Enhanced pro-inflammatory chemokine/cytokine response triggered by pathogenic Entamoeba histolytica : basis of invasive disease

Fecal microbiota transplantation from protozoa-exposed donors downregulates immune response in a germ-free mouse model, its role in immune response and physiology of the intestine

Intestinal parasites are part of the intestinal ecosystem and have been shown to establish close interactions with the intestinal microbiota. However, little is known about the influence of intestinal protozoa on the regulation of the immune response. In this study, we analyzed the regulation of the immune response of germ-free mice transplanted with fecal microbiota (FMT) from individuals with multiple parasitic protozoans (P) and non-parasitized individuals (NP). We determined the production of intestinal cytokines, the lymphocyte populations in both the colon and the spleen, and the genetic expression of markers of intestinal epithelial integrity. We observed a general downregulation of the intestinal immune response in mice receiving FMT-P. We found significantly lower intestinal production of the cytokines IL-6, TNF, IFN-γ, MCP-1, IL-10, and IL-12 in the FMT-P. Furthermore, a significant decrease in the proportion of CD3+, CD4+, and Foxp3+ T regulatory cells (Treg) was observed in both, the colon and spleen with FMT-P in contrast to FMT-NP. We also found that in FMT-P mice there was a significant decrease in tjp1 expression in all three regions of the small intestine; ocln in the ileum; reg3γ in the duodenum and relmβ in both the duodenum and ileum. We also found an increase in colonic mucus layer thickness in mice colonized with FMT-P in contrast with FMT-NP. Finally, our results suggest that gut protozoa, such as Blastocystis hominis, Entamoeba coli, Endolimax nana, Entamoeba histolytica/E. dispar, Iodamoeba bütschlii, and Chilomastix mesnili consortia affect the immunoinflammatory state and induce functional changes in the intestine via the gut microbiota. Likewise, it allows us to establish an FMT model in germ-free mice as a viable alternative to explore the effects that exposure to intestinal parasites could have on the immune response in humans.

Distinct cytokine profiles in malaria coinfections: A systematic review

BACKGROUND

Few data exist on the distinct cytokine profiles of individuals with malaria coinfections and other diseases. This study focuses on data collation of distinct cytokine profiles between individuals with malaria coinfections and monoinfections to provide evidence for further diagnostic or prognostic studies.

METHODS

We searched five medical databases, including Embase, MEDLINE, PubMed, Ovid, and Scopus, for articles on cytokines in malaria coinfections published from January 1, 1983 to May 3, 2022, after which the distinct cytokine patterns between malaria coinfection and monoinfection were illustrated in heat maps.

RESULTS

Preliminary searches identified 2127 articles, of which 34 were included in the systematic review. Distinct cytokine profiles in malaria coinfections with bacteremia; HIV; HBV; dengue; filariasis; intestinal parasites; and schistosomiasis were tumor necrosis factor (TNF), interferon (IFN)-γ, IFN-α, interleukin (IL)-1, IL-1 receptor antagonist (Ra), IL-4, IL-7, IL-12, IL-15, IL-17; TNF, IL-1Ra, IL-4, IL-10, IL-12, IL-18, CCL3, CCL5, CXCL8, CXCL9, CXCL11, granulocyte colony-stimulating factor (G-CSF); TNF, IFN-γ, IL-4, IL-6, IL-10, IL-12, CCL2; IFN-γ, IL-1, IL-4, IL-6, IL-10, IL-12, IL-13, IL-17, CCL2, CCL3, CCL4, G-CSF; IL-1Ra, IL-10, CXCL5, CXCL8, CXCL10; TNF, IL-2, IL-4, IL-6, IL-10; and TNF, IFN-γ, IL-4, IL-5, IL-10, transforming growth factor-β, CXCL8, respectively.

CONCLUSION

This systematic review provides information on distinct cytokine profiles of malaria coinfections and malaria monoinfections. Further studies should investigate whether specific cytokines for each coinfection type could serve as essential diagnostic or prognostic biomarkers for malaria coinfections.

Entamoeba Species in South Africa: Correlations With the Host Microbiome, Parasite Burdens, and First Description of Entamoeba bangladeshi Outside of Asia

Background

Diarrhea is frequent in communities without clean water, which include low-income South African populations in Giyani and Pretoria. In these populations, the amount of diarrhea caused by Entamoeba histolytica, inclusive of all ages, sexes, and human immunodeficiency virus status, is uncertain. Infection with E. histolytica can modulate the host microbiota, and a key species indicative of this is the Prevotella copri pathobiont.

Methods

A cross-sectional study of patients attending gastroenterology clinics was conducted to determine the frequency and burden of 4 Entamoeba species and P. copri.

Results

Entamoeba species were present in 27% of patients (129/484), with E. histolytica detected in 8.5% (41), E. dispar in 8% (38), E. bangladeshi in 4.75% (23), and E. moshkovskii in 0%. This is the first description of E. bangladeshi outside Bangladesh. In E. histolytica-positive samples, the levels of both the parasite and P. copri were lower in nondiarrheal samples, validating the results of a study in Bangladesh (P = .0034). By contrast, in E. histolytica-negative samples positive for either of the nonpathogenic species E. dispar or E. bangladeshi, neither P. copri nor Entamoeba levels were linked to gastrointestinal status.

Conclusions

Nonmorphologic identification of this parasite is essential. In South Africa, 3 morphologically identical Entamoeba were common, but only E. histolytica was linked to both disease and changes in the microbiota.

Entamoeba histolytica Calreticulin Induces the Expression of Cytokines in Peripheral Blood Mononuclear Cells Isolated From Patients With Amebic Liver Abscess

Calreticulin (CRT) is a highly conserved protein in the endoplasmic reticulum that plays important roles in the regulation of key cellular functions. Little is known about the participation of E. histolytica CRT (EhCRT) in the processes of pathogenicity or in the modulation of the host immune response. The aim of this study was to evaluate the role of CRT in the proliferation and the cytokine profile in peripheral blood mononuclear cells (PBMCs) from patients with amebic liver abscess (ALA) during the acute phase (AP-ALA) of the disease compared to patients during the resolution phase (R-ALA). The PBMCs from each participant were cocultured with EhCRT and tested by the colorimetric method to evaluate their proliferation index (PI). The supernatants were subjected to an enzyme-linked immunosorbent assay (ELISA) to evaluate the concentration of cytokines. The mean values of all groups were compared using the independent t-test. When the PIs of individuals without diagnosis of liver abscess (NEG) were compared, there were no statistically significant differences in the proliferation of PBMCs between patients with AP-ALA and R-ALA when stimulated with EhCRT or concanavalin A (ConA). However, the levels of interleukins [IL-6, IL-10, granulocyte colony stimulating factor (GCSF), and transforming growth factor β1 (TGFβ1)] were higher in patients with AP-ALA, whereas in patients with R-ALA, higher levels of interferon gamma (IFNγ) were detected. These results suggest that EhCRT acts as a mitogen very similar to the activity of ConA. In addition, EhCRT is an excellent immunogen for the specific activation of PBMCs, inducing the differential expression of ILs depending on the outcome of disease, determining the type of immune response: a Th2 cytokine profile during the acute phase and a Th1 profile during the resolution phase.

Differential expression of pathogenic genes of Entamoeba histolytica vs E. dispar in a model of infection using human liver tissue explants

We sought to establish an ex vivo model for examining the interaction of E. histolytica with human tissue, using precision-cut liver slices (PCLS) from donated organs. E. histolytica- or E. dispar-infected PCLS were analyzed at different post-infection times (0, 1, 3, 24 and 48 h) to evaluate the relation between tissue damage and the expression of genes associated with three factors: a) parasite survival (peroxiredoxin, superoxide dismutase and 70 kDa heat shock protein), b) parasite virulence (EhGal/GalNAc lectin, amoebapore, cysteine proteases and calreticulin), and c) the host inflammatory response (various cytokines). Unlike E. dispar (non-pathogenic), E. histolytica produced some damage to the structure of hepatic parenchyma. Overall, greater expression of virulence genes existed in E. histolytica-infected versus E. dispar-infected tissue. Accordingly, there was an increased expression of EhGal/GalNAc lectin, Ehap-a and Ehcp-5, Ehcp-2, ehcp-1 genes with E. histolytica, and a decreased or lack of expression of Ehcp-2, and Ehap-a genes with E. dispar. E. histolytica-infected tissue also exhibited an elevated expression of genes linked to survival, principally peroxiredoxin, superoxide dismutase and Ehhsp-70. Moreover, E. histolytica-infected tissue showed an overexpression of some genes encoding for pro-inflammatory interleukins (ILs), such as il-8, ifn-γ and tnf-α. Contrarily, E. dispar-infected tissue displayed higher levels of il-10, the gene for the corresponding anti-inflammatory cytokine. Additionally, other genes were investigated that are important in the host-parasite relationship, including those encoding for the 20 kDa heat shock protein (HSP-20), the AIG-1 protein, and immune dominant variable surface antigen, as well as for proteins apparently involved in mechanisms for the protection of the trophozoites in different environments (e.g., thioredoxin-reductase, oxido-reductase, and 9 hypothetical proteins). Some of the hypothetical proteins evidenced interesting overexpression rates, however we should wait to their characterization. This finding suggest that the present model could be advantageous for exploring the complex interaction between trophozoites and hepatocytes during the development of ALA, particularly in the initial stages of infection.

Differential regulation of proinflammatory cytokine expression by mitogen-activated protein kinases in macrophages in response to intestinal parasite infection

Blastocystis is a common enteric protistan parasite that can cause acute, as well as chronic, infection and is associated with irritable bowel syndrome (IBS). However, the pathogenic status of Blastocystis infection remains unclear. In this study, we found that Blastocystis antigens induced abundant expression of proinflammatory cytokines, including interleukin 1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α), in mouse intestinal explants, in mouse colitis colon, and in macrophages. Further investigation utilizing RAW264.7 murine macrophages showed that Blastocystis treatment in RAW264.7 macrophages induced the activation of ERK, JNK, and p38, the three major groups of mammalian mitogen-activated protein (MAP) kinases that play essential roles in the expression of proinflammatory cytokines. ERK inhibition in macrophages significantly suppressed both mRNA and protein expression of IL-6 and TNF-α and mRNA expression of IL-1β. On the other hand, JNK inhibition resulted in reductions in both c-Jun and ERK activation and significant suppression of all three proinflammatory cytokines at both the mRNA and protein levels. Inhibition of p38 suppressed only IL-6 protein expression with no effect on the expression of IL-1β and TNF-α. Furthermore, we found that serine proteases produced by Blastocystis play an important role in the induction of ERK activation and proinflammatory cytokine expression by macrophages. Our study thus demonstrated for the first time that Blastocystis could induce the expression of various proinflammatory cytokines via the activation of MAP kinases and that infection with Blastocystis may contribute to the pathogenesis of inflammatory intestinal diseases through the activation of inflammatory pathways in host immune cells, such as macrophages.

Peroxynitrite and peroxiredoxin in the pathogenesis of experimental amebic liver abscess

The molecular mechanisms by which Entamoeba histolytica causes amebic liver abscess (ALA) are still not fully understood. Amebic mechanisms of adherence and cytotoxic activity are pivotal for amebic survival but apparently do not directly cause liver abscess. Abundant evidence indicates that chronic inflammation (resulting from an inadequate immune response) is probably the main cause of ALA. Reports referring to inflammatory mechanisms of liver damage mention a repertoire of toxic molecules by the immune response (especially nitric oxide and reactive oxygen intermediates) and cytotoxic substances released by neutrophils and macrophages after being lysed by amoebas (e.g., defensins, complement, and proteases). Nevertheless, recent evidence downplays these mechanisms in abscess formation and emphasizes the importance of peroxynitrite (ONOO⁻). It seems that the defense mechanism of amoebas against ONOO⁻, namely, the amebic thioredoxin system (including peroxiredoxin), is superior to that of mammals. The aim of the present text is to define the importance of ONOO⁻ as the main agent of liver abscess formation during amebic invasion, and to explain the superior capacity of amoebas to defend themselves against this toxic agent through the peroxiredoxin and thioredoxin system.

Immunogenicity and protective efficacy of heparan sulphate binding proteins of Entamoeba histolytica in a guinea pig model of intestinal amoebiasis

Entamoeba histolytica infection is associated with considerable morbidity and mortality in the form of intestinal and extraintestinal amoebiasis. No vaccine is yet available for amoebiasis. Heparan Sulphate Binding Proteins (HSBPs) from E. histolytica were evaluated for immunogenicity and protective efficacy in a Guinea pig model. Animals were immunized subcutaneously with 30μg of HSBP by three weekly inoculations. The immunogenicity of HSBP was determined by antibody response (IgG, IgM and IgA), splenocyte proliferation assay and in vitro direct amoebicidal assay with splenic lymphocytes and monocytes from vaccinated and control animals. The efficacy of the vaccine was evaluated by challenge infection to vaccinated and control animals by intra-caecal inoculation of E. histolytica trophozoites and comparing gross and histopathological findings in caeca of these animals. HSBP was found to induce specific anti-amoebic response as seen by specific antibody production and direct amoebicidal activity of splenocytes. The vaccine also showed partial protection against challenge infection in vaccinated animals as shown by mild/absent lesions and histopathological findings.

CCR9+ T cells contribute to the resolution of the inflammatory response in a mouse model of intestinal amoebiasis

Analysis of the mechanisms underlying the inflammatory response in amoebiasis is important to understand the immunopathology of the disease. Mucosal associated effector and regulatory T cells may play a role in regulating the inflammatory immune response associated to Entamoeba histolytica infection in the colon. A subpopulation of regulatory T cells has recently been identified and is characterized by the expression of the chemokine receptor CCR9. In this report, we used CCR9 deficient (CCR9(-/-)) mice to investigate the role of the CCR9(+) T cells in a murine model of E. histolytica intestinal infection. Intracecal infection of CCR9(+/+), CCR9(+/-) and CCR9(-/-) mice with E. histolytica trophozoites, revealed striking differences in the development and nature of the intestinal inflammatory response observed between these strains. While CCR9(+/+) and CCR9(+/-) mice were resistant to the infection and resolved the pathogen-induced inflammatory response, CCR9(-/-) mice developed a chronic inflammatory response, which was associated with over-expression of the cytokines IFN-γ, TNF-α, IL-4, IL-6 and IL-17, while IL-10 was not present. In addition, increased levels of CCL11, CCL20 and CCL28 chemokines were detected by qRT-PCR in CCR9(-/-) mice. E. histolytica trophozoites were identified in the lumen of the cecum of CCR9(-/-) mice at seven days post infection (pi), whereas in CCR9(+/+) mice trophozoites disappeared by day 1 pi. Interestingly, the inflammation observed in CCR9(-/-) mice, was associated with a delayed recruitment of CD4(+)CD25(+)FoxP3(+) T cells to the cecal epithelium and lamina propria, suggesting that this population may play a role in the early regulation of the inflammatory response against E. histolytica, likely through IL-10 production. In support of these data, CCR9(+) T cells were also identified in colon tissue sections obtained from patients with amoebic colitis. Our data suggest that a population of CCR9(+)CD4(+)CD25(+)FoxP3(+) T cells may participate in the control and resolution of the inflammatory immune response to E. histolytica infection.

Proinflammatory and regulatory cytokines and chemokines in infants with uncomplicated and severe Plasmodium falciparum malaria

Cytokine and chemokine levels were studied in infants (<5 years) with uncomplicated (MM) and severe malaria tropica (SM), and in Plasmodium falciparum infection-free controls (NEG). Cytokine plasma levels of interleukin (IL)-10, IL-13, IL-31 and IL-33 were strongly elevated in MM and SM compared to NEG (P<0·0001). Inversely, plasma concentrations of IL-27 were highest in NEG infants, lower in MM cases and lowest in those with SM (P<0·0001, NEG compared to MM and SM). The levels of the chemokines macrophage inflammatory protein (MIP3)-α/C-C ligand 20 (CCL20), monokine induced by gamma interferon (MIG)/CXCL9 and CXCL16 were enhanced in those with MM and SM (P<0·0001 compared to NEG), and MIP3-α/CCL20 and MIG/CXCL9 were correlated positively with parasite density, while that of IL-27 were correlated negatively. The levels of 6Ckine/CCL21 were similar in NEG, MM and SM. At 48-60 h post-anti-malaria treatment, the plasma concentrations of IL-10, IL-13, MIG/CXCL9, CXCL16 and MIP3-α/CCL20 were clearly diminished compared to before treatment, while IL-17F, IL-27, IL-31 and IL-33 remained unchanged. In summary, elevated levels of proinflammatory and regulatory cytokines and chemokines were generated in infants during and after acute malaria tropica. The proinflammatory type cytokines IL-31 and IL-33 were enhanced strongly while regulatory IL-27 was diminished in those with severe malaria. Similarly, MIP3-α/CCL20 and CXCL16, which may promote leucocyte migration into brain parenchyma, displayed increased levels, while CCL21, which mediates immune surveillance in central nervous system tissues, remained unchanged. The observed cytokine and chemokine production profiles and their dynamics may prove useful in evaluating either the progression or the regression of malarial disease.

Expression of cytokines and their regulation during amoebic liver abscess development

Amoebic liver abscess (ALA) is the most important extraintestinal complication of Entamoeba histolytica infection. Amoebic liver abscess development causes severe destruction of the liver tissue concomitant with a strong inflammatory reaction. We analyse the in situ expression of TNF-α, IFN-γ, IL-1β, 1L-8 and IL-10 at different stages of ALA development in a susceptible animal model. Results showed that after inoculation, neutrophils (PMN) and some macrophages infiltrated the liver and were positive for TNF-α and IFN-γ at the acute phase of amoeba infection. The presence of these cytokines was transient and decreased as tissue damage progressed. In contrast, IL-1β and IL-8 were detected mainly in neutrophils and macrophages from the periods of acute infection to subacute and chronic infection and decreased when granulomas were formed. The IL-10 was expressed in PMN and mononuclear cells and only during a short period at the onset of acute infection. The qRT-PCR of mRNA revealed a relationship with the expression of the cytokines in cells found in the ALA. Furthermore, our data suggest that IL-10 does not regulate local production of these cytokines. Our results indicate that an exacerbated inflammatory milieu is established and contributes to liver tissue damage and probably supports the survival of the parasites.

In vivo programmed cell death of Entamoeba histolytica trophozoites in a hamster model of amoebic liver abscess

Entamoeba histolytica trophozoites can induce host cell apoptosis, which correlates with the virulence of the parasite. This phenomenon has been seen during the resolution of an inflammatory response and the survival of the parasites. Other studies have shown that E. histolytica trophozoites undergo programmed cell death (PCD) in vitro, but how this process occurs within the mammalian host cell remains unclear. Here, we studied the PCD of E. histolytica trophozoites as part of an in vivo event related to the inflammatory reaction and the host-parasite interaction. Morphological study of amoebic liver abscesses showed only a few E. histolytica trophozoites with peroxidase-positive nuclei identified by terminal deoxynucleotidyltransferase enzyme-mediated dUTP nick end labelling (TUNEL). To better understand PCD following the interaction between amoebae and inflammatory cells, we designed a novel in vivo model using a dialysis bag containing E. histolytica trophozoites, which was surgically placed inside the peritoneal cavity of a hamster and left to interact with the host's exudate components. Amoebae collected from bags were then examined by TUNEL assay, fluorescence-activated cell sorting (FACS) and transmission electron microscopy. Nuclear condensation and DNA fragmentation of E. histolytica trophozoites were observed after exposure to peritoneal exudates, which were mainly composed of neutrophils and macrophages. Our results suggest that production of nitric oxide by inflammatory cells could be involved in PCD of trophozoites. In this modified in vivo system, PCD appears to play a prominent role in the host-parasite interaction and parasite cell death.

Expression of immune modulator cytokines in human fulminant amoebic colitis

Human fulminant amoebic colitis (FAC) is characterized by ulceration and inflammation of the colon. The specific mixture of pro-inflammatory and anti-inflammatory cytokines may participate in either the host defense or in the pathogenesis of amoebic colitis. Therefore, we studied the expression of IL-8, IL-10, IL-4, TGF-beta and IFN-gamma in human FAC patients and controls through immunohistochemistry analysis. The number of cells expressing IL-8, IL-4 and IL-10 was significantly enhanced in all FAC samples compared to the control samples. However, the expression of TGF- beta in patients was low in the colonic mucosa and high in the lamina propria compared with the control. No expression of IFN-gamma was found in the controls or FAC samples. The production of IL-8 by intestinal epithelial cells may play a role in the pathogenesis of amoebic infection, because this cytokine attracts neutrophils, which lead to an inflammatory reaction that results in tissue damage. The predominant expression of the macrophage down-regulating cytokines, IL-4, IL-10 and TGF-beta, or the Th2-type immune response could inhibit a cell-mediated immune response, which in turn would facilitate parasite invasion in these tissues.

Invasive amebiasis: a microcirculatory disorder?

The two current models of invasive amebiasis both hold that direct contact of toxic molecules and amebas with tissue produces the necrotic areas characteristic of this disorder. Whereas one model characterizes these toxic molecules as amebic products (e.g., lectins, amebapores, cysteine proteinases and other proteolytic enzymes), the other describes them as products of the inflammatory response (e.g., cytokines, nitric oxide, reactive oxygen intermediates and cytotoxic granules). Both these models can account for necrotic areas with many amebas present and with acute inflammation, but not those with few or no amebas present or with scarce inflammation. A new model poses that an inadequate immune response leads to a continuous and prolonged activation of endothelial cells (ECs) by amebas, amebic molecules and cytokines, which triggers the mechanisms leading to necrosis. Other toxic molecules later contribute to EC activation: nitric oxide, reactive oxygen intermediates, the activated complement and proteases. Hyperactivated endothelial cells continuously express adhesion molecules (e.g., ICAM-1 and E-selectin), pro-coagulant molecules (e.g., tissue factor, von Willebrand factor, and the plasminogen activator inhibitor), resulting in ever greater inflammation and thrombosis, which eventually reduces or blocks blood flow in some vessels and starves certain tissue areas of an adequate oxygen and nutrient supply. When necrotic areas first develop, they are surrounded by inflammatory cells due to the acute inflammation at this stage. However, these cells are starved of oxygen and essential nutrients by the same microcirculatory dysfunction. The increasing concentration of nitric oxide during amebiasis eventually has an anti-inflammatory and vasodilating effect, creating a new mechanism for the microcirculatory dysfunction. This local microcirculatory dysfunction can explain necrotic areas in the presence of many, few, or no amebas, with abundant or scarce inflammation.

Recent discoveries in the pathogenesis and immune response toward Entamoeba histolytica

Entamoeba histolytica is an enteric dwelling human protozoan parasite that causes the disease amoebiasis, which is endemic in the developing world. Over the past four decades, considerable effort has been made to understand the parasite and the disease. Improved diagnostics can now differentiate pathogenic E. histolytica from that of the related but nonpathogenic Entamoeba dispar, thus minimizing screening errors. Classically, the triad of Gal-lectin, cysteine proteinases and amoebapores of the parasite were thought to be the major proteins involved in the pathogenesis of amoebiasis. However, other amoebic molecules such as lipophosphopeptidoglycan, perioxiredoxin, arginase, and lysine and glutamic acid-rich proteins are also implicated. Recently, the genome of E. histolytica has been sequenced, which has widened our scope to study additional virulence factors. E. histolytica genome-based approaches have now confirmed the presence of Golgi apparatus-like vesicles and the machinery for glycosylation, thus improving the chances of identifying potential drug targets for chemotherapeutic intervention. Apart from Gal-lectin-based vaccines, promising vaccine targets such as serine-rich E. histolytica protein have yielded encouraging results. Considerable efforts have also been made to skew vaccination responses towards appropriate T-helper cell immunity that could augment the efficacy of vaccine candidates under study. Thus, ongoing efforts mining the information made available with the sequencing of the E. histolytica genome will no doubt identify and characterize other important potential vaccine/drug targets and lead to effective immunologic strategies for the control of amoebiasis.