Innate resistance to Entamoeba histolytica in murine models

Host genetic backgrounds: the key to determining parasite-host adaptation

Parasitic diseases pose a significant threat to global public health, particularly in developing countries. Host genetic factors play a crucial role in determining susceptibility and resistance to infection. Recent advances in molecular and biological technologies have enabled significant breakthroughs in understanding the impact of host genes on parasite adaptation. In this comprehensive review, we analyze the host genetic factors that influence parasite adaptation, including hormones, nitric oxide, immune cells, cytokine gene polymorphisms, parasite-specific receptors, and metabolites. We also establish an interactive network to better illustrate the complex relationship between host genetic factors and parasite-host adaptation. Additionally, we discuss future directions and collaborative research priorities in the parasite-host adaptation field, including investigating the impact of host genes on the microbiome, developing more sophisticated models, identifying and characterizing parasite-specific receptors, utilizing patient-derived sera as diagnostic and therapeutic tools, and developing novel treatments and management strategies targeting specific host genetic factors. This review highlights the need for a comprehensive and systematic approach to investigating the underlying mechanisms of parasite-host adaptation, which requires interdisciplinary collaborations among biologists, geneticists, immunologists, and clinicians. By deepening our understanding of the complex interactions between host genetics and parasite adaptation, we can develop more effective and targeted interventions to prevent and treat parasitic diseases. Overall, this review provides a valuable resource for researchers and clinicians working in the parasitology field and offers insights into the future directions of this critical research area.

Effect of Electroacupuncture at Siguan Acupoints on Expression of BDNF and TrkB Proteins in the Hippocampus of Post-Stroke Depression Rats

To study the effect of electroacupuncture at the Siguan acupoints on the expression of hippocampal brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) in post-stroke depression (PSD) rats, in order to explore its possible mechanism Fifty specific pathogen-free (SPF)-grade adult male Sprague-Dawley (SD) rats were randomly divided into a blank group, stroke group, PSD group, Siguan acupoint group and fluoxetine group according to the random number method. PSD rats were modeled with middle cerebral artery occlusion combined with chronic unpredictable mild stress. After successful modeling, electroacupuncture was applied to Siguan acupoints for a total of 21 days at 30 min/session/day. The rats in the fluoxetine group were fed intragastrically according to body weight, once a day, for a total of 21 days. The rats in each group were bound and intragastrically administered distilled water every day. The depressive behavior of rats was measured according to the horizontal and vertical scores of the open field test and the sucrose water consumption, and the changes in the number of BDNF- and TrkB-positive cells in the hippocampus of rats were observed by immunohistochemistry. After modeling, the behavioral indicators and the numbers of BDNF- and TrkB-positive cells in each model group were significantly lower than those in the blank group (P < 0.01). After treatment, the behavioral indicators and the numbers of BDNF- and TrkB-positive cells in the Siguan acupoint group and fluoxetine group were significantly higher than that in the PSD group (P < 0.01). During the treatment, the horizontal and vertical scores of the Siguan acupoint group were significantly increased on the seventh day of treatment, and the difference was statistically significant when compared with the PSD group (P < 0.05). The sucrose water consumption was significantly increased on the 14th day of treatment, and the difference was significant when compared with the PSD group (P < 0.05), both of which were earlier than that in the fluoxetine group. During the treatment, there was no significant difference between the two groups (P > 0.05). Electroacupuncture at Siguan acupoints has the same antidepressant effect as fluoxetine, and is more effective than fluoxetine in relieving depression in PSD rats. Its mechanism may be related to the activation of the expression of BDNF and its receptor TrkB.

Intestinal amoebiasis: 160 years of its first detection and still remains as a health problem in developing countries

Amoebiasis is a parasitic disease caused by Entamoeba histolytica (E. histolytica), an extracellular enteric protozoan. This infection mainly affects people from developing countries with limited hygiene conditions, where it is endemic. Infective cysts are transmitted by the fecal-oral route, excysting in the terminal ileum and producing invasive trophozoites (amoebae). E. histolytica mainly lives in the large intestine without causing symptoms; however, possibly as a result of so far unknown signals, the amoebae invade the mucosa and epithelium causing intestinal amoebiasis. E. histolytica possesses different mechanisms of pathogenicity for the adherence to the intestinal epithelium and for degrading extracellular matrix proteins, producing tissue lesions that progress to abscesses and a host acute inflammatory response. Much information has been obtained regarding the virulence factors, metabolism, mechanisms of pathogenicity, and the host immune response against this parasite; in addition, alternative treatments to metronidazole are continually emerging. An accesible and low-cost diagnostic method that can distinguish E. histolytica from the most nonpathogenic amoebae and an effective vaccine are necessary for protecting against amoebiasis. However, research about the disease and its prevention has been a challenge due to the relationship between E. histolytica and the host during the distinct stages of the disease is multifaceted. In this review, we analyze the interaction between the parasite, the human host, and the colon microbiota or pathogenic microorganisms, which together give rise to intestinal amoebiasis.

Efficient and reproducible experimental infections of rats with Blastocystis spp

Although Blastocystis spp. infect probably more than 1 billion people worldwide, their clinical significance is still controversial and their pathophysiology remains poorly understood. In this study, we describe a protocol for an efficient and reproducible model of chronic infection in rats, laying the groundwork for future work to evaluate the pathogenic potential of this parasite. In our experimental conditions, we were unable to infect rats using vacuolar forms of an axenically cultivated ST4 isolate, but we successfully established chronic infections of 4 week-old rats after oral administration of both ST3 and ST4 purified cysts isolated from human stool samples. The infection protocol was also applied to 4 week-old C57BL/9, BALB/C and C3H mice, but any mouse was found to be infected by Blastocystis. Minimal cyst inoculum required for rat infection was higher with ST3 (105) than with ST4 (102). These results were confirmed by co-housing experiments highlighting a higher contagious potential of ST4 in rats compared to ST3. Finally, experiments mimicking fecal microbiota transfer from infected to healthy animals showed that Blastocystis spp. could easily infect a new host, even though its intestinal microbiota is not disturbed. In conclusion, our results provide a well-documented and robust rat model of Blastocystis chronic infection, reproducing "natural" infection. This model will be of great interest to study host parasite interactions and to better evaluate clinical significance of Blastocystis.

Immune Response of Amebiasis and Immune Evasion by Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite and the causative agent of amebiasis. It is estimated approximately 1% of humans are infected with E. histolytica, resulting in an estimate of 100,000 deaths annually. Clinical manifestations of amebic infection range widely from asymptomatic to severe symptoms, including dysentery and extra-intestinal abscesses. Like other infectious diseases, it is assumed that only ~20% of infected individuals develop symptoms, and genetic factors of both the parasite and humans as well as the environmental factors, e.g., microbiota, determine outcome of infection. There are multiple essential steps in amebic infection: degradation of and invasion into the mucosal layer, adherence to the intestinal epithelium, invasion into the tissues, and dissemination to other organs. While the mechanisms of invasion and destruction of the host tissues by the amebae during infection have been elucidated at the molecular levels, it remains largely uncharacterized how the parasite survive in the host by evading and attacking host immune system. Recently, the strategies for immune evasion by the parasite have been unraveled, including immunomodulation to suppress IFN-γ production, elimination of immune cells and soluble immune mediators, and metabolic alterations against reactive oxygen and nitrogen species to fend off the attack from immune system. In this review, we summarized the latest knowledge on immune reaction and immune evasion during amebiasis.

An ex-vivo human intestinal model to study Entamoeba histolytica pathogenesis

Amoebiasis (a human intestinal infection affecting 50 million people every year) is caused by the protozoan parasite Entamoeba histolytica. To study the molecular mechanisms underlying human colon invasion by E. histolytica, we have set up an ex vivo human colon model to study the early steps in amoebiasis. Using scanning electron microscopy and histological analyses, we have established that E. histolytica caused the removal of the protective mucus coat during the first two hours of incubation, detached the enterocytes, and then penetrated into the lamina propria by following the crypts of Lieberkühn. Significant cell lysis (determined by the release of lactodehydrogenase) and inflammation (marked by the secretion of pro-inflammatory molecules such as interleukin 1 beta, interferon gamma, interleukin 6, interleukin 8 and tumour necrosis factor) were detected after four hours of incubation. Entamoeba dispar (a closely related non-pathogenic amoeba that also colonizes the human colon) was unable to invade colonic mucosa, lyse cells or induce an inflammatory response. We also examined the behaviour of trophozoites in which genes coding for known virulent factors (such as amoebapores, the Gal/GalNAc lectin and the cysteine protease 5 (CP-A5), which have major roles in cell death, adhesion (to target cells or mucus) and mucus degradation, respectively) were silenced, together with the corresponding tissue responses. Our data revealed that the signalling via the heavy chain Hgl2 or via the light chain Lgl1 of the Gal/GalNAc lectin is not essential to penetrate the human colonic mucosa. In addition, our study demonstrates that E. histolytica silenced for CP-A5 does not penetrate the colonic lamina propria and does not induce the host's pro-inflammatory cytokine secretion.

Entamoeba histolytica is the causative agent of amoebiasis, a human disease. Like other enteric infections, the lack of animal models enhances the difficulty of studying the development of amoebiasis. To date, no experimental model has been developed that reproduces the invasive intestinal amoebic lesions seen in human colon. We present the first study that examines, using human colon explants, the early steps of the human colonic barrier invasion by E. histolytica. With this ex vivo integrative model we have investigated both parasite behaviour and the human tissue response. Remarkably, in this model E. histolytica was able to cross and destroy the intestinal barrier evoking a tissue inflammatory response, while E. dispar, a non-pathogenic species, was unable to penetrate nor induce tissue responses. Furthermore, we have explored the role of three virulence factors during the invasive process, using gene-silenced E. histolytica trophozoites, particularly the kinetics of invasion, tissue destruction and induction of an early inflammatory responses. This is, to our knowledge, the first time that their role is highlighted in a complex human system. Our study provides new insights in the molecular mechanisms involved in the early steps of human colon invasion by E. histolytica.

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.

Innate immunity prevents tissue invasion by Entamoeba histolytica

Although innate and adaptive immunity both play a role in amoebiasis, the mechanisms involved in the elimination of Entamoeba histolytica are poorly understood. To provide more information about the innate immune mechanisms that may confer protection against invasive amoebiasis, we administered inflammatory substances (bacillus Calmette-Guérin, lipopolysaccharide, complete Freund's adjuvant, or mineral oil) into the peritoneum of hamsters. The animals were then challenged with pathogenic trophozoites of E. histolytica and, after 7 days, the protective host response was analysed. We found that the nonspecific inflammatory response induced in the peritoneum was sufficient to prevent liver invasion by E. histolytica. In vitro experiments showed that the killing of trophozoites was mediated by peritoneal macrophages and a protein of 68 kDa with peroxidase activity.

The role of the secretory immune response in the infection by Entamoeba histolytica

Intestinal infection with the protozoan parasite Entamoeba histolytica elicits a local immune response with rising of specific secretory IgA (sIgA) antibodies detectable in several compartments associated to mucosa. Anti-amoebic sIgA antibodies have been reported in faeces, saliva, bile and breast milk from dysenteric patients and research trying to elucidate their role in protection has recently intensified. IgA antibodies inhibit the in vitro adherence of E. histolytica trophozoites to epithelial cell monolayers by recognizing several membrane antigens, including the galactose-binding lectin (Gal-lectin), main surface molecule involved in adherence, and the serine and cystein-rich proteins, all of them potential vaccine candidates. In fact, the presence of sIgA anti-Gal lectin in faeces of patients recovered from amoebic liver abscess (ALA) was associated with immunity to E. dispar. Moreover, the combined nasal and intraperitoneal vaccination of C3H/HeJ mice with native and recombinant Gal-lectin protected mice against an intracecal challenge with virulent E. histolytica trophozoites, protection that seemed to be associated with the induction of specific intestinal sIgA antibodies. Therefore, the stimulation of intestinal secretory response by mucosal delivery of amoebic antigens has been positioned as a promising strategy for inducing protection against human amoebiasis.