HcFAR, a functional inhibitor of goat TGF-β1 identified from excretory and secretory products of Haemonchus contortus

Enzymes involved in trehalose-chitin synthesis in Haemonchus contortus could be vaccine candidates for goats

BACKGROUND

Trehalose-6-phosphate synthase (HcTPS) and trehalose-6-phosphate phosphatase (HcGOB) are key enzymes for trehalose synthesis in Haemonchus contortus. In addition, previous studies have also demonstrated that HcTPS and HcGOB can regulate the function of host immune cells in vitro, and are important immunosuppressive molecules. Therefore, this study evaluated the potential of HcTPS and HcGOB as vaccine candidates through in vitro and in vivo experiments.

METHODS

To evaluate the inhibitory effects of polyclonal antibodies on egg hatching and larval development, anti-rHcTPS and anti-rHcGOB antibodies were incubated separately with eggs and first-stage larvae (L1s) under controlled in vitro conditions. For immunization studies, recombinant proteins (rHcTPS and rHcGOB) were formulated with Quil-A adjuvant, and administered to goats through subcutaneous injection. Vaccine efficacy against Haemonchus contortus infection was determined through comprehensive analysis of multiple parasitological parameters, including: (1) egg abnormality rate, (2) hatching success rate, (3) reduction egg output rates, and (4) reduction in adult worm burden.

RESULTS

The results of in vitro experiments showed that polyclonal antibodies against HcTPS and HcGOB had no effect on the hatching rate of eggs, but significantly affected the development from L1s to infectious third stage larvae (L3s). After immunization with recombinant HcTPS protein (rHcTPS) and recombinant HcGOB protein (rHcGOB), high levels of antigen-specific immunoglobulin G (IgG) were produced in goats, and remained till the end of the experiment. Compared with the Quil-A adjuvant control group, the number of deformed eggs in the rHcTPS protein- immunized group and the rHcGOB protein- immunized group were significantly increased. In the rHcTPS protein-immunized group and the rHcGOB protein-immunized group, the deformity rate of eggs was 9.59% and 17.30%, respectively, and the hatching rate of eggs was reduced by 11.27% and 13.71%, respectively. Moreover, compared with the Quil-A adjuvant control group, the number of eggs and adults in the HcTPS protein- immunized group decreased by 64.47% and 60.93%, respectively, and the number of eggs and adults in the rHcGOB protein- immunized group decreased by 63.97% and 69.54%, respectively. Furthermore, compared with the control group (Quil-A adjuvant), the trehalose content in the rHcTPS protein- immunized group and the rHcGOB protein- immunized group was also significantly reduced.

CONCLUSIONS

These findings indicate that rHcTPS and rHcGOB exhibit superior immune protective effects, rendering them promising candidates for vaccine development.

Fatty acid- and retinol-binding protein 6 does not control worm fatty acid content in Caenorhabditis elegans but might play a role in Haemonchus contortus parasitism

BACKGROUND

Nematodes have lost the ability to synthesise necessary lipids de novo and have complementally evolved the capacity to acquire fatty acids and their derivatives from a diet or host animal. Nematode-specific fatty acid- and retinol-binding protein (FAR) family is one approach that facilitates lipid acquisition, representing an Achilles heel and potential target against roundworms of socioeconomic significance. However, little is known about their detailed functional roles in either free-living or parasitic nematodes.

METHODS

A genome-wide identification and curation were performed to screen the FAR family members of Haemonchus contortus. Their transcription patterns in worms were also analysed to identify the targets. Ligand binding assay and molecular docking were conducted to verify the fatty acid binding activities of FAR proteins of interest. RNA interference (RNAi) and heterologous expression (rescuing) experiments were designed to explore the potential roles of the selected FAR protein in nematodes. Localisation of the protein was shown in sections of paraffin-embedded worms after an immunohistochemistry (IHC) assay.

RESULTS

Here, an orthologue of far-6 in the model organism Caenorhabditis elegans (Ce-far-6) was functionally characterised in a parasitic nematode, H. contortus (Hc-far-6). It is demonstrated that knockdown of Ce-far-6 gene did not affect worm fat content, reproduction, or lifespan, but decreased worm body length at an early life stage of C. elegans. In particular, the Ce-far-6 mutant associated phenotype was completely rescued by Hc-far-6, suggesting a conserved functional role. Surprisingly, there were distinct tissue expression patterns of FAR-6 in the free-living C. elegans and parasitic H. contortus. High transcriptional level of Hc-far-6 and dominant expression of FAR-6 in the intestine of the parasitic stage of H. contortus link this gene/protein to nematode parasitism.

CONCLUSIONS

These findings substantially enhance our understanding of far genes and the associated lipid biology of this important parasitic nematode at a molecular level, and the approaches established are readily applicable to the studies of far genes in a broad range of parasites.

Histidine acid phosphatase domain-containing protein from Haemonchus contortus is a stimulatory antigen for the Th1 immune response of goat PBMCs

Background

Histidine acid phosphatase (HAP), a member of the histidine phosphatase superfamily, is widely found in parasites and is also a potential vaccine antigen or drug target. However, the biological function of HAP in Haemonchus contortus is still unclear.

Methods

We cloned the HAP gene from H. contortus (Hc-HAP) and expressed the purified recombinant Hc-HAP (rHc-HAP) protein. The transcription of the Hc-HAP gene in the eggs, infective third-stage larvae (L3s), exsheathed third-stage larvae (xL3s) and adults (females/males) was analyzed by quantitative real-time-PCR (qPCR). An immunofluorescence assay was also used to detect the localization of Hc-HAP expression in adult worms. The effect of rHc-HAP on the function of peripheral blood mononuclear cells (PBMCs) was observed by co-culture of rHc-HAP protein with goat PBMCs.

Results

The qPCR results revealed that the Hc-HAP gene was transcribed at a higher level in the L3 and xL3 stages that there were gender differences in transcription at the adult stage, with females exhibiting higher transcription than males. Moreover, Hc-HAP was mainly expressed in adult intestinal microvilli. Additionally, western blot results revealed that rHc-HAP could be detected in goat sera artificially infected with H. contortus. In the experiments, rHc-HAP bound to goat PBMCs and released nitric oxide. The rHc-HAP also induced the expression of interferon gamma (IFN-γ) and the phosphorylated STAT 1 transcription factor, while inhibiting interleukin-4 expression.

Conclusions

The results shows that rHc-HAP stimulated the IFN-γ/STAT1 signaling pathway and enabled polarization of PBMCs toward T-helper 1 immune responses.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05411-7.