Effects of Trichinella spiralis and its serine protease inhibitors on intestinal mucosal barrier function

Trichinella spiralis (T. spiralis) is a highly pathogenic zoonotic nematode that poses significant public health risks and causes substantial economic losses. Understanding its invasion mechanisms is crucial. This study explored how the serine protease inhibitors (SPIs) secreted by T. spiralis affect the host's intestinal epithelial barrier. Furthermore, the effects of T. spiralis infection on the jejunal barrier function in mice were investigated. The histopathological analysis indicated significant damage to the jejunum, which peaked at day 7 post-infection (dpi). The results of RT-qPCR and western blotting revealed marked reductions in tight junction proteins (ZO-1, occludin, claudin-3), mucins (MUC-1, MUC-2), and anti-inflammatory cytokines (TGF-β, IL-10) from 1 to 15 dpi. There was also increased expression of Toll-like receptors (TLR-1, TLR-2, TLR-4) and pro-inflammatory cytokines (TNF-α, IL-1β). Recombinant SPIs (rKaSPI, rAdSPI) were purified, co-cultured with intestinal epithelial cells (IPECs), and used in mouse models. The protein expression changes in IPECs and mice were consistent with those in T. spiralis-infected tissues. Both SPIs caused the down-regulation of ZO-1, occludin, claudin-3, MUC-1, MUC-2, TGF-β, and IL-10 while up-regulating TLR-4 and pro-inflammatory cytokines. As a result, the intestinal barrier was disrupted, and inflammation was exacerbated. Notably, rAdSPI had a more pronounced effect. In summary, T. spiralis infection caused significant jejunal damage and disrupted the intestinal barrier. T. spiralis-secreted SPIs, especially serpin-type serine protease inhibitors (AdSPI), were pivotal in facilitating invasion by compromising the host's intestinal barrier and promoting inflammation. This study provides insights into T. spiralis invasion mechanisms and the potential targets for trichinellosis prevention and control.

Oral non-viral gene delivery platforms for therapeutic applications

Since gene therapy can regulate gene and protein expression directly, it has a great potential to prevent or treat a variety of genetic or acquired diseases through vaccines such as viral infections, cystic fibrosis, and cancer. Owing to their high efficacy, in vivo gene therapy trials are usually conducted intravenously, which is usually costly and invasive. There are several advantages to oral drug administration over intravenous injections, such as better patient compliance, ease of use, and lower cost. However, gene therapy is successful if the oligonucleotides can cross the cell membrane easily and reach the nucleus after the endosomal escape. In order to accomplish this task and deliver the cargo to the intended location, appropriate delivery systems should be introduced. This review summarizes oral delivery systems developed for effective gene delivery, vaccination, and treatment of various diseases. Studies have also shown that oral delivery approaches are potentially applicable to treat various diseases, especially inflammatory bowel disease, stomach, and colorectal cancers. Also, the current review provides an update overview on the development of non-viral and oral gene delivery techniques for gene therapy and vaccination purposes.

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.

Acceleration of Trichinella spiralis worm expulsion by leukotriene B4 receptor binding inhibition

AIMS

Helminth infection typically induces a Th2 inflammatory response that is characterized by eosinophilia, high levels of IgE and mast cells. LTB4 is generated from innate immune cells, such as neutrophils, macrophages and mast cells, in response to a range of stimuli. It mainly acts on myeloid leukocytes, inducing the activation of integrins, adhesion to endothelium walls, and chemotaxis.

METHODS AND RESULTS

The objective of the present study was to determine the role of the LTB4 receptor in Trichinella spiralis expulsion. We treated mice with the LTB4 receptor antagonist before infection with T. spiralis. We observed that the number of mast cells and worm infection decreased following treatment with the BLT antagonist during the intestinal phase. We also demonstrated that blocking the LTB4 receptor inhibited neutrophil and eosinophil infiltration.

CONCLUSIONS

Further studies are required to investigate the specific mechanism of mast cell number decrease and worm infection and the in vitro interactions between LTB4 and worm expulsion.

Resiniferatoxin promotes adult worm expulsion in Trichinella spiralis-infected rats by Th2 immune response modulation

BACKGROUND

The immune response during T spiralis infection is characterized by an increase in eosinophils and mast cells, as well as Th2 cytokine production, such as interleukin (IL)-4, IL-10 and IL-13, promoting T spiralis expulsion from the host. However, this response damages the host, favouring the parasite survival. In the search for new pharmacological strategies that protect against T spiralis infection, a recent study showed that treatment with resiniferatoxin (RTX) modulates the Th1 cytokines production, reducing muscle parasite burden.

OBJECTIVE

To evaluate the effect of RTX treatment on the Th2 cytokines production, the number of eosinophils, mast cells and the intestinal expulsion of T spiralis.

METHODS

Serum levels of IL-4, IL-10 and IL-13 were quantified by ELISA; the number of eosinophils, mast cells and the adult worms of T spiralis in the small intestine was quantified.

RESULTS

RTX treatment increased serum levels of IL-4, IL-10 and IL-13, and it decreases intestinal eosinophilia, however, favours the mastocytosis, promoting T spiralis intestinal expulsion.

CONCLUSIONS

These findings suggest that RTX is capable to modulate the Th2 immune response, promoting T spiralis expulsion, which contributes to the defence against T spiralis infection, placing the RTX as a potential immunomodulatory drug.

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.

Trichinella spiralis muscle larvae release extracellular vesicles with immunomodulatory properties

AIMS

Extracellular vesicles (EVs) represent a newly discovered but universal communication tool between cells or organisms. However, few data exist on nematode EVs and none for Trichinella spiralis. Here, we aimed to investigate whether T spiralis muscle larvae produce EVs, whether they carry immunomodulatory proteins and whether they have a role in immunomodulation as a component of excretory-secretory muscle larvae products (ES L1).

METHODS AND RESULTS

EVs were enriched from conditioned medium of T spiralis muscle larvae. Transmission electron microscopy images showed T spiralis EVs to be 30-80 nm in size, and Western blot confirmed the presence of two out of three glycoproteins with the immunodominant epitope characteristic for muscle larvae of the genus Trichinella. Using a peripheral blood mononuclear cell (PBMC) stimulation assay, it was shown that these EVs elevated production of IL10 and IL6.

CONCLUSION

T spiralis muscle larvae produce EVs. Those EVs carry immunomodulatory proteins and have the capacity independently to induce regulatory responses in the same way as the T spiralis excretory-secretory muscle larvae products from which they were isolated.

Glycans in the roles of parasitological diagnosis and host-parasite interplay

The investigation of the glycan repertoire of several organisms has revealed a wide variation in terms of structures and abundance of glycan moieties. Among the parasites, it is possible to observe different sets of glycoconjugates across taxa and developmental stages within a species. The presence of distinct glycoconjugates throughout the life cycle of a parasite could relate to the ability of that organism to adapt and survive in different hosts and environments. Carbohydrates on the surface, and in excretory-secretory products of parasites, play essential roles in host-parasite interactions. Carbohydrate portions of complex molecules of parasites stimulate and modulate host immune responses, mainly through interactions with specific receptors on the surface of dendritic cells, leading to the generation of a pattern of response that may benefit parasite survival. Available data reviewed here also show the frequent aspect of parasite immunomodulation of mammalian responses through specific glycan interactions, which ultimately makes these molecules promising in the fields of diagnostics and vaccinology.

Therapeutic Effects of Resiniferatoxin Related with Immunological Responses for Intestinal Inflammation in Trichinellosis

The immune response against Trichinella spiralis at the intestinal level depends on the CD4⁺ T cells, which can both suppress or promote the inflammatory response through the synthesis of diverse cytokines. During the intestinal phase, the immune response is mixed (Th1/Th2) with the initial predominance of the Th1 response and the subsequent domination of Th2 response, which favor the development of intestinal pathology. In this context, the glucocorticoids (GC) are the pharmacotherapy for the intestinal inflammatory response in trichinellosis. However, its therapeutic use is limited, since studies have shown that treatment with GC suppresses the host immune system, favoring T. spiralis infection. In the search for novel pharmacological strategies that inhibit the Th1 immune response (proinflammatory) and assist the host against T. spiralis infection, recent studies showed that resiniferatoxin (RTX) had anti-inflammatory activity, which decreased the serum levels of IL-12, INF-γ, IL-1β, TNF-α, NO, and PGE₂, as well the number of eosinophils in the blood, associated with decreased intestinal pathology and muscle parasite burden. These researches demonstrate that RTX is capable to inhibit the production of Th1 cytokines, contributing to the defense against T. spiralis infection, which places it as a new potential drug modulator of the immune response.

Differential immune responses in mice infected with the tissue-dwelling nematode Trichinella zimbabwensis

To improve diagnostic tools, immunotherapies and vaccine development for trichinellosis surveillance and control there is a need to understand the host immune responses induced during infection with Trichinella zimbabwensis, a tissue-dwelling nematode. In this study, we sought to determine immune responses induced in mice during T. zimbabwensis infection. The parasite strain used (Code ISS1209) was derived from a naturally infected crocodile (Crocodylus niloticus) and is the main Trichinella species prevalent in southern Africa. Sixty 6- to 8-week-old female BALB/c mice were randomly assigned to two equal groups: T. zimbabwensis-infected (n= 30) and the non-infected control group (n= 30). Levels of serum tumour necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), interleukin-4 (IL-4) as well as parasite-specific IgM, IgG, IgG1, IgG2a, IgG2b and IgG3 antibody responses were determined using enzyme-linked immunosorbent assay (ELISA). The cytokines and antibodies provided information on T-helper 1 (Th1)- and Th2-type, T-regulatory and antibody responses. Results showed that during the intestinal stage of infection, higher levels of parasite-specific IgM, IgG, IgG1 (P <  0.05) and IL-10 and TNF-α (P <  0.001) were observed in the Trichinella-infected group compared with the non-infected control group. In the parasite establishment and tissue migration phases, levels of IgG1 and IgG3 were elevated (P <  0.001), while those of IgM (P <  0.01) declined on days 21 and 35 post infection (pi) compared to the enteric phase. Our findings show that distinct differences in Th1- and Th2-type and T-regulatory responses are induced during the intestinal, tissue migration and larval establishment stages of T. zimbabwensis infection.

Secretory Products of Trichinella spiralis Muscle Larvae and Immunomodulation: Implication for Autoimmune Diseases, Allergies, and Malignancies

Trichinella spiralis has the unique ability to make itself "at home" by creating and hiding in a new type of cell in the host body that is the nurse cell. From this immunologically privileged place, the parasite orchestrates a long-lasting molecular cross talk with the host through muscle larvae excretory-secretory products (ES L1). Those products can successfully modulate parasite-specific immune responses as well as responses to unrelated antigens (either self or nonself in origin), providing an anti-inflammatory milieu and maintaining homeostasis. It is clear, based on the findings from animal model studies, that T. spiralis and its products induce an immunomodulatory network (which encompasses Th2- and Treg-type responses) that may allow the host to deal with various hyperimmune-associated disorders as well as tumor growth, although the latter still remains unclear. This review focuses on studies of the molecules released by T. spiralis, their interaction with pattern recognition receptors on antigen presenting cells, and subsequently provoked responses. This paper also addresses the immunomodulatory properties of ES L1 molecules and how the induced immunomodulation influences the course of different experimental inflammatory and malignant diseases.

Immunoproteomic profile of Trichinella spiralis adult worm proteins recognized by early infection sera

Background

Trichinellosis, a widespread zoonosis, is regarded as an emerging or reemerging disease. Effective treatment and prognosis of trichinellosis depends on early diagnosis of the infection. The objective of this study was to identify sensitive and specific antigens for early diagnosis or effective vaccine antigens for preventing infection.

Methods

The somatic proteins of T. spiralis adult worms were separated by two-dimensional gel electrophoresis (2-DE). The separated proteins were probed with early infection sera from swine or mice infected with T. spiralis for 7 days. The primary immunoreactive spots were characterized by MALDI-TOF/TOF-MS analysis in combination with bioinformatics. The identified proteins were annotated using WEGO based on their functions. The immunodominant protein was chosen for expression as recombinant protein in E. coli and the purified recombinant protein was used to confirm its antigenicity by Western blot with the same infection sera.

Results

Approximately 300 spots were separated by 2-DE, with molecular weights ranging from 10 to 130 kDa, and pI values ranging from pH 4 to 10. The sera from swine and mice infected with T. spiralis for 7 days recognized 64 proteins. MALDI-TOF/TOF-MS analysis identified 55 proteins, some with different isoforms. Finally, 40 individual immunoreactive proteins were obtained with a wide range of biological functions. Several proteins, such as heat shock protein 70, 14-3-3 protein, and cysteine protease could be used as immunodiagnostic or vaccine antigens. Among these identified proteins, the highly immunodominant Ts14-3-3 was chosen for expression in E. coli and purified recombinant Ts14-3-3 was able to be strongly recognized by the same T. spiralis infected sera used for identifying these antigens, therefore the most promising antigen for early immunodiagnosis of Trichinella infection.

Conclusions

A total of 64 proteins from the adult worm were recognized by early infection sera from swine and mice infected with T. spiralis for 7 days. Several proteins, are of particular interest as immunodiagnostic or vaccine antigens, especially with Ts14-3-3 as most promising due to its highly immunogenicity during early infection, expressed protein can be recognized by Trichinella early infection sera and the native Ts14-3-3 expression in both adult and larval stages.

A distinctive Western blot pattern to recognize Trichinella infections in humans and pigs

Trichinellosis is a zoonotic disease caused by parasites of the genus Trichinella, which have a cosmopolitan distribution. For diagnostic purposes, a confirmatory test for ELISA-positive human and pig sera such as Western blotting is required, due to the high number of ELISA false positive sera. The objective of this study was to identify the Trichinella-specific antigens most frequently recognized by sera from Trichinella-infected humans and pigs, so as to define a distinctive pattern of Trichinella infection in sera from infected hosts using Western blots which allow false positive sera to be distinguished from true positive sera. Using excretory/secretory antigens, 450 human sera were tested by Western blotting: 150 from persons with a confirmed diagnosis of trichinellosis and 300 from persons who did not have trichinellosis but who tested positive by ELISA (i.e., false positives). We also tested 210 pig sera: (i) 30 from pigs experimentally infected with Trichinella spiralis; (ii) 90 from naturally T. spiralis-infected pigs; and (iii) 90 from pigs not infected with Trichinella, as shown after artificial digestion of the diaphragm pillars, yet which tested positive by ELISA (i.e., false positives). All true positive sera (i.e., sera from persons with confirmed trichinellosis as well as sera from naturally and experimentally infected pigs), reacted with a three-band pattern ranging in size from 48-72kDa. A distinctive pattern for recognizing Trichinella spp. infections in humans and pigs by Western blots is defined; it shows a sensitivity of 100% and it allows sera from Trichinella-infected humans and pigs to be distinguished from sera from persons and pigs that were not infected with Trichinella spp. (100% specificity).

Expulsion of secondary Trichinella spiralis infection in rats occurs independently of mucosal mast cell release of mast cell protease II

Our aim was to elucidate the contribution of mucosal mast cells to the effector phase of a secondary immune response to Trichinella spiralis. During secondary infection, rats expel 90-99% of T. spiralis first-stage larvae from the intestine in a matter of hours. This phenomenon appears to be unique to rats and has been called rapid expulsion. Primary intestinal infection by T. spiralis induces mastocytosis, and mast cell degranulation occurs when challenged rats exhibit rapid expulsion. These observations have engendered the view that mast cells mediate rapid expulsion. In this study, we report that immunization of adult Albino Oxford rats by an infection limited to the muscle phase did not induce intestinal mastocytosis, yet such rats exhibited rapid expulsion when challenged orally. Although mastocytosis was absent, the protease unique to mucosal mast cells, rat mast cell protease II (RMCPII), was detected in sera at the time of expulsion. We further evaluated mast cell activity in neonatal rats that display rapid expulsion. Pups born to infected dams displayed rapid expulsion, and RMCPII was detected in their sera. By feeding pups parasite-specific mAbs or polyclonal Abs before challenge infection, it was possible to dissociate mast cell degranulation from parasite expulsion. These results indicate that rapid expulsion can occur in the absence of either intestinal mastocytosis or RMCPII release. Furthermore, release of RMCPII is not sufficient to cause expulsion. The data argue against a role for mast cells in the mechanism underlying the effector phase of protective immunity against T. spiralis in rats.

Differential activation of mast cells by antigens from Trichinella spiralis muscle larvae, adults, and newborn larvae

Mast cell (MC) hyperplasia and activation are prominent features in Trichinella spiralis infection. Indeed a temporal correlation has been shown between the kinetics of intestinal mastocytosis, release of inflammatory mediators from MC, and adult worm loss, which constitutes a major component of the defense against T. spiralis infection. It is well known that during the intestinal phase of trichinellosis, muscle larvae (ML) and adult worms (AD) enter into contact with the host; however, interaction with MC may also occur during migration of newborn larvae (NBL). Therefore, it is plausible that antigens from these developmental stages could activate MC. We have previously demonstrated by in vitro assays that T. spiralis muscle larval (TSL-1) antigens activate MC through an Ig-independent mechanism leading to the release of histamine, MC protease 5, IL-4 and TNF alpha. In this work we evaluated whether total antigens from AD or NBL could activate unsensitized MC and we compared this activation with the activation seen when MC are stimulated with TSL-1 antigens. MC activation was also tested with affinity chromatography purified antigens from NBL using the monoclonal antibody CE-4 that recognizes NBL surface components. The results obtained in this study showed that AD total extracts and TSL-1 antigens induced the release of histamine but not beta-hexosaminidase from unsensitized MC, suggesting a selective secretion of MC mediators. In contrast, NBL total extracts or purified NBL antigens did not induce the release of either histamine or beta-hexosaminidase from MC. Interestingly, AD and ML are the stages that interact with the host during the intestinal phase of infection. The mechanisms involved in TSL-1 and AD activation of unsensitized MC may function together with other mechanisms of MC activation in host protection against T. spiralis.

Validation of an enzyme-linked immunosorbent assay for diagnosis of human trichinellosis

Trichinellosis is a zoonotic disease caused by the consumption of raw or semiraw meat from different animals harboring Trichinella larvae in their muscles. Since there are no pathognomonic signs, diagnosis can be difficult; for this reason, serology is important. The objective of this study was to validate an enzyme-linked immunosorbent assay (ELISA) using excretory/secretory antigens to detect anti-Trichinella immunoglobulin G antibodies in human sera. A total of 3,505 human serum samples were tested. A receiver-operator characteristic (ROC) curve analysis was performed. The accuracy of the test was determined by calculating the area under the curve, which was equal to 0.999, indicating high accuracy. The coefficient of variation calculated for data from four serum samples in eight working sessions was no higher than 5% for the positive sera or 14% for the negative sera. Moreover, the analysis of the differences in optical density between duplicates indicated a high repeatability for the ELISA. At the ROC optimized cutoff, the sensitivity and specificity of the test were, respectively, 99.2% and 90.6% (specificity of 95.6% when excluding the samples from multiparasitized persons from Tanzania). The validated ELISA showed good performance in terms of sensitivity, repeatability, and reproducibility, whereas the specificity was limited. These results suggest that this test is suitable for detecting anti-Trichinella antibodies in human sera for diagnostic purposes, whereas its use in epidemiological surveys could be questionable.

Mexican immunoparasitology: what is done and has to be done

In this special issue of Parasite Immunology, the reader will find reviewed some of the hottest topics in immunoparasitology, with emphasis on the most studied parasite species in Mexico. For instance, the immunological conditions that appear favorable for the survival or destruction of the parasite in the intermediate and definitive hosts in cysticercosis, as well as the use of immunodiagnostic tests in epidemiological/intervention studies are discussed in two different articles. The role that alternatively activated macrophages plays in modulating host immunity is also discussed, while in the field of Leishmaniasis, the reader will find reviewed the role that CD8+ T cells play in the host defense during the human infection. The role that antibodies may play as biomarkers of protective or pathological cellular immune events in Toxoplasma gondii infections, as well as the new insights about the regulation of the inflammatory immune response by the cytokine/chemokine network in amebiasis, are topics reviewed. The use that TSL-1 antigens may have in the development of more sensitive and specific diagnosis of human and animal trichinellosis as well as the role that the neuroimmunoendocrine network plays during schistosomiasis are also presented. We hope that our readers will find fascinating and enticing, the first ever Special Issue devoted to Mexican Immunoparasitology.