Search

Previous studies have indicated that elimination of parasitemia in Trypanosoma musculi infection is brought about by immunoglobulin G2a antibodies, C3, and an effector cell. Experiments were designed to identify the putative effector cell by using several approaches. Infected C5-deficient or C5-sufficient mice treated with silica particles or given 900 rads of radiation 3 days earlier effectively eliminated trypanosomes following administration of immune plasma (IP). Silica-treated, noninfected mice given T. musculi preincubated with IP also cleared the parasites. Radiolabeling studies revealed that uptake of the cleared trypanosomes by the liver in normal mice was relatively low (24%) and fell only slightly (19%) in silica-treated mice. In contrast, uptake of radiolabeled sheep erythrocytes by the liver was normally much higher (47%) and fell drastically (7%) in silica-treated mice. Mice were then immunocompromised by 900 rads of radiation, silica particles, and anti-platelet serum combined before IP-sensitized trypanosomes were given. Leukocyte and platelet counts were both reduced by 95% and sheep erythrocyte uptake by the liver fell from 77 to 5%; however, greater than 99% of the injected trypanosomes were cleared in these mice and uptake of radiolabeled trypanosomes by the liver was similar to that of normal mice. Lastly, in anesthetized mice in which Kupffer cells were excluded surgically from the circulation, greater than 99% of the IP-sensitized trypanosomes disappeared rapidly from the blood. Only 7% of the radiolabel was found in the liver versus 60% in sham-operated mice. The results are interpreted as showing that hepatic Kupffer cells play a minor role in the immune elimination of T. musculi. Likewise, radiosensitive leukocytes and platelets are unlikely to be sole candidates for the putative effector cell that mediates a cure of murine trypanosomiasis.

Blastocystis hominis is commonly found in the intestinal tract of humans. Although the pathogenicity of this unicellular parasite is controversial, anti-protozoan agents are usually administered to infected individuals. At present, the first choice of chemotherapeutic agent is Metronidazole as described in the literature. In this study, we evaluated the effects of metronidazole and Trimethoprim/Sulfamethoxazole (TMP/SMX) on persons infected with B.hominis. A total of 104 subjects infected with B. hominis were admitted to the laboratory from 2002 to 2003. All individuals were non-immunocompromised and subjects were monitored for 1 year after treatment. All stool samples were microscopically examined after staining with iodine and by culturing in an egg slant medium. Of the 104 infected individuals (52+/-16 years of age, M:F=60:44) with B. hominis infection, 28 were discharging large numbers of parasites before treatment. Of 28 severely infected individuals, 12 were treated with metronidazole/250-750 mg at a regimen of 3 x/day/10 days and 4 of the 12 were eradicated. Nine individuals were treated with TMP/SMX/1 tab at a regimen of 3 x/day/10 days and 2 of the 9 were eradicated. For severe B. hominis infections, it appears that metronidazole and TMP/SMX are effective in some individuals, but not all.

In this study, we examined the contribution of the monokine interleukin-1 (IL-1) in mouse resistance to the intracellular pathogen Mycobacterium avium. The effect of neutralizing endogenous IL-1 in mouse macrophage resistance to M. avium infection was investigated. Infection of mouse peritoneal macrophages with M. avium B101 was shown to result in significant IL-1 beta release by cells at 4 and 7 days postinfection. Addition of IL-1 receptor antagonist (IL-1ra) at doses of 5 micrograms daily, which neutralized endogenous IL-1, failed to significantly modify the intracellular growth of M. avium. Mice were injected with M. avium B101 by the intravenous route, and the growth of the mycobacteria was monitored in the organs of intact mice and in those of mice that received repeated high doses of IL-1ra. The infection with M. avium elicited the production of large amounts of IL-1 in the lungs, livers, and spleens. Repeated injections of IL-1ra into M. avium-infected mice resulted in moderately enhanced growth of the bacilli in the livers and spleens but in much enhanced growth in the lungs. The enhanced growth of M. avium in the lungs correlated with a diminished inflammatory influx of cells (particularly neutrophils) in the bronchoalveolar space. These data argue for a role for IL-1 in host resistance to M. avium infections.

In this contribution, we examined the involvement of the cytokine IL-10 in the progression of experimental murine Mycobacterium avium infections in susceptible BALB/c mice. Addition of anti-IL-10 antibodies in the supernatants of peritoneal macrophages infected with virulent M. avium resulted in a significantly enhanced mycobacteriostatic activity of macrophages. In BALB/c mice infected with the B101 or B102 virulent M. avium strains, examination of the cytokine release profile in splenocytes from infected mice showed that infection was associated with an initial copious release of both IFN-gamma and IL-10. IL-10 production increased as the infection progressed, whereas IFN-gamma levels diminished. Infected mice were given repeated infusions of a rat mAb against mouse IL-10 or rat IgM. Examination of IgM serum levels in anti-IL-10-treated mice (infected or not) showed that depletion of endogenous IL-10 resulted in much decreased IgM levels. Results showed that infusions of large dosages of the monoclonal anti-IL-10 resulted in a very significantly diminished bacterial growth in the spleens. These findings indicate that IL-10 may have a negative impact on resistance to M. avium infections, due, at least in part, to decreased macrophage activity.

Summary C57BL/6 mice were instilled intranasally with optimal doses [150 μg of antigen 3 days a week) of the actinomycete Faeni rectivirgula to induce an experimental hypersensitivity pneumonitis. Some control mice received normal rat IgG as controls, whereas other mice received 1 mg weekly of rat anti-murine interferon gamma (IFN-γ) antibody by the intraperitoneal route and 200 μg by the intranasal route given 2 days before and during the challenge period before each instillation. Control mice developed a clear hypersensitivity pneumonitis characterized by an early neutrophilic response at 3 days and a later influx of mononuclear cells (nine- to tenfold increase in cell number. P < 0.001 vs saline instilled mice at 4 weeks post-treatment). F. rectivirgula instillation determined a sharp increase in the lung index (80% increase in lung weight, P < 0.005 vs saline treated mice), as well as a significant fibrosis at 4 weeks (twofold increase in lung hydroxyproline levels). Cytokine measurements showed that tumour necrosis factor alpha (TNFα) was present in the broncho-alveolar lavage (BAL) of challenged mice at 4 weeks when the BAL was obtained 8 hr after the last challenge (130 U/ml). Treatment of mice with the monoclonal antibody against IFN-γ was associated with very few changes in the number of cells in the BAL of challenged mice. The lung index of challenged mice was significantly reduced by infusion of the anti-IFN-γ antibody. Anti-IFN-γ treatment resulted in decreased levels of TNFα in the BAL of F. rectivirgula after 4 weeks of treatment (56 U/ml, P < 0.01). Moreover, depletion of endogenous IFN-γ in F. rectivirgula-instilled mice resulted in a diminished lung fibrotic response (P < 0.01 vs mice treated with F. rectivirgula and control antibody). We also studied the effect of exogenous IFN-γ administration on the development of lung disease. Groups of mice received recombinant gamma interferon (IFN-γ) (1000 U) intraperitoneally just before the first treatment and also daily, whereas controls received saline or IFN-γ alone (no F. rectivirgula challenge). After 4 weeks of treatment, mice were killed and various markers of the disease were evaluated. As mentioned before, bronchoalveolar lavage (BAL) cell number was increased tenfold in mice treated with F. rectivirgula, whereas mice given F. rectivirgula and IFN-γ had only a threefold increase in BAL cell number, determined mostly by a decrease in alveolar macrophage recruitment in the lungs. The BAL of mice treated with F. rectivirgula alone contained 72 U/ml of tumour necrosis factor alpha (TNFα) and 42 U/ml of interleukin-1 (IL-1) after 4 weeks of instillation, whereas BAL from mice given F. rectivirgula and 103 U of IFN-γ had 18 U/ml of TNFα and 22 U/ml of IL-1 (both P < 0.01 vs F. rectivirgula-only treated mice). Infusion of 103 U of IFN-γ daily significantly reduced lung fibrosis in F. rectivirgula-instilled mice (a c. 50% reduction in hydroxyproline levels: P < 0.01). Overall, these results suggest that IFN-γ has a bidirectional role in the development of mouse HP, with a potential for pro-inflammatory or anti-inflammatory properties, maybe depending on the quantity generated.

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 (D KB) 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°C in 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 strains of E. histolytica .

Two new species of helminths, Fastigiuris prudhoei from Ochotona rufescens Gray, 1842, and Trichuris mofidii from Rhombomys opimus Lichtenstein, 1823, have been identified and described from mammals collected in Iran.

Depletion of complement in hamsters by means of treatment with cobra venom factor resulted in an aggravation of pathology resulting from experimentally induced hepatic amoebiasis, such that animals inoculated intrahepatically with 1 × 105Entamoeba histolytica trophozoites (but not with 4 × 104 trophozoites) had a significantly reduced survival time and significant loss of body weight, as compared with normal controls. Complement-depleted hamsters inoculated with both doses of amoebae developed significantly bigger amoebic liver abscesses and amoebic metastatic foci than their respective controls, not depleted of complement.

At the age of 4 months, a boy in Isfahan, Iran, was examined because of an illness, of several weeks, characterized by irritability, cough, diarrhea, sweating, and pallor. After each exacerbation of his illness, he had expelled four worms, which proved to be Moniliformis moniliformis. During the next 5 months, five M. moniliformis were expelled; all were male worms. Repeated stool examinations revealed no helminths or helminth eggs, but Giardia lamblia was found on one occasion. The child had moderate anemia and leukocytosis, with 4% eosinophils. Fourteen days after treatment with thiabendazole, the ninth worm was expelled, and on the 15th day eggs of M. moniliformis were found in a stool specimen. A rat captured in the patient's home was infected with a female M. moniliformis containing eggs. Cockroaches and a lizard caught in the home were not infected with this or other parasites. We believe that a grain beetle in barley, eaten by the child, may have been the intermediate host.

The role of macrophages in hepatic amoebiasis in hamsters has been investigated by means of antimacrophage serum prepared in rabbits. Animals treated with normal rabbit serum or antimacrophage serum, as well as untreated controls, were inoculated intrahepatically with 10(5) axenic trophozoites of Entamoeba histolytica. In hamsters treated with antimacrophage serum before intrahepatic inoculation of amoebae, the mean weight of the metastatic foci was significantly greater than in normal rabbit serum-treated or untreated controls. Treatment of hamsters with antimacrophage serum both before and after administration of amoebae not only increased significantly the size of the abscess in the liver but also allowed dissemination of metastatic foci to other organs.

The lost pathogenicity of two strains of Entamoeba histolytica, one isolated in 1924 and the other in 1967, grown in axenic culture for the past 5 and 6 years respectively, was restored by supplementing the culture medium with cholesterol through a number of transfers. The number of passages in the cholesterol-supplemented medium, necessary to restore a certain degree of pathogenicity of the two strains in hamsters, was proportional to the total time of in vitro cultivation of the strain, and not just the time of cultivation under axenic conditions. Pathogenicity, once restored, persisted for a long time after cholesterol treatment was stopped.

The role of the spleen in hepatic amoebiasis in hamsters was studied. In hamsters receiving an intrahepatic inoculation of 10(5) trophozoites of axenic Entamoeba histolytica at 7 or 14 days postsplenectomy, the mean weight of metastatic foci increased significantly when compared with sham-splenectomized or intact controls. In contrast, when both splenectomy and intrahepatic inoculation with amoebae were carried out at the same time, there was not only a significant increase in the mean weight of metastatic foci but also in the liver abscess. It is suggested that the spleen is important for host defense against E. histolytica infection, especially in the reduction in the degree of metastatic spread from the primary site.

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.

Entamoeba histolytica strain 200:NIH cultured axenically for about 15 years produced lesions and abscesses in inbred adult hamsters following intrahepatic, intraperitoneal, and intradermal inoculation. These amebae, even in much higher doses, inoculated into the ceca of adult and young hamsters failed to produce lesions or to become established there. On the other hand, 200:NIH axenic amebae passaged through hamster liver (substrain 200:NIH-L) were able to become established and to produce lesions in the ceca of very young hamsters (1- and 3-week-old), the degree of pathogenicity appearing to be inversely proportional to age of the hamster.

Schizorchis arfaai sp. n. is described from the wood-mouse in the Caspian area of Iran and its morphological characteristics compared with those of the five previously known species of Schizorchis Hansen, 1948.

Hamsters were injected intradermally with axenic trophozoites of a pathogenic strain of Entamoeba histolytica, and controls similarly with culture medium. Localized lesions were produced in all animals injected with amebae. After the lesions healed all the animals were challenged intrahepatically with axenic amebae. Extensive liver abscesses were produced in all the controls, but a small abscess in only one of the vaccinated hamsters. In the protected animals the indirect hemagglutination antibody titers were high (I:512), while in the controls they ranged between 1:32 and 1:128. In the vaccinated hamster with the small abscess the IHA titer was 1:32. To investigate a possibility of autoimmune regulation in amebiasis, sera of hamsters with experimental amebic liver abscesses were acidified and tested by counter-current-immunoeletrophoresis against untreated autologous sera and amebic antigen. In most cases there was a direct correlation between the two titers. With human antisera in autologous systems there was reactivity against anti-amebic IgG antibodies. These experiments showed that autoimmune complexes may be present in cases of hepatic amebiasis. As in chronic hepatitis and some malignancies, it is possible that immune complexes have an immunoregulatory function in amebiasis.

The course of intestinal infection by Entamoeba histolytica was examined in nu/nu BALB/c mice. Mice were inoculated intracecally with 2.5 X 10(5) polyxenic trophozoites and killed at various times after injection. There was no significant difference in the number of E. histolytica trophozoites recovered in the ceca of nu/+ and T cell-deficient nu/nu mice for the first 25 days after amebic injection. Thirty days following amebic injection the number of trophozoites recovered in the ceca of nu/nu mice was significantly higher than the control mice. Silica treatment increased the growth of parasites in the ceca of nu/nu mice when compared with control groups. These data suggest that both macrophages and T lymphocytes play an important role in host defense against amebic infection in nude mice.

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.

The lost pathogenicity of two strains of Entamoeba histolytica, one isolated in 1924 and the other in 1967, grown in axenic culture for the past five and six years respectively, was restored by supplementing the culture medium with cholesterol through a number of transfers. The number of passages in the cholesterol supplemented medium, necessary to restore a certain degree of pathogenicity of the two strains in hamsters, was proportional to the total time of in vitro cultivation of the strain, and not just the time of cultivation under axenic conditions. Pathogenicity, once restored, persisted for a long time after cholesterol treatment was stopped.

The effect of r-TNF on T. musculi is complex. When trypanosomes are incubated in culture with this monokine, TNF exerts a direct anti-trypanosomal effect (Table 3). Similarly, if mice are treated with TNF during the later stages of infection, after the parasitaemia has stabilized, it hastens the elimination of the trypanosomes (Table 2). When TNF is given to mice from the early stage of infection onwards, it enhances the growth of the parasites (Table 1). (This enhanced early growth probably masks any subsequent anti-trypanosomal effect of TNF exerted later in infection). The ability of TNF to promote parasite multiplication is observed even more clearly in in vitro experiments, when peritoneal exudate cells are added to the T. musculi cultures (Table 4). It is conceivable, therefore, that the enhancing effect of TNF in vivo is mediated via a cell present in thioglycollate-induced peritoneal exudate, which mostly comprises macrophages. In summary, the results of these experiments suggest that r-TNF exerts a direct anti-trypanosomal effect while simultaneously promoting the growth of the parasite through an indirect effect mediated via the host's cells, possibly the macrophages.

Summary Genetic susceptibility to Entamoeba histolytica infection in nine inbred strains and one outbred strain of mice was studied. The number of E. histolytica trophozoites in the ceca of the mice was examined 5 days after intracecal inoculation of axenic amoebae. C3H/HeCr, BALB/c, NZB/BIN, BIO.A, DBA/2 and C57BL/6 were susceptible whereas A/J, CE, DBA/1 and CD-I mouse strains were relatively resistant. Examination of F1 hybrid animals derived from susceptible B10.A and resistant A/J strains of mice showed that susceptibility was dominant over resistance. Segregation analysis of backcross and F2 progeny derived from the same progenitor strains is compatible with the hypothesis that susceptibility to E. histolytica infection in mice is controlled by a single, dominent gene which has been designated Enh. No association was found between the H-2 haplotype and the trait of susceptibility to amoebiasis, indicating that the major histocompatibility complex does not play a major role in regulating the early phase of the response to infection with E. histolytica.

Treatment with Corynebacterium parvum or BCG, or infection with live Listeria monocytogenes was found to protect mice against subsequent infection with Entamoeba histolytica. Complete protection was obtained in mice treated with 10(7) (colony forming units) of BCG but not with 10(5). Partial protection was achieved with 10(6) of BCG. These data provide evidence that non-specific immunity plays an important role in the host defense against amoebic infection.

In addition to the six species of Trichostrongylus already reported from man, T. capricola has been found among the population of a nomadic tribe and the inhabitants of three villages in Isfahan Province in the central part of Iran. The prevalence of infection with this species among 40 nomads treated was 22.5%, with an average of 5 worms per infection. Among 30 villagers who were treated, 4 (13.3%) passed this species with an average of 2.5 worms per infection. T. capricola was also found in all of 10 sheep and 10 goats examined in each of the two areas.

Summary The effect of human recombinant TNF on the growth of T. musculi has been investigated. When added to parasites cultured in vitro, TNF inhibited their growth. In the presence of thioglycollate-elicited peritoneal exudate cells, the opposite effect was seen and TNF enhanced the growth of trypanosomes in vitro. Similarly, administration of TNF in vivo during the course of infection led to a net increase in the parasite population. It is suggested that TNF exerts a direct anti-trypanosomal effect while simultaneously promoting the growth of the parasite through an indirect effect mediated via the host's cells, possibly the macrophages.

The response to reinfection with Ethiopian Leishmania donovani was evaluated in genetically determined noncure (H-2d) B10.D2 mice that are able to resolve infection due to sublethal irradiation pretreatment after inoculation with a low parasite dose and in C57BL/10 mice that demonstrate the genetically determined cure (H-2b) response to L. donovani. It was found that after resolution of primary infection, C57BL/10 (cure) mice and sublethally irradiated B10.D2 (noncure) mice were resistant to rechallenge with L. donovani. Noncure mice inoculated with a low dose of amastigotes were not, however, solidly immune to reinfection. Adoptive-cell transfer experiments were then done to determine the T-cell subset that was associated with resistance to reinfection, and thus the development of immunity, in sublethally irradiated B10.D2 noncure mice and in C57BL/10 cure mice. T-cell-enriched preparations from spleens of immune donors were treated with subset-specific antibodies and complement prior to adoptive transfer in unprimed recipients. The results of the adoptive transfer experiments provide evidence that the genetically determined cure (H-2b) response in C57BL/10 mice and the cure response in genetically determined noncure (H-2d) B10.D2 mice brought about by sublethal irradiation pretreatment are mediated primarily by an L3T4+ Lyt-2- T cell.

The effect of hydrogen peroxide and hypochlorite on culture forms of Entamoeba histolytica trophozoites was examined by using two strains of E. histolytica, virulent (IP:0682:1) and nonvirulent (DKB). The amoebae were incubated with various concentrations of hydrogen peroxide and hypochlorite, and their viability was determined at different times after incubation. When the viability of the virulent and nonvirulent strains was compared to different oxidant strengths, it became apparent that the virulent strain was less susceptible than the nonvirulent one to the cytotoxic effect of hydrogen peroxide and hypochlorite. Our studies further showed that the toxic effect was both time and dose dependent. To confirm that the killing of amoebae in this system was associated with the presence of hydrogen peroxide, amoebae were incubated with hydrogen peroxide and catalase. Catalase reduced the killing effect of hydrogen peroxide to the control level. These data confirmed previous observations of the susceptibility of amoebic trophozoites to hydrogen peroxide and also demonstrated susceptibility to hypochlorite.

The development of experimental amebic liver abscess in hamsters was inhibited by a previous infection with the nematode parasite Trichinella spiralis, such that liver abscesses were present in 26% of hamsters with T. spiralis infection and in 80% of T. spiralis-free controls. The protective effect of T. spiralis infection is believed to be exerted through a non-specific activation of cellular immunity, with macrophages as probable effector cells.

In vitro agglutinability of trophozoites of three Entamoeba histolytica strains, cultivated under axenic conditions in the presence of concanavalin A (Con A), was shown to be related to the degree of their pathogenicity for experimental animals and of the concentration of Con A. Seven strains of E. invadens tested also agglutinated in the presence of Con A, and the degree of agglutination was proportional to the concentration of the lectin. Three strains of E. histolytica-like "Laredo-type" amebae, a strain of E. terrapinae, and a strain of E. moshkovskii agglutinated very slightly, only in the presence of the highest concentration of Con A tested.

Infection with species of Trichostrongylus is common among man and animals in most parts of Iran, and human infections with T. orientalis, T. colubriformis, T. vitrinus, T. axei, T. capricola, T. probolurus, T. skrjabini, and a possibly new, unnamed species have been reported. All are found in Isfahan, central Iran, where the overall prevalence is 67% and the predominant species are T. orientalis and T. colubriformis. Among 737 nomads migrating from the central parts to the south, 86% were found to be infected with one or more of five species (in order of frequency): T. colubriformis, T. orientalis, T. axei. T. capricola, and T. vitrinus. In Khuzestan, southwest Iran, human infections with T. orientalis, T. colubriformis, T. axei, and T. vitrinus with an overall prevalence of 71% have been reported. In the northern parts, along the Caspian Sea, the rate is 7% and the species found. in order of frequency, are T. colubriformis, T. axei, T. vitrinus, and T. orientalis. Trichostrongylus infections are also found in the northwest but are rarely seen in the northeast. In most areas females are more frequently and more heavily infected than are males. All species found in man, except the new, unnamed species, are also found in sheep, goats, cattle, and camels; the number of species found and the order of their frequency differ in various animals and in different areas. Infection in other mammals, such as hares (T. retortaeformis and T. orientalis) and porcupines (T. orientalis), has also been reported.

The role of macrophages in hepatic amoebiasis in hamsters has been investigated by means of their treatment with bacille Calmette-Guerin (BCG) for activation, and with silica for elimination of these cells. Silica-treated animals inoculated intrahepatically with 1 x 10(5) trophozoites of Entamoeba histolytica developed amoebic abscesses in the liver and more metastases to other organs than control animals, and this effect was silica-dose-dependent. In contrast, BCG-treated animals developed significantly smaller abscesses in the liver and fewer metastatic foci. These data suggest that macrophages are involved in host defence against the establishment of amoebic liver abscess and metastatic dissemination of amoebae.

The role of macrophages in intestinal amoebiasis in mice has been investigated. The effect of injuring host macrophages on the course of infection was examined by using strains selected as being either genetically susceptible (C3H/HeJ, C57BL/6) or genetically resistant (A/J) to amoebiasis. Mice were treated with an intravenous injection of silica particles 1 day before infection with 2.5 X 10(5) or 5 X 10(5) polyxenic trophozoites of Entamoeba histolytica. The animals were killed at various times after infection, and the parasite burden in the cecum was measured. Silica treatment dramatically increased the growth of parasites in the susceptible mice. The same trend was evident, although less marked, in the resistant mice. The effect of silica treatment in experimental amoebiasis was much more pronounced in animals inoculated with 5 X 10(5) amoebae than in those with 2.5 X 10(5) amoebae. These data suggest that macrophages play an important role in host defense against amoebiasis in mice.

SUMMARY The effect of T-cell depletion on experimental hepatic amoebiasis in hamsters was investigated. Thymectomized and anti-T-cell (ATS) treated animals as well as sham-operated and unoperated controls were inoculated intrahepatically, following laparotomy, at 7 weeks of age with 1 × 105 axenic trophozoites of Entamoeba histolytica. In neonatally thymectomized hamsters the mean weight of the liver abscess 10 days post-inoculation was significantly greater than in neonatally sham-operated or unoperated controls, but there was no significant difference between these groups of animals in the size of metastatic foci to other organs. On the other hand, a combination of neonatal thymectomy and ATS treatment enhanced both the size of the primary abscess in the liver and the size of metastases to other sites. Adult thymectomy did not have a significant effect either on the size of the primary abscess or on metastatic dissemination of amoebae from the liver. Treatment of hamsters with ATS shortly before or after intrahepatic challenge increased significantly the size of the abscess, but similar treatment 2–3 weeks prior to challenge had no effect. These observations suggest that thymus-dependent cell-mediated immunity plays an important role in the host response to E. histolytica infection.

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.