The immune protection induced by a serine protease from the Trichinella spiralis adult administered as DNA and protein vaccine

Quantitative label-free proteomic analysis of excretory-secretory proteins in different developmental stages of Trichinella spiralis

Trichinella spiralis (T. spiralis) is a zoonotic parasitic nematode with a unique life cycle, as all developmental stages are contained within a single host. Excretory-secretory (ES) proteins are the main targets of the interactions between T. spiralis and the host at different stages of development and are essential for parasite survival. However, the ES protein profiles of T. spiralis at different developmental stages have not been characterized. The proteomes of ES proteins from different developmental stages, namely, muscle larvae (ML), intestinal infective larvae (IIL), preadult (PA) 6 h, PA 30 h, adult (Ad) 3 days post-infection (dpi) and Ad 6 dpi, were characterized via label-free mass spectrometry analysis in combination with bioinformatics. A total of 1217 proteins were identified from 9341 unique peptides in all developmental stages, 590 of which were quantified and differentially expressed. GO classification and KEGG pathway analysis revealed that these proteins were important for the growth of the larvae and involved in energy metabolism. Moreover, the heat shock cognate 71 kDa protein was the centre of protein interactions at different developmental stages. The results of this study provide comprehensive proteomic data on ES proteins and reveal that these ES proteins were differentially expressed at different developmental stages. Differential proteins are associated with parasite survival and the host immune response and may be potential early diagnostic antigen or antiparasitic vaccine candidates.

Recent Advances in Tick Antigen Discovery and Anti-Tick Vaccine Development

Ticks can seriously affect human and animal health around the globe, causing significant economic losses each year. Chemical acaricides are widely used to control ticks, which negatively impact the environment and result in the emergence of acaricide-resistant tick populations. A vaccine is considered as one of the best alternative approaches to control ticks and tick-borne diseases, as it is less expensive and more effective than chemical controls. Many antigen-based vaccines have been developed as a result of current advances in transcriptomics, genomics, and proteomic techniques. A few of these (e.g., Gavac® and TickGARD®) are commercially available and are commonly used in different countries. Furthermore, a significant number of novel antigens are being investigated with the perspective of developing new anti-tick vaccines. However, more research is required to develop new and more efficient antigen-based vaccines, including on assessing the efficiency of various epitopes against different tick species to confirm their cross-reactivity and their high immunogenicity. In this review, we discuss the recent advancements in the development of antigen-based vaccines (traditional and RNA-based) and provide a brief overview of recent discoveries of novel antigens, along with their sources, characteristics, and the methods used to test their efficiency.

Evaluation of anti-tick efficiency in rabbits induced by DNA vaccines encoding Haemaphysalis longicornis lipocalin homologue

Haemaphysalis longicornis is an obligate haematophagous ectoparasite, transmitting a variety of pathogens, which brings great damage to human health and animal husbandry development. Lipocalins (LIP) are a family of proteins that transport small hydrophobic molecules and also involve in immune regulation, such as the regulation of cell homeostasis, inhibiting the host's inflammatory response and resisting the contractile responses in host blood vessels. Therefore, it is one of the candidate antigens for vaccines. Based on previous studies, we constructed the recombinant plasmid pcDNA3.1-HlLIP of LIP homologue from H. longicornis (HlLIP). ELISA results showed that rabbits immunized with pcDNA3.1-HlLIP produced higher anti-rHlLIP antibody levels compared with the pcDNA3.1 group, indicating that pcDNA3.1-HlLIP induced the humoral immune response of host. Adult H. longicornis infestation trial in rabbits demonstrated that the engorgement weight, oviposition and hatchability of H. longicornis fed on rabbits immunized with pcDNA3.1-HlLIP decreased by 7.07%, 14.30% and 11.70% respectively, compared with that of the pcDNA3.1 group. In brief, DNA vaccine of pcDNA3.1-HlLIP provided immune protection efficiency of 30% in rabbits. This study demonstrated that pcDNA3.1-HlLIP can partially protect rabbits against H. longicornis, and it is possible to develop a new candidate antigen against ticks.

Oral vaccination of mice with attenuated Salmonella encoding Trichinella spiralis calreticulin and serine protease 1.1 confers protective immunity in BALB/c mice

BACKGROUND

Trichinella spiralis is a foodborne parasitic nematode which is a serious risk to meat safety. Development of anti-Trichinella vaccine is needed to control Trichinella infection in food animals. In this study, two novel T. spiralis genes (calreticulin and serine protease 1.1) in combination were used to construct oral DNA vaccines, and their induced protective immunity was evaluated in a murine model.

METHODOLOGY/PRINCIPAL FINDINGS

TsCRT+TsSP1.1, TsCRT and TsSP1.1 DNA were transformed into attenuated Salmonella typhimurium ΔcyaSL1344. Oral vaccination of mice with TsCRT+TsSP1.1, TsCRT and TsSP1.1 DNA vaccines elicited a gut local mucosal sIgA response and systemic Th1/Th2 mixed response. Oral vaccination with TsCRT+TsSP1.1 induced obviously higher level of serum specific antibodies, mucosal sIgA and cellular immune response than either of single TsCRT or TsSP1.1 DNA vaccination. Oral vaccination of mice with TsCRT+TsSP1.1 exhibited a 53.4% reduction of enteral adult worms and a 46.05% reduction of muscle larvae, conferred a higher immune protection than either of individual TsCRT (44.28 and 42.46%) or TsSP1.1 DNA vaccine (35.43 and 29.29%) alone. Oral vaccination with TsCRT+TsSP1.1, TsCRT and TsSP1.1 also obviously ameliorated inflammation of intestinal mucosa and skeletal muscles of vaccinated mice after challenge.

CONCLUSIONS

TsCRT and TsSP1.1 might be regarded the novel potential targets for anti-Trichinella vaccines. Attenuated Salmonella-delivered DNA vaccine provided a prospective approach to control T. spiralis infection in food animals.

Oral Vaccination of Mice With Trichinella spiralis Putative Serine Protease and Murine Interleukin-4 DNA Delivered by Invasive Lactiplantibacillus plantarum Elicits Protective Immunity

Trichinellosis is a serious zoonotic parasitic disease caused by Trichinella spiralis (T. spiralis) that causes considerable economic losses for the global pig breeding and food industries. As such, there is an urgent need for a vaccine that can prevent T. spiralis infection. Previous studies have reported that recombinant invasive Lactococcus lactis (LL) expressing Staphylococcus aureus fibronectin binding protein A (LL-FnBPA+) can transfer DNA vaccines directly to dendritic cells (DCs) across an epithelial cell monolayer, leading to significantly higher amounts of heterologous protein expression compared to non-invasive Lactococcus lactis. In this study, the invasive bacterium Lactiplantibacillus plantarum (L. plantarum) expressing FnBPA was used as a carrier to deliver a novel oral DNA vaccine consisting of T. spiralis adult putative serine protease (Ts-ADpsp) and murine interleukin (IL)-4 DNA to mouse intestinal epithelial cells. Experimental mice were orally immunized 3 times at 10-day intervals. At 10 days after the last vaccination, mice were challenged with 350 T. spiralis infective larvae by oral inoculation. Immunization with invasive L. plantarum harboring pValac-Ts-ADpsp/pSIP409-FnBPA induced the production of anti-Ts-ADpsp-specific IgG of serum, type 1 and 2 helper T cell cytokines of mesenteric lymph node (MLN) and spleen, secreted (s) IgA of intestinal lavage, and decreased T. spiralis burden and intestinal damage compared to immunization with non-invasive L. plantarum expressing Ts-ADpsp (pValac-Ts-ADpsp/pSIP409). Thus, invasive L. plantarum expressing FnBPA and IL-4 stimulates both mucosal and cellular immune response to protect against T. spiralis infection, highlighting its therapeutic potential as an effective DNA vaccine for trichinellosis.

Vaccines as a Strategy to Control Trichinellosis

Trichinellosis caused by Trichinella spiralis is a worldwide food-borne parasitic zoonosis. Several approaches have been performed to control T. spiralis infection, including veterinary vaccines, which contribute to improving animal health and increasing public health by preventing the transmission of trichinellosis from animals to humans. In the past several decades, many vaccine studies have been performed in effort to control T. spiralis infection by reducing the muscle larvae and adult worms burden. Various candidate antigens, selected from excretory-secretory (ES) products and different functional proteins involved in the process of establishing infection have been investigated in rodent or swine models to explore their protective effect against T. spiralis infection. Moreover, different types of vaccines have been developed to improve the protective effect against T. spiralis infection in rodent or swine models, such as live attenuated vaccines, natural antigen vaccines, recombinant protein vaccines, DNA vaccines, and synthesized epitope vaccines. However, few studies of T. spiralis vaccines have been performed in pigs, and future research should focus on exploring the protective effect of different types of vaccines in swine models. Here, we present an overview of the strategies for the development of effective T. spiralis vaccines and summarize the factors of influencing the effectiveness of vaccines. We also discuss several propositions in improving the effectiveness of vaccines and may provide a route map for future T. spiralis vaccines development.

Oral immunization with attenuated Salmonella encoding an elastase elicits protective immunity against Trichinella spiralis infection

Elastase belongs to the serine protease family. Previous studies showed that Trichinella spiralis elastase (TsE) was highly expressed in intestinal infective larvae (IIL). Recombinant TsE (rTsE) promoted the larval intrusion of enteral epithelium cells (IECs), whereas anti-rTsE antibodies and siRNA impeded larval intrusion. Subcutaneous vaccination of mice with rTsE showed a partial protective immunity, suggesting that TsE might be a promising vaccine target against Trichinella infection. In this study, complete TsE cDNA sequence was cloned into pcDNA3.1, and the rTsE DNA was transformed into attenuated S. typhimurium strain ΔcyaSL1344. Oral vaccination of mice with TsE DNA elicited a systemic Th1/Th2/Treg mixed immune response and gut local mucosal sIgA response. Immunized mice exhibited a significant immune protection against T. spiralis larval challenge, as demonstrated by a 52.48% reduction of enteral adult worms and a 69.43% reduction of muscle larvae. The protection might be related to the TsE-induced production of intestinal mucus, specific anti-TsE sIgA and IgG, and secretion of IFN-γ, IL-2, IL-4 and IL-10, which protected gut mucosa from larval intrusion, suppressed worm development and impeded female reproduction. The results demonstrated that attenuated Salmonella-delivered TsE DNA vaccine provided a prospective strategy for the control of Trichinella infection in food animals.

Vaccination of mice with recombinant novel aminopeptidase P and cathepsin X alone or in combination induces protective immunity against Trichinella spiralis infection

Trichinella spiralis is a major foodborne zoonotic parasitic nematode which has a serious threat to meat food safety. Development of anti-Trichinella vaccine is requisite for control and elimination of Trichinella infection in food animals to ensure meat safety. Aminopeptidase P (TsAPP) and cathepsin X (TsCX) are two novel proteins identified in T. spiralis intestinal infectious L1 larvae (IIL1). The objective of this study was to investigate the protective immunity elicited by immunization with TsAPP and TsCX alone and TsAPP-TsCX in combination in a mouse model. The results demonstrate that subcutaneous vaccination of mice with rTsAPP, rTsCX or rTsAPP + rTsCX elicited a systemic humoral response (high levels of serum IgG, IgG1/IgG2a and IgA) and significant local gut mucosal sIgA responses. The vaccination with rTsAPP, rTsCX or rTsAPP + rTsCX also induced a systemic and local mixed Th1/Th2 response, as demonstrated by clear elevation levels of IFN-γ and IL-4 in vaccinated mice. Vaccination of mice with rTsAPP+rTsCX exhibited a 63.99 % reduction of intestinal adult worms and 68.50% reduction of muscle larva burdens, alleviated inflammation of intestinal mucosal and muscle tissues, and provided a higher immune protection than that of vaccination with rTsAPP or rTsCX alone. The results demonstrated that TsAPP and TsCX might be considered novel candidate target molecules for anti-Trichinella vaccines.

Oral vaccination with attenuated Salmonella encoding the Trichinella spiralis 43-kDa protein elicits protective immunity in BALB/c mice

A vaccine against Trichinella spiralis infection is urgently needed to interrupt its transmission from domestic animals to humans. However, no vaccine against T. spiralis is currently available. Our previous study demonstrated that the use of the 43-kDa glycoprotein present in excretory-secretory (ES) proteins of muscle larvae (ML) as an intramuscular DNA vaccine led to a 52.1% protection rate against T. spiralis infection. Attenuated Salmonella strains have the advantage of eliciting mucosal immunity, which is important for controlling T. spiralis infections at the intestinal stage and can be provided as vaccines via oral or intranasal routes. Therefore, in this study, complete 43-kDa glycoprotein (Ts43) sequences of T. spiralis were cloned into the vector pYA3681, and the recombinant plasmid pYA3681-Ts43 was transformed into the attenuated Salmonella typhimurium strain χ11802. The results showed that oral vaccination of mice with attenuated Salmonella carrying the recombinant plasmid pYA3681-Ts43 induced an evident elevation of the local intestinal mucosal sIgA and serum IgG antibody responses. The flow cytometry results showed that the percentages of CD4⁺ T cells and secreted IFN-γ, IL-4, and IL-17A in CD4⁺ T cells were significantly increased in the spleen and mesenteric lymph node (MLN) lymphocytes of the vaccinated groups. In addition, increased levels of the IFN-γ, IL-4, and IL-17A cytokines were also observed in the serum of the immunized groups. The above immune response results in the immunized groups demonstrated that protective immunity was elicited in this study. Finally, vaccinated mice demonstrated a significant 45.9% reduction in ML burden after infection with T. spiralis. This study demonstrated that oral vaccination with Ts43 delivered by attenuated Salmonella elicited local and systemic concurrent Th1/Th2/Th17 immune responses and provided partial protection against T. spiralis infection in BALB/c mice. This is a prospective strategy for the prevention and control of trichinellosis.

Evaluation on two types of paramyosin vaccines for the control of Haemaphysalis longicornis infestations in rabbits

BACKGROUND

Haemaphysalis longicornis is an obligate hematophagous ectoparasite that transmits a variety of pathogens causing life-threatening diseases in humans and animals. Paramyosin (Pmy) is not only an invertebrate-specific myofibrillar protein but also an important immunomodulatory protein. Therefore, it is one of the ideal candidate antigens for vaccines.

METHODS

We conducted two vaccine trials to evaluate the protective efficacy of Pmy recombinant protein (rPmy) and peptide vaccine (KLH-LEE). Each rabbit was immunized with three doses of rPmy or KLH-LEE adjuvanted with Freund's complete/incomplete at 500 μg/dose at 2-week intervals before challenge with 40 female H. longicornis/rabbit. PBS plus adjuvant, Trx or KLH was used as control group. The antibodies of rabbits were detected by ELISA. Then, female ticks were fed on the rabbits until detachment.

RESULTS

ELISA results showed that both vaccines induced rabbits to produce antibodies. Compared with the Trx group, the engorgement weight, oviposition and hatchability of the rPmy group decreased by 8.87%, 26.83% and 38.86%, respectively. On the other hand, engorgement weight, oviposition and hatchability of female ticks in the KLH-LEE group correspondingly resulted in 27.03%, 53.15% and 38.40% reduction compared with that of the KLH group. Considering the cumulative effect of vaccination on the evaluated parameters, results showed 60.37% efficacy of the rPmy vaccine formulation and 70.86% efficacy in the KLH-LEE group.

CONCLUSIONS

Pmy and particularly epitope LEE have potential for further development of an effective candidate vaccine to protect the host against tick infection. GRAPHIC ABSTARCT.

The immune protection induced by a serine protease from the Trichinella spiralis adult against Trichinella spiralis infection in pigs

Trichinellosis is a major foodborne parasitosis caused by Trichinella spiralis. In the present study, a serine protease gene from an adult T. spiralis (Ts-Adsp) cDNA library was cloned, expressed in Escherichia coli and purified by Ni-affinity chromatography. Previous studies of our laboratory have found that mice vaccinated with recombinant Ts-Adsp protein (rTs-Adsp) exhibited partial protection against T. spiralis infection. In this study, the protective effect of rTs-Adsp against T. spiralis infection in pigs was further explored. The cell-mediated and humoral immune responses induced by rTs-Adsp were measured, including the dynamic trends of specific antibody levels (IgG, IgG1, IgG2a and IgM), as well as the levels of cytokines (IFN-γ, IL-2, IL-4, and IL-10) in the serum. Moreover, the changes in T lymphocytes, B lymphocytes, and neutrophils were measured to evaluate cellular immune responses in pigs vaccinated with rTs-Adsp. The results indicated that a Th1-Th2 mixed immune response with Th1 predominant was induced by rTs-Adsp after vaccination. Flow cytometric analysis showed that the proportions of CD4⁺ T cells, B cells, and neutrophils in the immunized groups were significantly increased. Furthermore, pigs vaccinated with rTs-Adsp exhibited a 50.9% reduction in the muscle larvae burden, compare with pigs from the PBS group five weeks after challenged. Our results suggested that rTs-Adsp elicited partial protection and it could be a potential target molecule for preventing and controlling Trichinella transmission from pigs to human.

Trichinellosis is a global foodborne parasitic disease caused by consuming raw or poorly cooked meat. The porcine products are the most common source. Therefore, it will have a great significance for public health security and human health to prevent and control the trichinellosis. We previously found that mice vaccinated with recombinant Adsp protein (rTs-Adsp) exhibited partial protection against T. spiralis infection. In this study, the protective effect of rTs-Adsp against challenge infections with T. spiralis in pigs was further explored. We found that rTs-Adsp elicited partial protection and it could be an important target molecule for preventing and controlling T. spiralis transmission from pigs to human.