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

The monodomain Kunitz protein EgKU-7 from the dog tapeworm Echinococcus granulosus is a high-affinity trypsin inhibitor with two interaction sites

Typical Kunitz proteins (I2 family of the MEROPS database, Kunitz-A family) are metazoan competitive inhibitors of serine peptidases that form tight complexes of 1:1 stoichiometry, mimicking substrates. The cestode Echinococcus granulosus, the dog tapeworm causing cystic echinococcosis in humans and livestock, encodes an expanded family of monodomain Kunitz proteins, some of which are secreted to the dog host interface. The Kunitz protein EgKU-7 contains, in addition to the Kunitz domain with the anti-peptidase loop comprising a critical arginine, a C-terminal extension of ∼20 amino acids. Kinetic, electrophoretic, and mass spectrometry studies using EgKU-7, a C-terminally truncated variant, and a mutant in which the critical arginine was substituted by alanine, show that EgKU-7 is a tight inhibitor of bovine and canine trypsins with the unusual property of possessing two instead of one site of interaction with the peptidases. One site resides in the anti-peptidase loop and is partially hydrolyzed by bovine but not canine trypsins, suggesting specificity for the target enzymes. The other site is located in the C-terminal extension. This extension can be hydrolyzed in a particular arginine by cationic bovine and canine trypsins but not by anionic canine trypsin. This is the first time to our knowledge that a monodomain Kunitz-A protein is reported to have two interaction sites with its target. Considering that putative orthologs of EgKU-7 are present in other cestodes, our finding unveils a novel piece in the repertoire of peptidase-inhibitor interactions and adds new notes to the evolutionary host-parasite concerto.

Improved biodistribution and enhanced immune response of subunit vaccine using a nanostructure formed by self-assembly of ascorbyl palmitate

New adjuvant strategies are needed to improve protein-based subunit vaccine immunogenicity. We examined the potential to use nanostructure of 6-O-ascorbyl palmitate to formulate ovalbumin (OVA) protein and an oligodeoxynucleotide (CpG-ODN) (OCC). In mice immunized with a single dose, OCC elicited an OVA-specific immune response superior to OVA/CpG-ODN solution (OC). Rheological studies demonstrated OCC's self-assembling viscoelastic properties. Biodistribution studies indicated that OCC prolonged OVA and CpG-ODN retention at injection site and lymph nodes, reducing systemic spread. Flow-cytometry assays demonstrated that OCC promoted OVA and CpG-ODN co-uptake by Ly6ChiCD11bhiCD11c+ monocytes. OCC and OC induced early IFN-γ in lymph nodes, but OCC led to higher concentration. Conversely, mice immunized with OC showed higher serum IFN-γ concentration compared to those immunized with OCC. In mice immunized with OCC, NK1.1+ cells were the IFN-γ major producers, and IFN-γ was essential for OVA-specific IgG2c switching. These findings illustrate how this nanostructure improves vaccine's response.

Unveiling Novel Kunitz- and Waprin-Type Toxins in the Micrurus mipartitus Coral Snake Venom Gland: An In Silico Transcriptome Analysis

Kunitz-type peptide expression has been described in the venom of snakes of the Viperidae, Elapidae and Colubridae families. This work aimed to identify these peptides in the venom gland transcriptome of the coral snake Micrurus mipartitus. Transcriptomic analysis revealed a high diversity of venom-associated Kunitz serine protease inhibitor proteins (KSPIs). A total of eight copies of KSPIs were predicted and grouped into four distinctive types, including short KSPI, long KSPI, Kunitz-Waprin (Ku-WAP) proteins, and a multi-domain Kunitz-type protein. From these, one short KSPI showed high identity with Micrurus tener and Austrelaps superbus. The long KSPI group exhibited similarity within the Micrurus genus and showed homology with various elapid snakes and even with the colubrid Pantherophis guttatus. A third group suggested the presence of Kunitz domains in addition to a whey-acidic-protein-type four-disulfide core domain. Finally, the fourth group corresponded to a transcript copy with a putative 511 amino acid protein, formerly annotated as KSPI, which UniProt classified as SPINT1. In conclusion, this study showed the diversity of Kunitz-type proteins expressed in the venom gland transcriptome of M. mipartitus.

Evaluation of Th1/Th2, regulatory cytokines and transcriptional factor FoxP3 in sheep immunized with a partially protective and non-protective vaccine and challenged with Fasciola hepatica

Gene expression for Th1/Th2 cytokines (IL-4 and IFN-ɣ), regulatory cytokines (TGF-β and IL-10) and the transcriptional factor FoxP3 was analyzed in the liver and hepatic lymph nodes (HLN) from sheep immunized with partially protective and non-protective vaccine candidates and challenged with Fasciola hepatica. FoxP3 T cells were also evaluated by immunohistochemistry (IHQ). The most remarkable difference between the partially protected vaccinated (V1) group and the non-protected vaccinated (V2) group was a more severe expansion of FoxP3 T cells recorded by IHQ in both the liver and HLN of the V2 group as compared to the V1 group, whereas no differences were found between the V2 group and the infected control (IC) group. Similar results were recorded for FoxP3 gene expression although significant differences among V1 and V2 groups were only significant in the HLN, while FoxP3 gene expression was very similar in the V2 and IC groups both in the liver and HLN. No significant differences for the remaining cytokines were recorded between the V1 and V2 groups, but in the liver the V2 group shows significant increases of IFN-ɣ and IL-10 as compared to the uninfected control (UC) group whereas the V1 group did not. The lower expansion of FoxP3 T cells and lower increase of IFN-ɣ and IL-10 in the partially protected vaccinated group may be related with lower hepatic lesions and fluke burdens recorded in this group as compared to the other two infected groups. The most relevant change in regulatory cytokine gene expression was the significant increase of TGF-β in the liver of IC, V1 and V2 groups as compared to the UC group, which could be related to hepatic lesions.

Identification and prioritisation of potential vaccine candidates using subtractive proteomics and designing of a multi-epitope vaccine against Wuchereria bancrofti

This study employed subtractive proteomics and immunoinformatics to analyze the Wuchereria bancrofti proteome and identify potential therapeutic targets, with a focus on designing a vaccine against the parasite species. A comprehensive bioinformatics analysis of the parasite's proteome identified 51 probable therapeutic targets, among which "Kunitz/bovine pancreatic trypsin inhibitor domain-containing protein" was identified as the most promising vaccine candidate. The candidate protein was used to design a multi-epitope vaccine, incorporating B-cell and T-cell epitopes identified through various tools. The vaccine construct underwent extensive analysis of its antigenic, physical, and chemical features, including the determination of secondary and tertiary structures. Docking and molecular dynamics simulations were performed with HLA alleles, Toll-like receptor 4 (TLR4), and TLR3 to assess its potential to elicit the human immune response. Immune simulation analysis confirmed the predicted vaccine's strong binding affinity with immunoglobulins, indicating its potential efficacy in generating an immune response. However, experimental validation and testing of this multi-epitope vaccine construct would be needed to assess its potential against W. bancrofti and even for a broader range of lymphatic filarial infections given the similarities between W. bancrofti and Brugia.

Antibody detection against Kunitz-type protein in Fasciola hepatica experimentally infected sheep using enzyme-linked immunosorbent assay (ELISA)

Fasciolosis is a parasitic disease considered as emerging and neglected by the WHO. Sheep are highly susceptible to this disease, and affected flocks experience decreased productivity due to increased mortality, and the reduced quality of their products, such as wool and meat. To effectively control this disease, reliable and early diagnosis is essential for making decisions regarding antiparasitic application and/or the removal of affected animals. Currently, the diagnosis of F. hepatica in sheep relies on the detection of parasite eggs in faeces, a method that becomes reliable from week 10 post-infection. Consequently, there is a need for earlier diagnostic tools based on immune response. However, obtaining antigens for antibody detection has proven to be difficult and expensive. The aim of this study was to evaluate members of the Kunitz protein family of F. hepatica expressed in the form of a fusion protein in the serological diagnosis of F. hepatica in sheep. The performance of three recombinant F. hepatica Kunitz-type inhibitors (FhKT1.1, FhKT1.3, and FhKT4) was compared with a synthetic Kunitz-type peptide (sFhKT) in sera from sheep experimentally infected with F. hepatica, using an ELISA. Of these, FhKT1.1 showed the most promising diagnostic indicators, exhibiting high precision and low cross-reactivity, and thus potential for standardized production. The results of our study demonstrated that the application of FhKT1.1 is a valuable tool for early-stage diagnosis of F. hepatica in sheep. Such an early diagnosis can aid in implementing timely interventions and effectively managing the disease in sheep populations.

A promising new target to control fasciolosis: Fasciola hepatica leucine aminopeptidase 2

Parasite M17 leucine aminopeptidases (LAPs) have been associated with critical roles in different key functions such as the nutrition, migration, and invasion of the natural host. Native or recombinant LAP used as a vaccine antigen has proved effective to elicit protection against Fasciola hepatica infection in sheep, pointing to potential vaccine candidates against fascioliasis in ruminant species. Previously, the FhLAP1, abundantly secreted in vitro by the mature adult parasite was used as a vaccine antigen obtaining promising protection results against F. hepatica challenge in small ruminants. Here, we report the biochemical characterization of a second recombinant LAP (FhLAP2) associated with the juvenile stage of F. hepatica. FhLAP2 showed aminopeptidase activity using different synthetic substrates, including leucine, arginine, and methionine and was increased in the presence of Mn+ 2 and Mg+ 2. The activity was inhibited by bestatin, 1,10-phenanthroline, and EDTA, specific inhibitors of aminopeptidase and/or metalloproteases. Finally, the recombinant FhLAP2 functional form was tested in combination with Freund's incomplete adjuvant in an immunization trial in mice followed by an experimental challenge with F. hepatica metacercariae. The immunization with FhLAP2/FIA resulted in a significant reduction of parasite recovery compared to control groups. The immunized group elicited total specific IgG and subclasses IgG1 and IgG2 antibody responses. This study highlights the potential of a new candidate vaccine formulation with potential applications in natural ruminant hosts, especially those targeting the juvenile stage.

Liver Proteome Alterations in Red Deer (Cervus elaphus) Infected by the Giant Liver Fluke Fascioloides magna

Liver fluke infections are recognised as diseases with worldwide distribution and considerable veterinary and public health importance. The giant liver fluke, Fascioloides magna, is an important non-native parasite which has been introduced to Europe, posing a threat to the survival of local wildlife populations such as red deer (Cervus elaphus). The aim of the study was to analyse differences in liver proteomes between F. magna-infected and control red deer groups using a label-based high-throughput quantitative proteomics approach. The proteomics analysis identified 234 proteins with differential abundance between the control and infected groups. Our findings showed that F. magna infection in this definitive host is associated with changes in the metabolism of proteins and fatty acids, oxidative stress, fibrosis, and signaling pathways. The identified proteins and associated biological pathways represent a valuable contribution to the understanding of host-parasite interactions and the pathogenesis of liver fluke infection.

Lyotropic Liquid Crystalline Nanostructures as Drug Delivery Systems and Vaccine Platforms

Lyotropic liquid crystals result from the self-assembly process of amphiphilic molecules, such as lipids, into water, being organized in different mesophases. The non-lamellar formed mesophases, such as bicontinuous cubic (cubosomes) and inverse hexagonal (hexosomes), attract great scientific interest in the field of pharmaceutical nanotechnology. In the present review, an overview of the engineering and characterization of non-lamellar lyotropic liquid crystalline nanosystems (LLCN) is provided, focusing on their advantages as drug delivery nanocarriers and innovative vaccine platforms. It is described that non-lamellar LLCN can be utilized as drug delivery nanosystems, as well as for protein, peptide, and nucleic acid delivery. They exhibit major advantages, including stimuli-responsive properties for the “on demand” drug release delivery and the ability for controlled release by manipulating their internal conformation properties and their administration by different routes. Moreover, non-lamellar LLCN exhibit unique adjuvant properties to activate the immune system, being ideal for the development of novel vaccines. This review outlines the recent advances in lipid-based liquid crystalline technology and highlights the unique features of such systems, with a hopeful scope to contribute to the rational design of future nanosystems.

Bioinformatic comparison of Kunitz protease inhibitors in Echinococcus granulosus sensu stricto and E. multilocularis and the genes expressed in different developmental stages of E. granulosus s.s

Background

Cystic and alveolar echinococcosis caused by the tapeworms Echinococcus granulosus sensu stricto (s.s.) and E. multilocularis, respectively, are important zoonotic diseases. Protease inhibitors are crucial for the survival of both Echinococcus spp. Kunitz-type inhibitors play a regulatory role in the control of protease activity. In this study,we identified Kunitz-type domain protease inhibitors(KDPIs) present in the genomes of these two tapeworms and analyzed the gene sequences using computational, structural bioinformatics and phylogenetic approaches to evaluate the evolutionary relationships of these genes. Hi-seq transcriptome analysis showed that E. granulosuss.s. KDPIs were differentially expressed in the different developmental stages. We validated some of the genes expressed in adult worm, protoscolex and cyst germinal membrane of E. granulosuss.s. and E. multilocularis by quantitative PCR.

Results

A total of 19 genes from E. multilocularis and 23 genes from E. granulosuss.s. were predicted to be KDPIs with the most containing a single Kunitz-domain. A maximum likelihood method phylogenetic tree indicated that the E. granulosuss.s. and E. multilocularis Kunitz domain peptides were divided into three branches containing 9 clusters. The ratio of positively charged residues and neutral residues are different between E. multilocularis and E. granulosuss.s. KDPIs. We also found that E. multilocularis had higher percentage of sequences containing signal peptides (17/19, 89.47%) than that of E. granulosuss.s. (14/23, 60.87%). Transcript analysis showed all the E. granulosuss.s. KDPI genes were expressed differentially in four developmental stages of the worm. Transcription analysis showed that 9 KDPIs (including EG_07244,EGR_08716 and EGR_10096) were highly upregulated in adult worm, and 2 KDPIs (EG_09268 and EG_09490) were highly expressed in the cyst germinal membrane. Quantitative gene expression analysis(qPCR) of four genes confirmed the expression of these genes. EGR_08716 and its homologous gene (EmuJ_001137000) were highly and specifically expressed in adult worms of the two worms.

Conclusions

A total 19 and 23 KDPIs were identified in the genomes of E. multilocularis and E. granulosus s.s. , respectively. The differential expression of these KDPIs in different stages may indicate their different roles in the different hosts. The difference in characterization of KDPIs may be associated with the different pathology of metacestode stage of these two parasites.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08219-4.

Construction of a multiepitope vaccine candidate against Fasciola hepatica: an in silico design using various immunogenic excretory/secretory antigens

BACKGROUND

Fasciola hepatica is an important pathogen that causes liver fluke disease in definitive hosts such as livestock animals and humans. Various excretory/secretory products have been used in serological diagnosis and vaccination studies targeting fasciolosis. There are no commercial vaccines against fasciolosis yet. Bioinformatic analysis based on computational methods have lower cost and provide faster output compared to conventional vaccine antigen discovery techniques. The aim of this study was to predict B- and T-cell specific epitopes of four excretory/secretory antigens (Kunitz-type serine protease inhibitor, cathepsin L1, helminth defense molecule, and glutathione S-transferase) of Fasciola hepatica and to construct a multiepitope vaccine candidate against fasciolosis.

METHODS AND RESULTS

Initially, nonallergic and the highest antigenic B- and T- cell epitopes were selected and then, physico-chemical parameters, secondary and tertiary structures of designed multiepitope vaccine candidate were predicted. Tertiary structure was refined and validated using online bioinformatic tools. Linear and discontinuous B-cell epitopes and disulfide bonds were determined. Finally, molecular docking analysis for MHC-I and MHC-II receptors was performed.

CONCLUSION

This multi-epitope vaccine candidate antigen, with high immunological properties, can be considered as a promising vaccine candidate for animal experiments and wet lab studies.