Immunization of rats against Fasciola hepatica using crude antigens conjugated with Freund's adjuvant or oligodeoxynucleotides

A Vaccine Based on Kunitz-Type Molecule Confers Protection Against Fasciola hepatica Challenge by Inducing IFN-γ and Antibody Immune Responses Through IL-17A Production

Fasciola hepatica is helminth parasite found around the world that causes fasciolosis, a chronic disease affecting mainly cattle, sheep, and occasionally humans. Triclabendazole is the drug of choice to treat this parasite. However, the continuous use of this drug has led to the development of parasite resistance and, consequently, the limitation of its effectiveness. Hence, vaccination appears as an attractive option to develop. In this work, we evaluated the potential of F. hepatica Kunitz-type molecule (FhKTM) as an antigen formulated with a liquid crystal nanostructure formed by self-assembly of 6-O-ascorbyl palmitate ester (Coa-ASC16) and the synthetic oligodeoxynucleotide containing unmethylated cytosine-guanine motifs (CpG-ODN) during an experimental model of fasciolosis in mice, and we further dissected the immune response associated with host protection. Our results showed that immunization of mice with FhKTM/CpG-ODN/Coa-ASC16 induces protection against F. hepatica challenge by preventing liver damage and improving survival after F. hepatica infection. FhKTM/CpG-ODN/Coa-ASC16-immunized mice elicited potent IFN-γ and IL-17A with high levels of antigen-specific IgG1, IgG2a, and IgA serum antibodies. Strikingly, IL-17A blockade during infection decreased IgG2a and IgA antibody levels as well as IFN-γ production, leading to an increase in mortality of vaccinated mice. The present study highlights the potential of a new vaccine formulation to improve control and help the eradication of F. hepatica infection, with potential applications for natural hosts such as cattle and sheep.

Fasciola hepatica Extracellular Vesicles isolated from excretory-secretory products using a gravity flow method modulate dendritic cell phenotype and activity

Parasite-released extracellular vesicles (EVs) deliver signals to the host immune system that are critical to maintaining the long-term relationship between parasite and host. In the present study, total EVs (FhEVs) released in vitro by adults of the helminth parasite Fasciola hepatica were isolated using a recently described gravity flow method that protects their structural integrity. The FhEVs molecular cargo was defined using proteomic analysis and their surface topology characterised by glycan microarrays. The proteomic analysis identified 618 proteins, 121 of which contained putative N-linked glycosylation sites while 132 proteins contained putative O-linked glycosylation sites. Glycan arrays revealed surface-exposed glycans with a high affinity for mannose-binding lectins indicating the predominance of oligo mannose-rich glycoproteins, as well as other glycans with a high affinity for complex-type N-glycans. When added to bone-marrow derived dendritic cells isolated FhEV induced a novel phenotype that was categorised by the secretion of low levels of TNF, enhanced expression of cell surface markers (CD80, CD86, CD40, OX40L, and SIGNR1) and elevation of intracellular markers (SOCS1 and SOCS3). When FhEV-stimulated BMDCs were introduced into OT-II mice by adoptive transfer, IL-2 secretion from skin draining lymph nodes and spleen cells was inhibited in response to both specific and non-specific antigen stimulation. Immunisation of mice with a suspension of FhEV did not elicit significant immune responses; however, in the presence of alum, FhEVs induced a mixed Th1/Th2 immune response with high antigen specific antibody titres. Thus, we have demonstrated that FhEVs induce a unique phentotype in DC capable of suppressing IL-2 secretion from T-cells. Our studies add to the growing immuno-proteomic database that will be an important source for the discovery of future parasite vaccines and immunotherapeutic biologicals.

A Survey on the Adjuvant Role of Naloxone Alone or Combined with Alum in Vaccination Against Fasciolosis in BALB/c Mice

BACKGROUND

Fasciolosis is a zoonotic parasitic disease imposing a heavy load of livestock losses worldwide.

PURPOSE

We aimed to evaluate immune-stimulatory effects of naloxone (NLX), an opioid receptor antagonist, in combination with alum in mice vaccinated with excretory-secretory antigens (E/S) of Fasciola hepatica.

METHODS

8-week-old female BALB/c mice were subcutaneously vaccinated using E/S antigens of F. hepatica. Experimental groups (14 mice per group) included: vaccine (E/S antigen), alum vaccine (E/S antigen plus alum), NLX vaccine (E/S antigen plus NLX), and alum-NLX vaccine (E/S antigen plus a mixture of alum-NLX). The control group was infused with PBS. Lymphocyte proliferation and the levels of IFN-γ, IL-4, IgG2a, IgG1, and total IgG were measured.

RESULTS

Mice vaccinated with NLX or alum-NLX adjuvants showed significantly higher rates of lymphocyte proliferation, IFN-γ, total IgG, and IgG2a levels. The mice that were injected with alum showed a significantly higher concentration of IL-4. Ratios of IFN-γ/Il-4 and IgG2a/IgG1 were significantly higher in the NLX and alum-NLX groups in comparison with the groups vaccinated either with alum or without any adjuvant. A significantly higher protection rate (62.5%) was seen in mice vaccinated with the alum-NLX adjuvant compared to the other groups.

CONCLUSION

NLX can be effective in conferring cellular immunity and protection against F. hepatica. It is recommended to consider this agent as a potential adjuvant in vaccines against fasciolosis.

CpG oligodeoxynucleotides with crude parasite antigens reduce worm recovery in Opisthorchis viverrini infected hamsters

Opisthorchis viverrini, a human liver fluke, is still an endemic parasitic infection in Thailand and nearly all countries in Southeast Asia. O. viverrini induces a chronic stage of infection in hamsters. During the first 2 weeks of infection, Th1 inducing cytokine, IL-12, increased but was down regulated in chronic infection. In this study it was found that unmethylated-CpG ODN (oligodeoxynucleotides) 1826 increased hamster mononuclear cell proliferation and stimulated IFN-γ production in vitro. The IFN-γ levels in hamster sera were significantly increased in hamsters injected with CpG ODN 1826 alone or plus crude somatic antigens (CSAg). Further investigation using the flow cytometer found that CD4⁺T cells and IFN-γ⁺ CD4⁺T cells (Th1-like cells) in the hamster blood were significantly increased. The role of these cells in the protective responses in hamsters was evaluated by challenging with 25 metacercaria and observation for 3 months. The number of worms recovered was significantly reduced in the hamsters injected with CpG ODN 1826 with CSAg, but not in CpG ODN 1826 alone groups when compared to PBS control. The percent of reduction in hamsters against this parasite were 32.95% and 21.49% in the CpG ODN 1826 with CSAg and CpG ODN 1826 alone. This study indicates that CpG ODN 1826 plus parasite antigens elicit a Th1-like response that leads to the enhancement of worm reduction.

A mucin-like peptide from Fasciola hepatica induces parasite-specific Th1-type cell immunity

Fasciolosis, caused by the liver fluke Fasciola hepatica, is a major parasitic disease of livestock that causes significant economic losses worldwide. Although drugs are effective against liver flukes, they do not prevent reinfection, and continuous treatment is costly. Moreover, resistant fluke strains are emerging. In this context, vaccination is a good alternative since it provides a cost-effective long-term prevention strategy to control fasciolosis. In this paper, we evaluate the Fhmuc peptide as a potential vaccine against fasciolosis. This peptide derives from a mucin-like protein highly expressed in the infective stage of Fasciola hepatica. Mucin-like molecules expressed by parasites can contribute to several infection processes by protecting the parasite from host proteases and recognition by the immune system. We show that the Fhmuc peptide induces Th1-like immune responses specific for F. hepatica excretion-secretion products (FhESP) with a high production of IFNγ. We also investigated whether this peptide could protect animals from infection, and present preliminary data indicating that animals treated with Fhmuc exhibited reduced liver damage compared to non-immunised animals and that this protection was associated with a recruitment of B and T lymphocytes in the peritoneum, as well as eosinophils and mature dendritic cells. These results suggest that the mucin-like peptide Fhmuc could constitute a potential vaccine candidate against fasciolosis and pave the way towards the development of vaccines against parasites.

Fasciola hepatica Kunitz type molecule decreases dendritic cell activation and their ability to induce inflammatory responses

The complete repertoire of proteins with immunomodulatory activity in Fasciola hepatica (Fh) has not yet been fully described. Here, we demonstrated that Fh total extract (TE) reduced LPS-induced DC maturation, and the DC ability to induce allogeneic responses. After TE fractionating, a fraction lower than 10 kDa (F<10 kDa) was able to maintain the TE properties to modulate the DC pro- and anti-inflammatory cytokine production induced by LPS. In addition, TE or F<10 kDa treatment decreased the ability of immature DC to stimulate the allogeneic responses and induced a novo allogeneic CD4+CD25+Foxp3+ T cells. In contrast, treatment of DC with T/L or F<10 kDa plus LPS (F<10/L) induced a regulatory IL-27 dependent mechanism that diminished the proliferative and Th1 and Th17 allogeneic responses. Finally, we showed that a Kunitz type molecule (Fh-KTM), present in F<10 kDa, was responsible for suppressing pro-inflammatory cytokine production in LPS-activated DC, by printing tolerogenic features on DC that impaired their ability to induce inflammatory responses. These results suggest a modulatory role for this protein, which may be involved in the immune evasion mechanisms of the parasite.

Protective immunization of hamsters against Opisthorchis viverrini infection is associated with the reduction of TGF-β expression

Opisthorchis viverrini infection is a significant health problem in Thailand and other countries in Southeast Asia. There is little known about the mechanisms of the immune response to O. viverrini in immunoprotection. However, it has been reported that this parasite can suppress both cell and antibody mediated immune responses. The TGF-β and IL-10 are immunosuppressive cytokines that play an important role in inhibition of host immune response leading to worm survival. In this study, we immunized hamsters to protect against O. viverrini infection and the IL-4, IL-10, TGF-β and IFN-γ expression in spleen was investigated by real time PCR analysis. An O. viverrini-crude somatic antigen preparation (CSAg) administered with complete Freund's adjuvant (CFA) or with alum was used to stimulate immune responses in O. viverrini-primed hamsters. The greatest percent protection (48.4%) was seen following immunization with CSAg plus alum. The mean number±SD of worms recovered in the PBS control, CFA alone, CSAg plus CFA, alum alone and CSAg plus alum was 17.4±2.3, 17.1±3.3, 14.5±3.8, 14.5±2.3 and 9±2.7, respectively. Significant protection correlated with the reduction of TGF-β and IL-10, but not IL-4, IFN-γ expressions. Since TGF-β expression is significantly increased in the spleens of hamsters with opisthorchiasis, stimulation of this cytokine by parasite antigens was confirmed by using CSAg and primary hamster spleen cells. Antigen fractions with molecular masses of 81-92, 64-72 and 19-21.4kDa were found to significantly induce TGF-β production. Our results suggested that TGF-β induction by O. viverrini may have an important role in parasite survival.

Adoptive transfer of dendritic cells pulsed with Fasciola hepatica antigens and lipopolysaccharides confers protection against fasciolosis in mice

Dendritic cells (DCs) can function as adjuvants able to mediate protection against different pathogens. Given that successful vaccination against Fasciola hepatica is mostly related to the induction of Th1 responses, we studied the potential of DCs loaded with F. hepatica antigens and lipopolysaccharide (LPS) (which promote DCs maturation) as a vaccine against fasciolosis in BALB/c mice. However, only a semimature phenotype was achieved when DCs were simultaneously cultured with an F. hepatica total extract (TE) and LPS. The activation status of TE-loaded DCs was enhanced when these cells were treated with TE 90 minutes before being stimulated with LPS (TE90 DCs). More importantly, a single vaccination of mice with TE90 DCs stimulated a systemic Th1 response and conferred protection against hepatic damage induced by F. hepatica infection. Thus, TE90 DCs may prove to be a useful new tool for vaccination against F. hepatica.

Quantitation of cytokine mRNA by real-time RT-PCR during a vaccination trial in a rabbit model of fascioliasis

Use of the rabbit as disease model has long been hampered by a lack of immunological assays specific to this species. In the present study we developed a SYBR Green-based, real-time RT-PCR protocol to quantitate cytokine mRNA in freshly harvested rabbit peripheral mononuclear cells. The method was validated in the course of a vaccination trial in which animals vaccinated with the recombinant antigen FhSAP2 were challenged with Fasciola hepatica metacercariae. Changes in the levels of rabbit interleukin (IL)-2, IL-4, IL-6, IL-10, tumor necrosis factor-alpha (TNFalpha), and interferon-gamma (IFNgamma) mRNA were determined. Messenger RNA from the universally expressed housekeeping gene GAPDH was used as an amplification control and allowed for correction of variations in the efficiencies of RNA extraction and reverse transcription. Rabbits vaccinated with FhSAP2 showed an 83.3% reduction in liver fluke burden after challenge infection when compared to non-vaccinated controls. All cytokine mRNAs were found at detectable levels; however, the levels of IFNgamma, TNFalpha, IL-2 and IL-10 were significantly higher in the vaccinated group compared to the non-vaccinated group. These results suggest that protection conferred by FhSAP2 protein could be associated with a mixed Th1/Th2 immune response in which Th1 cytokines are dominant. The real-time RT-PCR method described herein can be a useful tool for monitoring changes in basic immune functions in the rabbit model of fascioliasis and may also aid in studies of human diseases for which the rabbit is an important experimental model.

CpG-oligodeoxynucleotide is a potent adjuvant with an Entamoeba histolytica Gal-inhibitable lectin vaccine against amoebic liver abscess in gerbils

The protozoan parasite Entamoeba histolytica causes invasive amoebiasis characterized by amoebic dysentery and liver abscesses (ALA). The E. histolytica galactose/N-acetyl-D-galactosamine-inhibitable lectin (Gal-lectin), an immunogenic surface molecule involved in colonization and invasion, is a promising vaccine candidate against amoebiasis. Gal-lectin is known to induce Th1 cytokines in macrophages and spleen cells in vitro, and a Th1 response is thought to be protective against ALA. In this study, we report the use of cytosine guanine oligodeoxynucleotide (CpG-ODN) as adjuvant to augment Th1 responses against Gal-lectin in the gerbil model of ALA. Gerbils were vaccinated intramuscularly with the native Gal-lectin plus CpG-ODN or a paired non-CpG control GpC-ODN, and control gerbils received CpG-ODN alone. One week after the last boost gerbils were challenged intrahepatically with 10(6) amoebae. Gerbils receiving CpG-ODN as adjuvant with Gal-lectin were completely protected against the development of ALA, whereas 50% of gerbils receiving GpC-ODN and Gal-lectin developed ALA and 85% of controls developed ALA. Stronger lymphoproliferation in response to the Gal-lectin and higher prechallenge titers of serum Gal-lectin-specific antibodies, capable of blocking amoebic adherence, were observed when CpG-ODN was used as adjuvant. Gerbils vaccinated with CpG-ODN and Gal-lectin also had significantly higher levels of gamma interferon, interleukin-12 (IL-12), and IL-2 mRNA than controls. These data indicate that CpG-ODN can enhance the Th1 responses, which improve the protective effects of Gal-lectin. This is the first report of the use of CpG as a potent Th1 adjuvant with Gal-lectin to increase protection against ALA formation.

Immunogenicity of two Echinococcus granulosus antigens EgA31 and EgTrp in mice

Here, we investigate in mice the immunogenicity of two antigens EgA31 and EgTrp which are expressed by the larval stage of Echinococcus granulosus. These recombinant proteins were used alone or as a mixture (EgA31-EgTrp) to immunize BALB/c mice. By flow cytometry, we have shown that the ratio CD4+/CD8+ of splenocytes were significantly higher in the antigen-immunized groups. The specific antibody in the sera and cytokine producing splenocytes was evaluated by enzyme-linked immunosorbent assay. EgA31, EgTrp or EgA31-EgTrp elicited high antibody titer of IgG and IgA. Among IgG isotypes, IgG1 was predominant for each antigen tested alone or combined. The production of IL-12, IFN-gamma, IL-10 and IL-6 cytokines was significantly higher in mice immunized with recombinant proteins. Our results suggest that, in BALB/c mice, a mixed Th1/Th2, response to EgA31, EgTrp and EgA31-EgTrp is obtained. The use of both antigens separately or in combination as candidate vaccine proteins is discussed.