Effect of immunosuppression on the size and metastasis of amoebic liver abscesses in hamsters

Amoebic Liver Abscess and Indigenous Alcoholic Beverages in the Tropics

Amoebic liver abscess (ALA) seen commonly in the tropics is predominantly confined to adult males, especially those who consume locally brewed alcohol, although intestinal amoebiasis occurs in all age groups and in both genders. Whether the role of alcohol in the development of ALA is incidental and casual or whether alcohol is causally implicated has been debated. It has been argued that socioeconomic factors and poor sanitary conditions are the primary culprits that casually link alcohol to ALA. However, there has emerged an abundance of data that implicates alcohol in a more causal role in facilitating the extraintestinal invasion of the infective protozoan and the subsequent development of ALA. These factors include the role of alcohol in host immunity, parasitic proliferation, and invasion and in creating a conducive hepatic microenvironment. The contributory role of alcohol-induced increase in hepatic iron stores and lipid content is discussed. Late-stage liver disease with fibrosis seems to be protective for the development of ALA. Further research is necessary to elucidate the many possible mechanisms that predispose to hepatic amoebiasis, so that appropriate individual and population-based preventive measures can be implemented.

Metronidazole treatment for acute phase amoebic liver abscess in patients co-infected with HIV

Metronidazole is the drug of choice for invasive amoebiasis; however, it is not known whether its dose or duration require modification in HIV infection when treating invasive amoebiasis. Seven HIV-positive patients with acute phase amoebic liver abscess were treated with daily oral administration of 1500 mg of metronidazole for 10 days. None of the patients required abscess drainage, and metronidazole was effective in all patients without serious side-effects. The CD4 cell count or HIV viral load did not appear to influence the efficacy of metronidazole therapy.

Crosstalk at the initial encounter: interplay between host defense and ameba survival strategies

The host-parasite relationship is based on a series of interplays between host defense mechanisms and parasite survival strategies. Progress has been made in understanding the role of host immune response in amebiasis. While host cells elaborate diverse mechanisms for pathogen expulsion, amebae have also developed complex strategies to modulate host immune response and facilitate their own survival. This paper will give an overview of current research on the mutual interactions between host and Entamoeba histolytica in human and experimental amebiasis. Understanding this crosstalk is crucial for the effective design and implementation of new vaccines and drugs for this leading parasitic disease.

Host-pathogen interaction in amebiasis and progress in vaccine development

Entamoeba histolytica, the causative organism of invasive intestinal and extraintestinal amebiasis, infects approximately 50 million people each year, causing an estimated 40 to 100 thousand deaths annually. Because amebae only infect humans and some higher non-human primates, an anti-amebic vaccine could theoretically eradicate the organism. Uncontrolled epidemiologic studies indicate that acquired immunity to amebic infection probably occurs and that such a vaccine might be feasible. Application of molecular biologic techniques has led to rapid progress towards understanding how Entamoeba histolytica causes disease, and to the identification of several amebic proteins associated with virulence. These proteins are now being evaluated as potential vaccine components. Parenteral and oral vaccine preparations containing recombinant amebic proteins have been effective in preventing disease in a gerbil model of amebic liver abscess. Although systemic and mucosal cellular and humoral immunity both appear to play a role in protection against Entamoeba histolytica, the relative importance of each in the human immune response remains unknown. No animal model of intestinal amebiasis currently exists, moreover, so it has been impossible to evaluate protection against colonization and colitis. Further investigation of the fundamental mechanisms by which Entamoeba histolytica causes disease and of the human immune response to amebic infection is necessary to assess the true feasibility of an anti-amebic vaccine.

Entamoeba histolytica trophozoites induce an inflammatory cytokine response by cultured human cells through the paracrine action of cytolytically released interleukin-1 alpha

Infection with the protozoan parasite Entamoeba histolytica results in a high mortality worldwide. To initiate infection, E. histolytica trophozoites in the bowel lumen penetrate the epithelium, and cause extensive lysis of host cells. The acute amebic lesions in animal models are characterized by infiltration with inflammatory cells, particularly neutrophils. The acute host response is likely important for determining whether the infection will spread systemically, but little is known regarding the signals which initiate an acute inflammatory response to E. histolytica. In the studies reported herein, we used an in vitro model system to define the proinflammatory signals produced by epithelial and other host cells in response to infection with E. histolytica trophozoites. Coculture of human epithelial and stromal cells and cell lines with trophozoites is shown to increase expression and secretion of an array of chemoattractant and proinflammatory cytokines, including IL-8, GRO alpha, GM-CSF, IL-1 alpha, and IL-6. Moreover, high-level secretion of those cytokines is regulated by the paracrine action of cytolytically released IL-1 alpha. A second mechanism for trophozoite-induced IL-8 production involves trophozoite-target cell contact via a galactose-inhibitable amebic adherence protein, and appears to be mediated through increased intracellular calcium levels. These studies define novel mechanisms through which acute inflammation can be initiated in the host in response to a cytolytic pathogen, such as E. histolytica.

In vitro effect of recombinant interferon gamma in combination with LPS on amoebicidal activity of murine Kupffer cells

The present study examines the role of liver macrophages (Kupffer cells), of C57BL/6 mice, as effector cells responsible for the killing of Entamoeba histolytica trophozoites in vitro. It was shown that unstimulated Kupffer cells were inefficient in the killing of E. histolytica trophozoites in vitro. Interferon gamma (IFN-gamma) alone was not able to activate Kupffer cells to amoebicidal state. However, Interferon gamma and lipopolysaccharide (LPS) acted synergistically in this phenomenon. It seems that the acquisition of amoebicidal activity is associated with the involvement of hydrogen peroxide, because the addition of catalase partially decreases the killing of this parasite by Kupffer cells. In addition, it appears that the amoebicidal activity of IFN-gamma-treated Kupffer cells is contact-dependent. Our results indicate that the immunologic production of IFN-gamma is important in the activation of Kupffer cells for controlling this parasite and that Kupffer cells are strong effector cells against the amoebae.

Entamoeba histolytica extract and interferon-gamma activation of macrophage-mediated amoebicidal function

The effect of recombinant murine interferon-gamma (IFN-gamma) and E. histolytica extract (E.h.E.) on macrophage (M phi) activation for amoebicidal activity was examined. Peritoneal macrophages were harvested from C57BL/6 and A/J mice and preincubated with IFN-gamma and/or E.h.E. It was found that amoebicidal activity could be induced in both C57BL/6 and A/J-derived macrophages by pretreatment with IFN-gamma and E.h.E. Pretreatment of the M phi with E. histolytica extract or IFN-gamma alone did not result in the activation of significant cytotoxic activity against E. histolytica trophozoites. In the presence of IFN-gamma, E.h.E. had a dose-dependent effect on the activation of M phi amoebicidal function.

The effect of immunosuppressive and immunostimulatory treatment on experimental amoebiasis

Immunosuppressive treatments consisting of ionizing irradiation or drugs were employed in inbred and outbred mice and in golden hamsters. Following treatment, mice were challenged intracaecally or intrahepatically with virulent, axenically-grown Entamoeba histolytica. Hamsters were challenged by intraperitoneal injection of the amoebae. Many of the experimental animals died of the combined effects of treatment and challenge. Mice remained essentially refractory to infection with E. histolytica regardless of the immunosuppressive means employed. Liver infection rates in treated and control hamsters were largely similar to one another, i.e. immunosuppressive treatment had no effect on resistance to infection. Our inability to alter the susceptibility of mice and hamsters to amoebic infection by suppressing components of the immune system does not enable us to draw any clearcut conclusions as to the effect of immunosuppression on human amoebiasis. Of the various immunostimulatory materials employed in hamsters, including polysaccharides, BCG and muramyl peptides, only glucan displayed protective capacity against infection with E. histolytica, making it an effective protective agent in an extracellular parasitic infection in addition to its published effectiveness in intracellular protozoal infections. Peritoneal cells extracted from hamsters injected intraperitoneally with E. histolytica seemed capable of reducing the infectivity of virulent amoebae after coincubation in vitro, as shown by reduced infection rates in challenged hamsters. Apparently polymorphonuclear cells, which constituted the vast majority of the extracted cells 24 hours after the stimulatory injection, can, under certain conditions, diminish the infectivity of E. histolytica.

In vitro effect of human recombinant tumor necrosis factor on Entamoeba histolytica trophozoites

The effect of tumor necrosis factor (TNF) on E. histolytica trophozoites was examined by using three virulent (IP: 0682:1, HM-1: IMSS, 200: NIH) and one nonvirulent (DKB) strain of E. histolytica. Various concentrations of recombinant TNF were added to E. histolytica trophozoites and the total parasite numbers and their viability were periodically assessed by microscopic observation and trypan blue staining after incubation at 37 degrees C in a nonhumidified chamber. In this study, concentrations of 10(1)-10(6) units of TNF were used. Over a concentration range of 10(4)-10(6) units, the number of trophozoites was significantly lowered in the amoebic cultures containing TNF as compared to untreated controls. It was also found that the effect of TNF was dependent on the densities of both virulent and non-virulent strains of E. histolytica trophozoites in axenic conditions. TNF has no significant affect on the growth of amoebae at the lower starting number of amoebae. The amoebae cultured at the higher density were growth-inhibited significantly in comparison with the control groups. When the growth of the virulent and nonvirulent strains of amoebae was compared in TNF treated culture, it was found that TNF has an inhibitory effect on both the virulent and nonvirulent strans of E. histolytica.

Effects of gamma interferon on syntheses of DNA and proteins by Entamoeba histolytica

To define the participation of cell-mediated immunity in resistance to amebic infection through the action of soluble mediators or lymphokines (LKs), including gamma interferon (IFN-gamma), we studied their effect on Entamoeba histolytica. Supernatants from cultures of lymphoid cells, which had been stimulated in vitro with concanavalin A and were rich in lymphokines (LRSNs), and recombinant IFN-gamma were used. LRSN and recombinant IFN-gamma inhibited the growth of E. histolytica trophozoites in vitro. These LKs did not show a cytotoxic effect on the ameba, but they did inhibit rather significantly protein and DNA syntheses of the protozoa. Interestingly, LRSN incubated at 4 degrees C in the presence of trophozoites lost the ability to inhibit the replication of vesicular stomatitis virus. IFN-gamma inactivated at pH 2 had no effect on DNA synthesis by the ameba, thus suggesting that IFN-gamma is responsible for the observed inhibition of parasite growth. Furthermore, the IFN-gamma inhibitory effect was abolished by a monoclonal antibody specific for this LK. The results suggest that IFN-gamma may participate in protection against amebiasis infection through the activity of mediators released by lymphocytes during infection.

Entamoeba histolytica depresses chemiluminescence in stimulated human polymorphonuclear leukocytes

Effect of Entamoeba histolytica proteinase/toxin (Ehp/t) on the luminol-dependent chemiluminescence (CL) in stimulated human polymorphonuclear leukocytes (PMN) was studied. The role of superoxide (SO) and hydroxyl (OH) anions in the Ehp/t-associated enhancement/inhibition of CL was also studied using specific scavengers and a biological response modifier, muramyldipeptide (MDP). Ehp/t was isolated from axenic trophozoites of the HM-1:IMSS strain of virulent strain of E. histolytica. Proteinase activity was assayed on a synthetic substrate, Z-arg-arg-AFC and cytotoxicity was tested on HeLa cell monolayers. PMN isolated from blood were incubated with Ehp/t prior to stimulation by phorbol myristateacetate (PMA, 2 micrograms/ml), serum-treated zymosan (2.5 mg/ml) and glucan (2 mg/ml). CL was monitored in an LKB (Wallac) Luminometer. Ehp/t was found to depress up to 90% of CL induced by PMA, glucan and zymosan. Such a depression was Ehp/t concentration-dependent. A 150 micrograms/ml concentration of Ehp/t, obtained from a 0.015-1.5 mg/ml concentration range tested at different incubation times and temperatures, was used in most of our experiments. Incubation time and temperature optima were 15 min and 37 degrees C, respectively. Ehp/t partially inhibited the CL associated with SO and OH. MDP, in the presence of Ehp/t, enhanced CL response in human PMN to about 67% with reference to normal CL without inhibitor. PMN were confirmed to play a vital role in amebic tissue invasion mechanisms.

Activation of macrophages by Entamoeba histolytica extracts in mice

The effect of Entamoeba histolytica extracts on the production of inflammatory macrophages and the release of hydrogen peroxide (H2O2) and superoxide (O2-) from these cells was examined in C57BL/6 mice. Two different strains of E. histolytica, either virulent (IP:0682:1) or nonvirulent (DKB), were used in this study. The number of macrophages recovered from the peritoneal cavity of mice treated 5 days previously with 150 micrograms of either strain of amoebic extracts was significantly higher than in the saline-treated groups. Macrophages from mice treated with 150 micrograms of the IP:0682:1 strain of amoebic extracts exhibited a powerful burst of oxidative metabolis when triggered with phorbol myristate acetate (PMA). Extract from the non-virulent strain was much less effective in activating macrophages for the production of oxidative metabolites. Thus, a crude extract preparation from E. histolytica, particularly the virulent strain, induces a strong macrophage inflammatory response in which the cells also produce high levels of H2O2 and O2-.

Isolation of the galactose-binding lectin that mediates the in vitro adherence of Entamoeba histolytica

Entamoeba histolytica adheres to human colonic mucus, colonic epithelial cells, and other target cells via a galactose (Gal) or N-acetyl-D-galactosamine (GalNAc) inhibitable surface lectin. Blockade of this adherence lectin with Gal or GalNAc in vitro prevents amebic killing of target cells. We have identified and purified the adherence lectin by two methods: affinity columns derivatized with galactose monomers or galactose terminal glycoproteins, and affinity columns and immunoblots prepared with monoclonal antibodies that inhibit amebic adherence. By both methods the adherence lectin was identified as a 170-kD secreted and membrane-bound amebic protein. The surface location of the lectin was confirmed by indirect immunofluorescence. Purified lectin competitively inhibited amebic adherence to target cells by binding to receptors on the target Chinese hamster ovary cells in a Gal-inhibitable manner.

Development of inflammation and augmented chemotactic responsiveness of murine peritoneal macrophages following treatment with Entamoeba histolytica trophozoites

The accumulation of inflammatory cells in the peritoneal cavity of C57BL/6 mice was examined following intraperitoneal injection of Entamoeba histolytica trophozoites. Two different strains of E. histolytica were used: a virulent strain (IP:0682:1) and a non-virulent strain (DKB). Injection of 10(6) trophozoites of either strain resulted in significant increases in the numbers of total peritoneal cells, macrophages and polymorphonuclear cells as compared to either saline-injected control mice or mice injected with 10-fold lower doses of trophozoites. The in vitro chemotactic response of macrophages from amoebae-induced exudates was also examined. Macrophages from mice treated with strain IP:0682:1 or DKB strain trophozoites were more responsive to complement-derived chemotactic factors than macrophages from saline-injected mice. This increase was significant on day 2 and persisted at enhanced levels until day 20 when the experiment was terminated. In addition, it was found that trophozoites activated normal mouse serum resulting in the production of serum-derived chemotactic activity.

Immunosuppression and splenomegaly in Entamoeba histolytica infection in mice

Intestinal amoebiasis caused by Entamoeba histolytica trophozoites in mice is accompanied by a depression in the ability of this host to develop an immune response to sheep red blood cells. The number of splenic plaque-forming cells was reduced in mice inoculated intracecally with 2.5 x 10(5) trophozoites at 15, 25, 40, 65 and 75 days after infection when compared with non-infected mice. It was found that there was no significant difference between the spleen weight of the infected and non-infected control animals at 5 and 10 days following infection. However, a significant increase in spleen weight was observed by 15 days of infection and the spleens remained enlarged until termination of the experiment at 75 days. Thus, there was an inverse correlation between the PFC response and the spleen weight of infected animals.

The effect of splenectomy on resistance of mice to Entamoeba histolytica infection

The role of the spleen in amoebic infection was examined in mice, using strains selected as being either genetically-susceptible (C57BL/6) or genetically-resistant (A/J) to amoebiasis. Splenectomized and sham-operated animals were inoculated intracaecally with 2.5 X 10(5) polyxenic trophozoites of E. histolytica at 6, 12 and 15 days post-splenectomy. The animals were killed 6 or 12 days after infection and the parasite burden was evaluated. Removal of the spleen in both susceptible and resistant mouse strains rendered these hosts extremely resistant to amoebic infection by this criterion. Gross examination of the caeca of non-splenectomized, genetically-susceptible mice showed numerous ulcers over the mucosal surface when compared to the splenectomized group which had superficial lesions or none. These observations suggest that the spleen plays a suppressive role in early anti-amoebic resistance.

Interaction of human leukocytes and Entamoeba histolytica. Killing of virulent amebae by the activated macrophage

Capable effector mechanisms in the human immune response against the cytolytic, protozoan parasite Entamoeba histolytica have not been described. To identify a competent human effector cell, we studied the in vitro interactions of normal human polymorphonuclear neutrophils, peripheral blood mononuclear cells (PBMC), monocytes (MC), and MC-derived macrophages with virulent axenic amebae (strain HMI-IMSS). Amebae killed neutrophils, PBMC, MC, and MC-derived macrophages (P less than 0.001), without loss of parasite viability. The addition of heat-inactivated immune serum did not enable leukocytes to kill amebae, nor did it protect these host cells from amebae. MC-derived macrophages, activated with lymphokine elicited by the mitogens conconavalin A, phytohemagglutinin, or an amebic soluble protein preparation (strain HK9), killed 55% of amebae by 3 h in a trypan blue exclusion assay (P less than 0.001); during this time, 40% of the activated macrophages died. Lysis of amebae was confirmed using 111Indium oxine radiolabeled parasites and was antibody independent. Macrophage death appeared to be due to the deleterious effect of lysed amebae rather than the contact-dependent effector mechanisms of E. histolytica. Adherence between activated macrophages and amebae was greater than that between other leukocytes and amebae (P less than 0.001). Microscopic observations, kinetic analysis of the killing of amebae by activated macrophages, and suspension of amebae with adherent activated macrophages in a 10% dextran solution indicated that contact by activated macrophages was necessary to initiate the killing of amebae. Catalase but not superoxide dismutase inhibited the amebicidal capacity of activated macrophages (P less than 0.001). However, activated macrophages from an individual with chronic granulomatous disease were able to kill amebae, but not as effectively as normal cells (P less than 0.01). In summary, activated MC-derived macrophages killed virulent E. histolytica trophozoites through a contact-dependent, antibody-independent mechanism involving oxidative-dependent and -independent processes.

Entamoeba histolytica: antibody responses and lymphoreticular changes in gerbils (Meriones unguiculatus) in response to experimental liver abscess and amebic extract infection

Antibody responses and histological changes in hepatic lymph nodes and spleen of gerbils (Meriones unguiculatus) during the course of experimental hepatic amebiasis (5-60 days), or in those injected with extracts of Entamoeba histolytica, are described. Lymph node and spleen responses in infected animals paralleled the proliferation of the amebic liver abscess. However, spleen follicle responses were similar in animals that received low or high doses of the amebic extract and differed histologically from those with amebic liver abscess. Liver abscesses, up to 30 days postinfection (pi), doubled in weight between 10 and 15 and between 20 and 30 days pi. Early changes (10 days pi) in the lymphoreticular tissues were characterized by increased size and weight of the organs, hyperplastic follicles, and blastogenesis in the T-dependent areas. At 20 and 30 days pi, the size of spleen follicles increased and there was depletion of lymphocytes from the periarterial area (PAA), as well as gross extension of the red pulp, accompanied by extramedullary erythropoiesis and megakaryocytosis. The paracortical areas (PCA) of lymph nodes were depleted of lymphocytes and histiocytosis throughout the organ, and there was intense plasma cell activity in the medulla. At 60 days pi, lymphocyte repopulation was noted in the PCA and PAA; germinal centers were depleted of blast cells and the spleen red pulp had contracted. Antiamebic antibody titers were low throughout the infection. Changes in the cellularity of the lymphoid organs are discussed in relation to the proliferation of the amebic liver abscesses in infected animals and in those which were injected with the amebic extract.

Passive transfer of immunity against hepatic amoebiasis in the hamster by cells

The role of passive cell-mediated transfer of immunity in hepatic amoebiasis in hamsters was studied. The transfer of peritoneal cells from hamsters vaccinated against or protected from hepatic amoebiasis and from those with hepatic amoebiasis, as well as of spleen cells from vaccinated or protected, but not from infected hamsters, conferred immunity against hepatic amoebiasis in recipient normal hamsters. Treatment of the spleen cells from protected hamsters with anti T-cell serum abolished their ability to transfer immunity. It appears that the effector mechanism in this system is T-cell dependent.

In vitro amoebicidal activity of immune cells

The amoebicidal activity of peripheral blood lymphocytes and spleen and peritoneal cells from hamsters vaccinated against or protected from hepatic amoebiasis and from those with hepatic amoebiasis was investigated. Peripheral blood lymphocytes and peritoneal and spleen cells from vaccinated or protected animals can kill trophozoites of Entamoeba histolytica in vitro. In contrast, spleen cells from infected hamsters showed no significant cytotoxic effect on the parasite. These data suggest that cellular immunity plays an important role in host defense against hepatic amoebiasis.