Border maneuvers: deployment of mucosal immune defenses against Toxoplasma gondii

Ileal inflammation is reduced due to treatment with a metalloprotease from BmooMP-α-I snake venom in an experimental model of Toxoplasma gondii infection

The selection process for advanced therapies in patients with inflammatory bowel diseases (IBDs) must prioritize safety, especially when considering new biologic agents or oral molecule modulators. In C57BL/6 mice, oral infection with Toxoplasma gondii induces intestinal inflammation through excessive tumor necrosis factor (TNF) production, making TNF neutralization a potential therapeutic intervention. Considering this, the present study aimed to evaluate the therapeutic effects of BmooMP-α-I, a snake venom metalloprotease isolated from Bothrops moojeni, which could promote TNF hydrolysis, in treating T. gondii-induced ileitis. The results showed that C57BL/6 mice orally infected with 50 cysts of T. gondii from the Me49 strain and treated with BmooMP-α-I exhibited prolonged survival and improved morbidity scores. Additionally, the treatment ameliorated both the macroscopic and microscopic aspects of the intestine, reduced macrophage influx, and decreased the production of inflammatory mediators by mesenteric lymph node cells. These findings provide compelling experimental evidence supporting the ability of BmooMP-α-I to alleviate ileal inflammation. Considering that the currently available therapeutic protocols are not completely effective and often result in side effects, the exploration of alternative strategies involving novel therapeutic agents, as demonstrated in this study, has the potential to significantly enhance the quality of life for patients suffering from inflammatory bowel diseases.

Toxoplasma gondii Reactivation Aggravating Cardiac Function Impairment in Mice

BACKGROUND

Toxoplasma gondii (T. gondii) reactivation is common, especially among immunocompromised individuals, such as AIDS patients. The cardiac involvement associated with toxoplasmosis, however, is usually obscured by neurological deterioration. The aim of this study was to observe the alterations in cardiac functions in various landmark periods after infection and to assess whether reactivation more seriously damages the heart.

METHODS

We established three infection models in mice using TgCtwh6, a major strain of T. gondii prevalent in China. The groups included an acute group, chronic latent group, and reactivation group. We evaluated the cardiac function impairment via H & E staining, Masson staining, echocardiography, myocardial enzyme profiles, and cardiac troponin, and detected the expression of inflammatory factors and antioxidant factors with Western blotting. Immunofluorescence was used to detect the expression of the macrophage marker F4/80.

RESULTS

Our results showed that damage to the heart occurred in the acute and reactivation groups. Impaired cardiac function manifested as a decrease in heart rate and a compensatory increase in left ventricular systolic function. Serum levels of cardiac enzymes also increased dramatically. In the chronic phase, myocardial fibrosis developed, diastolic functions became severely impaired, inflammation persisted, and macrophage expression was slightly reduced. Ultimately, reactivation infection exacerbated damage to cardiac function in mice, potentially leading to diastolic heart failure. Macrophages were strongly activated, and myocardial fibrosis was increased. In addition, the antioxidant capacity of the heart was severely affected by the infection.

CONCLUSIONS

Taken together, these results suggested that the reactivation of T. gondii infection could aggravate injury to the heart, which could be associated with a host-cell-mediated immune response and strong cytokine production by macrophages, thus representing a novel insight into the pathogenic mechanism of toxoplasmosis.

Experimental infection of sheep at mid-pregnancy with archetypal type II and type III Toxoplasma gondii isolates exhibited different phenotypic traits

Toxoplasma gondii is a major cause of reproductive failure in small ruminants. Genotypic diversity of T. gondii strains has been associated with variations in phenotypic traits in in vitro and murine models. However, whether such diversity could influence the outcome of infection in small ruminants remains mostly unexplored. Here, we investigate the outcome of oral challenge in sheep at mid-pregnancy with 10 sporulated oocysts from three different T. gondii isolates belonging to archetypal II and III and selected according to their genetic and phenotypic variations shown in previous studies. Seventy-three pregnant sheep were divided in four groups: G1 infected with TgShSp1 isolate (type II, ToxoDB#3), G2 with TgShSp16 isolate (type II, ToxoDB#3), G3 with TgShSp24 isolate (type III, ToxoDB#2) and G4 of uninfected control sheep. Two different approaches were carried out within this study: (i) the outcome for the pregnancy after infection (n = 33) and (ii) the lesions and parasite tropism and burden at 14 and 28 days post infection (dpi) (n = 40). The onset of hyperthermia and seroconversion occurred one and two days later, respectively in G1 when compared to G2 and G3. However, sheep that suffered from reproductive failure, either by abortion, foetal dead at the time of euthanasia or stillbirth were similar among infected groups (50%, 40% and 47%, respectively). Histological lesions in placentomes and foetal tissues from euthanized animals from the second approach were only detected at 28 dpi and mainly in G1. At 14 dpi, T. gondii-DNA was only detected in G1 in the 11% of the placentomes. However, at 28 dpi the frequency of detection in placentomes was higher in G1 (96%) than in G2 and G3 (7% and 47%, respectively) besides in foetuses was lower in G2 (20%) than in G1 and G3 (100% and 87%, respectively). Regarding late abortions, stillbirths, and lambs of G1, G2 and G3, the frequency of microscopic lesions was similar between groups (79%, 78% and 67%, respectively) whereas T. gondii-DNA was evidenced in 100%, 55% and 100%, respectively. These recently obtained T. gondii isolates led to similar reproductive losses but intra- and inter-genotype variations in the rise of hyperthermia, dynamics of antibodies, frequency of lesions and parasite detection and distribution. Thus, the different phenotypic traits of the isolates could influence the outcome of the infection and mechanisms responsible for it, and further investigations are warranted.

ILCs-Crucial Players in Enteric Infectious Diseases

Research of the last decade has remarkably increased our understanding of innate lymphoid cells (ILCs). ILCs, in analogy to T helper (Th) cells and their cytokine and transcription factor profile, are categorized into three distinct populations: ILC1s express the transcription factor T-bet and secrete IFNγ, ILC2s depend on the expression of GATA-3 and release IL-5 and IL-13, and ILC3s express RORγt and secrete IL-17 and IL-22. Noteworthy, ILCs maintain a level of plasticity, depending on exposed cytokines and environmental stimuli. Furthermore, ILCs are tissue resident cells primarily localized at common entry points for pathogens such as the gut-associated lymphoid tissue (GALT). They have the unique capacity to initiate rapid responses against pathogens, provoked by changes of the cytokine profile of the respective tissue. Moreover, they regulate tissue inflammation and homeostasis. In case of intracellular pathogens entering the mucosal tissue, ILC1s respond by secreting cytokines (e.g., IFNγ) to limit the pathogen spread. Upon infection with helminths, intestinal epithelial cells produce alarmins (e.g., IL-25) and activate ILC2s to secrete IL-13, which induces differentiation of intestinal stem cells into tuft and goblet cells, important for parasite expulsion. Additionally, during bacterial infection ILC3-derived IL-22 is required for bacterial clearance by regulating antimicrobial gene expression in epithelial cells. Thus, ILCs can limit infectious diseases via secretion of inflammatory mediators and interaction with other cell types. In this review, we will address the role of ILCs during enteric infectious diseases.

Intestinal immune responses to commensal and pathogenic protozoa

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

Anti-Toxoplasma gondii IgM Long Persistence: What Are the Underlying Mechanisms?

Diagnosis of Toxoplasma gondii acute infection was first attempted by detection of specific IgM antibodies, as for other infectious diseases. However, it was noted that this immunoglobulin declines slowly and may last for months or even years. Apart from the diagnostic problem imposed on clinical management, this phenomenon called our attention due to the underlying phenomena that may be causing it. We performed a systematic comparison of reports studying IgM antibody kinetics, and the data from the papers were used to construct comparative plots and other graph types. It became clear that this phenomenon is quite generalized, and it may also occur in animals. Moreover, this is not a technical issue, although some tests make more evident the prolonged IgM decay than others. We further investigated biological reasons for its occurrence, i.e., infection dynamics (micro-reactivation–encystment, reinfection and reactivation), parasite strain relevance, as well as host innate, natural B cell responses and Ig class-switch problems inflicted by the parasite. The outcomes of these inquiries are presented and discussed herein.

Induction of IL-12p40 and type 1 immunity by Toxoplasma gondii in the absence of the TLR-MyD88 signaling cascade

Toxoplasma gondii is an orally acquired pathogen that induces strong IFN-γ based immunity conferring protection but that can also be the cause of immunopathology. The response in mice is driven in part by well-characterized MyD88-dependent signaling pathways. Here we focus on induction of less well understood immune responses that do not involve this Toll-like receptor (TLR)/IL-1 family receptor adaptor molecule, in particular as they occur in the intestinal mucosa. Using eYFP-IL-12p40 reporter mice on an MyD88^-/- background, we identified dendritic cells, macrophages, and neutrophils as cellular sources of MyD88-independent IL-12 after peroral T. gondii infection. Infection-induced IL-12 was lower in the absence of MyD88, but was still clearly above noninfected levels. Overall, this carried through to the IFN-γ response, which while generally decreased was still remarkably robust in the absence of MyD88. In the latter mice, IL-12 was strictly required to induce type I immunity. Type 1 and type 3 innate lymphoid cells (ILC), CD4⁺ T cells, and CD8⁺ T cells each contributed to the IFN-γ pool. We report that ILC3 were expanded in infected MyD88^-/- mice relative to their MyD88^+/+ counterparts, suggesting a compensatory response triggered by loss of MyD88. Furthermore, bacterial flagellin and Toxoplasma specific CD4⁺ T cell populations in the lamina propria expanded in response to infection in both WT and KO mice. Finally, we show that My88-independent IL-12 and T cell mediated IFN-γ production require the presence of the intestinal microbiota. Our results identify MyD88-independent intestinal immune pathways induced by T. gondii including myeloid cell derived IL-12 production, downstream type I immunity and IFN-γ production by ILC1, ILC3, and T lymphocytes. Collectively, our data reveal an underlying network of immune responses that do not involve signaling through MyD88.

Toxoplasma gondii is an apicomplexan parasite estimated to infect 30–50% of humans worldwide. The parasite normally establishes latency in brain and muscle tissue marked by persistent asymptomatic infection. T. gondii masterfully strikes a balance between eliciting strong, anti-parasite immunity while also persisting in the host. Although the murine host recognizes Toxoplasma profilin via MyD88 and Toll-like receptors 11/12, humans lack these receptors and MyD88 deficient patients retain resistance to T. gondii infection. Given these observations, it is important to identify MyD88 independent pathways of immunity. Using an oral infection mouse model, we identified cellular sources of IL-12 and IFN-γ, two cytokines that are essential for host resistance to this microbial pathogen. We determined how these responses are impacted by the presence and absence of MyD88 and the intestinal microbiota. Our data demonstrate that T. gondii triggers MyD88-independent innate and adaptive immunity in the intestinal mucosa that requires the presence of intestinal microbes. These pathways may be conserved among species and understanding how they work in rodents will likely help determine how humans recognize and respond to T. gondii infection.

Pathophysiology of ocular toxoplasmosis: Facts and open questions

Infections with the protozoan parasite Toxoplasma gondii are frequent, but one of its main consequences, ocular toxoplasmosis (OT), remains poorly understood. While its clinical description has recently attracted more attention and publications, the underlying pathophysiological mechanisms are only sparsely elucidated, which is partly due to the inherent difficulties to establish relevant animal models. Furthermore, the particularities of the ocular environment explain why the abundant knowledge on systemic toxoplasmosis cannot be just transferred to the ocular situation. However, studies undertaken in mouse models have revealed a central role of interferon gamma (IFNγ) and, more surprisingly, interleukin 17 (IL17), in ocular pathology and parasite control. These studies also show the importance of the genetic background of the infective Toxoplasma strain. Indeed, infections due to exotic strains show a completely different pathophysiology, which translates in a different clinical outcome. These elements should lead to more individualized therapy. Furthermore, the recent advance in understanding the immune response during OT paved the way to new research leads, involving immune pathways poorly studied in this particular setting, such as type I and type III interferons. In any case, deeper knowledge of the mechanisms of this pathology is needed to establish new, more targeted treatment schemes.

Evaluation of CpG-ODN-Adjuvanted Toxoplasma Gondii Virus-Like Particle Vaccine upon One, Two, and Three Immunizations

Successful vaccines against specific pathogens often require multiple immunizations and adjuvant usage. Yet, assessing the protective efficacy of different immunization regimens with adjuvanted Toxoplasma gondii vaccines remains elusive. In this study, we investigated the vaccine efficacy induced by CpG-ODN-adjuvanted T. gondii virus-like particles (VLPs) after challenge infection with T. gondii (ME49) in mice (BALB/c) upon one, two, and three immunizations. Immunization with adjuvanted T. gondii VLPs induced higher levels of T. gondii-specific IgG and/or IgA antibody responses, germinal center (GC) B cells, total B cells, and CD4⁺ and CD8⁺ T cells compared with unadjuvanted VLPs. Increasing the number of immunizations was strongly correlated with enhanced protective immunity against T. gondii in mice, with the highest protection being demonstrated in mice thrice-immunized with either adjuvanted T. gondii VLPs or VLPs alone. Notably, lesser bodyweight reductions and cerebral cyst counts were observed in mice receiving multiple immunizations with the adjuvanted VLPs, thereby confirming the effectiveness of adjuvanted boost immunizations. These results demonstrated that multiple immunizations with T. gondii VLPs is an effective approach, and the CpG-ODN can be developed as an effective adjuvant for T. gondii VLP vaccines.

From Entry to Early Dissemination-Toxoplasma gondii's Initial Encounter With Its Host

Toxoplasma gondii is a zoonotic intracellular parasite, able to infect any warm-blooded animal via ingestion of infective stages, either contained in tissue cysts or oocysts released into the environment. While immune responses during infection are well-studied, there is still limited knowledge about the very early infection events in the gut tissue after infection via the oral route. Here we briefly discuss differences in host-specific responses following infection with oocyst-derived sporozoites vs. tissue cyst-derived bradyzoites. A focus is given to innate intestinal defense mechanisms and early immune cell events that precede T. gondii's dissemination in the host. We propose stem cell-derived intestinal organoids as a model to study early events of natural host-pathogen interaction. These offer several advantages such as live cell imaging and transcriptomic profiling of the earliest invasion processes. We additionally highlight the necessity of an appropriate large animal model reflecting human infection more closely than conventional infection models, to study the roles of dendritic cells and macrophages during early infection.

Cross-Domain and Viral Interactions in the Microbiome

The importance of the microbiome to human health is increasingly recognized and has become a major focus of recent research. However, much of the work has focused on a few aspects, particularly the bacterial component of the microbiome, most frequently in the gastrointestinal tract. Yet humans and other animals can be colonized by a wide array of organisms spanning all domains of life, including bacteria and archaea, unicellular eukaryotes such as fungi, multicellular eukaryotes such as helminths, and viruses. As they share the same host niches, they can compete with, synergize with, and antagonize each other, with potential impacts on their host. Here, we discuss these major groups making up the human microbiome, with a focus on how they interact with each other and their multicellular host.

Toxoplasma gondii Manipulates Expression of Host Long Noncoding RNA during Intracellular Infection

Long noncoding RNA (lncRNA) are non-protein-coding transcripts greater than 200 nucleotides that regulate gene expression. The field of transcriptomics is only beginning to understand the role of lncRNA in host defense. Little is known about the role of lncRNA in the response to infection by intracellular pathogens such as Toxoplasma gondii. Using a microarray, we examined the differential expression of 35,923 lncRNAs and 24,881 mRNAs in mouse bone-marrow-derived macrophages during infection with high- and low-virulence T. gondii strains. We found that 1,522 lncRNA molecules were differentially regulated during infection with the high-virulence Type I strain, versus 528 with the less-virulent Type II strain. Of these lncRNAs, 282 were co-regulated with a nearby or overlapping mRNA–including approximately 60 mRNAs with immune-related functions. We validated the microarray for 4 lncRNAs and 4 mRNAs using qRT-PCR. Using deletion strains of T. gondii, we found that the secretory kinase ROP16 controls upregulation of lncRNAs Csf1-lnc and Socs2-lnc, demonstrating that the parasite directly manipulates host lncRNA expression. Given the number of regulated lncRNAs and the magnitude of the expression changes, we hypothesize that these molecules constitute both an additional regulatory layer in the host response to infection and a target for manipulation by T. gondii.

Parasite-Microbiota Interactions With the Vertebrate Gut: Synthesis Through an Ecological Lens

The vertebrate gut teems with a large, diverse, and dynamic bacterial community that has pervasive effects on gut physiology, metabolism, and immunity. Under natural conditions, these microbes share their habitat with a similarly dynamic community of eukaryotes (helminths, protozoa, and fungi), many of which are well-known parasites. Both parasites and the prokaryotic microbiota can dramatically alter the physical and immune landscape of the gut, creating ample opportunities for them to interact. Such interactions may critically alter infection outcomes and affect overall host health and disease. For instance, parasite infection can change how a host interacts with its bacterial flora, either driving or protecting against dysbiosis and inflammatory disease. Conversely, the microbiota can alter a parasite's colonization success, replication, and virulence, shifting it along the parasitism-mutualism spectrum. The mechanisms and consequences of these interactions are just starting to be elucidated in an emergent transdisciplinary area at the boundary of microbiology and parasitology. However, heterogeneity in experimental designs, host and parasite species, and a largely phenomenological and taxonomic approach to synthesizing the literature have meant that common themes across studies remain elusive. Here, we use an ecological perspective to review the literature on interactions between the prokaryotic microbiota and eukaryotic parasites in the vertebrate gut. Using knowledge about parasite biology and ecology, we discuss mechanisms by which they may interact with gut microbes, the consequences of such interactions for host health, and how understanding parasite-microbiota interactions may lead to novel approaches in disease control.

Histopathological lesions in encephalon and heart of mice infected with Toxoplasma gondii increase after Lycopodium clavatum 200dH treatment

In many cases, symptoms of toxoplasmosis are mistaken for the ones of other infectious diseases. Clinical signs are rare in immunocompetent people. However, when they arise, in the acute phase of infection, several organs are affected due to the rapid spread of tachyzoites through the bloodstream. In the present study, the reduction of tachyzoites in peripheral blood of mice of G72 (infected 72h after treatment) and G48 (infected 48h after treatment and treated three more times), when compared with IC (infected and non-treated), suggests protective effect exerted by Lycopodium clavatum. If on the one hand L. clavatum brought benefits, reducing parasitemia, on the other hand, the parasitism became exacerbated. Histopathological analysis demonstrated focal, multifocal and diffuse inflammatory infiltrates, ranging from absent, discreet, moderate to intense, in heart and encephalon of mice of NIC (non-infected and non-treated), IC, G48 and G72 groups, respectively. In the perivascular region and meninges, the injuries were enlarged. The presence of tachyzoites was demonstrated through immunohistochemical (IHC) assay in myocardium. Toxoplasma gondii induced increase of collagen fibers in myocardium of mice of G72 and G48 groups, compared with IC (p<0.05) and NIC (p<0.001). The presence of inflammatory infiltrates, as well as the progressive fibrosis, caused myocardial remodeling in animals treated with L. clavatum. Counterstaining with H&E suggests TGF-β expression by mononuclear cells in the inflammatory infiltrate. Based on our results, we can conclude that the adopted regimen and potency exerted a protective effect, reducing parasitemia. However, it intensified the histopathological lesions in encephalon and heart of mice infected with T. gondii.

Chronic infection with Toxoplasma gondii induces death of submucosal enteric neurons and damage in the colonic mucosa of rats

Intestinal epithelial secretion is coordinated by the submucosal plexus (SMP). Chemical mediators from SMP regulate the immunobiological response and direct actions against infectious agents. Toxoplasma gondii is a worldwide parasite that causes toxoplasmosis. This study aimed to determine the effects of chronic infection with T. gondii on the morphometry of the mucosa and the submucosal enteric neurons in the proximal colon of rats. Male adult rats were distributed into a control group (n = 10) and an infected group (n = 10). Infected rats received orally 500 oocysts of T. gondii (ME-49). After 36 days, the rats were euthanized and samples of the proximal colon were processed for histology to evaluate mucosal thickness in sections. Whole mounts were stained with methylene blue and subjected to immunohistochemistry to detect vasoactive intestinal polypeptide. The total number of submucosal neurons decreased by 16.20%. Vasoactive intestinal polypeptide-immunoreactive neurons increased by 26.95%. Intraepithelial lymphocytes increased by 62.86% and sulfomucin-producing goblet cells decreased by 22.87%. Crypt depth was greater by 43.02%. It was concluded that chronic infection with T. gondii induced death and hypertrophy in the remaining submucosal enteric neurons and damage to the colonic mucosa of rats.

The Interplay of Host Microbiota and Parasitic Protozoans at Mucosal Interfaces: Implications for the Outcomes of Infections and Diseases

Infections by parasitic protozoans are largely neglected, despite threatening millions of people, particularly in developing countries. With descriptions of the microbiota in humans, a new frontier of investigation is developing to decipher the complexity of host-parasite-microbiota relationships, instead of the classic reductionist approach, which considers host-parasite in isolation. Here, we review with specific examples the potential roles that the resident microbiota can play at mucosal interfaces in the transmission of parasitic protozoans and in the progress of infection and disease. Although the mechanisms underlying these relationships remain poorly understood, some examples provide compelling evidence that specific components of the microbiota can potentially alter the outcomes of parasitic infections and diseases in humans. Most findings suggest a protective role of the microbiota, which might lead to exploratory research comprising microbiota-based interventions to prevent and treat protozoal infections in the future. However, these infections are often accompanied by an unbalanced microbiota and, in some specific cases, apparently, these bacteria may contribute synergistically to disease progression. Taken together, these findings provide a different perspective on the ecological nature of protozoal infections. This review focuses attention on the importance of considering polymicrobial associations, i.e., parasitic protozoans and the host microbiota, for understanding these human infections in their natural microbial context.

Impact of Toxoplasma gondii on Dendritic Cell Subset Function in the Intestinal Mucosa

The function of mucosal dendritic cell (DC) subsets in immunity and inflammation is not well understood. In this study, we define four DC subsets present within the lamina propria and mesenteric lymph node compartments based on expression of CD103 and CD11b. Using IL-12p40 YFP (Yet40) reporter mice, we show that CD103(+)CD11b(-) mucosal DCs are primary in vivo sources of IL-12p40; we also identified CD103(-)CD11b(-) mucosal DCs as a novel population producing this cytokine. Infection was preferentially found in CD11b(+) DCs that were negative for CD103. Lamina propria DCs containing parasites were negative for IL-12p40. Instead, production of the cytokine was strictly a property of noninfected cells. We also show that vitamin A metabolism, as measured by ALDH activity, was preferentially found in CD103(+)CD11b(+) DC and was strongly downregulated in all mucosal DC subsets during infection. Finally, overall apoptosis of lamina propria DC subsets was increased during infection. Combined, these results highlight the ability of intestinal Toxoplasma infection to alter mucosal DC activity at both the whole population level and at the level of individual subsets.