Toxoplasma gondii infection triggers chronic cachexia and sustained commensal dysbiosis in mice

Therapeutic potential of Garcinia kola against experimental toxoplasmosis in rats

Cerebral toxoplasmosis, the most common opportunistic infection in immunocompromised individuals, is increasingly reported in immunocompetent individuals due to mutant strains of Toxoplasma gondii, which, furthermore, are reported to be resistant to available treatments. We assessed the therapeutic potential of Garcinia kola, a medicinal plant reported to have antiplasmodial and neuroprotective properties, against experimental toxoplasmosis in rats. Severe toxoplasmosis was induced in male Wistar rats (156.7 ± 4.1 g) by injecting them with 10 million tachyzoites in suspension in 500 µl of saline (intraperitoneal), and exclusive feeding with a low-protein diet [7% protein (weight by weight)]. Then, animals were treated with hexane, dichloromethane, and ethyl acetate fractions of Garcinia kola. Footprints were analysed and open-field and elevated plus maze ethological tests were performed when symptoms of severe disease were observed in the infected controls. After sacrifice, blood samples were processed for Giemsa staining, organs were processed for haematoxylin and eosin staining, and brains were processed for Nissl staining and cell counting. Compared with non-infected animals, the infected control animals had significantly lower body weights (30.27%↓, P = 0.001), higher body temperatures (P = 0.033) during the sacrifice, together with signs of cognitive impairment and neurologic deficits such as lower open-field arena centre entries (P < 0.001), elevated plus maze open-arm time (P = 0.029) and decreased stride lengths and step widths (P < 0.001), as well as neuronal loss in various brain areas. The ethyl acetate fraction of Garcinia kola prevented or mitigated most of these signs. Our data suggest that the ethyl acetate fraction of Garcinia kola has therapeutic potential against cerebral toxoplasmosis.

Mining parasites for their potential as novel therapeutic agents against cancer

Despite recent advances in the management and therapeutic of cancer, the treatment of the disease is limited by its high cost and severe side effects. In this scenario, there is an unmet need to identify novel treatment alternatives for this dreaded disease. Recently there is growing evidence that parasites may cause anticancer effects because of a negative correlation between parasitic infections and tumour growth despite some parasites that are known to exhibit pro-carcinogenic effects. It has been observed that parasites exert an anticancer effect either by activating the host's immune response or by secreting certain molecules that exhibit anticancer potential. The activation of the immune response by these parasitic organisms results in the inhibition of some of the hallmarks of cancer such as tumour proliferation, angiogenesis, and metastasis. This review summarizes the current advances as well as the mechanisms underlying the possible implications of this diverse group of organisms as anticancer agents.

iNOS is necessary for GBP-mediated T. gondii clearance in murine macrophages via vacuole nitration and intravacuolar network collapse

Toxoplasma gondii is an obligate intracellular parasite of rodents and humans. Interferon-inducible guanylate binding proteins (GBPs) are mediators of T. gondii clearance, however, this mechanism is incomplete. Here, using automated spatially targeted optical micro proteomics we demonstrate that inducible nitric oxide synthetase (iNOS) is highly enriched at GBP2+ parasitophorous vacuoles (PV) in murine macrophages. iNOS expression in macrophages is necessary to limit T. gondii load in vivo and in vitro. Although iNOS activity is dispensable for GBP2 recruitment and PV membrane ruffling; parasites can replicate, egress and shed GBP2 when iNOS is inhibited. T. gondii clearance by iNOS requires nitric oxide, leading to nitration of the PV and collapse of the intravacuolar network of membranes in a chromosome 3 GBP-dependent manner. We conclude that reactive nitrogen species generated by iNOS cooperate with GBPs to target distinct structures in the PV that are necessary for optimal parasite clearance in macrophages.

The intersection of host in vivo metabolism and immune responses to infection with kinetoplastid and apicomplexan parasites

SUMMARYProtozoan parasite infection dramatically alters host metabolism, driven by immunological demand and parasite manipulation strategies. Immunometabolic checkpoints are often exploited by kinetoplastid and protozoan parasites to establish chronic infection, which can significantly impair host metabolic homeostasis. The recent growth of tools to analyze metabolism is expanding our understanding of these questions. Here, we review and contrast host metabolic alterations that occur in vivo during infection with Leishmania, trypanosomes, Toxoplasma, Plasmodium, and Cryptosporidium. Although genetically divergent, there are commonalities among these pathogens in terms of metabolic needs, induction of the type I immune responses required for clearance, and the potential for sustained host metabolic dysbiosis. Comparing these pathogens provides an opportunity to explore how transmission strategy, nutritional demand, and host cell and tissue tropism drive similarities and unique aspects in host response and infection outcome and to design new strategies to treat disease.

A novel enemy of cancer: recent investigations into protozoan anti-tumor properties

Cancer remains a significant global health issue, despite advances in screening and treatment. While existing tumor treatment protocols such as surgery, chemotherapy, radiotherapy, targeted therapy, and immunotherapy have proven effective in enhancing the prognosis for some patients, these treatments do not benefit all patients. Consequently, certain types of cancer continue to exhibit a relatively low 5-year survival rate. Therefore, the pursuit of novel tumor intervention strategies may help improve the current effectiveness of tumor treatment. Over the past few decades, numerous species of protozoa and their components have exhibited anti-tumor potential via immune and non-immune mechanisms. This discovery introduces a new research direction for the development of new and effective cancer treatments. Through in vitro experiments and studies involving tumor-bearing mice, the anti-tumor ability of Toxoplasma gondii, Plasmodium, Trypanosoma cruzi, and other protozoa have unveiled diverse mechanisms by which protozoa combat cancer, demonstrating encouraging prospects for their application. In this review, we summarize the anti-tumor ability and anti-tumor mechanisms of various protozoa and explore the potential for their clinical development and application.

Gut microbiota mediates anxiety-like behaviors induced by chronic infection of Toxoplasma gondii in mice

BACKGROUND

Chronic infection with the neurotropic parasite Toxoplasma gondii (T. gondii) can cause anxiety and gut microbiota dysbiosis in hosts. However, the potential role of gut microbiota in anxiety induced by the parasite remains unclear.

METHODS

C57BL/6J mice were infected with 10 cysts of T. gondii. Antibiotic depletion of gut microbiota and fecal microbiota transplantation experiments were utilized to investigate the causal relationship between gut microbiota and anxiety. Anxiety-like behaviors were examined by the elevated plus maze test and the open field test; blood, feces, colon and amygdala were collected to evaluate the profiles of serum endotoxin (Lipopolysaccharide, LPS) and serotonin (5-hydroxytryptamine, 5-HT), gut microbiota composition, metabolomics, global transcriptome and neuroinflammation in the amygdala. Furthermore, the effects of Diethyl butylmalonate (DBM, an inhibitor of mitochondrial succinate transporter, which causes the accumulation of endogenous succinate) on the disorders of the gut-brain axis were evaluated.

RESULTS

Here, we found that T. gondii chronic infection induced anxiety-like behaviors and disturbed the composition of the gut microbiota in mice. In the amygdala, T. gondii infection triggered the microglial activation and neuroinflammation. In the colon, T. gondii infection caused the intestinal dyshomeostasis including elevated colonic inflammation, enhanced bacterial endotoxin translocation to blood and compromised intestinal barrier. In the serum, T. gondii infection increased the LPS levels and decreased the 5-HT levels. Interestingly, antibiotics ablation of gut microbiota alleviated the anxiety-like behaviors induced by T. gondii infection. More importantly, transplantation of the fecal microbiota from T. gondii-infected mice resulted in anxiety and the transcriptomic alteration in the amygdala of the antibiotic-pretreated mice. Notably, the decreased abundance of succinate-producing bacteria and the decreased production of succinate were observed in the feces of the T. gondii-infected mice. Moreover, DBM administration ameliorated the anxiety and gut barrier impairment induced by T. gondii infection.

CONCLUSIONS

The present study uncovers a novel role of gut microbiota in mediating the anxiety-like behaviors induced by chronic T. gondii infection. Moreover, we show that DBM supplementation has a beneficial effect on anxiety. Overall, these findings provide new insights into the treatment of T. gondii-related mental disorders.

Gut microbiota differences induced by Toxoplasma gondii seropositivity in stray cats in South Korea

T. gondii is a highly prevalent parasite worldwide, with cats serving as its final host. However, few studies have investigated the impact of T. gondii infection on cat gut microbiota. Therefore, this study examined the influence of T. gondii infection on the gut microbiota of stray cats and identified potential pathogens in their feces. This study examined T. gondii infection through blood of stray cats and the influence of microbiota in their feces using 16S rRNA gene amplicon sequencing. The results revealed significant differences in gut microbiota composition and diversity between the T. gondii seropositive and seronegative groups. Seropositive samples displayed a lower number of operational taxonomic units and reduced Shannon index than the seronegative samples. The seropositive and seronegative groups exhibited enrichment of taxa, including Escherichia and Enterobacteriaceae and Collinsella, Bifidobacterium, and Roseburia, respectively. Furthermore, potential pathogen species, including Campylobacter, Escherichia, and Streptococcus, were identified in the fecal samples. These findings suggest that T. gondii infection significantly impacts gut microbiota composition and diversity in stray cats. Additionally, an increased potential pathogen load, represented by Escherichia spp., was observed. These results underscore the importance of monitoring the prevalence of zoonotic pathogens in stray cats, as they can serve as reservoirs for zoonotic diseases.

Effects of Lactobacilli acidophilus and/or spiramycin as an adjunct in toxoplasmosis infection challenged with diabetes

The current study assessed the anti-parasitic impact of probiotics on Toxoplasma gondii infection either solely or challenged with diabetes in Swiss albino mice. The study design encompassed group-A (diabetic), group-B (non-diabetic), and healthy controls (C). Each group was divided into infected-untreated (subgroup-1); infected and spiramycin-treated (subgroup-2); infected and probiotic-treated (subgroup-3); infected and spiramycin+ probiotic-treated (subgroup-4). Diabetic-untreated animals exhibited acute toxoplasmosis and higher cerebral parasite load. Overall, various treatments reduced intestinal pathology, improved body weight, and decreased mortalities; nevertheless, probiotic + spiramycin exhibited significant differences. On day 7 post-infection both PD-1 and IL-17A demonstrated higher scores in the intestine of diabetic-untreated mice compared with non-diabetics and healthy control; whereas, claudin-1 revealed worsening expression. Likewise, on day 104 post-infection cerebral PD-1 and IL-17A showed increased expressions in diabetic animals. Overall, treatment modalities revealed lower scores of PD-1 and IL-17A in non-diabetic subgroups compared with diabetics. Intestinal and cerebral expressions of IL-17A and PD-1 demonstrated positive correlations with cerebral parasite load. In conclusion, toxoplasmosis when challenged with diabetes showed massive pathological features and higher parasite load in the cerebral tissues. Probiotics are a promising adjunct to spiramycin by ameliorating IL-17A and PD-1 in the intestinal and cerebral tissues, improving the intestinal expression of claudin-1, and efficiently reducing the cerebral parasite load.

Inducible nitric oxide synthase (iNOS) is necessary for GBP-mediated T. gondii restriction in murine macrophages via vacuole nitration and intravacuolar network collapse

Toxoplasma gondii is an obligate intracellular, protozoan pathogen of rodents and humans. T. gondii's ability to grow within cells and evade cell-autonomous immunity depends on the integrity of the parasitophorous vacuole (PV). Interferon-inducible guanylate binding proteins (GBPs) are central mediators of T. gondii clearance, however, the precise mechanism linking GBP recruitment to the PV and T. gondii restriction is not clear. This knowledge gap is linked to heterogenous GBP-targeting across a population of vacuoles and the lack of tools to selectively purify the intact PV. To identify mediators of parasite clearance associated with GBP2-positive vacuoles, we employed a novel protein discovery tool automated spatially targeted optical micro proteomics (autoSTOMP). This approach identified inducible nitric oxide synthetase (iNOS) enriched at levels similar to the GBPs in infected bone marrow-derived myeloid cells. iNOS expression on myeloid cells was necessary for mice to control T. gondii growth in vivo and survive acute infection. T. gondii infection of IFNγ-primed macrophage was sufficient to robustly induce iNOS expression. iNOS restricted T. gondii infection through nitric oxide synthesis rather than arginine depletion, leading to robust and selective nitration of the PV. Optimal parasite restriction by iNOS and vacuole nitration depended on the chromosome 3 GBPs. Notably, GBP2 recruitment and ruffling of the PV membrane occurred in iNOS knockouts, however, these vacuoles contained dividing parasites. iNOS activity was necessary for the collapse of the intravacuolar network of nanotubular membranes which connects parasites to each other and the host cytosol. Based on these data we conclude reactive nitrogen species generated by iNOS cooperate with the chromosome 3 GBPs to target distinct biology of the PV that are necessary for optimal parasite clearance in murine myeloid cells.

Tricarboxylic acid (TCA) cycle, sphingolipid, and phosphatidylcholine metabolism are dysregulated in T. gondii infection-induced cachexia

Cachexia is a life-threatening disease characterized by chronic, inflammatory muscle wasting and systemic metabolic impairment. Despite its high prevalence, there are no efficacious therapies for cachexia. Mice chronically infected with the protozoan parasite Toxoplasma gondii represent a novel animal model recapitulating the chronic kinetics of cachexia. To understand how perturbations to metabolic tissue homeostasis influence circulating metabolite availability we used mass spectrometry analysis. Despite the significant reduction in circulating triacylglycerides, non-esterified fatty acids, and glycerol, sphingolipid long-chain bases and a subset of phosphatidylcholines (PCs) were significantly increased in the sera of mice with T. gondii infection-induced cachexia. In addition, the TCA cycle intermediates α-ketoglutarate, 2-hydroxyglutarate, succinate, fumarate, and malate were highly depleted in cachectic mouse sera. Sphingolipids and their de novo synthesis precursors PCs are the major components of the mitochondrial membrane and regulate mitochondrial function consistent with a causal relationship in the energy imbalance driving T. gondii-induced chronic cachexia.

Polysaccharide of Ganoderma lucidum Ameliorates Cachectic Myopathy Induced by the Combination Cisplatin plus Docetaxel in Mice

Cachexia is a lethal muscle-wasting syndrome associated with cancer and chemotherapy use. Mounting evidence suggests a correlation between cachexia and intestinal microbiota, but there is presently no effective treatment for cachexia. Whether the Ganoderma lucidum polysaccharide Liz-H exerts protective effects on cachexia and gut microbiota dysbiosis induced by the combination cisplatin plus docetaxel (cisplatin + docetaxel) was investigated. C57BL/6J mice were intraperitoneally injected with cisplatin + docetaxel, with or without oral administration of Liz-H. Body weight, food consumption, complete blood count, blood biochemistry, and muscle atrophy were measured. Next-generation sequencing was also performed to investigate changes to gut microbial ecology. Liz-H administration alleviated the cisplatin + docetaxel-induced weight loss, muscle atrophy, and neutropenia. Furthermore, upregulation of muscle protein degradation-related genes (MuRF-1 and Atrogin-1) and decline of myogenic factors (MyoD and myogenin) after treatment of cisplatin and docetaxel were prevented by Liz-H. Cisplatin and docetaxel treatment resulted in reducing comparative abundances of Ruminococcaceae and Bacteroides, but Liz-H treatment restored these to normal levels. This study indicates that Liz-H is a good chemoprotective reagent for cisplatin + docetaxel-induced cachexia. IMPORTANCE Cachexia is a multifactorial syndrome driven by metabolic dysregulation, anorexia, systemic inflammation, and insulin resistance. Approximately 80% of patients with advanced cancer have cachexia, and cachexia is the cause of death in 30% of cancer patients. Nutritional supplementation has not been shown to reverse cachexia progression. Thus, developing strategies to prevent and/or reverse cachexia is urgent. Polysaccharide is a major biologically active compound in the fungus Ganoderma lucidum. This study is the first to report that G. lucidum polysaccharides could alleviate chemotherapy-induced cachexia via reducing expression of genes that are known to drive muscle wasting, such as MuRF-1 and Atrogin-1. These results suggest that Liz-H is an effective treatment for cisplatin + docetaxel-induced cachexia.

Cachexia: A systemic consequence of progressive, unresolved disease

Cachexia, a systemic wasting condition, is considered a late consequence of diseases, including cancer, organ failure, or infections, and contributes to significant morbidity and mortality. The induction process and mechanistic progression of cachexia are incompletely understood. Refocusing academic efforts away from advanced cachexia to the etiology of cachexia may enable discoveries of new therapeutic approaches. Here, we review drivers, mechanisms, organismal predispositions, evidence for multi-organ interaction, model systems, clinical research, trials, and care provision from early onset to late cachexia. Evidence is emerging that distinct inflammatory, metabolic, and neuro-modulatory drivers can initiate processes that ultimately converge on advanced cachexia.

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-Tumor Effect of Parasitic Protozoans

The immune system may aberrantly silence when against “altered self”, which consequently may develop into malignancies. With the development of tumor immunology and molecular biology, the deepened understanding of the relationship between parasites and tumors shifts the attitude towards parasitic pathogens from elimination to utilization. In recent years, the antitumor impact implemented by protozoan parasites and the derived products has been confirmed. The immune system is activated and enhanced by some protozoan parasites, thereby inhibiting tumor growth, angiogenesis, and metastasis in many animal models. In this work, we reviewed the available information on the antitumor effect of parasitic infection or induced by parasitic antigen, as well as the involved immune mechanisms that modulate cancer progression. Despite the fact that clinical trials of the protozoan parasites against tumors are limited and the specific mechanisms of the effect on tumors are not totally clear, the use of genetically modified protozoan parasites and derived molecules combined with chemotherapy could be an important element for promoting antitumor treatment in the future.

Persisting Microbiota and Neuronal Imbalance Following T. gondii Infection Reliant on the Infection Route

Toxoplasma gondii is a highly successful parasite capable of infecting all warm-blooded animals. The natural way of infection in intermediate hosts is the oral ingestion of parasite-contaminated water or food. In murine experimental models, oral infection (p.o.) of mice with T. gondii is applied to investigate mucosal and peripheral immune cell dynamics, whereas intraperitoneal infection (i.p.) is frequently used to study peripheral inflammation as well as immune cell – neuronal interaction in the central nervous system (CNS). However, the two infection routes have not yet been systematically compared along the course of infection. Here, C57BL/6 mice were infected p.o. or i.p. with a low dose of T. gondii cysts, and the acute and chronic stages of infection were compared. A more severe course of infection was detected following i.p. challenge, characterized by an increased weight loss and marked expression of proinflammatory cytokines particularly in the CNS during the chronic stage. The elevated proinflammatory cytokine expression in the ileum was more prominent after p.o. challenge that continued following the acute phase in both i.p. or p.o. infected mice. This resulted in sustained microbial dysbiosis, especially after p.o. challenge, highlighted by increased abundance of pathobionts from the phyla proteobacteria and a reduction of beneficial commensal species. Further, we revealed that in the CNS of i.p. infected mice CD4 and CD8 T cells displayed higher IFNγ production in the chronic stage. This corresponded with an increased expression of C1q and CD68 in the CNS and reduced expression of genes involved in neuronal signal transmission. Neuroinflammation-associated synaptic alterations, especially PSD-95, VGLUT, and EAAT2 expression, were more pronounced in the cortex upon i.p. infection highlighting the profound interplay between peripheral inflammation and CNS homeostasis.

4-Arylthiosemicarbazide Derivatives as Toxoplasmic Aromatic Amino Acid Hydroxylase Inhibitors and Anti-inflammatory Agents

Approximately one-third of the human population is infected with the intracellular cosmopolitan protozoan Toxoplasma gondii (Tg), and a specific treatment for this parasite is still needed. Additionally, the increasing resistance of Tg to drugs has become a challenge for numerous research centers. The high selectivity of a compound toward the protozoan, along with low cytotoxicity toward the host cells, form the basis for further research, which aims at determining the molecular targets of the active compounds. Thiosemicarbazide derivatives are biologically active organic compounds. Previous studies on the initial preselection of 58 new 4-arylthiosemicarbazide derivatives in terms of their anti-Tg activity and selectivity made it possible to select two promising derivatives for further research. One of the important amino acids involved in the proliferation of Tg and the formation of parasitophorous vacuoles is tyrosine, which is converted by two unique aromatic amino acid hydroxylases to levodopa. Enzymatic studies with two derivatives (R: para-nitro and meta-iodo) and recombinant aromatic amino acid hydroxylase (AAHs) obtained in the E. coli expression system were performed, and the results indicated that toxoplasmic AAHs are a molecular target for 4-arylthiosemicarbazide derivatives. Moreover, the drug affinity responsive target stability assay also confirmed that the selected compounds bind to AAHs. Additionally, the anti-inflammatory activity of these derivatives was tested using THP1-Blue™ NF-κB reporter cells due to the similarity of the thiosemicarbazide scaffold to thiosemicarbazone, both of which are known NF-κB pathway inhibitors.

Interleukin-32γ in the Control of Acute Experimental Chagas Disease

Chagas disease (CD) is an important parasitic disease caused by Trypanosoma cruzi. Interleukin-32 (IL-32) plays an important role in inflammation and in the development of Th1/Th17 acquired immune responses. We evaluated the influence of IL-32γ on the immune response profile, pathogenesis of myocarditis in acute experimental CD, and control of the disease. For this, C57BL/6 wild-type (WT) and IL-32γTg mice were infected subcutaneously with 1,000 forms of Colombian strain of T. cruzi. In the histopathological analyzes, T. cruzi nests, myocarditis, and collagen were quantified in cardiac tissue. Cytokine productions (IL-32, IFN-γ, TNF-α, IL-10, and IL-17) were measured in cardiac homogenate by ELISA. The IL-32γTg mice showed a better control of parasitemia and T. cruzi nests in the heart than WT mice. Infected-WT and -IL-32γTg mice showed similar levels of IFN-γ, TNF-α, and IL-17, but IL-10 was significantly higher expressed in IL-32γTg than in WT mice. The cytokine profile found in IL-32γTg animals contributed to body weight maintenance, parasitemia control, and survival. Our results indicate that the presence of human IL-32γ in mice infected with the Colombian strain of T. cruzi is important for infection control during the acute phase of Chagas disease.

The Colombian Strain of Trypanosoma cruzi Induces a Proinflammatory Profile, Neuronal Death, and Collagen Deposition in the Intestine of C57BL/6 Mice Both during the Acute and Early Chronic Phase

The objective of this study was to evaluate the histopathological changes caused by infection with the Colombian strain of Trypanosoma cruzi (T. cruzi) in the acute and chronic experimental phases. C57Bl/6 mice were infected with 1000 trypomastigote forms of the Colombian strain of T. cruzi. After 30 days (acute phase) and 90 days (early chronic phase) of infection, the animals were euthanized, and the colon was collected and divided into two parts: proximal and distal. The distal portion was used for histopathological analysis, whereas the proximal portion was used for quantification of pro- and anti-inflammatory cytokines. In addition, the weight of the animals and parasitemia were assessed. The infection induced gradual weight loss in the animals. In addition, the infection induced an increase in interferon gamma (IFNγ) and tumor necrosis factor-alpha (TNF-α) in the intestine in the acute phase, in which this increase continued until the early chronic phase. The same was observed in relation to the presence of intestinal inflammatory infiltrates. In relation to interleukin (IL)-10, there was an increase only in the early chronic phase. The Colombian strain infection was also able to induce neuronal loss in the myenteric plexus and deposition of the collagen fibers during the acute phase. The Colombian strain of T. cruzi is capable of causing histopathological changes in the intestine of infected mice, especially in inducing neuronal destructions. Thus, this strain can also be used to study the intestinal form of Chagas disease in experimental models.

The interplay of immunology and cachexia in infection and cancer

Diverse inflammatory diseases, infections and malignancies are associated with wasting syndromes. In many of these conditions, the standards for diagnosis and treatment are lacking due to our limited understanding of the causative molecular mechanisms. Here, we discuss the complex immunological context of cachexia, a systemic catabolic syndrome that depletes both fat and muscle mass with profound consequences for patient prognosis. We highlight the main cytokine and immune cell-driven pathways that have been linked to weight loss and tissue wasting in the context of cancer-associated and infection-associated cachexia. Moreover, we discuss the potential immunometabolic consequences of cachexia on the basis of newly identified pathways and explore the multilayered area of immunometabolic crosstalk both upstream and downstream of tissue catabolism. Collectively, this Review highlights the intricate relationship of the immune system with cachexia in the context of malignant and infectious diseases.

Understanding the gut microbiota and sarcopenia: a systematic review

BACKGROUND

Gut microbiota dysbiosis and sarcopenia commonly occur in the elderly. Although the concept of the gut-muscle axis has been raised, the casual relationship is still unclear. This systematic review analyses the current evidence of gut microbiota effects on muscle/sarcopenia.

METHODS

A systematic review was performed in PubMed, Embase, Web of Science, and The Cochrane Library databases using the keywords (microbiota* OR microbiome*) AND (sarcopen* OR muscle). Studies reporting the alterations of gut microbiota and muscle/physical performance were analysed.

RESULTS

A total of 26 pre-clinical and 10 clinical studies were included. For animal studies, three revealed age-related changes and relationships between gut microbiota and muscle. Three studies focused on muscle characteristics of germ-free mice. Seventy-five per cent of eight faecal microbiota transplantation studies showed that the recipient mice successfully replicated the muscle phenotype of donors. There were positive effects on muscle from seven probiotics, two prebiotics, and short-chain fatty acids (SCFAs). Ten studies investigated on other dietary supplements, antibiotics, exercise, and food withdrawal that affected both muscle and gut microbiota. Twelve studies explored the potential mechanisms of the gut-muscle axis. For clinical studies, 6 studies recruited 676 elderly people (72.8 ± 5.6 years, 57.8% female), while 4 studies focused on 244 young adults (29.7 ± 7.8 years, 55.4% female). The associations of gut microbiota and muscle had been shown in four observational studies. Probiotics, prebiotics, synbiotics, fermented milk, caloric restriction, and exercise in six studies displayed inconsistent effects on muscle mass, function, and gut microbiota.

CONCLUSIONS

Altering the gut microbiota through bacteria depletion, faecal transplantation, and various supplements was shown to directly affect muscle phenotypes. Probiotics, prebiotics, SCFAs, and bacterial products are potential novel therapies to enhance muscle mass and physical performance. Lactobacillus and Bifidobacterium strains restored age-related muscle loss. Potential mechanisms of microbiome modulating muscle mainly include protein, energy, lipid, and glucose metabolism, inflammation level, neuromuscular junction, and mitochondrial function. The role of the gut microbiota in the development of muscle loss during aging is a crucial area that requires further studies for translation to patients.

Behavioral alterations in long-term Toxoplasma gondii infection of C57BL/6 mice are associated with neuroinflammation and disruption of the blood brain barrier

The Apicomplexa protozoan Toxoplasma gondii is a mandatory intracellular parasite and the causative agent of toxoplasmosis. This illness is of medical importance due to its high prevalence worldwide and may cause neurological alterations in immunocompromised persons. In chronically infected immunocompetent individuals, this parasite forms tissue cysts mainly in the brain. In addition, T. gondii infection has been related to mental illnesses such as schizophrenia, bipolar disorder, depression, obsessive-compulsive disorder, as well as mood, personality, and other behavioral changes. In the present study, we evaluated the kinetics of behavioral alterations in a model of chronic infection, assessing anxiety, depression and exploratory behavior, and their relationship with neuroinflammation and parasite cysts in brain tissue areas, blood-brain-barrier (BBB) integrity, and cytokine status in the brain and serum. Adult female C57BL/6 mice were infected by gavage with 5 cysts of the ME-49 type II T. gondii strain, and analyzed as independent groups at 30, 60 and 90 days postinfection (dpi). Anxiety, depressive-like behavior, and hyperactivity were detected in the early (30 dpi) and long-term (60 and 90 dpi) chronic T. gondii infection, in a direct association with the presence of parasite cysts and neuroinflammation, independently of the brain tissue areas, and linked to BBB disruption. These behavioral alterations paralleled the upregulation of expression of tumor necrosis factor (TNF) and CC-chemokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES) in the brain tissue. In addition, increased levels of interferon-gamma (IFNγ), TNF and CCL2/MCP-1 were detected in the peripheral blood, at 30 and 60 dpi. Our data suggest that the persistence of parasite cysts induces sustained neuroinflammation, and BBB disruption, thus allowing leakage of cytokines of circulating plasma into the brain tissue. Therefore, all these factors may contribute to behavioral changes (anxiety, depressive-like behavior, and hyperactivity) in chronic T. gondii infection.

Chronic Toxoplasma gondii infection enhances susceptibility to colitis

Oral infection with Toxoplasma gondii results in dysbiosis and enteritis, both of which revert to normal during chronic infection. However, whether infection leaves a lasting impact on mucosal responses remains uncertain. Here we examined the effect of the chemical irritant dextran sodium sulfate (DSS) on intestinal damage and wound healing in chronically infected mice. Our findings indicate that prior infection with T. gondii exacerbates damage to the colon caused by DSS and impairs wound healing by suppressing stem cell regeneration of the epithelium. Enhanced tissue damage was attributable to inflammatory monocytes that emerge preactivated from bone marrow, migrate to the intestine, and release inflammatory mediators, including nitric oxide. Tissue damage was reversed by neutralization of inflammatory monocytes or nitric oxide, revealing a causal mechanism for tissue damage. Our findings suggest that chronic infection with T. gondii enhances monocyte activation to increase inflammation associated with a secondary environmental insult.

Maternal natural killer cells at the intersection between reproduction and mucosal immunity

Many maternal immune cells populate the decidua, which is the mucosal lining of the uterus transformed during pregnancy. Here, abundant natural killer (NK) cells and macrophages help the uterine vasculature adapt to fetal demands for gas and nutrients, thereby supporting fetal growth. Fetal trophoblast cells budding off the forming placenta and invading deep into maternal tissues come into contact with these and other immune cells. Besides their homeostatic functions, decidual NK cells can respond to pathogens during infection, but in doing so, they may become conflicted between destroying the invader and sustaining fetoplacental growth. We review how maternal NK cells balance their double duty both in the local microenvironment of the uterus and systemically, during toxoplasmosis, influenza, cytomegalovirus, malaria and other infections that threat pregnancy. We also discuss recent developments in the understanding of NK-cell responses to SARS-Cov-2 infection and the possible dangers of COVID-19 during pregnancy.

Like father, like son: Pulmonary thromboembolism due to inflammatory or hereditary condition? Two case reports

BACKGROUND

Venous thromboembolism, which includes deep venous thrombosis and pulmonary embolism, is a well-known causal disorder with high morbidity and mortality rates. Inherited or acquired conditions affecting components of coagulation and fibrinolysis systems have been linked to venous thromboembolism pathogenesis as they may lead to a pro-inflammatory state in human bodies. Toxoplasmosis is a zoonosis that potentially leads to acute systemic cachectic-inflammatory effects in experimental animal models but is not yet proven in humans. It is known that venous thrombosis can occur during acute inflammatory/infectious diseases, although it is not well established with regard to toxoplasmosis alone.

CASE SUMMARY

A 70-year-old Caucasian man and his 32-year-old son developed general malaise, chills, fever, and myalgia, having established a diagnosis of toxoplasmosis. Twenty days later, they presented dry cough leading to further investigations that revealed an incidental deep venous thrombosis plus pulmonary embolism in them both. Thrombophilia screening showed both patients had a factor V Leiden mutation heterozygosis. Father and son completely recovered without any sequalae after anticoagulant treatment. They have not presented symptom recurrence of either medical disorder during 1 year of follow-up.

CONCLUSION

Toxoplasmosis may enhance the risk of venous thromboembolism in patients showing factor V Leiden mutation heterozygosis.

The Role of Macrophages During Mammalian Tissue Remodeling and Regeneration Under Infectious and Non-Infectious Conditions

Several infectious pathologies in humans, such as tuberculosis or SARS-CoV-2, are responsible for tissue or lung damage, requiring regeneration. The regenerative capacity of adult mammals is limited to few organs. Critical injuries of non-regenerative organs trigger a repair process that leads to a definitive architectural and functional disruption, while superficial wounds result in scar formation. Tissue lesions in mammals, commonly studied under non-infectious conditions, trigger cell death at the site of the injury, as well as the production of danger signals favouring the massive recruitment of immune cells, particularly macrophages. Macrophages are also of paramount importance in infected injuries, characterized by the presence of pathogenic microorganisms, where they must respond to both infection and tissue damage. In this review, we compare the processes implicated in the tissue repair of non-infected versus infected injuries of two organs, the skeletal muscles and the lungs, focusing on the primary role of macrophages. We discuss also the negative impact of infection on the macrophage responses and the possible routes of investigation for new regenerative therapies to improve the recovery state as seen with COVID-19 patients.

Inflammatory Bowel Diseases and Sarcopenia: The Role of Inflammation and Gut Microbiota in the Development of Muscle Failure

Sarcopenia represents a major health burden in industrialized country by reducing substantially the quality of life. Indeed, it is characterized by a progressive and generalized loss of muscle mass and function, leading to an increased risk of adverse outcomes and hospitalizations. Several factors are involved in the pathogenesis of sarcopenia, such as aging, inflammation, mitochondrial dysfunction, and insulin resistance. Recently, it has been reported that more than one third of inflammatory bowel disease (IBD) patients suffered from sarcopenia. Notably, the role of gut microbiota (GM) in developing muscle failure in IBD patient is a matter of increasing interest. It has been hypothesized that gut dysbiosis, that typically characterizes IBD, might alter the immune response and host metabolism, promoting a low-grade inflammation status able to up-regulate several molecular pathways related to sarcopenia. Therefore, we aim to describe the basis of IBD-related sarcopenia and provide the rationale for new potential therapeutic targets that may regulate the gut-muscle axis in IBD patients.

Social preference is maintained in mice with impaired startle reflex and glutamate/D-serine imbalance induced by chronic cerebral toxoplasmosis

Toxoplasma gondii is an opportunistic protozoan pathogen with a wide geographic distribution. The chronic phase of toxoplasmosis is often asymptomatic in humans and is characterized by tissue cysts throughout the central nervous system and muscle cells. T. gondii and other pathogens with tropism for the central nervous system are considered risk factors in the etiology of several neuropsychiatric disorders, such as schizophrenia and bipolar disorder, besides neurological diseases. Currently, it is known that cerebral toxoplasmosis increases dopamine levels in the brain and it is related to behavioral changes in animals and humans. Here we evaluate whether chronic T. gondii infection, using the cystogenic ME-49 strain, could induce behavioral alterations associated with neuropsychiatric disorders and glutamatergic neurotransmission dysfunction. We observed that the startle amplitude is reduced in the infected animals as well as glutamate and D-serine levels in prefrontal cortical and hippocampal tissue homogenates. Moreover, we did not detect alterations in social preference and spontaneous alternation despite severe motor impairment. Thus, we conclude that behavioral and cognitive aspects are maintained even though severe neural damage is observed by chronic infection of C57Bl/6 mice with the ME-49 strain.

The Toxoplasma Polymorphic Effector GRA15 Mediates Seizure Induction by Modulating Interleukin-1 Signaling in the Brain

Toxoplasmic encephalitis can develop in individuals infected with the protozoan parasite Toxoplasma gondii and is typified by parasite replication and inflammation within the brain. Patients often present with seizures, but the parasite genes and host pathways involved in seizure development and/or propagation are unknown. We previously reported that seizure induction in Toxoplasma-infected mice is parasite strain dependent. Using quantitative trait locus mapping, we identify four loci in the Toxoplasma genome that potentially correlate with seizure development. In one locus, we identify the polymorphic virulence factor, GRA15, as a Toxoplasma gene associated with onset of seizures. GRA15 was previously shown to regulate host NF-κB-dependent gene expression during acute infections, and we demonstrate a similar role for GRA15 in brains of toxoplasmic encephalitic mice. GRA15 is important for increased expression of interleukin 1 beta (IL-1β) and other IL-1 pathway host genes, which is significant since IL-1 signaling is involved in onset of seizures. Inhibiting IL-1 receptor signaling reduced seizure severity in Toxoplasma-infected mice. These data reveal one mechanism by which seizures are induced during toxoplasmic encephalitis.

Association between Toxoplasma gondii infection and metabolic syndrome in obese adolescents: A possible immune-metabolic link

Background Toxoplasmosis as a global disease is considered as a triggering factor responsible for development of several clinical diseases. However, Toxoplasma gondii (T. gondii) is an understudied parasite of potential interest in obesity research. The current study aimed to explore the role of latent T. gondii infection in the pathogenesis of metabolic syndrome (MetS) in obese adolescents through studying the relationship between serum interferon-gamma [IFN-γ] and serum chemerin in context of MetS components. Methods Eighty-three obese adolescents were serologically screened for T. gondii-IgG antibodies and compared to 35 age-matched healthy T. gondii-seronegative controls. Participants were evaluated for anthropometric measurements, total-fat mass [FM], trunk-FM, serum lipid profile, IFN-γ, and chemerin levels. Homeostatic Model Assessment of insulin resistance (HOMA-IR) was calculated. Results The prevalence of MetS was significantly higher within obese T. gondii-seropositive group compared to obese T. gondii-seronegative group (P = 0.033). Seropositive obese MetS group displayed significantly higher trunk-FM, HOMA-IR, chemerin, and IFN-γ compared to seronegative obese MetS group. Serum chemerin and IFN-γ were strongly correlated (P < 0.001) and were positively correlated with BMI, WC, total-FM, trunk-FM, HOMA-IR, cholesterol, triglycerides and negatively correlated with HDLC. HOMA-IR was a common predictor for serum chemerin (P = 0.030) and IFN-γ (P < 0.001). Conclusions The study results suggest that T. gondii infection may exert an immune-metabolic effect that may have a potential role in the development of MetS among obese adolescents.

Eukaryotic and Prokaryotic Microbiota Interactions

The nature of the relationship between the communities of microorganisms making up the microbiota in and on a host body has been increasingly explored in recent years. Microorganisms, including bacteria, archaea, viruses, parasites and fungi, have often long co-evolved with their hosts. In human, the structure and diversity of microbiota vary according to the host’s immunity, diet, environment, age, physiological and metabolic status, medical practices (e.g., antibiotic treatment), climate, season and host genetics. The recent advent of next generation sequencing (NGS) technologies enhanced observational capacities and allowed for a better understanding of the relationship between distinct microorganisms within microbiota. The interaction between the host and their microbiota has become a field of research into microorganisms with therapeutic and preventive interest for public health applications. This review aims at assessing the current knowledge on interactions between prokaryotic and eukaryotic communities. After a brief description of the metagenomic methods used in the studies were analysed, we summarise the findings of available publications describing the interaction between the bacterial communities and protozoa, helminths and fungi, either in vitro, in experimental models, or in humans. Overall, we observed the existence of a beneficial effect in situations where some microorganisms can improve the health status of the host, while the presence of other microorganisms has been associated with pathologies, resulting in an adverse effect on human health.

Beneficial effects of Strongyloides venezuelensis antigen extract in acute experimental toxoplasmosis

BACKGROUND

Toxoplasma gondii is a protozoan with worldwide distribution and triggers a strong Th1 immune response in infected susceptible hosts. On the contrary, most helminth infections are characterized by Th2 immune response and the use of helminth-derived antigens to regulate immune response in inflammatory disorders has been broadly investigated.

OBJECTIVES

The aim of this study was to investigate whether treatment with Strongyloides venezuelensis antigen extract (SvAg) would alter immune response against T gondii.

METHODS

C57BL/6 mice were orally infected with T gondii and treated with SvAg, and parasitological, histological and immunological parameters were investigated.

RESULTS

It was observed that SvAg treatment improved survival rates of T gondii-infected mice. At day 7 post-infection, the parasite load was lower in the lung and small intestine of infected SvAg-treated mice than untreated infected mice. Remarkably, SvAg-treated mice infected with T gondii presented reduced inflammatory lesions in the small intestine than infected untreated mice and decreased intestinal and systemic levels of IFN-γ, TNF-α and IL-6. In contrast, SvAg treatment increased T gondii-specific IgA serum levels in infected mice.

CONCLUSIONS

S venezuelensis antigen extract has anti-parasitic and anti-inflammatory properties during T gondii infection suggesting as a possible alternative to parasite and inflammation control.

CD8 T cells drive anorexia, dysbiosis, and blooms of a commensal with immunosuppressive potential after viral infection

Infections elicit immune adaptations to enable pathogen resistance and/or tolerance and are associated with compositional shifts of the intestinal microbiome. However, a comprehensive understanding of how infections with pathogens that exhibit distinct capability to spread and/or persist differentially change the microbiome, the underlying mechanisms, and the relative contribution of individual commensal species to immune cell adaptations is still lacking. Here, we discovered that mouse infection with a fast-spreading and persistent (but not a slow-spreading acute) isolate of lymphocytic choriomeningitis virus induced large-scale microbiome shifts characterized by increased Verrucomicrobia and reduced Firmicute/Bacteroidetes ratio. Remarkably, the most profound microbiome changes occurred transiently after infection with the fast-spreading persistent isolate, were uncoupled from sustained viral loads, and were instead largely caused by CD8 T cell responses and/or CD8 T cell-induced anorexia. Among the taxa enriched by infection with the fast-spreading virus, Akkermansia muciniphila, broadly regarded as a beneficial commensal, bloomed upon starvation and in a CD8 T cell-dependent manner. Strikingly, oral administration of A. muciniphila suppressed selected effector features of CD8 T cells in the context of both infections. Our findings define unique microbiome differences after chronic versus acute viral infections and identify CD8 T cell responses and downstream anorexia as driver mechanisms of microbial dysbiosis after infection with a fast-spreading virus. Our data also highlight potential context-dependent effects of probiotics and suggest a model in which changes in host behavior and downstream microbiome dysbiosis may constitute a previously unrecognized negative feedback loop that contributes to CD8 T cell adaptations after infections with fast-spreading and/or persistent pathogens.

T. gondii infection induces IL-1R dependent chronic cachexia and perivascular fibrosis in the liver and skeletal muscle

Cachexia is a progressive muscle wasting disease that contributes to death in a wide range of chronic diseases. Currently, the cachexia field lacks animal models that recapitulate the long-term kinetics of clinical disease, which would provide insight into the pathophysiology of chronic cachexia and a tool to test therapeutics for disease reversal. Toxoplasma gondii (T. gondii) is a protozoan parasite that uses conserved mechanisms to infect rodents and human hosts. Infection is lifelong and has been associated with chronic weight loss and muscle atrophy in mice. We have recently shown that T. gondii-induced muscle atrophy meets the clinical definition of cachexia. Here, the longevity of the T. gondii-induced chronic cachexia model revealed that cachectic mice develop perivascular fibrosis in major metabolic organs, including the adipose tissue, skeletal muscle, and liver by 9 weeks post-infection. Development of cachexia, as well as liver and skeletal muscle fibrosis, is dependent on intact signaling through the type I IL-1R receptor. IL-1α is sufficient to activate cultured fibroblasts and primary hepatic stellate cells (myofibroblast precursors in the liver) in vitro, and IL-1α is elevated in the sera and liver of cachectic, suggesting a mechanism by which chronic IL-1R signaling could be leading to cachexia-associated fibrosis.

The molecular biology and immune control of chronic Toxoplasma gondii infection

Toxoplasma gondii is an incredibly successful parasite owing in part to its ability to persist within cells for the life of the host. Remarkably, at least 350 host species of T. gondii have been described to date, and it is estimated that 30% of the global human population is chronically infected. The importance of T. gondii in human health was made clear with the first reports of congenital toxoplasmosis in the 1940s. However, the AIDS crisis in the 1980s revealed the prevalence of chronic infection, as patients presented with reactivated chronic toxoplasmosis, underscoring the importance of an intact immune system for parasite control. In the last 40 years, there has been tremendous progress toward understanding the biology of T. gondii infection using rodent models, human cell experimental systems, and clinical data. However, there are still major holes in our understanding of T. gondii biology, including the genes controlling parasite development, the mechanisms of cell-intrinsic immunity to T. gondii in the brain and muscle, and the long-term effects of infection on host homeostasis. The need to better understand the biology of chronic infection is underscored by the recent rise in ocular disease associated with emerging haplotypes of T. gondii and our lack of effective treatments to sterilize chronic infection. This Review discusses the cell types and molecular mediators, both host and parasite, that facilitate persistent T. gondii infection. We highlight the consequences of chronic infection for tissue-specific pathology and identify open questions in this area of host-Toxoplasma interactions.

IL-1R Regulates Disease Tolerance and Cachexia in Toxoplasma gondii Infection

Toxoplasma gondii is an obligate intracellular parasite that establishes life-long infection in a wide range of hosts, including humans and rodents. To establish a chronic infection, pathogens often exploit the trade-off between resistance mechanisms, which promote inflammation and kill microbes, and tolerance mechanisms, which mitigate inflammatory stress. Signaling through the type I IL-1R has recently been shown to control disease tolerance pathways in endotoxemia and Salmonella infection. However, the role of the IL-1 axis in T. gondii infection is unclear. In this study we show that IL-1R-/- mice can control T. gondii burden throughout infection. Compared with wild-type mice, IL-1R-/- mice have more severe liver and adipose tissue pathology during acute infection, consistent with a role in acute disease tolerance. Surprisingly, IL-1R-/- mice had better long-term survival than wild-type mice during chronic infection. This was due to the ability of IL-1R-/- mice to recover from cachexia, an immune-metabolic disease of muscle wasting that impairs fitness of wild-type mice. Together, our data indicate a role for IL-1R as a regulator of host homeostasis and point to cachexia as a cost of long-term reliance on IL-1-mediated tolerance mechanisms.

Automated Spatially Targeted Optical Microproteomics (autoSTOMP) to Determine Protein Complexity of Subcellular Structures

Spatially targeted optical microproteomics (STOMP) is a method to study region-specific protein complexity in primary cells and tissue samples. STOMP uses a confocal microscope to visualize structures of interest and to tag the proteins within those structures by a photodriven cross-linking reaction so that they can be affinity purified and identified by mass spectrometry (eLife 2015, 4, e09579). However, the use of a custom photo-cross-linker and the requirement for extensive user intervention during sample tagging have posed barriers to the utilization of STOMP. To address these limitations, we built automated STOMP (autoSTOMP) which uses a customizable code in SikuliX to coordinate image capture and cross-linking functions in Zeiss Zen Black with image processing in FIJI. To increase protocol accessibility, we implemented a commercially available biotin-benzophenone photo-cross-linking and purification protocol. Here we demonstrate that autoSTOMP can efficiently label, purify, and identify proteins belonging to 1-2 μm structures in primary human foreskin fibroblasts or mouse bone marrow-derived dendritic cells infected with the protozoan parasite Toxoplasma gondii (Tg). AutoSTOMP can easily be adapted to address a range of research questions using Zeiss Zen Black microscopy systems and LC-MS protocols that are standard in many research cores.

Gut Microbiota, Muscle Mass and Function in Aging: A Focus on Physical Frailty and Sarcopenia

Human gut microbiota is able to influence the host physiology by regulating multiple processes, including nutrient absorption, inflammation, oxidative stress, immune function, and anabolic balance. Aging is associated with reduced microbiota biodiversity, increased inter-individual variability, and over-representation of pathobionts, and these phenomena may have great relevance for skeletal muscle mass and function. For this reason, the presence of a gut-muscle axis regulating the onset and progression of age-related physical frailty and sarcopenia has been recently hypothesized. In this narrative review, we summarize the studies supporting a possible association between gut microbiota-related parameters with measures of muscle mass, muscle function, and physical performance in animal models and humans. Reduced muscle mass has been associated with distinct microbiota composition and reduced fermentative capacity in mice, and the administration of probiotics or butyrate to mouse models of muscle wasting has been associated with improved muscle mass. However, no studies have targeted the human microbiome associated with sarcopenia. Limited evidence from human studies shows an association between microbiota composition, involving key taxa such as Faecalibacterium and Bifidobacterium, and grip strength. Similarly, few studies conducted on patients with parkinsonism showed a trend towards a different microbiota composition in those with reduced gait speed. No studies have assessed the association of fecal microbiota with other measures of physical performance. However, several studies, mainly with a cross-sectional design, suggest an association between microbiota composition and frailty, mostly assessed according to the deficit accumulation model. Namely, frailty was associated with reduced microbiota biodiversity, and lower representation of butyrate-producing bacteria. Therefore, we conclude that the causal link between microbiota and physical fitness is still uncertain due to the lack of targeted studies and the influence of a large number of covariates, including diet, exercise, multimorbidity, and polypharmacy, on both microbiota composition and physical function in older age. However, the relationship between gut microbiota and physical function remains a very promising area of research for the future.

Disease Tolerance in Toxoplasma Infection

Toxoplasma gondii is a successful protozoan parasite that cycles between definitive felid hosts and a broad range of intermediate hosts, including rodents and humans. Within intermediate hosts, this obligate intracellular parasite invades the small intestine, inducing an inflammatory response. Toxoplasma infects infiltrating immune cells, using them to spread systemically and reach tissues amenable to chronic infection. An intact immune system is necessary to control life-long chronic infection. Chronic infection is characterized by formation of parasite cysts, which are necessary for survival through the gastrointestinal tract of the next host. Thus, Toxoplasma must evade sterilizing immunity, but still rely on the host's immune response for survival and transmission. To do this, Toxoplasma exploits a central cost-benefit tradeoff in immunity: the need to escalate inflammation for pathogen clearance vs. the need to limit inflammation-induced bystander damage. What are the consequences of sustained inflammation on host biology? Many studies have focused on aspects of the immune response that directly target Toxoplasma growth and survival, commonly referred to as "resistance mechanisms." However, it is becoming clear that a parallel arm of the immune response has evolved to mitigate damage caused by the parasite directly (for example, egress-induced cell death) or bystander damage due to the inflammatory response (for example, reactive nitrogen species, degranulation). These so-called "disease tolerance" mechanisms promote tissue function and host survival without directly targeting the pathogen. Here we review changes to host metabolism, tissue structure, and immune function that point to disease tolerance mechanisms during Toxoplasma infection. We explore the impact tolerance programs have on the health of the host and parasite biology.