Immunological approaches for the control of fasciolosis

Sigma-Class Glutathione Transferases (GSTσ): A New Target with Potential for Helminth Control

Glutathione transferases (GSTs EC 2.5.1.18) are critical components of phase II metabolism, instrumental in xenobiotics' metabolism. Their primary function involves conjugating glutathione to both endogenous and exogenous toxic compounds, which increases their solubility and enables their ejection from cells. They also play a role in the transport of non-substrate compounds and immunomodulation, aiding in parasite establishment within its host. The cytosolic GST subfamily is the most abundant and diverse in helminths, and sigma-class GST (GSTσ) belongs to it. This review focuses on three key functions of GSTσ: serving as a detoxifying agent that provides drug resistance, functioning as an immune system modulator through its involvement in prostaglandins synthesis, and acting as a vaccine antigen.

The Epidemiology and Control of Liver Flukes in Cattle and Sheep

Fasciola hepatica, Fasciola gigantica, and Fascioloides magna are liver flukes causing disease in cattle and sheep. Damage to the liver due to F hepatica and F gigantica results in clinical disease and/or production losses. F magna seems to have little effect in cattle but causes high mortality in sheep. The fluke life cycle involves an aquatic or amphibious snail intermediate host and thus requires suitable moisture and temperature conditions. F magna requires the presence of deer. Drug treatment is the mainstay of control and needs to be applied considering the life cycle and epidemiology of the parasite.

Immunization with the recombinant myosin regulatory light chain (FhrMRLC) in Adjuplex® adjuvant elicits a Th1-biased immune response and a reduction of parasite burden in Fasciola hepatica infected rats

The aim of this study was to assess the immune response and the protective efficacy elicited by the vaccination with the recombinant Fasciola hepatica myosin regulatory light chain (FhrMRLC) in Adjuplex® adjuvant against the infection with F. hepatica in rats. Four groups of 15 animals each were used for the study, one group was immunized with the recombinant F. hepatica MRLC in Adjuplex® adjuvant and the other groups remained as adjuvant, positive and negative control groups. The parasitological study showed that a statistically significant reduction of 65.1% and 82.1% in fluke burden and fecal egg count, respectively, was detected in vaccinated animals. In addition, vaccination with FhrMRLC induced a well-defined humoral and cellular immune response characterized by a significant production of specific IgG and IL-2, IL-12, TNF-α and IFN-γ; which confirms the immunogenic capacity of the FhrMRLC.

Feline platynosomiasis: analysis of the association of infection levels with pathological and biochemical findings

Abstract Platynosomiasis is a common feline hepatic disease caused by Platynosomum fastosum (Trematoda - Dicrocoelidae), which is also known as ‘lizard poisoning’. Most reports of feline platynosomiasis show that this disease is sporadic and manifests with uncommon lesions; its pathogenicity is still not well understood. This study aimed to describe liver injuries and enzymatic changes associated with natural P. fastosum infection in 47 stray cats in an endemic area. Overall, 38.3% (18/47) of cats were parasitized, and 2,358 flukes (P. fastosum) were collected (131 – mean intensity of parasitism; 50.2 – mean abundance). The alanine transaminase (ALT) measure was significantly higher in parasitized animals, while alkaline phosphatase (ALP) showed no statistical difference between parasitized and non-parasitized animals. In infected animals, gross pathological lesions and microscopic liver injuries ranged from mild to severe, and were similar to those in previous descriptions of feline platynosomiasis. Nonetheless, the intensity of parasitism was not related to the severity of macroscopic or microscopic hepatic injuries. However, feline platynosomiasis should be considered in the differential diagnosis of feline liver disorders, as well as, in any program of helminth control, even if no clinical abnormalities are present.

Exploring and Expanding the Fatty-Acid-Binding Protein Superfamily in Fasciola Species

The liver flukes Fasciola hepatica and F. gigantica infect livestock worldwide and threaten food security with climate change and problematic control measures spreading disease. Fascioliasis is also a foodborne disease with up to 17 million humans infected. In the absence of vaccines, treatment depends on triclabendazole (TCBZ), and overuse has led to widespread resistance, compromising future TCBZ control. Reductionist biology from many laboratories has predicted new therapeutic targets. To this end, the fatty-acid-binding protein (FABP) superfamily has proposed multifunctional roles, including functions intersecting vaccine and drug therapy, such as immune modulation and anthelmintic sequestration. Research is hindered by a lack of understanding of the full FABP superfamily complement. Although discovery studies predicted FABPs as promising vaccine candidates, it is unclear if uncharacterized FABPs are more relevant for vaccine formulations. We have coupled genome, transcriptome, and EST data mining with proteomics and phylogenetics to reveal a liver fluke FABP superfamily of seven clades: previously identified clades I-III and newly identified clades IV-VII. All new clade FABPs were analyzed using bioinformatics and cloned from both liver flukes. The extended FABP data set will provide new study tools to research the role of FABPs in parasite biology and as therapy targets.

Liver fluke vaccines in ruminants: strategies, progress and future opportunities

The development of a vaccine for Fasciola spp. in livestock is a challenge and would be advanced by harnessing our knowledge of acquired immune mechanisms expressed by resistant livestock against fluke infection. Antibody-dependent cell-mediated cytotoxicity directed to the surface tegument of juvenile/immature flukes is a host immune effector mechanism, suggesting that antigens on the surface of young flukes may represent prime candidates for a fluke vaccine. A Type 1 immune response shortly after fluke infection is associated with resistance to infection in resistant sheep, indicating that vaccine formulations should attempt to induce Type 1 responses to enhance vaccine efficacy. In cattle or sheep, an optimal fluke vaccine would need to reduce mean fluke burdens in a herd below the threshold of 30-54 flukes to ensure sustainable production benefits. Fluke infection intensity data suggest that vaccine efficacy of approximately 80% is required to reduce fluke burdens below this threshold in most countries. With the increased global prevalence of triclabendazole-resistant Fasciolahepatica, it may be commercially feasible in the short term to introduce a fluke vaccine of reasonable efficacy that will provide economic benefits for producers in regions where chemical control of new drug-resistant fluke infections is not viable. Commercial partnerships will be needed to fast-track new candidate vaccines using acceptable adjuvants in relevant production animals, obviating the need to evaluate vaccine antigens in rodent models.

Antigenic components, isolation and partial characterization of excretion-secretion fraction of Paramphistomum cervi

The immunogenic components of adult Paramphistomum cervi excretion-secretion (ES) fraction were revealed by SDS-PAGE and immunoblotting technique using sera from cattle naturally infected with P. cervi, Fasciola gigantica, strongylids, Trichuris sp., and Strongyloides sp. By SDS-PAGE, it was found that the ES fraction comprised 13 distinct protein bands. Immunoblotting analysis of these proteins exhibited nine prominent antigenic bands which were recognized by paramphistomosis antisera. These antigenic proteins had molecular weights ranging from 10-170 kDa. One antigenic protein band of 40 kDa was found to give a consistent reaction with sera from all infected cattle. Its diagnostic sensitivity, specificity and accuracy using this test were 100%, 98.9% and 99.3%, respectively. The positive and negative predictive values were 98% and 100%, respectively. The 40 kDa antigen was partially purified by gel filtration and ion-exchange chromatography. The antigenicity of 40 kDa protein for diagnosis of P. cervi infection was confirmed by immunoblotting and indirect ELISA (at 1:78,125 dilution) using a pool of sera and individual serum samples from infected cattle. The present findings suggest that the 40 kDa protein may be used as a diagnostic antigen for paramphistomosis.

IL-10 and TGF-beta1 are associated with variations in fluke burdens following experimental fasciolosis in sheep

Infection with Fasciola hepatica causes an economically important disease in ruminants. Variability in parasite load may indicate innate differences in the host immune system. This study aimed to investigate the immunological mechanisms that are associated with variability in parasite burden following experimental F. hepatica infection in cross-bred sheep. Of a total of 16 animals, four were randomly chosen as uninfected controls, and the remainder infected with 100 viable metacercariae. Uninfected animals were used as the control group for evaluation of cytokine gene expression levels. For comparative analysis, specific animals were selected on the basis of extremes of fluke burdens, and were categorised into light (n = 4) and heavy burdened (n = 3) cohorts. Serum antibody levels, haematological parameters, and expression of IL-4 and IFN-gamma genes in hepatic lymph nodes were equivalent in both groups. However, significant differences in mitogen-specific lymphocyte proliferation in vitro and in expression of TGF-beta1 and IL-10 genes in hepatic lymph nodes were observed at acute and chronic phases of infection, respectively. These results provide useful information in developing further understanding of natural resistance to fasciolosis in sheep.

Bovine fasciolosis: prevalence, effects of treatment on productivity and cost benefit analysis in five districts of Punjab, Pakistan

The present study reports the prevalence, effects of treatment and cost benefit analysis of bovine fasciolosis in five districts of Punjab Province viz Sargodha, Jhang, Muzaffargarh, Lodhran and Layyah. From each of the five districts, 80 animals were selected and fortnightly screened through standard coprological procedures for a period of one year for the presence of eggs of Fasciola species. Of 4800 faecal samples analyzed, 1222 (25.46%) were found positive for fasciolosis. The occurrence of Fasciola (F.) gigantica (22.40%) was higher (P<0.05) than F. hepatica (3.06%). Highest month-wise prevalence (P<0.05) of fasciolosis was found in winter (39.08%) followed in decreasing order by spring (29.50%), autumn (20.33%) and summer (12.92%). District-wise prevalence of fasciolosis was highest (P<0.05) in Sargodha (40.31%) and lowest in Layyah (11.77%) while other districts were having intermediate values of prevalence of fasciolosis. Species-wise prevalence of fasciolosis was found higher (P<0.05) in buffaloes (30.50%) as compared to cattle (20.42%). However, there were no age and sex-related differences (P>0.05) in prevalence of fasciolosis. A strong positive association of grazing (OR=1.81), mixed farming of small and large ruminants (OR=1.39), stagnant pond bathing (OR=2.24) and river/canal bathing (OR=2.06) was found with the prevalence of fasciolosis as compared to stall feeding, separate farming of small and large ruminants and rivers/canal/tap water bathing, respectively. Post-treatment average milk increase of 0.62 L per animal per day with 0.35% higher fat was observed in fasciolicide-treated animals with the cost benefit ratio of 3.9. The results provided significant data on the epidemiology of five districts of Punjab province which may be helpful for the planners and small holder dairy farmers for control of fasciolosis in the study districts.

A study of the liver of goats immunized with a synthetic peptide of the Sm14 antigen and challenged with Fasciola hepatica

A synthetic peptide of the Sm14 antigen of Schistosoma mansoni was used to immunize goats against experimental challenge with Fasciola hepatica. The goats used consisted of: group 1 (unimmunized and uninfected [controls]); group 2 (unimmunized and infected); group 3 (immunized and infected). Compared with group 2, the animals of group 3 showed at necropsy a reduction in hepatic worm burden; however, because of variability in the two groups this reduction was not statistically significant. A gross morphometric study of the hepatic changes revealed a correlation between lesions and worm burdens in group 3. No significant differences in damaged areas were found between groups 2 and 3, except that group 2 had more severe bile duct hyperplasia. A striking hepatic inflammatory infiltration of CD3+ T lymphocytes and IgG+ plasma cells was found in both groups 2 and 3, especially the latter.

Discovery and validation of serum biomarkers expressed over the first twelve weeks of Fasciola hepatica infection in sheep

Serum biomarkers associated with Fasciola hepatica infection of Corriedale sheep were analysed during the first 12 weeks of infection using surface-enhanced laser desorption ionisation time of flight mass spectrometry (SELDI-TOF MS). In the discovery phase of analysis, pooled sera collected at week 0 and at each week p.i. to week 12 were fractionated by anion-exchange chromatography and the protein mass fingerprints obtained in individual fractions were in the M/z range 1.5-150 kDa. A total of 2302 protein clusters (peaks) were identified that varied between time-points following infection with peaks increasing or decreasing in intensity, or showing transient variation in intensity, during the 12 weeks of parasite challenge. In the validation phase, candidate biomarkers in sera of individual sheep at weeks 3 and 9 p.i. were analysed, identifying 100 protein peaks, many of which are small peptides <10 kDa in size: 54% of these peaks were up-regulated in intensity at week 3 or 9 p.i. Twenty-six biomarkers were chosen for further study, ranging in size from 1832 to 89,823 Da: six biomarkers were up-regulated at weeks 3 and 9 p.i., 16 biomarkers were up-regulated only at week 9 p.i. and four biomarkers were down-regulated at week 9 p.i. Two biomarkers up-regulated at week 9 were identified as transferrin (77.2 kDa) and Apolipoprotein A-IV (44.3 kDa), respectively. The results show that the interaction between the host and F. hepatica is complex, with changes in biomarker patterns beginning within 3 weeks of infection and either persisting to weeks 9-12 or showing transient changes during infection. Identification of biomarkers expressed during ovine fasciolosis may provide insights into mechanisms of pathogenesis and immunity to Fasciola and may assist in the rational development and delivery of vaccines.

Partial purification and characterization ofGigantocotyle explanatumsomatic antigens

Soluble extracts ofGigantocotyle explanatum, isolated from the liver of buffaloBubalus bubaliswere fractionated on Sephadex G-200 columns. Nine major fractions referred to as F1, F2, F3, F4, F5, F6, F7, F8 and F9 were separated. Each fraction was tested by ELISA for antigenicity using sera fromG. explanatum-infected field buffaloes. Fractions F1 and F2 were highly antigenic, F3, F4, F6 and F7 were moderately antigenic and F5, F8 and F9 were poorly antigenic. Analyses by SDS–PAGE revealed that each fraction comprised several polypeptide(s) in the molecular weight range of <29 to >205 kDa. Results of Western blotting indicated that not all polypeptides which appeared in the SDS–PAGE were antigenic. The antigenic molecules of each fraction were mostly in the low molecular weight range of <14 to >94 kDa with the polypeptides in the range of >14, 14, 18, 21–25 and 34–36 kDa.

Peritoneal lavage cells of Indonesian thin-tail sheep mediate antibody-dependent superoxide radical cytotoxicity in vitro against newly excysted juvenile Fasciola gigantica but not juvenile Fasciola hepatica

Indonesian thin-tail (ITT) sheep resist infection by Fasciola gigantica by an immunological mechanism within 2 to 4 weeks of infection yet are susceptible to F. hepatica infection. Studies of ITT sheep show that little liver damage occurs following F. gigantica infection, suggesting that the invading parasites are killed within the peritoneum or shortly after reaching the liver. We investigated whether cells isolated from the peritoneums of ITT sheep could kill newly excysted juvenile F. gigantica in vitro and act as a potential mechanism of resistance against F. gigantica infection. Peritoneal cells from F. gigantica-infected sheep, rich in macrophages and eosinophils, mediated antibody-dependent cytotoxicity against juvenile F. gigantica in vitro. Cytotoxicity was dependent on contact between the parasite and effector cells. Isolated mammary gland eosinophils of F. gigantica-infected sheep, or resident peritoneal monocytes/macrophages from uninfected sheep, also killed the juvenile parasites in vitro. By using inhibitors, we show that the molecular mechanism of killing in these assays was dependent on the production of superoxide radicals by macrophages and eosinophils. In contrast, this cytotoxic mechanism was ineffective against juvenile F. hepatica parasites in vitro. Analysis of superoxide dismutase activity and mRNA levels showed that activity and gene expression were higher in F. hepatica than in F. gigantica, suggesting a possible role for this enzyme in the resistance of F. hepatica to superoxide-mediated killing. We suggest that ovine macrophages and eosinophils, acting in concert with a specific antibody, may be important effector cells involved in the resistance of ITT sheep to F. gigantica.

Host responses during experimental infection with Fasciola gigantica or Fasciola hepatica in Merino sheep I. Comparative immunological and plasma biochemical changes during early infection

This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in Merino sheep during the first 10 weeks of infection with Fasciola gigantica and Fasciola hepatica. One group of sheep were uninfected, four groups of sheep received incremental challenge doses of F. gigantica metacercariae (50, 125, 225 and 400, respectively) and the sixth group was challenged with 250 F. hepatica metacercariae. At 10 weeks post infection (wpi), sheep challenged with F. hepatica showed the greatest fluke recovery (mean 119, range 84-166); a significantly higher biomass of parasites recovered (2.5-fold greater than the highest dose of F. gigantica); and a greater mean % parasite recovery (39.3%, range 27-55%) than any group challenged with F. gigantica. Within the groups dosed with F. gigantica a strong dose-dependent response was observed in both fluke recovery and fluke biomass with increasing dose of metacercariae. The mean % parasite recovery of F. gigantica infected groups 1-5 were 26, 23, 26 and 25%, respectively, suggesting a uniform viability of parasite establishment independent of infection dose. At 6 wpi, elevated levels of plasma GLDH were observed in the F. gigantica infected groups compared to the uninfected sheep (p<0.005) whereas the F. hepatica challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p<0.001). Elevated levels of GGT as an indicator of epithelial damage in the bile duct was only seen in the group challenged with F. hepatica at 10 wpi when it rose from below 100 IU/l to approximately 250 IU/l (p<0.0001) whereas no detectable increase in GGT was observed in any of the groups challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a second peak at 9 wpi, corresponding to the period of migration of juvenile fluke in the liver and the time when adult flukes are migrating into the bile duct, respectively. This biphasic response was also evident in the changes in the eosinophil counts and serum haemoglobin levels. There was a trend toward higher parasite-specific IgG2 titres in sheep infected with lower worm burdens, suggesting that higher F. gigantica or F. hepatica burdens suppress IgG2 responses. The findings of this study suggest that, in early infection in a permissive host, F. hepatica appears to be more pathogenic than F. gigantica because of its rapid increase in size and the speed of its progression through the migratory phases of its life cycle.

Molecular and immunological characterization of encoding gene and 14-3-3 protein 1 in Fasciola gigantica

A cDNA encoding Fg14-3-3 protein 1 was cloned by immunoscreening of an adult-stage Fasciola gigantica cDNA library using a rabbit antiserum against tegumental antigens of the parasite. The protein has a deduced amino acid sequence of 252 residues and a calculated molecular weight of 28.7 kDa. It shows sequence identity values between 57.6 and 58.1% to the human 14-3-3 beta, zeta, theta, and eta proteins and is in a phylogenetic cluster with the 14-3-3 protein 1 of Schistosoma spp. Nucleic acid analyses indicate that the Fg14-3-3 protein 1 is encoded by a single copy gene and that this gene is expressed as a transcript of 1250 nucleotides. In adult and 4-week-old parasites the gene's transcriptional and translational products were localized in the gut epithelium, parenchyma, tegument cells, and in the reproductive organs. An antiserum against recombinant Fg14-3-3 protein 1 detected a slightly smaller 14-3-3 protein in the parasite's excretion/secretion material and showed cross-reactivity with 14-3-3 proteins in extracts of other trematodes and mouse. Antibodies against Fg14-3-3 protein were detected in the sera of rabbits as early as 2 weeks after infection with metacercariae of F. gigantica and the antibody titre increased continuously over a 10-week observation period.

Characterization of specific and cross-reacting antigens of Fasciola gigantica by immunoblotting

Somatic antigens of F. gigantica, G. explanatum, S. spindale and hydatid cyst ingredients were analysed to identify the cross-reactive antigens among them using Western blot technique. When probed with F. gigantica infected cattle sera, the immunodominant 156 kDa and 28 kDa proteins of F. gigantica was found common amongst the antigens prepared from hydatid cysts ingredients like germinal layer, fertile and sterile, hydatid fluid, fertile and sterile, while another protein of 34 kDa was shared between F. gigantica and antigen prepared from protoscolices. In F. gigantica-buffalo system the proteins of 34 kDa and 28 kDa were found reactive with most of the antigens tested. Immunoaffinity chromatography using, F. gigantica infected rabbit immunoglobulins as legands isolated the immunodominant 34 kDa and 28 kDa proteins in dimer form and the same were found immunodominant in F. gigantica-cattle, F. gigantica-buffalo and F. gigantica-sheep system. No cross-reaction was noted with the sera of goats experimentally infected with Paramphistomum epiclitum. ELISA with the immunodominant proteins of 34 kDa and 28 kDa could be a feasible diagnostic tool for the early detection of bovine fasciolosis.

Comparison of modulation of sheep, mouse and buffalo lymphocyte responses by Fasciola hepatica and Fasciola gigantica excretory-secretory products

In order to explain the difference in susceptibility to Fasciola hepatica and F. gigantica between animal species, the activity of their excretory-secretory products (FhESP and FgESP, respectively) on concanavalin A (ConA)-induced proliferation of different animal species (sheep, mouse and buffalo) lymphocytes was compared. At high doses, FhESP inhibited proliferation of lymphocytes of all the animal species tested, and at low doses they inhibited the proliferation of sheep lymphocytes and increased the proliferation of buffalo and mouse lymphocytes. The effects of FgESP were similar but the intensity of FgESP inhibition was less than FhESP. The immunomodulatory effects of FhESP or FgESP could not alone explain the susceptibility level of hosts to Fasciola spp. The immunomodulatory molecules of FhESP and FgESP and their role in the course of Fasciola spp. infection should be further investigated.

Immunology of the host–parasite relationship in fasciolosis (Fasciola hepaticaandFasciola gigantica)

The protective resolution of liver fluke (Fasciola hepatica and Fasciola gigantica) infection is a dynamic interplay between the host's effector responses and the parasite's defence and immunomodulatory systems. The evidence suggests that the juvenile or immature parasite is the target of protective host immune responses but the effector mechanisms employed vary between hosts. Moreover, F. hepatica and F. gigantica differ in their susceptibility to these killing mechanisms. In the rat, in vitro killing of juvenile F. hepatica involves an antibody-dependent cell cytotoxicity mediated by nitric oxide produced by activated monocytes and (or) macrophages. However, monocytes and (or) macrophages from Indonesian sheep do not produce nitric oxide yet can effectively kill juvenile F. gigantica in vitro and in vivo by a mechanism that is ineffective against F. hepatica. These data show that disease progression or resolution in fasciolosis is determined both by biochemical differences between Fasciola species and by host-dependent factors. Understanding the genetic basis for these differences is a key question for the future. Fasciola hepatica and F. gigantica actively modulate the host immune response, downregulating type 1 responses during infection. It is important to determine whether such modulation of the immune response by Fasciola spp. directly leads to enhanced parasite survival in the various hosts.

Exploiting natural immunity to helminth parasites for the development of veterinary vaccines

The development of subunit vaccines against most parasitic helminth infections will require a better understanding of the different components of a natural rejection process including (1) recognition of parasite antigens; (2) induction of protective immune response phenotypes; and (3) activation of appropriate immune effector mechanisms. While novel technologies have allowed significant progress to be made in the identification of candidate vaccine antigens, the large scale production of these antigens and their presentation to the host with appropriate adjuvant systems remains a major problem in vaccine research. Identification of the molecular interactions involved in the innate immune response to helminth infections and the application of new genomic and proteomic technologies are likely to lead to major advances in these research fields. Gastrointestinal nematode parasites and liver fluke are the most important helminth parasites of production animals. In recent years, a lot of new knowledge has been gathered on the immunobiology of the host-parasite interactions in these two infection systems, which has allowed new vaccination strategies to be considered. Functional genomic technologies such as gene expression analysis by microarrays, promise to further advance our understanding of the molecular pathways leading to protection against parasite infections. This will not only have implications for vaccine research, but also provide novel targets for drug development and genetic selection.

Detection of circulating 54kDa antigen in sera of bovine calves experimentally infected with F. gigantica

The antibody response and circulating antigen levels in bovine calves, infected experimentally with Fasciola gigantica, were monitored using enzyme-linked immunoelectrotransfer blot (EITB) and sandwich ELISA, respectively. By EITB, the infected calves' sera recognized the polypeptides in the range of 54-58 kDa as early as 2 weeks post-infection. By 12th week post-infection, the lower two polypeptides of 12 and 8 kDa had disappeared. In sandwich ELISA, the circulating 54 kDa and whole worm antigen of F. gigantica were detected in the sera samples of infected calves as early as 2 weeks post-infection and persisted until the end of experiment (26th week PI). The 54 kDa antigen of F. gigantica appears to be specific and possesses promising immunodiagnostic potential for early prepatent diagnosis of bovine fasciolosis.

Failure of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental Fasciola hepatica infection

The potential of a recombinant Schistosoma bovis 28-kDa glutathione S-transferase (rSb28GST) to protect cattle against Fasciola hepatica was tested in a vaccination trial. Thirty two calves were randomly divided into four groups of eight animals. Calves of the three vaccine groups received two intramuscular injections at 3 weeks interval, of 0.250mg rSb28GST in either aluminium hydroxide (Al(OH)(3)), Quil A, or PBS emulsified in an equal volume of Freund's complete adjuvant (FCA).Animals of the control group received injections of Al(OH)(3)/PBS only. All animals were challenged orally with a total of 360 metacercariae of F. hepatica, spread over 6 weeks. All groups of vaccinated animals produced measurable IgG antibody titers to rSb28GST after vaccination. Animals immunised with FCA adjuvanted vaccine had the highest and more durable antibody titers and only sera from this group recognised an approximately 24kDa protein band from F. hepatica, that is thought to be a F. hepatica GST. Despite a good antibody response differences in cumulative faecal egg output between the groups were not statistically significant. In addition, no significant difference was found between groups in terms of total worm numbers or percentage of immature flukes recovered at necropsy. In conclusion, the recombinant S. bovis 28kDa GST was not found to adequately protect cattle against experimental F. hepatica challenge, using either aluminium hydroxide, Quil A or FCA as adjuvant.

Cloning and partial characterization of a Boophilus microplus (Acari: Ixodidae) glutathione S-transferase

A cDNA of glutathione S-transferase (GST) was isolated from a cDNA library of salivary glands of Boophilus microplus. The recombinant protein was purified by glutathione affinity chromatography and assayed upon the chromogenic substrate CDNB. The 864 bp cloned fragment was sequenced and showed an open reading frame coding for a protein of 220 amino acids. Expression of the GST gene was tested by RT-PCR in tick tissues and larvae mRNA. Comparison of the deduced amino acid sequence with GSTs from other species revealed that the enzyme is closely related to the mammalian class mu GSTs.

Expression and characterisation of a Psoroptes ovis glutathione S-transferase

The astigmatid mite Psoroptes ovis is the causative agent of sheep scab, a highly contagious parasitic disease of sheep. Infection causes severe allergic dermatitis, resulting in damage to the fleece and hide, loss of condition and occasional mortality. Interest in the P. ovis allergens led us to characterise a glutathione S-transferase (GST) which displays homology to GST allergens isolated from the house dust mite, Dermatophagoides pteronyssinus and the cockroach, Blatella germanica. A cDNA encoding a mu-class GST from P. ovis was expressed in Escherichia coli and the recombinant protein purified for biochemical analysis. SDS-PAGE analysis indicated that the purified product was homogeneous and had an apparent molecular weight of 30 kDa. The recombinant GST (rGST) is active towards the substrate 1-chloro-2,4-dinitrobenzene (CDNB), whereas 1,2-dichloro-4-nitrobenzene (DCNB) is a poor substrate. The recombinant protein was also tested for recognition by IgE and IgG antibodies in serum from P. ovis naïve and P. ovis infested sheep. Neither IgE nor IgG antibodies were detected to the rGST. Prausnitz--Küstner testing with rGST did not provoke a characteristic weal and flare response. Biopsies collected at the PK test sites were stained for eosinophils, neutrophils, mast cells and basophils. Neutrophil, mast cell and basophil counts were not significantly different to the controls. Eosinophil numbers were significantly higher than controls, but were not due to an IgE response.

Vaccination of sheep against Fasciola hepatica with homologous fatty acid binding proteins

The current study was designed to test the immunoprophylactic properties of native (nFh12) and recombinant (rFh15) antigens from Fasciola hepatica in sheep subsequently infected with the fluke. Thirty lambs were divided into six groups according to various patterns of immunisation and times of infection and necropsy. The antigens were emulsified in Freund's adjuvant. Levels of specific anti-nFh12 and anti-rFh15 antibodies rose rapidly by 2 weeks after the first immunisation and were always significantly higher in immunised-infected sheep than in control-infected sheep. On completion of the trial there was no difference in fluke burden between groups vaccinated with either of the antigens and non-immunised controls. However, worm size and faecal egg counts were significantly diminished in the sheep vaccinated with either of the antigens, suggesting an anti-fecundity effect. This is the first report of experimental vaccination of sheep against F. hepatica with purified native and recombinant antigens related to fatty acid binding proteins.

The liver flukes Fasciola gigantica and Fasciola hepatica express the leucocyte cluster of differentiation marker CD77 (globotriaosylceramide) in their tegument

Glycosphingolipids from the parasitic liver flukes Fasciola gigantica and Fasciola hepatica were isolated and their carbohydrate moieties were structurally analysed by methylation analysis, exoglycosidase treatment, on-target exoglycosidase cleavage and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. For both liver fluke species, the ceramide monohexosides Gal1-ceramide and Glc1-ceramide were found in relative amounts of 1.0 to 0.1, respectively. From F. gigantica, the ceramide dihexoside was isolated in sufficient amounts to be structurally determined as lactosylceramide, Gal beta4-Glc1-ceramide, while for both liver fluke species the ceramide trihexoside was shown to be Gal alpha4Gal beta4-Glc1-ceramide, which is designated as either globotriaosylceramide, Pk-blood group antigen or CD77 leucocyte cluster of differentiation antigen. To our knowledge, this is the first report on the expression of globo-series glycosphingolipids in non-mammalian species. Ceramide analysis of ceramide monohexosides yielded as major components octadecanoic and 2-hydroxyoctadecanoic fatty acids together with C18- and C20-phytosphingosines. By the use of an anti-CD77 monoclonal antibody and the Escherichia coli Shiga toxin B1 subunit, globotriaosylceramide could be immunolocalised to the tegument of F. hepatica cryosections. The sharing of CD77 between liver flukes and their mammalian hosts fits in with the concept of molecular mimicry, which is closely parallel to the established imitation of host CD15 (Lewis X) displayed by the blood fluke Schistosoma mansoni.

Humoral immune response in calves to single-dose, trickle and challenge infections with Fasciola hepatica

In cattle experimentally infected with Fasciola hepatica, parasite specific IgG1 and IgG2 responses were studied. Additionally parasite specific IgE production was assessed by the Passive Cutaneous Anaphylaxis reaction. The primary infection was administered either as a single-dose or as a trickle infection over a 4-week period. Animals were challenged 4 months later. Titres of IgG1 and IgG2 against excretory-secretory parasite products (FhESAg), and against a whole-worm extract (FhSomAg) were measured by enzyme-linked immunosorbent assay (ELISA) in relation to weight gain, serum hepatic enzyme levels, and fluke infection rate. At necropsy, the mean number of flukes recovered was similar in both infected groups. The two ELISAs specific for bovine IgG1 showed analogous sensitivity and specificity (92% and 94%). Cross-reactivity was observed towards Echinococcus granulosus, Cysticercus tenuicollis, and C. ovis but not towards C. bovis, Cooperia spp., and Ostertagia spp. FhESAg gave rise to apparently more stable specific IgG1 titres as compared to FhSomAg. Mean IgG1 titres were significantly higher in the single-dose-infected group than in the trickle-infected group during the early migratory phase of the infection (week 2 to week 4 (FhSomAg) or week 6 (FhESAg)). IgG2 values were consistently lower than IgG1 levels. The kinetic response of both isotypes yielded a similar pattern. Specific IgE antibodies were detected in cattle of both infected groups from week 2 post-primary infection (PPI) onwards. The mean serum glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gammaGT) activities were significantly higher in the single-dose-infected group for 3 weeks around peak levels (12-14 weeks PPI and 14-16 weeks PPI for GLDH and gammaGT respectively). Western blotting revealed a major antigenic fraction in FhESAg (26-30 kDa) recognized specifically by sera from F. hepatica infected calves as early as 6-8 weeks PPI. Experimental challenge caused no statistically significant modification of any parameter (IgG1 and IgG2 titres, enzymatic activities, immunoblotting) used to monitor the course of the infection. No correlation was found between fluke size and number, and antibody titres, suggesting that IgG1 production has little protective effect against F. hepatica infection.

Immune responses in Indonesian thin tail and Merino sheep during a primary infection with Fasciola gigantica: lack of a specific IgG2 antibody response is associated with increased resistance to infection in Indonesian sheep

After a primary infection with Fasciola gigantica, the immune responses in a resistant (Indonesian thin tail) and a susceptible (Merino) breed of sheep were analysed. The number of adult flukes recovered from the livers of the Indonesian thin tail sheep were significantly lower than those found in the Merino animals. On days 8, 14 and 25 p.i., Indonesian thin tail sheep exhibited a significantly higher eosinophilia than Merino sheep, whereas neutrophilia was significantly elevated in the Indonesian thin tail sheep on days 36 and 48 p.i. Serum from both sheep breeds demonstrated IgM, IgG1 and IgE responses to F. gigantica. In contrast, the Indonesian thin tail sheep produced significantly lower levels of IgG2 antibodies relative to the high level detected in Merino sheep. The IgE response was biphasic in both sheep breeds with the first response detected by day 14 and the second response developing from days 30 to 60 p.i. Western blotting showed that a similar profile of adult fluke antigens was recognised by IgG1 and IgE antibodies in both the Indonesian thin tail and Merino sheep. The IgE response was directed to a major antigen at about 92 kDa. We postulate that IgG2 could act as a blocking antibody for protective effector responses against F. gigantica in sheep and that the Indonesian thin tail sheep, by downregulating IgG2 responses, have an enhanced capacity for killing F. gigantica in vivo.

Liver pathology and immune response in experimental Fasciola hepatica infections of goats

The relationship between the immune response and the pathogenesis of the disease was studied in different primary and secondary experimental Fasciola hepatica infections of goats. The establishment of the infection, measured as percentage of recovered flukes at the necropsy, was similar in primarily and secondarily infected animals (between 19.7% and 24.3%), but the hepatic damage was much more severe in secondarily infected goats, as revealed by the levels of serum hepatic enzymes GGT and LDH. Primary infection evolves to chronic fasciolosis that did not induce the development of resistance, since goats were highly susceptible to secondary infection, showing severe acute and chronic hepatic lesions that led to the death of some animals in each group. The immune response to the infection was proved by the production of specific IgG antibodies to ESP of F. hepatica and the involvement of CD3+ T lymphocytes and lambda IgG+ plasma cells in the hepatic infiltrate. Secondary infection did not induce any difference in either IgG response or in the cellular composition of the infiltrate of hepatic lesions, although this was much more extended. However, neither antibodies nor cell-mediated response were protective: there was no correlation between IgG levels and fluke burden and there was no evidence of cell-mediated killing of the parasite. This suggests the existence of some immune evasion mechanisms in goat infection with F. hepatica. The parasite may depress the local inflammatory and immune response, as suggested by the scarcity of CD3+ T cells in the infiltrate surrounding acute migratory tunnels. Moreover, in secondary infected goats can be suspected an immunological damage of the liver, since a very severe infiltrate of immune cells replaced wide areas of hepatic parenchyma and an immune-mediated damage of hepatocytes could occur.

Evaluation of antigens of Fasciola gigantica as vaccines against tropical fasciolosis in cattle

Vaccine trials were conducted in Brahman cross cattle evaluating the efficacy of 4 native antigens purified from adult Fasciola gigantica flukes, and 1 recombinant F. gigantica antigen, as vaccines against tropical fasciolosis. The antigens tested were native glutathione S-transferase, cathepsin L, paramyosin, fatty acid binding protein (FABP), and a recombinant FABP expressed in E. coli, and were formulated in 1 or more of several adjuvants (Quil A, Squalene Montanide 80, MF59-100, Auspharm, NAGO, polylactoglycolide microspheres, Algammulin, DEAE, Freund's). Vaccination induced low, moderate or high antibody titres to the various antigens which were dependent on the adjuvant. Low but significant reductions in fluke burdens (31%, P < 0.026) and fluke wet weight (36%, P < 0.041) were only observed in cattle vaccinated with the native FABP in Freund's adjuvant. There was no correlation between total antibody titres to FABP and protection. The protection observed in cattle vaccinated with native FABP of F. gigantica supports the notion that this class of proteins is a useful target for protection of animals against Fasciola and extends the efficacy of FABPs to the tropical liver fluke. This is the first report of vaccination of cattle against F. gigantica with a purified protein.