible cattle develop clinical signs within a 7–14 days of exposure, which often progress to severe pulmonary edema and death. Control of East Coast fever in affected regions of Africa is largely prohibited by the lack of an affordable and efficacious vaccine. Furthermore, pastoralist farmers in affected regions of Africa often lack resources to prevent losses due to East Coast fever, so these production losses play a significant role in food security and protein availability. Experimental immunization of cattle with a recombinant T. parva-derived antigen, p67, has shown promise in preventing East Coast fever, but this antigen is extremely difficult to produce in full-length in sufficient quantities, and results of immunization studies using truncated recombinant p67 products are highly inconsistent. In this study, p67 antigen production was optimized and produced for use in future immunization studies. Optimization of p67-based immunization strategies is an important step forward in the development of a sustainable, next-generation vaccine against T. parva, which is urgently needed to minimize losses associated with East Coast fever.

Production, Quality Control, Stability and Pharmacotoxicity of a Malaria Vaccine Comprising Three Highly Similar PfAMA1 Protein Molecules to Overcome Antigenic Variation

Plasmodium falciparum apical membrane antigen 1 (PfAMA1) is a leading asexual blood stage vaccine candidate for malaria. In preparation for clinical trials, three Diversity Covering (DiCo) PfAMA1 ectodomain proteins, designed to overcome the intrinsic polymorphism that is present in PfAMA1, were produced under Good Manufacturing Practice (GMP) in Pichia pastoris. Using identical methodology, the 3 strains were cultivated in 70-L scale fed-batch fermentations and PfAMA1-DiCos were purified by two chromatography steps, an ultrafiltration/diafiltration procedure and size exclusion chromatography, resulting in highly pure (>95%) PfAMA1-DiCo1, PfAMA1 DiCo2 and PfAMA1 DiCo3, with final yields of 1.8, 1.9 and 1.3 gram, respectively. N-terminal determinations showed that approximately 50% of each of the proteins lost 12 residues from their N-terminus, in accordance with SDS-PAGE (2 main bands) and MS-data. Under reducing conditions a site of limited proteolytic cleavage within a disulphide bonded region became evident. The three proteins quantitatively bound to the mAb 4G2 that recognizes a conformational epitope, suggesting proper folding of the proteins. The lyophilized Drug Product (1:1:1 mixture of PfAMA1-DiCo1, DiCo2, DiCo3) fulfilled all pre-set release criteria (appearance, dissolution rate, identity, purity, protein content, moisture content, sub-visible particles, immuno-potency (after reconstitution with adjuvant), abnormal toxicity, sterility and endotoxin), was stable in accelerated and real-time stability studies at -20°C for over 24 months. When formulated with adjuvants selected for clinical phase I evaluation, the Drug Product did not show adverse effect in a repeated-dose toxicity study in rabbits. The Drug Product has entered a phase Ia/Ib clinical trial.

Production of recombinant PvDBPII, receptor binding domain of Plasmodium vivax Duffy binding protein, and evaluation of immunogenicity to identify an adjuvant formulation for vaccine development

Plasmodium vivax is dependent on interaction with the Duffy antigen receptor for chemokines (DARC) for invasion of human erythrocytes. The P. vivax Duffy binding protein (PvDBP) mediates interaction of P. vivax merozoites with DARC. The DARC receptor-binding domain lies in a conserved N-terminal cysteine-rich region of PvDBP referred to as region II (PvDBPII). PvDBPII is an attractive vaccine candidate since antibodies raised against PvDBPII block erythrocyte invasion by P. vivax. Here, we describe methods to produce recombinant PvDBPII in its correctly folded conformation. A synthetic gene optimized for expression of PvDBPII in Escherichia coli and fed batch fermentation process based on exponential feeding strategy was used to achieve high levels of expression of recombinant PvDBPII. Recombinant PvDBPII was isolated from inclusion bodies, refolded by rapid dilution and purified by ion exchange chromatography. Purified recombinant PvDBPII was characterized for identity, purity and functional activity using standardized release assays. Recombinant PvDBPII formulated with various human compatible adjuvants including glycosylpyranosyl lipid A-stable emulsion (GLA-SE) and alhydrogel was used for immunogenicity studies in small animals to downselect a suitable formulation for clinical development. Sera collected from immunized animals were tested for recognition of PvDBPII and inhibition of PvDBPII-DARC binding. GLA-SE formulations of PvDBPII yielded higher ELISA and binding inhibition titres compared to PvDBPII formulated with alhydrogel. These data support further development of a recombinant vaccine for P. vivax based on PvDBPII formulated with GLA-SE.

In vitro evaluation of a soluble Leishmania promastigote surface antigen as a potential vaccine candidate against human leishmaniasis

PSA (Promastigote Surface Antigen) belongs to a family of membrane-bound and secreted proteins present in several Leishmania (L.) species. PSA is recognized by human Th1 cells and provides a high degree of protection in vaccinated mice. We evaluated humoral and cellular immune responses induced by a L. amazonensis PSA protein (LaPSA-38S) produced in a L. tarentolae expression system. This was done in individuals cured of cutaneous leishmaniasis due to L. major (CCLm) or L. braziliensis (CCLb) or visceral leishmaniasis due to L. donovani (CVLd) and in healthy individuals. Healthy individuals were subdivided into immune (HHR-Lm and HHR-Li: Healthy High Responders living in an endemic area for L. major or L. infantum infection) or non immune/naive individuals (HLR: Healthy Low Responders), depending on whether they produce high or low levels of IFN-γ in response to Leishmania soluble antigen. Low levels of total IgG antibodies to LaPSA-38S were detected in sera from the studied groups. Interestingly, LaPSA-38S induced specific and significant levels of IFN-γ, granzyme B and IL-10 in CCLm, HHR-Lm and HHR-Li groups, with HHR-Li group producing TNF-α in more. No significant cytokine response was observed in individuals immune to L. braziliensis or L. donovani infection. Phenotypic analysis showed a significant increase in CD4+ T cells producing IFN-γ after LaPSA-38S stimulation, in CCLm. A high positive correlation was observed between the percentage of IFN-γ-producing CD4+ T cells and the released IFN-γ. We showed that the LaPSA-38S protein was able to induce a mixed Th1 and Th2/Treg cytokine response in individuals with immunity to L. major or L. infantum infection indicating that it may be exploited as a vaccine candidate. We also showed, to our knowledge for the first time, the capacity of Leishmania PSA protein to induce granzyme B production in humans with immunity to L. major and L. infantum infection.

Immunogenicity and antigenicity of Plasmodium vivax merozoite surface protein 10

Among the proteins involved in the invasion by merozoite, the glycosylphosphatidylinositol-anchored proteins (GPI-APs) are suggested as potential vaccine candidates because of their localization to apical organelles and the surface; these candidates are predicted to play essential roles during invasion. As a GPI-AP, Plasmodium vivax merozoite surface protein 10 (PvMSP-10) induces high antibody titers. However, such high antibody titers have shown no protective efficacy for animals challenged with P. vivax parasites in a previous study. To adequately evaluate the immunogenicity and further characterize PvMSP-10 in order to understand its vaccine potential, we assessed its immunogenicity by immunizing BALB/c mice with cell-free expressed recombinant PvMSP-10 protein. The antigenicity of MSP-10 was analyzed, and we found 42% sensitivity and 95% specificity using serum samples from P. vivax-infected Korean patients. The IgG1 and IgG3 were the predominant immunoreactive antibodies against PvMSP-10 in vivax patient sera, and IgG1 and IgG3 and Th1-type cytokines were predominantly secreted in PvMSP-10-immunized mice. We conclude that the immunogenicity and antigenicity of MSP-10 may serve as a potential vaccine against vivax malaria.

Approaches towards DNA vaccination against a skin ciliate parasite in fish

Rainbow trout (Oncorhynchus mykiss) were immunized with plasmid DNA vaccine constructs encoding selected antigens from the parasite Ichthyophthirius multifiliis. Two immobilization antigens (I-ags) and one cysteine protease were tested as genetic vaccine antigen candidates. Antigenicity was evaluated by immunostaining of transfected fish cells using I-ag specific mono- and polyclonal antibodies. I. multifiliis specific antibody production, regulation of immune-relevant genes and/or protection in terms of parasite burden or mortality was measured to evaluate the induced immune response in vaccinated fish. Apart from intramuscular injection, needle free injection and gene gun delivery were tested as alternative administration techniques. For the I-ags the complement protein fragment C3d and the termini of the viral haemorrhagic septicaemia virus glyco(G)protein (VHSV G) were tested as opsonisation and cellular localisation mediators, respectively, while the full length viral G protein was tested as molecular adjuvant. Expression of I-ags in transfected fish cells was demonstrated for several constructs and by immunohistochemistry it was possible to detect expression of a secreted form of the Iag52B in the muscle cells of injected fish. Up-regulations of mRNA coding for IgM, MHC I, MHC II and TCR β, respectively, were observed in muscle tissue at the injection site in selected trials. In the spleen up-regulations were found for IFN-γ and IL-10. The highest up-regulations were seen following co-administration of I-ag and cysteine protease plasmid constructs. This correlated with a slight elevation of an I. multifiliis specific antibody response. However, in spite of detectable antigen expression and immune reactions, none of the tested vaccination strategies provided significant protection. This might suggest an insufficiency of DNA vaccination alone to trigger protective mechanisms against I. multifiliis or that other or additional parasite antigens are required for such a vaccine to be successful.

The profile of snoRNA-derived microRNAs that regulate expression of variant surface proteins in Giardia lamblia

In the current investigation, we analysed all the known small nucleolar RNAs (snoRNAs) in the deeply branching protozoan parasite Giardia lamblia for potential microRNAs (miRNAs) that might be derived from them. Two putative miRNAs have since been identified by Northern blot, primer extension, 3' RACE and co-immunoprecipitation with Giardia Argonaute (GlAgo), and designated miR6 and miR10. Giardia Dicer (GlDcr) is capable of processing the snoRNAs into the corresponding miRNAs in vitro. Potential miR6 and miR10 binding sites in Giardia genome were predicted bio-informatically. A miR6 binding site was found at the 3' untranslated regions (UTR) of 44 variant surface protein (vsp) genes, whereas a miR10 binding site was identified at the 3' end of 159 vsp open-reading frames. Thirty-three of these vsp genes turned out to contain binding sites for both miR6 and miR10. A reporter mRNA tagged with the 3' end of vsp1267, which contains the target sites for both miRNAs, was translationally repressed by both miRNAs in Giardia. Episomal expression of an N-terminal c-myc tagged VSP1267 was found significantly repressed by introducing either miR6 or miR10 into the cells and the repressive effects were additive. When the 2'-O-methyl antisense oligos (ASOs) of either miR6 or miR10 was introduced, however, there was an enhancement of tagged VSP1267 expression suggesting an inhibition of the repressive effects of endogenous miR6 or miR10 by the ASOs. Of the total 220 vsp genes in Giardia, we have now found 178 of them carrying putative binding sites for all the miRNAs that have been currently identified, suggesting that miRNAs are likely the regulators of VSP expression in Giardia.

The MASP family of Trypanosoma cruzi: changes in gene expression and antigenic profile during the acute phase of experimental infection

BACKGROUND

Trypanosoma cruzi is the etiological agent of Chagas disease, a debilitating illness that affects millions of people in the Americas. A major finding of the T. cruzi genome project was the discovery of a novel multigene family composed of approximately 1,300 genes that encode mucin-associated surface proteins (MASPs). The high level of polymorphism of the MASP family associated with its localization at the surface of infective forms of the parasite suggests that MASP participates in host-parasite interactions. We speculate that the large repertoire of MASP sequences may contribute to the ability of T. cruzi to infect several host cell types and/or participate in host immune evasion mechanisms.

METHODS

By sequencing seven cDNA libraries, we analyzed the MASP expression profile in trypomastigotes derived from distinct host cells and after sequential passages in acutely infected mice. Additionally, to investigate the MASP antigenic profile, we performed B-cell epitope prediction on MASP proteins and designed a MASP-specific peptide array with 110 putative epitopes, which was screened with sera from acutely infected mice.

FINDINGS AND CONCLUSIONS

We observed differential expression of a few MASP genes between trypomastigotes derived from epithelial and myoblast cell lines. The more pronounced MASP expression changes were observed between bloodstream and tissue-culture trypomastigotes and between bloodstream forms from sequential passages in acutely infected mice. Moreover, we demonstrated that different MASP members were expressed during the acute T. cruzi infection and constitute parasite antigens that are recognized by IgG and IgM antibodies. We also found that distinct MASP peptides could trigger different antibody responses and that the antibody level against a given peptide may vary after sequential passages in mice. We speculate that changes in the large repertoire of MASP antigenic peptides during an infection may contribute to the evasion of host immune responses during the acute phase of Chagas disease.

Plant expressed coccidial antigens as potential vaccine candidates in protecting chicken against coccidiosis

Coccidiosis is a disease caused by intracellular parasites belonging to the genus Eimeria. In the present study, we transiently expressed two coccidial antigens EtMIC1 and EtMIC2 as poly histidine-tagged fusion proteins in tobacco. We have evaluated the protective efficacy of plant expressed EtMIC1 as monovalent and as well as bi-valent formulation where EtMIC1 and EtMIC2 were used in combination. The protective efficacy of these formulations was evaluated using homologous challenge in chickens. We observed better serum antibody response, weight gain and reduced oocyst shedding in birds immunized with EtMIC1 and EtMIC2 as bivalent formulation compared to monovalent formulation. However, IFN-γ response was not significant in birds immunized with EtMIC1 compared to the birds immunized with EtMIC2. Our results indicate the potential use of these antigens as vaccine candidates.

Algae-produced Pfs25 elicits antibodies that inhibit malaria transmission

Subunit vaccines are significantly more expensive to produce than traditional vaccines because they are based primarily on recombinant proteins that must be purified from the expression system. Despite the increased cost, subunit vaccines are being developed because they are safe, effective, and can elicit antibodies that confer protection against diseases that are not currently vaccine-preventable. Algae are an attractive platform for producing subunit vaccines because they are relatively inexpensive to grow, genetically tractable, easily scaled to large volumes, have a short generation time, and are devoid of inflammatory, viral, or prion contaminants often present in other systems. We tested whether algal chloroplasts can produce malaria transmission blocking vaccine candidates, Plasmodium falciparum surface protein 25 (Pfs25) and 28 (Pfs28). Antibodies that recognize Pfs25 and Pfs28 disrupt the sexual development of parasites within the mosquito midgut, thus preventing transmission of malaria from one human host to the next. These proteins have been difficult to produce in traditional recombinant systems because they contain tandem repeats of structurally complex epidermal growth factor-like domains, which cannot be produced in bacterial systems, and because they are not glycosylated, so they must be modified for production in eukaryotic systems. Production in algal chloroplasts avoids these issues because chloroplasts can fold complex eukaryotic proteins and do not glycosylate proteins. Here we demonstrate that algae are the first recombinant system to successfully produce an unmodified and aglycosylated version of Pfs25 or Pfs28. These antigens are structurally similar to the native proteins and antibodies raised to these recombinant proteins recognize Pfs25 and Pfs28 from P. falciparum. Furthermore, antibodies to algae-produced Pfs25 bind the surface of in-vitro cultured P. falciparum sexual stage parasites and exhibit transmission blocking activity. Thus, algae are promising organisms for producing cysteine-disulfide-containing malaria transmission blocking vaccine candidate proteins.

Evidence for in vitro and in vivo expression of the conserved VAR3 (type 3) plasmodium falciparum erythrocyte membrane protein 1

BACKGROUND

Members of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion antigen family are major contributors to the pathogenesis of P. falciparum malaria infections. The PfEMP1-encoding var genes are among the most diverse sequences in nature, but three genes, var1, var2csa and var3 are found conserved in most parasite genomes. The most severe forms of malaria disease are caused by parasites expressing a subset of antigenically conserved PfEMP1 variants. Thus the ubiquitous and conserved VAR3 PfEMP1 is of particular interest to the research field. Evidence of VAR3 expression on the infected erythrocyte surface has never been presented, and var3 genes have been proposed to be transcribed and expressed differently from the rest of the var gene family members.

METHODS

In this study, parasites expressing VAR3 PfEMP1 were generated using anti-VAR3 antibodies and the var transcript and PfEMP1 expression profiles of the generated parasites were investigated. The IgG reactivity by plasma from children living in malaria-endemic Tanzania was tested to parasites and recombinant VAR3 protein. Parasites from hospitalized children were isolated and the transcript level of var3 was investigated.

RESULTS

Var3 is transcribed and its protein product expressed on the surface of infected erythrocytes. The VAR3-expressing parasites were better recognized by children´s IgG than a parasite line expressing a Group B var gene. Two in 130 children showed increased recognition of parasites expressing VAR3 and to the recombinant VAR3 protein after a malaria episode and the isolated parasites showed high levels of var3 transcripts.

CONCLUSIONS

Collectively, the presented data suggest that var3 is transcribed and its protein product expressed on the surface of infected erythrocytes in the same manner as seen for other var genes both in vitro and in vivo. Only very few children exhibit seroconversion to VAR3 following a malaria episode requiring hospitalization, supporting the previous conclusion drawn from var3 transcript analysis of parasites collected from children hospitalized with malaria, that VAR3 is not associated with severe anaemia or cerebral malaria syndromes in children.

Optimization of the expression of surface antigen SAG1/2 of Toxoplasma gondii in the yeast Pichia pastoris

Surface antigens are the most abundant proteins found on the surface of the parasite Toxoplasma gondii. Surface antigen 1 (SAG1) and Surface antigen 2 (SAG2) remain the most important and extensively studied surface proteins. These antigens have been identified to play a role in host cell invasion, immune modulation, virulence attenuation. Recombinant SAG1/2 was cloned and expressed in yeast Pichia pastoris. We describe here optimization of critical parameters involved in high yield expression of the recombinant SAG1/2. Our results suggest that recombinant SAG1/2 were best expressed at 30ºC, pH 6 and 1% methanol as the carbon source by X33 Pichia cells. Additional optimizations included the downstream process such as ammonium sulphate precipitation and dialysis. The fusion protein was purified using Ni-NTA purification system with 80% recovery. The purified protein was 100% specific and sensitive in detection of toxoplasmosis.

Identification of Leishmania proteins preferentially released in infected cells using change mediated antigen technology (CMAT)

Although Leishmania parasites have been shown to modulate their host cell's responses to multiple stimuli, there is limited evidence that parasite molecules are released into infected cells. In this study, we present an implementation of the change mediated antigen technology (CMAT) to identify parasite molecules that are preferentially expressed in infected cells. Sera from mice immunized with cell lysates prepared from L. donovani or L. pifanoi-infected macrophages were adsorbed with lysates of axenically grown amastigotes of L. donovani or L. pifanoi, respectively, as well as uninfected macrophages. The sera were then used to screen inducible parasite expression libraries constructed with genomic DNA. Eleven clones from the L. pifanoi and the L. donovani screen were selected to evaluate the characteristics of the molecules identified by this approach. The CMAT screen identified genes whose homologs encode molecules with unknown function as well as genes that had previously been shown to be preferentially expressed in the amastigote form of the parasite. In addition a variant of Tryparedoxin peroxidase that is preferentially expressed within infected cells was identified. Antisera that were then raised to recombinant products of the clones were used to validate that the endogenous molecules are preferentially expressed in infected cells. Evaluation of the distribution of the endogenous molecules in infected cells showed that some of these molecules are secreted into parasitophorous vacuoles (PVs) and that they then traffic out of PVs in vesicles with distinct morphologies. This study is a proof of concept study that the CMAT approach can be applied to identify putative Leishmania parasite effectors molecules that are preferentially expressed in infected cells. In addition we provide evidence that Leishmania molecules traffic out of the PV into the host cell cytosol and nucleus.

Leishmania are intracellular parasites that reside within parasitophorous vacuoles (PV) in phagocytes. From within these compartments parasites control the host cell's responses to multiple stimuli. There is limited knowledge of the molecules that Leishmania parasites elaborate in the host cell to target processes therein. Furthermore, the mechanism by which such molecules would access their targets beyond the PV is not known. In the study presented here, we implemented the change mediated antigen technology (CMAT) to identify parasite molecules that are preferentially expressed inside infected cells. The approach was based on the reasoning that parasites express ‘new’ or antigenically modified molecules in the intracellular environment; therefore antiserum that is reactive to infected cells would contain immunoglobulins that are specific to these ‘new’ molecules. After adsorption of the antiserum with axenically cultured parasites, the antiserum was used to screen a parasite genomic expression library to identify genes encoding the molecules that are preferentially expressed in infected cells. We present for the first time evidence that some of these CMAT molecules accumulate in the PV and then traffic into the host cell in vesicles of distinct morphologies. Furthermore, several of these parasite molecules become localized in discrete compartments within the host cell.

Optimization for high-level expression in Pichia pastoris and purification of truncated and full length recombinant SAG2 of Toxoplasma gondii for diagnostic use

SAG2 is one of the major surface antigens of the intracellular protozoan parasite Toxoplasma gondii. In the present study, truncated recombinant SAG2(S) and full length recombinant SAG2(T) of T. gondii were optimally produced (approximately 15 mg/liter) in Pichia pastoris expression system using BMMY medium at pH 3, 25 degrees C in 0.5-1% methanol and a time-course of 1-2 days. The recombinant proteins were purified using a commercial gel filtration purification system obtaining approximately 33% recovery. The purified SAG2(S) and SAG2(T) showed molecular masses of 45 and 36 kDa by SDS-PAGE, respectively. The recombinant proteins were evaluated by Western blotting with patients' sera and demonstrated 90% sensitivity and 100% specificity for detection of toxoplasmosis. This study provided a means for large-scale expression and purification of SAG2, which should be useful for diagnosis of toxoplasmosis.

An efficient approach to the production of vaccines against the malaria parasite

In malaria vaccine research, one of the major obstacles has been the difficulty of expressing recombinant malarial proteins and it is mainly due to the lack of an efficient methodology for the synthesis of sufficient quantity of quality proteins. We demonstrate that the wheat germ cell-free protein synthesis system can be applied for the successful production of leading malaria vaccine candidate antigens and, thus, prove that it may be a key tool for malaria vaccine research.

Production and characterization of an orally immunogenic Plasmodium antigen in plants using a virus-based expression system

Increasing numbers of plant-made vaccines and pharmaceuticals are entering the late stage of product development and commercialization. Despite the theoretical benefits of such production, expression of parasite antigens in plants, particularly those from Plasmodium, the causative parasites for malaria, have achieved only limited success. We have previously shown that stable transformation of tobacco plants with a plant-codon optimized form of the Plasmodium yoelii merozoite surface protein 4/5 (PyMSP4/5) gene resulted in PyMSP4/5 expression of up to approximately 0.25% of total soluble protein. In this report, we describe the rapid expression of PyMSP4/5 in Nicotiana benthamiana leaves using the deconstructed tobacco mosaic virus-based magnICON expression system. PyMSP4/5 yields of up to 10% TSP or 1-2 mg/g of fresh weight were consistently achieved. Characterization of the recombinant plant-made PyMSP4/5 indicates that it is structurally similar to PyMSP4/5 expressed by Escherichia coli. It is notable that the plant-made PyMSP4/5 protein retained its immunogenicity following long-term storage at ambient temperature within freeze-dried leaves. With assistance from a mucosal adjuvant the PyMSP4/5-containing leaves induced PyMSP4/5-specific antibodies when delivered orally to naïve mice or mice primed by a DNA vaccine. This study provides evidence that immunogenic Plasmodium antigens can be produced in large quantities in plants using the magnICON viral vector system.

Cloning and expression of Leishmania major superoxide dismutase B1: A potential target antigen for serodiagnosis of Leishmaniasis

BACKGROUND

Leishmaniasis- a neglected public health problem- is a group of diseases affecting an estimated 12 million people worldwide.

OBJECTIVE

In the present study, recombinant Leishmania major superoxide dismutase B1 (rLmSODB1) has been utilized as a potential antigen for the serodiagnosis of human cutaneous (CL) and visceral leishmaniasis (VL) in the endemic regions of southern part of Iran. Additionally, the sensitivity and specificity of ELISA-based serodiagnosis using rLmSODB1 and the soluble Leishmania antigen (SLA) were compared.

METHODS

For the first time, rLmSODB1 has been cloned successfully and used for ELISA-based serodiagnosis. Sera from 30 CL and 24 VL cases were included in this study. Additional studies were also done for the evaluation of cross-reactivity using sera from 41 endemic controls including normal endemic donors (n=20), systemic lupus erythematosus patients (n=5), rheumatoid arthritis patients (n=5), and patients with tuberculosis (n=11).

RESULTS

Analysis indicated that rLmSODB1 was recognized by 62.5% and 13.3% of sera from patients with VL and CL, showing a sensitivity of 72.7% and 53.6%, respectively. However 95.8% of VL and 30% of CL sera reacted with SLA, revealing sensitivities of 96% and 58.8%, respectively. Additionally, from 41 sera collected either from healthy subjects or patients affected with other diseases, 97.5% were negative with SLA or rLmSODB1 (specificity 97.6%).

CONCLUSION

These results show that rLmSODB1 almost does not react with sera from patients with tuberculosis and autoimmune diseases and may be considered as a candidate antigen for the specific immunodiagnosis of visceral leishmaniasis.

Transcriptional memory and switching in the Plasmodium falciparumrif gene family

The human malaria parasite Plasmodium falciparum expresses erythrocyte-surface directed variant antigens which are important virulence factors. Many are transcribed from multigene families and presumably their mode of expression is strictly controlled to guarantee immune evasion in the human host. In order to elucidate the dynamics of rif transcription and to investigate if rif switching is comparable to var switching we monitored rif variant gene expression in parasites with different cytoadhesive properties as well as after a number of reinvasions. We found identical transcripts in parasite lines with different adhesive phenotypes suggesting that rif genes do not have a critical role in determining the cytoadhesion specificity of infected erythrocytes. We show for the first time that rif genes may show a conserved mode of transcription, maintaining the previously dominant rif transcript in subsequent reinvasions, but also observed rapid switching at rates up to 45% per generation, much higher than for the var gene family.

Sir2 paralogues cooperate to regulate virulence genes and antigenic variation in Plasmodium falciparum

Cytoadherance of Plasmodium falciparum-infected erythrocytes in the brain, organs and peripheral microvasculature is linked to morbidity and mortality associated with severe malaria. Parasite-derived P. falciparum Erythrocyte Membrane Protein 1 (PfEMP1) molecules displayed on the erythrocyte surface are responsible for cytoadherance and undergo antigenic variation in the course of an infection. Antigenic variation of PfEMP1 is achieved by in situ switching and mutually exclusive transcription of the var gene family, a process that is controlled by epigenetic mechanisms. Here we report characterisation of the P. falciparum silent information regulator's A and B (PfSir2A and PfSir2B) and their involvement in mutual exclusion and silencing of the var gene repertoire. Analysis of P. falciparum parasites lacking either PfSir2A or PfSir2B shows that these NAD⁺-dependent histone deacetylases are required for silencing of different var gene subsets classified by their conserved promoter type. We also demonstrate that in the absence of either of these molecules mutually exclusive expression of var genes breaks down. We show that var gene silencing originates within the promoter and PfSir2 paralogues are involved in cis spreading of silenced chromatin into adjacent regions. Furthermore, parasites lacking PfSir2A but not PfSir2B have considerably longer telomeric repeats, demonstrating a role for this molecule in telomeric end protection. This work highlights the pivotal but distinct role for both PfSir2 paralogues in epigenetic silencing of P. falciparum virulence genes and the control of pathogenicity of malaria infection.

The unicellular parasite Plasmodium falciparum is the cause of the most severe form of malaria and is responsible for 300 million infections and ∼2 million deaths a year. Infected erythrocytes clump and block capillaries in the peripheral circulation, the brain, and placenta and are a major contributor to the pathology of malaria. A parasite-derived protein displayed on the surface of the infected erythrocyte is responsible for erythrocyte clumping in capillaries. Although 60 subtelomeric var genes can encode different versions of this “sticky” capillary-binding protein, only one protein is expressed at a time, and switches in expression between these genes causes variation of this pathogenic molecule enabling the parasite to evade the immune system. Here we identify two chromatin-modifying proteins that cooperate to mediate silencing and mutual exclusive expression of var genes. These proteins are thus important virulence factors of the malaria-causing parasite.

Investigation into two Sir2 histone deacetylases in the malaria-causing parasite revealstrans-acting epigenetic factors control mutually exclusive expression of a major subtelomeric virulence gene family.

Heterologous production of dense granule GRA7 antigen of Toxoplasma gondii in Escherichia coli

Infection with Toxoplasma gondii causes serious health problems in congenitally-infected and immunocompromised individuals. Numerous studies have shown usefulness of dense granule antigens of T. gondii in serodiagnosis of the infection and induction of protective immunity. This study describes cloning, expression, purification and antigenicity evaluation of recombinant GRA7 protein (rGRA7). DNA encoding GRA7, amino acids 18 to 236, was obtained from Toxoplasma gondii RH strain by polymerase chain reaction amplification and cloned in prokaryotic expression plasmid pET-28b(+). Sequence analysis showed 97% similarity between GRA7 gene fragment and published sequence of gra7. Recombinant protein was expressed in Escherichia coli and purified in a single step by immobilized metal ion affinity chromatography. Antigenicity of the protein was evaluated in Western blot analysis showing human sera from acute T. gondii infection strongly reacted with rGRA7 while sera from chronic infection weakly recognized the protein. Negative sera failed to react with rGRA7. The antigenic rGRA7 might be used, in combination with other T. gondii antigen, to develop more efficacious diagnostic tests and/or in vaccine formulations.

Bacterial production of dense granule antigen GRA8 of Toxoplasma gondii

BACKGROUND

Dense granule antigens (GRA antigens) of Toxoplasma gondii induce strong antibody response in humans and are considered as useful diagnostic antigens. Previous studies reported expression of amino terminal GRA8 protein in fusion with large tags such as glutathione-S-transferase. The present study aimed to produce soluble full length immunogenic GRA8 in bacteria.

METHODS

GRA8 complementary DNA (cDNA), encoding amino acids 24 to 258, was amplified from tachyzoites of RH strain and cloned in prokaryotic expression vector pET-28b(+). Expression of recombinant GRA8 (rGRA8) was analyzed by SDS-PAGE. Antigenicity and immunogenicity of the protein were evaluated by Western-blotting.

RESULTS

The cloned gene fragment exhibited complete similarity with the published sequence of gra8 gene by sequence analysis. rGRA8 was expressed in Escherichia coli in fusion with a very small tag and the soluble protein was purified by immobilized metal ion affinity chromatography. In immunoblot, serum sample from a rabbit immunized with rGRA8 recognized a single antigen of T. gondii tachyzoite at the expected molecular weight of native GRA8. Sera from acutely-infected pregnant women strongly reacted with rGRA8 in Western-blotting, while sera from chronically-infected or T. gondii-negative women failed to recognize the protein.

CONCLUSION

The full length soluble rGRA8 was successfully produced in E. coli and shown to be a highly immunogenic protein. As a result it could be used in immunological as well as molecular biology experiments.

Malaria sporozoite antigen-directed genome-wide response in transgenic Drosophila

Malaria kills a million people annually. Understanding the relationship between a causative parasite, Plasmodium falciparum, and the mosquito vector might suggest novel prevention approaches. We created and transformed into Drosophila two genes encoding, thrombospondin-related adhesive protein (TRAP) and circumsporozoite protein (CSP), found on the cell surface of Plasmodium sporozoites. To understand a model insect's response, we induced these proteins separately and together, performing whole genome microarray analysis measuring gene expression changes. Gene ontology classification of responding genes reveals that TRAP and CSP strongly and differentially influence Drosophila genes involved with cell motility and gene regulation, respectively; however, the most striking effects are on the immune system. While immune-related genes are but modestly elevated compared with responses to sepsis, there is a marked repression of the Toll pathway. This suggests: (1) how Plasmodium infection of the mosquito might use TRAP and CSP to modulate the host insect's physiology to promote sporozoite survival and transmission to man and (2) that approaches to elevate expression of the mosquito's Toll pathway might lead to novel methods of malaria prevention.

Comparison of the immunomodulatory effects of L. donovani and L. major excreted-secreted antigens, particulate and soluble extracts and viable parasites on human dendritic cells

In an experimental model of human monocyte-derived dendritic cells (DCs), the immunophenotype of mature DCs infected with Leishmania donovani and Leishmania major showed a weak decrease in the cell surface expression of CD40, CD86, HLA-DR and DC-SIGN compared with uninfected control DCs. This immunomodulatory effect was more pronounced after stimulation with excreted-secreted antigens (ESA) of both species but absent after stimulation with particulate and soluble extracts. Infection with viable promastigotes, as well as stimulation with ESA from L. donovani and L. major, decreased IL-10 and IL-12p70 secretion. To our knowledge, this is the first direct demonstration that ESA from Leishmania promastigotes can stimulate DCs in the same manner as viable promastigotes.

Efficient expression of a Toxoplasma gondii dense granule Gra4 antigen in tobacco leaves

A His-tagged truncated version of Toxoplasma gondii dense granule 4 protein (Gra4(163-345)) was transiently expressed in tobacco leaves. Two genetic constructions were used to accomplish this goal. In one of them, based in a Potato virus X (PVX) amplicon, the sequence encoding His-Gra4(163-345) was placed under control of an additional PVX coat protein subgenomic promoter. In the other, the same sequence was fused to an apoplastic transport signal and placed under the direction of the cauliflower mosaic virus 35S promoter. His-Gra4(163-345) accumulation in agroinfiltrated tobacco leaves was estimated by Western blot analysis using mouse anti-Gra4 antibody and a seropositive human serum. Here, we demonstrated the feasibility of producing a Gra4 antigen using transient expression methods in plants.

[Development of the recombinant SAG1 antigen of Toxoplasma gondii by high-density fermentation and identification of its immunoreactivity]

OBJECTIVE

To develop a technology for production of recombinant SAG1 of Toxoplasma gondii (T.g) in batches.

METHODS

The rSAG1 of T.g was expressed in E.coli by high-density fermentation and purified by Sephadex G-75 column chromatography after Ni-NTA agarose at native condition. The activity of rSAG1 and its efficacy in T.g diagnosis were identified by Western blotting and ELISA, respectively.

RESULTS

The optical density (OD) of the bacteria reached 20.21 after induction, and 300 g bacteria were harvested from 11.5 L broth. The rSAG1 was highly expressed in E.coli as a fusion protein, accounting for about 25.82% of the total bacterial protein. The purity of rSAG1 reached 98.54% after purification by Ni-NTA combined with Sephadex G-75 column chromatography. Western blotting revealed a distinct band reacting with the sera of rabbits vaccinated by T.g. Twenty-four of the 25 sera of mice infected with T.g and 36 of the 38 sera of human subjects with IgG antibody against T.g were detected by rSAG1-ELISA.

CONCLUSION

A large-scale production of immunoreactive SAG1 of T.g is developed by high-density fermentation and purification with Ni-NTA combined with Sephadex G-75 column chromatography.

Immunological responses to a 39.8kDa Plasmodium vivax tryptophan-rich antigen (PvTRAg39.8) among humans

Tryptophan-rich protein from P. yoelii called PypAg3 had shown protection in a murine model. We describe here its P. vivax orthologue named PvTRAg39.8 which is expressed during schizont stages of the parasite. The transcription initiation site was mapped to the -41 nucleotide position from the first AUG codon and thus established the ORF of PvTRAg39.8 which codes for a 322aa long protein. The sequence of this protein is highly conserved among the P. vivax isolates. Recombinant PvTRAg39.8 was expressed in E. coli, purified to electrophoretic homogeneity, and used for immunological studies. A majority of P. vivax-exposed individuals (90%, n=50) contained antibodies against the recombinant PvTRAg39.8. There was a switching of immunoglobulin isotypes against this antigen from IgG1 to IgG4 among individuals from the acute phase of P. vivax infection to convalescence. The PBMCs of 80% of the total 20 P. vivax-exposed individuals showed proliferation when stimulated with this antigen. The cytokine pattern produced by the PBMCs of the P. vivax-exposed individuals, after stimulation with this antigen, indicated a mixed type of immune response with a distinct bias towards the Th2 anti-inflammatory profile. Because of its high natural immunogenicity, conserved nature, and the protective properties of its P. yoelii counterpart, this protein may be a potential candidate for developing the immunotherapeutic reagents.

Default Pathway of var2csa switching and translational repression in Plasmodium falciparum

Antigenic variation is a subtle process of fundamental importance to the survival of a microbial pathogen. In Plasmodium falciparum malaria, PfEMP1 is the major variable antigen and adhesin expressed at the surface of the infected erythrocyte, which is encoded for by members of a family of 60 var-genes. Peri-nuclear repositioning and epigenetic mechanisms control their mono-allelic expression. The switching of PfEMP1 depends in part on variable transition rates and short-lived immune responses to shared minor epitopes. Here we show var-genes to switch to a common gene that is highly transcribed, but sparsely translated into PfEMP1 and not expressed at the erythrocyte surface. Highly clonal and adhesive P. falciparum, which expressed distinct var-genes and the corresponding PfEMP1s at onset, were propagated without enrichment or panning. The parasites successively and spontaneously switched to transcribe a shared var-gene (var2csa) matched by the loss of PfEMP1 surface expression and host cell-binding. The var2csa gene repositioned in the peri-nuclear area upon activation, away from the telomeric clusters and heterochromatin to transcribe spliced, full-length RNA. Despite abundant transcripts, the level of intracellular PfEMP1 was low suggesting post-transcriptional mechanisms to partake in protein expression. In vivo, off-switching and translational repression may constitute one pathway, among others, coordinating PfEMP1 expression.

Immunogenicity of Plasmodium yoelii merozoite surface protein 4/5 produced in transgenic plants

Malaria is a major global health problem for which effective control measures are urgently needed. Considerable effort has been focused on the development of effective vaccines against the causative parasite and protective vaccine trials are now being reported. Due to the relative poverty and lack of infrastructure in malaria-endemic areas, a successful immunisation strategy will depend critically on cheap and scaleable methods of vaccine production, distribution and delivery. One promising technology is transgenic plants, both as a bioreactor for the vaccine-manufacturing process as well as a matrix for oral immunisation. In this study, we investigated the feasibility of using transgenic plants to induce protective immunity against malaria infection using Plasmodium yoelii merozoite surface protein 4/5 (PyMSP4/5) in a mouse model of malaria infection. Our data show that the PyMSP4/5 protein can be produced in plants in a configuration that reacts with protective antibodies. Optimisation of codon usage for the PyMSP4/5 gene resulted in significantly increased antigen expression in plants. PyMSP4/5 protein from the codon-optimised construct accumulated to 0.25% of total soluble protein, a sixfold increase over the native gene sequence. Tobacco-made PyMSP4/5 was able to induce antigen-specific antibodies in mice following parenteral delivery, as well as boost the antibody responses induced by DNA vaccination when delivered parenterally or orally. We believe this is the first report to show that plant-made malaria antigens are immunogenic. However, the antibody levels were not high enough to protect the immunised mice against a lethal challenge with P. yoelii. Further strategies are needed to achieve a protective dose, including improvements to antigen expression levels in plants and strategies to enhance the immunogenicity of the expressed antigen.

[Glycophorins of human erythrocytes as receptors for the malaria parasite Plasmodium falciparum]

Malaria causes an estimated 300-500 million clinical cases in sub-Saharan Africa and Indochina. The most severe form of malaria is caused by Plasmodium falciparum, a parasite responsible for the death of 2 million children annually. Understanding the molecular basis of the parasite's invasion process is important for the development of new drugs and vaccines. Invasion of erythrocytes by the malaria parasite is a multistep process involving several specific interactions between the parasite's ligands and receptors on red blood cells. It was shown that glycophorins A, B, and C, sialoglycoproteins of human erythrocytes, act as receptors for Plasmodium falciparum ligands of the DBL family: EBA-175 and EBA-140 antigens. The binding specificity of EBA-175 is determined by the presence of sialic acid residues of the O-linked oligosaccharide chain clusters of glycphorin A and the amino-acid sequence, which contribute to their proper conformation. Glycophorin B, the next in terms of amount, can take on the role of glycophorin A as the receptor, but the glycophorin B- and sialic acid-dependent invasion of erythrocytes by Plasmodium falciparum involves a different parasite ligand. The third, and minor, glycophorin C appears to be the receptor for the antigen BAEBL, a paralogue of EBA-175. The binding of BAEBL to glycophorin C is dependent on the sialic acid residues of the O- and N-linked oligosaccharide chains and a peptide as well. It seems that the correct receptor site on glycophorin C needs to be elucidated in detail.

Development of two immunochromatographic tests for the serodiagnosis of bovine babesiosis

In this study, we developed two immunochromatographic tests (ICTs), which are nitrocellulose membrane-based immunoassays for the convenient and rapid serodiagnosis of bovine babesiosis caused by Babesia bovis (BoICT) and Babesia bigemina (BiICT). The efficacy of two ICTs was evaluated using 13 positive sera from experimentally infected cattle with B. bovis or B. bigemina. Clear results showed that the BoICT and ELISA detected antibodies in sera collected from 14 to 93 days post-infection, while BiICT and ELISA detected from 13 to 274 days post-infection. In additon, non-infected cattle, Neospora caninum, and Cryptosporidium parvum were negative in two ICTs. To evaluate the field utility of the ICTs, we tested 186 field bovine sera collected from cattle living in Yanbian (China) and Mato Grosso do Sul (Brazil). The results of ICTs were compared to those of classical serodiagnostic methods, enzyme-linked immunosorbent assay (ELISA) and the indirect immunofluorescence assay (IFAT). The overall concordances of BoICT were determined as 92.5 and 90.3% when the results of ELISA and IFAT were set as the reference standards, respectively. In contrast, those of BiICT showed 96.8 and 92.5% relative to the results of standard ELISA and IFAT, respectively. Conventional and rapid diagnosic devices for bovine babesiosis may provide a valuable tool in clinical and field applications.

Testing of four Leishmania vaccine candidates in a mouse model of infection with Leishmania (Viannia) braziliensis, the main causative agent of cutaneous leishmaniasis in the New World

We evaluated whether four recombinant antigens previously used for vaccination against experimental infection with Leishmania (Leishmania) major could also induce protective immunity against a challenge with Leishmania (Viannia) braziliensis, the species responsible for 90% of the 28,712 annual cases of cutaneous and mucocutaneous leishmaniasis recorded in Brazil during the year of 2004. Initially, we isolated the homolog genes encoding four L. (V.) braziliensis antigens: (i) homologue of receptor for activated C kinase, (ii) thiol-specific antioxidant, (iii) Leishmania elongation and initiation factor, and (iv) L. (L.) major stress-inducible protein 1. At the deduced amino acid level, all four open reading frames had a high degree of identity with the previously described genes of L. (L.) major being expressed on promastigotes and amastigotes of L. (V.) braziliensis. These genes were inserted into the vector pcDNA3 or expressed as bacterial recombinant proteins. After immunization with recombinant plasmids or proteins, BALB/c mice generated specific antibody or cell-mediated immune responses (gamma interferon production). After an intradermal challenge with L. (V.) braziliensis infective promastigotes, no significant reduction on the lesions was detected. We conclude that the protective immunity afforded by these four vaccine candidates against experimental cutaneous leishmaniasis caused by L. (L.) major could not be reproduced against a challenge with L. (V.) braziliensis. Although negative, we consider our results important since they suggest that studies aimed at the development of an effective vaccine against L. (V.) braziliensis, the main causative agent of cutaneous leishmaniasis in the New World, should be redirected toward distinct antigens or different vaccination strategies.

[Isolation of a field strain of Babesia bigemina (Piroplasma: Babesiidae) and establishment of in vitro culture for antigen production]

Isolation of a field strain of Babesia bigemina (Piroplasma: Babesiidae) and establishment of in vitro culture for antigen production. Bovine b abesiosis, caused by Babesia bigemina, is a barrier for livestock development; it results in high economic loss to Mexican livestock. Control requires adequate antigens for diagnosis and vaccination programs. However, because of antigenic variation among Babesia strains, it is necessary to use antigens prepared from local strains. The purpose of the present study was to isolate a local field strain and to establish the in vitro culture of B. bigemina by the evaluation of the constituent's concentration of culture media. Thirty engorged female Boophilus microplus were collected from cattle suffering clinical babesiosis (B. bigemina) in Yucatan state, Mexico. These ticks were sent to the laboratory for detection of Babesia sp. vermicules. Eggs were kept at 83-85 % humidity and 27 degrees C until hatching. Larvae were transferred to an esplenectomized calf (B-1). The resulting nymphs were transferred to an esplenectomized calf (B-2). Twelve days later, B. bigemina (local strain) was detected in calf B-2 and its infected blood was frozen in liquid nitrogen to initiate the in vitro culture. The Microaerophilus Stationary Phase (MASP) in vitro culture method was used to reactivate the parasite. Three different concentrations of culture media (70, 60 and 50%), serum (30, 40 and 50%) and uninfected red blood cells (5, 10 and 15 %) were used in order to know the convenient concentrations to obtain the highest percentage of infected red blood cells (PEI). The cultured strain was used to prepare antigens for the Immunofluorescence Antibody Test (IFAT) and several concentrations of serum and conjugate were tested. Strain isolation was successful; 30 days were needed to obtain a PEI of 1.5%. The isolated strain was frozen in liquid nitrogen and the parasites were reactivated with the in vitro culture MASP method. The concentration of culture media that produced the highest PEI (14%) (p < 0.05) was 30% serum, 70% M199 and 5%. Uninfected Red Blood cells antigens were successfully used in the IFAT and the best dilutions to differentiate between positive and negative controls were serum 1:80 and conjugate 1:80. The isolated B. bigemina local strain requires particular conditions of in vitro culture by the MASP method to reach high numbers of infected red blood cells, needed to prepare and provide high quality antigens for serological diagnosis of B. bigemina.

Identification of a necessary element for Toxoplasma gondii SAG1 gene expression

SAG1 codes for the stage-specific major surface antigen P30 of Toxoplasma gondii (T. gondii) tachyzoites. Six tandemly repeated, conserved 27 bp cassettes in the region from -231 to -70 bp were previously confirmed to be essential for high-level expression of SAG1 and serve as a positioning element directing the initiation of transcription. We demonstrate here that an element located between +19 and +28 bp is necessary for SAG1 gene expression by using deletion mutagenesis analysis and electrophoresis mobility shift assay (EMSA). This will provide an insight into the regulatory mechanisms of SAG1 gene expression.

Comparison of naturally acquired antibody responses against the C-terminal processing products of Plasmodium vivax Merozoite Surface Protein-1 under low transmission and unstable malaria conditions in Sri Lanka

We report here, for the first time, a comparison of naturally acquired antibody responses to the 42 and 19 kDa C-terminal processing products of Plasmodium vivax Merozoite Surface Protein-1 assayed by ELISA using p42 and p19 baculovirus-derived recombinant proteins, respectively. Test populations comprised patients with microscopy confirmed acute P. vivax infections from two regions endemic for vivax malaria where low transmission and unstable malaria conditions prevail, and a non-endemic urban area, in Sri Lanka. The antibody prevalence to the two proteins, both at the individual and population levels, tend to respond more to p42 than to p19 in all test areas, where >14% of individuals preferentially recognized p42, compared with <2% for p19. In patients with no previous exposure to malaria, 21% preferentially recognized p42, whereas none exclusively recognized p19. A significantly lower prevalence of anti-p19 IgM, but not anti-p42 IgM, was observed among residents from endemic areas compared with their non-endemic counterparts. Individuals from both endemic areas produced significantly less anti-p19 IgM compared with anti-p42 IgM. IgG1 was the predominant IgG isotype for both antigens in all individuals. With increasing exposure to malaria in both endemic areas, anti-p19 antibody responses were dominated by the functionally important IgG1 and IgG3 isotypes, with a concurrent reduction in IgM that was lacking in the non-endemic residents. This antibody switch was also reflected for PvAMA-1 as we previously reported with the identical battery of sera. In contrast, the antibody switch for p42 was restricted to endemic residents with more extensive exposure. These results suggest that an IgM-dominated antibody response against the p42 polymorphic region in endemic residents may interfere with the development of an IgG-dominated "protective" isotype shift to p19, that may complicate vaccine development.

[Combined expression of TSO45W-4BX from Taenia solium and porcine CD58 in Escherichia coli]

OBJECTIVE

To express the TSO45W-4BX of Taenia solium in combination with CD58 as a molecular adjuvant for improving the protective efficacy of the TSO45W-4BX recombinant vaccine.

METHODS

TSO45W-4BX and porcine CD58 genes were amplified by PCR, using recombinant plasmids pGEM-4B and pGEM-CD58 as template respectively. The CD58 fragment was inserted into the recombinant plasmid pGEX-4T-1 with directly ligated TSO45W-4BX. The transformant was induced with IPTG and followed by identifying the integrity of the recombinant containing TS045W-4BX and porcine CD58 with PCR and sequencing. The products were analyzed by SDS-PAGE and Western blotting.

RESULTS

The expression products of Mr 69,000 GST-4BX/CD58 and Mr 41,000 GST-4BX were present mainly in the form of inclusion bodies and soluble substance respectively, and both were recognized by sera of cysticercosis patients.

CONCLUSIONS

The TSO45W-4BX co-expressed with porcine CD58 conserves its immune reactivity.

[Expression and bioactivity of S1 scFv antibody against SAG1 of Toxoplasma gondii fused with green fluorescent protein]

OBJECTIVE

To construct, express and purify human scFv antibody (S1) against the recombinant SAG1 of Toxoplasma gondii and fused to green fluorescent protein (GFP), and observe its binding capacity to tachyzoite of Toxoplasma gondii.

METHODS

The GFP gene amplified from vector pEGFP-N1 was subcloned into procaryotic expression vector pET-26b (+), then the S1 scFv antibody gene amplified from phagmid pIT-2-S1 was cloned into downstream of GFP gene. The recombinant plasmid pET-26b-GFPS1 proved by DNA sequencing was transformed into E. coli BL21, and induced for fusion expression of GFPS1 with IPTG, the green fluorescence of E. coli BL21 harboring plasmid pET-26b-GFPS1 was observed under the fluorescence microscope. The expressed GFPS1 was purified with Ni2+ chelating HiTrap HP column, and detected with SDS-PAGE. Toxoplasma tachyzoites were incubated with the recombinant GFPS1, and the binding bioactivity was observed under the fluorescence microscope.

RESULTS

The fused gene of S1 and GFP was successfully cloned into procaryotic expression vector pET-26b proved by DNA sequencing. The green fluorescence of E. coli BL21 harboring plasmid pET-26b-GFPS1 was catched under the fluorescence microscope. The recombinant GFPS1 protein about Mr 53 000 was expressed in E. coli as inclusion body. The immunofluorescence detection verified that anti-rSAG1 scFv antibody S1 could specifically bind outer membrane of Toxoplasma tachyzoite.

CONCLUSIONS

The purified rGFPS1 shows a strong binding capacity to outer membrane of Toxoplasma tachyzoite using GFP as a labeling protein, and the constructed pET-26b-GFP can also be used for research on other targeting molecules.

Usefulness of the recombinant liver stage antigen-3 for an early serodiagnosis of Plasmodium falciparum infection

In order to develop tools for an early serodiagnosis of Plasmodium falciparum infection, we evaluated the usefulness of P. falciparum liver stage antigen-3 (LSA-3) as a serodiagnostic antigen. A portion of LSA-3 gene was cloned, and its recombinant protein (rLSA-3) was expressed in Escherichia coli and purified by column chromatography. The purified rLSA-3 and 120 test blood/serum samples collected from inhabitants in malaria-endemic areas of Mandalay, Myanmar were used for this study. In microscopic examinations of blood samples, P. falciparum positive rate was 39.1% (47/120) in thin smear trials, and 33.3% (40/120) in thick smear trials. Although the positive rate associated with the rLSA-3 (30.8%) was lower than that of the blood stage antigens (70.8%), rLSA-3 based enzyme-linked immunosorbent assay could detect 12 seropositive cases (10.0%), in which blood stage antigens were not detected. These results indicate that the LSA-3 is a useful antigen for an early serodiagnosis of P. falciparum infection.

Inefficient serotype knock down leads to stable coexistence of different surface antigens on the outer membrane in Paramecium tetraurelia

Expression of surface antigens is usually mutually exclusive, meaning that only one protein is present on the cell surface. With the RNAi feeding technology we induce serotype shifts in Paramecium tetraurelia which are demonstrated to be incomplete, meaning that the cells remain in a shifting state. The coexpression of "old" and "new" protein on the surface can be detected to be stable for more than 15 divisions over a 5-day feeding procedure, a time period different from that reported for temperature-induced shifts. A characteristic heterogenic distribution of the different surface antigens is demonstrated by double indirect-immunofluorescent-staining and we show antigen transport mechanisms related to the tips of cilia. Therefore, we discuss release mechanisms, potential sorting mechanisms for glycosylphosphatidylinositol-anchored proteins and the localizations of surface antigens, which are important for the reported classical immobilization reaction.

Determinants of Variant Surface Antigen Antibody Response in Severe Plasmodium falciparum Malaria in an Area of Low and Unstable Malaria Transmission

The variant surface antigens (VSA) of infected erythrocytes are important pathogenic markers, a set of variants (VSA(SM)), were assumed to be associated with severe malaria (SM), while SM constitutes clinically diverse forms, such as, severe malarial anemia (SMA) and cerebral malaria (CM). This study was conducted in Eastern Sudan, an area of seasonal and unstable malaria transmission. Parasites and plasma were obtained from patients with different clinical grades of malaria, and flow cytometry was used for analysis of VSA antibody (Ab) response. We found that individuals recognized a broader range of isolates had a higher level of VSA Ab against the recognized isolates (correlation coefficient, 0.727, P<0.001). Unexpectedly, at the time of malaria diagnosis, plasma from patients with CM recognized a significantly larger number of isolates than did the plasma from patients with SMA (P<0.001). Parasites obtained from patients with SMA or from children were better recognized than isolates obtained from patients with uncomplicated malaria or from adults, P<0.001, P=0.021, respectively. Taken together, the above findings suggest that the limitations in the VSA immunoglobulin G repertoire were most probably contributing to the pathogenesis of SMA but not to that of CM.

Identification of a new spore wall protein from Encephalitozoon cuniculi

Microsporidia form environmentally resistant spores that are critical for their host-to-host transmission and persistence in the environment. The spore walls of these organisms are composed of two layers, the exospore and the endospore. Two spore wall proteins (SWP1 and SWP2) have been previously identified in members of the Encephalitozoonidae family. These proteins localize to the exospore. The endospore is known to contain chitin, and a putative glycosylphosphatidylinositol (GPI)-anchored chitin deacetylase has been localized to the plasmalemma-endospore interface. Using proteomic techniques, we have identified a new spore wall protein (SWP3) that is located in the endospore. The gene for this protein is located on chromosome 1 and corresponds to the open reading frame ECU01_1270. SWP3 is predicted to have a signal peptide and to be GPI anchored. Consistent with these modifications, two-dimensional electrophoresis demonstrated that SWP3 has an acidic pI and a molecular mass of <20 kDa. By immunoelectron microscopy, this protein was found on the cell surface during sporogony and in the endospore in mature spores. SWP3 has several potential O-glycosylation sites, and it is possible that it is a mannosylated protein like the major polar tube protein (PTP1).

Naegleria fowleri: Functional expression of the Nfa1 protein in transfected Naegleria gruberi by promoter modification

To establish a transient transfection system in a Naegleria, we constructed three nfa1-pEGFP-N1 vectors by the promoter replacement and insertion of a nfa1 gene and transfected the DNAs into Naegleria gruberi using a lipid reagent. The transfection efficiency and usefulness of the three modified vectors were estimated by identifying the expressions of the EGFP and Nfa1 protein from N. gruberi. After transfection, the Nfa1 protein was functionally expressed on pseudopodia of N. gruberi. The strong GFP fluorescence was observed in N. gruberi transfected with the actin-nfa1-pEGFP-N1 vector, of which the CMV promoter region in the expression vector was replaced with the actin 5' UTR region. Additionally, when transgenic N. gruberi trophozoites were co-cultured with CHO target cells, the Nfa1 protein was also located on cytoplasm and pseudopodia, especially on a food cup that was formed in contact with target cells as it shown in pathogenic N. fowleri.

Evaluation of enzyme-linked immunosorbent assays, an immunofluorescent-antibody test, and two rapid tests (immunochromatographic-dipstick and gel tests) for serological diagnosis of symptomatic and asymptomatic Leishmania infections in dogs

Enzyme-linked immunosorbent assays (ELISAs) based on soluble antigens derived from promastigote or amastigote-like stages of Leishmania infantum and on the recombinant rK39 antigen, each in combination with different conjugates [anti-immunoglobulin G1 [IgG1], anti-IgG2, anti-IgG(gamma), and anti-IgG heavy plus light chains], were compared to an immunofluorescent-antibody test (IFAT) and two commercially available rapid test systems (DiaMed-Vet-IT Leish and ID-PaGIA canine leishmaniasis antibody test) for the detection of specific anti-Leishmania antibodies in symptomatic and asymptomatic dogs with proven L. infantum infections. ELISAs based on soluble promastigote and amastigote antigens had very high sensitivities in symptomatic (n = 30; 100%) and asymptomatic dogs (n = 17; 94.1 to 100%), except when combined with the anti-IgG1 conjugate (41.2 to 82.4%). Specificities were high for all combinations (n = 50; 96 to 100%). The rK39 ELISA detected fewer asymptomatic cases (sensitivities, 52.9 to 64.7%) but was highly specific (96 to 100%). The IFAT was 90% sensitive in symptomatic dogs but was significantly less sensitive in asymptomatic cases (29.4%). However, it had an excellent specificity (100%). Test performances of the rapid tests based on the rK39 antigen were comparable to the ELISAs based on the same antigen. ELISAs based on soluble promastigote or amastigote antigens seem to be most suited for the serological diagnosis of canine Leishmania infections in both symptomatic and asymptomatic dogs. IFAT and the rK39 ELISA lack sensitivity in asymptomatic cases but are highly specific. Rapid tests like the rK39 dipstick test or the ID-PaGIA are helpful for confirming clinically suspected cases because of their high specificities in symptomatic animals.

[Cloning and expression of the fused gene of rhoptry protein ROP2 and major surface protein P30 from Toxoplasma gondii]

OBJECTIVE

To clone and express the fused gene fragment coding rhoptry protein ROP2 and major surface protein P30 from Toxoplasma gondii as a preparation for the construction of the complex ROP2-P30 antigen by gene engineering.

METHODS

The gene fragment encoding P30 was amplified by PCR from T. gondii RH strain and subcloned into the recombinant plasmid pUC119/ROP2 already constructed. The recombinant plasmid pUC119/ROP2-P30 was digested by Sac I/HindIII and inserted into the same site of expression vector pET28b. The recombinant plasmid of pET28b/ROP2-P30 was transformed to E. coli and expressed under the induction of IPTG.

RESULTS

The gene fragment 700 bp encoding P30 was obtained from the total DNA of T. gondii by PCR. The recombinant plasmid pET28b/ROP2-P30 was successfully constructed, which was highly expressed in E. coli, a fusion protein with molecular weight of 69000.

CONCLUSION

The fusion gene encoding the rhoptry protein ROP2 and the major surface protein P30 of T. gondii has been successfully cloned and expressed to be an expected recombinant fusion protein ROP2-P30 with molecular weight 69000.

Use of full-length recombinant calflagin and its c fragment for improvement of diagnosis of Trypanosoma cruzi infection

Serological diagnosis of Trypanosoma cruzi infection is hampered by issues related to test specificity due to the cross-reactivity of most antigens with proteins of related parasites such as Leishmania spp. The recombinant calflagins are considered relevant antigens for the diagnosis of infection by Trypanosoma cruzi. In the present work, we describe two genes coding for putative calflagins in Leishmania major with the N-terminal moieties presenting high similarity with T. cruzi genes. This fact raised questions about their role in some cross-recognition of this antigen by sera from Leishmania spp.-infected individuals. The complete T. cruzi calflagin and two fragments of the protein, consisting of 146 amino acids of the N-terminal and 65 amino acids of the C-terminal regions, were expressed and evaluated against a panel of sera, which included well-characterized samples from T. cruzi, and Leishmania-infected patients. We were able to show that sera from Leishmania (Viannia) braziliensis-infected individuals recognized the recombinant full-length calflagin. Both the N-terminal and the complete protein presented the same high sensitivity (98.5% of sera from T. cruzi-infected patients was detected) but different specificities (94% and 98%, respectively, when evaluated against sera from people not infected by T. cruzi, including 15 sera from people infected with L. braziliensis). The C-terminal fragment presented low sensitivity (70%) but 100% specificity. We propose the use of these antigens in two sequential assays to optimize the serological diagnosis of T. cruzi infection in humans in geographic areas where Leishmania spp. infection is coendemic.

Plasmodium yoelii: axenic development of the parasite mosquito stages

Study of the parasite mosquito stages of Plasmodium and its use in the production of sporozoite vaccines against malaria has been hampered by the technical difficulties of in vitro development. Here, we show the complete axenic development of the parasite mosquito stages of Plasmodium yoelii. While we demonstrate that matrigel is not required for parasite development, soluble factors produced and secreted by Drosophila melanogaster S2 cells appear to be crucial for the ookinete to oocyst transition. Parasites cultured axenically are both morphologically and biologically similar to mosquito-derived ookinetes, oocysts, and sporozoites. Axenically derived sporozoites were capable of producing an infection in mice as determined by RT-PCR; however, the parasitemia was significantly much less than that produced by mosquito-derived sporozoites. Our cell free system for development of the mosquito stages of P. yoelii provides a simplified approach to generate sporozoites that may be for biological assays and genetic manipulations.

Phenotype and homing of CD4 tumor-specific T cells is modulated by tumor bulk

Technical difficulties in tracking endogenous CD4 T lymphocytes have limited the characterization of tumor-specific CD4 T cell responses. Using fluorescent MHC class II/peptide multimers, we defined the fate of endogenous Leishmania receptor for activated C kinase (LACK)-specific CD4 T cells in mice bearing LACK-expressing TS/A tumors. LACK-specific CD44(high)CD62L(low) CD4 T cells accumulated in the draining lymph nodes and had characteristics of effector cells, secreting IL-2 and IFN-gamma upon Ag restimulation. Increased frequencies of CD44(high)CD62L(low) LACK-experienced cells were also detected in the spleen, lung, liver, and tumor itself, but not in nondraining lymph nodes, where the cells maintained a naive phenotype. The absence of systemic redistribution of LACK-specific memory T cells correlated with the presence of tumor. Indeed, LACK-specific CD4 T cells with central memory features (IL-2(+)IFN-gamma(-)CD44(high)CD62L(high) cells) accumulated in all peripheral lymph nodes of mice immunized with LACK-pulsed dendritic cells and after tumor resection. Together, our data demonstrate that although tumor-specific CD4 effector T cells producing IFN-gamma are continuously generated in the presence of tumor, central memory CD4 T cells accumulate only after tumor resection. Thus, the continuous stimulation of tumor-specific CD4 T cells in tumor-bearing mice appears to hinder the systemic accumulation of central memory CD4 T lymphocytes.