Immunization with Trichinella spiralis Korean isolate larval excretory-secretory antigen induces protection and lymphocyte subset changes in rats

The cysteine protease ATG4B of Trichinella spiralis promotes larval invasion into the intestine of the host

The cysteine proteases of parasites are vital contributors that induce parasite migration to and invasion of host tissue. In this study, we analysed the cysteine protease ATG4B of Trichinella spiralis (TsATG4B) isolated from the soluble proteins of Trichinella spiralis (T. spiralis) adult worms to ascertain its biochemical properties and functions during invasion into the intestine of the host. The 43 kDa recombinant cysteine protease ATG4B protein (rTsATG4B) consists of a conserved peptidase_C54 domain and was expressed in Escherichia coli. Gelatine zymography showed that rTsATG4B could hydrolyse gelatine and that the hydrolytic activity was prevented by the cysteine protease inhibitor E-64 (pH 5.2). Immunofluorescence assays showed that TsATG4B is expressed at different stages and is localized at the cuticles and stichosomes of worms. Far-Western blotting and confocal microscopy revealed that rTsATG4B interacts with intestinal epithelial cells (IECs) and that it was subcellularly localized to the membrane and cytoplasm in IECs. Real‑time quantitative PCR (qPCR) results indicated that the transcription level of the TsATG4B gene was the higher in 6-day-old adult worms (6 days AW) than in any other stage. An in vitro larval invasion assay verified that rTsATG4B promoted larval invasion and that invasion was inhibited when rTsATG4B was pre-incubated with E-64, whereas anti-rTsATG4B serum inhibited larval invasion in a dose-dependent manner. Collectively, these results suggested that the enzymatic activity of TsATG4B significantly influences the hydrolysis process, which is necessary for larval invasion of the host intestinal epithelium.

A Multiple Antigen Peptide Vaccine Containing CD4+ T Cell Epitopes Enhances Humoral Immunity against Trichinella spiralis Infection in Mice

Multiepitope peptide vaccine has some advantages over traditional recombinant protein vaccine due to its easy and fast production and possible inclusion of multiple protective epitopes of pathogens. However, it is usually poorly immunogenic and needs to conjugate to a large carrier protein. Peptides conjugated to a central lysine core to form multiple antigen peptides (MAPs) will increase the immunogenicity of peptide vaccine. In this study, we constructed a MAP consisting of CD4⁺ T cell and B cell epitopes of paramyosin (Pmy) of Trichinella spiralis (Ts-Pmy), which has been proved to be a good vaccine candidate in our previous work. The immunogenicity and induced protective immunity of MAP against Trichinella spiralis (T. spiralis) infection were evaluated in mice. We demonstrated that mice immunized with MAP containing CD4⁺ T cell and B cell epitopes (MAP-TB) induced significantly higher protection against the challenge of T. spiralis larvae (35.5% muscle larva reduction) compared to the MAP containing B cell epitope alone (MAP-B) with a 12.4% muscle larva reduction. The better protection induced by immunization of MAP-TB was correlated with boosted antibody titers (both IgG1 and IgG2a) and mixed Th1/Th2 cytokine production secreted by the splenocytes of immunized mice. Further flow cytometry analysis of lymphocytes in spleens and draining lymph nodes demonstrated that mice immunized with MAP-TB specifically enhanced the generation of T follicular helper (Tfh) cells and germinal center (GC) B cells, while inhibiting follicular regulatory CD4⁺ T (Tfr) cells and regulatory T (Treg) cells. Immunofluorescence staining of spleen sections also confirmed that MAP-TB vaccination enhanced the formation of GCs. Our results suggest that CD4⁺ T cell epitope of Ts-Pmy is crucial in vaccine component for inducing better protection against T. spiralis infection.

Short-term in vitro culture of purity and highly functional rat bone marrow-derived mast cells

Mast cells (MCs) are responsible for the innate immune response. Rat MCs are more suitable than mouse MCs as models of specific parasite infection processes and ovalbumin-induced asthma. Rat peritoneum-derived MCs and RBL-2H3 cells (an MC cell line) are widely used in disease studies. However, the application of rat bone marrow-derived MCs (BMMCs) are poorly documented in terms of the methodology of rat BMMC isolation. Here, we describe a relatively rapid, efficient, and simple method for the cultivation of rat BMMCs. As compared to previous protocols, rat BMMCs produced with the proposed protocol exhibited advantages in differentiation, proliferation, lifespan, and functionality, which should prove useful for studies of mucosal MC diseases in specific rat models.

The development of methods for primary mast cells in vitro and ex vivo: An historical review

Mast cells (MCs) are tissue-based stationary effector cells that form the immune system's first-line defense against various challenges. They are developed from the bone marrow-derived progenitors to complete their differentiation and maturation in the tissues where they eventually establish residence. MCs have been implicated in many diseases, such as allergy, parasitic infection, and neoplastic disorders. Immortalized MC lines, such as RBL-2H3, HMC-1, and LAD-2, are useful for investigating the biological functions of MC only to some extents due to the restriction of degranulation evaluation, in vivo injection and other factors. Over the past few decades, technologies for acquiring primarily MCs have been continually optimized, and novel protocols have been proposed. However, no relevant publications have analyzed and summarized these techniques. In this review, the classical approaches for extracting MCs are generalized, and new methods with potential values are introduced. We also evaluate the advantages and applicability of diverse MC models. Since MCs exhibit substantial plasticity and functional diversity due to different origins, it is both necessary and urgent to select a reliable and suitable source of MCs for a particular study.

A novel antigenic cathepsin B protease induces protective immunity in Trichinella-infected mice

Trichinellosis is a foodborne disease that remains a public health hazard and an economic problem in food safety. Vaccines against the parasite can be an effective way to control this disease; however, commercial vaccines against Trichinella infection are not yet available. Trichinella cathepsin B proteins appear to be promising targets for vaccine development. Here, we reported for the first time the characterization of a novel cDNA that encodes Trichinella spiralis (T. spiralis) cathepsin B-like protease 2 gene (TsCPB2). The recombinant mature TsCPB2 protein was successfully expressed in E. coli system and purified with Ni-affinity chromatography. TsCPB2 expression was detected at all the developmental stages of T. spiralis and it was expressed as an excretory-secretory protein of T. spiralis muscle larvae. Immunization with TsCPB2 antigen induced a combination of humoral and cellular immune responses, which manifested as a mixed Th1/Th2 response, as well as remarkably elevated IgE level. Moreover, vaccination of mice with TsCPB2 that were subsequently challenged with T. spiralis larvae resulted in a 52.3% (P < .001) reduction in worm burden and a 51.2% (P < .001) reduction in muscle larval burden. Our results suggest that TsCPB2 induces protective immunity in Trichinella-infected mice and might be a novel vaccine candidate against trichinellosis.

Immuno-proteomic analysis of Trichinella spiralis, T. pseudospiralis, and T. papuae extracts recognized by human T. spiralis-infected sera

The present study explored potentially immunogenic proteins of the encapsulated (Trichinella spiralis) and non-encapsulated (T. pseudospiralis, T. papuae) species within the genus Trichinella. The somatic muscle larval extracts of each species were subjected to immunoblotting analysis using human T. spiralis-infected serum samples. Fifteen reactive bands of all three species were selected for further protein identification by liquid chromatography-tandem mass spectrometry, and their possible functions were ascertained using the gene ontology. Our findings showed immunogenic protein patterns with molecular mass in the range of 33-67 kDa. Proteomic and bioinformatic analysis revealed a wide variety of functions of 17 identified proteins, which are associated with catalytic, binding, and structural activities. Most proteins were involved in cellular and metabolic processes that contribute in the invasion of host tissues and the larval molting processes. The parasite proteins were identified as actin-5C, serine protease, deoxyribonuclease-2, and intermediate filament protein ifa-1. This information may lead to alternative tools for selection of potential diagnostic protein markers or aid in the design of vaccine candidates for prevention and control of Trichinella infection.

Immune responses induced by co-infection with Capillaria hepatica in Clonorchis sinensis-infected rats

Clonorchis sinensis and Capillaria hepatica are zoonotic parasites that mainly infect the liver and cause serious liver disorders. However, immunological parameters induced by co-infection with these parasites remain unknown. In this study, for the first time, we investigated immunological profiles induced by co-infection with C. hepatica (CH) in C. sinensis (CS)-infected rats (Sprague-Dawley). Rats were infected primarily with 50 metacercariae of C. sinensis; 4 weeks later, they were subsequently infected with 1000 infective C. hepatica eggs. Significantly higher levels of C. sinensis- or C. hepatica-specific IgG antibodies were found in the sera of rats. Interestingly, no cross-reacting antibody was observed between C. sinensis and C. hepatica infections. Significantly raised eosinophil levels were found in the blood of C. sinensis/C. hepatica co-infected rats (CS + CH) compared to the blood of rats infected singly with C. sinensis. Co-infected rats showed significantly higher levels of lymphocyte proliferation and cytokine production compared to a single C. sinensis infection. The worm burden of C. sinensis was significantly reduced in co-infected rats compared to the single C. sinensis infection. These results indicate that the eosinophils, lymphocyte proliferation and cytokine production induced by subsequent infection with C. hepatica in C. sinensis-infected rats might contribute to the observed C. sinensis worm reduction.

Evaluation of protective efficacy induced by virus-like particles containing a Trichinella spiralis excretory-secretory (ES) protein in mice

BACKGROUND

The frequent outbreaks of human trichinellosis globally underscore the need to develop effective vaccine. We hypothesized that a novel vaccine could improve vaccine efficacy against Trichinella spiralis.

METHODS

In this study, we developed virus-like particles (VLPs) containing the 53 KDa excretory/secretory (ES) protein of T. spiralis and the influenza matrix protein 1 (M1) as a core protein, and investigated the protective efficacy of the VLPs alone or with cholera toxin (CT) in a mouse model.

RESULTS

Intramuscular immunization induced T. spiralis-specific IgG, IgG1 and IgG2a antibody responses before and after challenge infections in the sera. These antibody responses were significantly enhanced in mice immunized with adjuvanted VLPs. Upon challenge infection, vaccinated mice showed significantly reduced worm burden in the diaphragm. Protective immune responses and efficacy of protection were significantly improved by immunization with VLPs together with CT adjuvant.

CONCLUSIONS

Our results are informative for a better understanding of the protective immunity induced by T. spiralis VLPs, and will provide insight into designing safe and effective vaccines.

Proteomic analysis and immunodetection of antigens from early developmental stages of Trichinella spiralis

Trichinella spiralis is an ubiquitous parasitic nematode that lives in muscle tissue of many hosts and causes trichinellosis in humans. Numerous efforts have been directed at specific detection of this infection and strategies for its control. TSL-1 and other antigens, mainly from muscle larvae (ML), have been used to induce partial protection in rodents. An improvement in protective immunity may be achieved by using antigens from other parasite stages. Further, identification of other parasite antigens may provide insights into their role in the host-parasite interaction. In this study, T. spiralis antigens from early developmental parasite stages, namely ML and pre-adult (PA) obtained at 6h, 18h and 30h post-infection, were identified by proteomic and mass spectrometry analyses. Our findings showed a differential expression of several proteins with molecular weights in the range of 13-224kDa and pI range of 4.54-9.89. Bioinformatic analyses revealed a wide diversity of functions in the identified proteins, which include structural, antioxidant, actin binding, peptidyl prolyl cis-trans isomerase, motor, hydrolase, ATP binding, magnesium and calcium binding, isomerase and translation elongation factor. This, together with the differential recognition of antigens from these parasite stages by antibodies present in intestinal fluid, in supernatants from intestinal explants, and in serum samples from mice infected with T. spiralis or re-infected with this parasite, provides information that may lead to alternatives in the design of vaccines against this parasite or for modulation of immune responses.

Enhanced protection against Clonorchis sinensis induced by co-infection with Trichinella spiralis in rats

Although co-infection with multiple parasites is a frequent occurrence, changes in the humoral immune response against a pre-existing parasite induced as a result of a subsequent parasitic infection remain undetermined. Here, we utilized enzyme-linked immunosorbent assay (ELISA) to investigate antibody responses, cytokine production and enhanced resistance in Clonorchis sinensis-infected rats (Sprague-Dawley) upon Trichinella spiralis infection. Higher levels of C. sinensis-specific IgG and IgA were elicited upon T. spiralis infection, and these levels remained higher than in rats infected with C. sinensis alone. Upon subsequent infection with T. spiralis, IgG antibodies against C. sinensis appeared to be rapidly boosted at day 3, and IgA antibodies were boosted at day 7. Challenge infection of C. sinensis-infected rats with T. spiralis induced substantial mucosal IgG and IgA responses in the liver and intestine and increases in antibody-secreting plasma cells in the spleen and bone marrow. Subsequent infection also appeared to confer effective control of liver C. sinensis loads, resulting in enhanced resistance. Memory B cells generated in response to C. sinensis infection were rapidly amplified into antibody-secreting cells upon T. spiralis infection. These results indicate that enhanced C. sinensis clearance induced by co-infection is associated with systemic and mucosal IgG and IgA responses.

An antigenic recombinant serine protease from Trichinella spiralis induces protective immunity in BALB/c mice

In this study, we report the cloning and characterization of a cDNA encoding a Trichinella serine protease gene (TspSP-1.3) from GenBank. The recombinant TspSP-1.3 protein (rTspSP-1.3) was expressed in an Escherichia coli expression system and purified with Ni-affinity chromatography. Real-time quantitative PCR analysis revealed that TspSP-1.3 was expressed at significantly higher levels in muscle larvae and adult worms than in newborn larvae. TspSP-1.3 was detected in excretory-secretory proteins of Trichinella spiralis with western blotting. Immunization with the rTspSP-1.3 antigen induced humoral immune responses, which manifested as elevated specific anti-rTspSP-1.3 IgG and IgE antibodies and a mixed Th1/Th2 response. To determine whether purified rTspSP-1.3 had good antigenicity and could be a vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with rTspSP-1.3 and subsequently challenged the mice with T. spiralis larvae. The results showed that mice vaccinated with rTspSP-1.3 exhibited an average reduction in the muscle larvae burden of 39 % relative to the control group. These results suggest that TspSP-1.3 could be a novel vaccine candidate for controlling Trichinella infection.

Effects of IL-3 and SCF on Histamine Production Kinetics and Cell Phenotype in Rat Bone Marrow-derived Mast Cells

BACKGROUND

Rat mast cells were regarded as a good model for mast cell function in immune response.

METHODS

Rat bone marrow mast cells (BMMC) were prepared both by recombinant rat IL-3 (rrIL-3) and by recombinant mouse stem cell factor (rmSCF), and investigated for both proliferation and differentiation in time course. Rat BMMC was induced by culture of rat bone marrow cells (BMCs) in the presence of both rrIL-3 (5 ng/ml) and rmSCF (5 ng/ml). Culture media were changed 2 times per week with the cell number condition of 5x10(4)/ml in 6 well plate. Proliferation was analyzed by cell number and cell counting kit-8 (CCK-8) and differentiation was by rat mast cell protease (RMCP) II and histamine.

RESULTS

Cell proliferation rates reached a maximum at 8 or 11 days of culture and decreased thereafter. However, both RMCP II production and histamine synthesis peaked after 11 days of culture. By real time RT-PCR, the level of histidine decarboxylase mRNA was more than 500 times higher on culture day 11 than on culture day 5. By transmission electron microscopy, the cells were heterogeneous in size and contained cytoplasmic granules. Using gated flow cytometry, we showed that cultured BMCs expressed high levels of FcepsilonRI and the mast cell antigen, ganglioside, on culture day 11.

CONCLUSION

These results indicate that rat BMMCs were generated by culturing BMCs in the presence of rrIL-3 and rmSCF and that the BMMCs have the characteristics of mucosal mast cells.

A bivalent influenza VLP vaccine confers complete inhibition of virus replication in lungs

The conventional egg-grown influenza vaccines are trivalent. To test the feasibility of using multivalent influenza virus-like particles (VLPs) as an alternative influenza vaccine, we developed cell-derived influenza VLPs containing the hemagglutinin (HA) of the H1 subtype virus A/PR/8/34 or the H3 subtype virus A/Aichi/2/68 (X31). Mice immunized intramuscularly with bivalent influenza VLPs containing H1 and H3 HAs induced neutralizing activities against the homologous and closely related H1N1 strains A/PR/8/34 and A/WSN/33 as well as the H3N2 strains A/Aichi/2/68 (X31) and A/Hong Kong/68, but not the A/Philippines/2/82 strain isolated 14 years later. HA sequence and structure analysis indicated that antigenic distance could be a major factor in predicting cross-protection by VLP vaccines. The bivalent influenza VLP vaccine demonstrated advantages in broadening the protective immunity after lethal challenge infections when compared to a monovalent influenza VLP vaccine. High levels of the inflammatory cytokine IL-6 were observed in naïve or unprotected immunized mice but not in protected mice upon lethal challenge. These results indicate that multivalent influenza VLP vaccines can be an effective antigen for developing safe and alternative vaccine to control the spread of influenza viruses.

Immunogenicity of virus-like particles containing modified human immunodeficiency virus envelope proteins

Extensive glycosylation and variable loops of the HIV envelope protein (Env) are reported to shield some neutralizing epitopes. Here, we investigated the immunogenicity of mutated HIV Envs presented in virus-like particles (VLPs). We immunized mice with simian human immunodeficiency virus (SHIV) VLPs containing mutant HIV Env with reduced glycosylation (3G), variable loop-deleted mutations (dV1V2), or combinations of both types of mutations (3G-dV2-1G), and evaluated immune responses. Immune sera from mice that received VLPs with modified HIV Envs (3G or dV1V2) showed higher neutralizing activities against the homologous HIV 89.6 virus as well as heterologous viruses when compared with wild type SHIV VLP-immunized mice. Lymphocytes from immunized mice produced HIV Env-specific cytokines, with the 3G-dV2-1G mutant producing high levels of cytokines. Interestingly, both dendritic cells and B cells were found to interact with VLPs suggesting that VLPs are effective immunogens. Therefore, this study suggests that VLPs containing modified HIV Env have the potential to be developed as candidate vaccines capable of inducing cellular and humoral immune responses including neutralizing activities.

Ginseng and Salviae herbs play a role as immune activators and modulate immune responses during influenza virus infection

We have investigated the adjuvant roles of common herbal medicines (ginseng, Salviae) and their effects on early immune responses during influenza virus infection in a mouse model. Intranasal co-administration with inactivated influenza virus A (PR8) and ginseng or Salviae extract increased the levels of influenza virus specific antibodies and neutralizing activities compared to immunization with PR8 alone, and provided protective immunity. Salviae co-administration significantly enhanced IFN-gamma and IL-2 cytokine producing splenocytes while ginseng induced high levels of IL-4 and IL-5 cytokine producing cells after challenge infection. Cells expressing an early activation marker CD69 and levels of a pro-inflammatory cytokine IL-6 were highly elevated in lungs from naïve mice during challenge virus infection, which might be a mechanism in lung inflammation leading to death. In contrast, immunized mice that were co-administered ginseng or Salviae modulated CD69 expressing immune cells, did not produce IL-6, and showed significant enhancement of influenza virus specific IgA antibody in lungs after challenge virus infection. Therefore, these results indicate that both ginseng and Salviae play a role as mucosal adjuvants against influenza virus as well as immuno-modulators during influenza virus infection.