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PubMedDate not supplied

The importance of trophozoites in transmission of toxoplasmosis: survival and pathogenity of Toxoplasma gondii trophozoites in liquid media.

It has been generally assumed that Toxoplasma gondii trophozoites cannot survive long outside the body, and that toxoplasmosis is transmitted by transplacental infection, cysts and oocysts. We tested the survival and pathogenicity of separated Toxoplasma trophozoites in saline, colostrum, and solutions of albumen and serum, and the penetration of Toxoplasma trophozoites from infected secretions through mucous membranes of nose, conjunctiva, and mouth. The trophozoites survived 24 h in saline, 3 days in 3.5% serum albumen, 3 days in colostrum, and 17-43 days in serum solutions. The infectivity of the trophozoites was highest after nasal instillation, second highest after instillation into conjunctiva, and lowest after instillation into the mouth. The infective dose was calculated. The results show that Toxoplasma trophozoites survive and remain infectious for a relatively long time in biological liquid media and can easily penetrate mucous membranes, and suggest a revised hypothesis for the transmission of Toxoplasmosis with the trophozoites as one important source of infection.

Animals↗
PubMed1980

Infective Toxoplasma gondii trophozoites attenuated by ultraviolet irradiation.

Both the virulence and infectivity of Toxoplasma gondii trophozoites are affected by increasing fluences of ultraviolet irradiation. All mice received unirradiated virulent trophozoites intraperitoneally died in an average of 5 days. All mice inoculated with trophozoites irradiated with 20 J m-2 died in an average of 8 days. Fluences of 35, 55, and 70 J m-2 resulted in 90, 20 and 0% deaths, respectively. Fluences up to 720 M m-2 did not increase the number of nonviable trophozoites. The minimum fluence which prevented mouse deaths (70 J m-2) also prevented trophozoite proliferation in baby hamster kidney (BHK-21) cell cultures. Minimum fluence-irradiated trophozoites attached to or entered BHK-21 cells or both at a rate similar to that for controls. BHK-21 cells fixed and stained 18 h after inoculation with unirradiated trophozoites contained both single and multiple trophozoites. In contrast, cell cultures inoculated with minimum fluence-irradiated trophozoites contained only single, nonreplicated trophozoites. No proliferation of trophozoites in these cultures was found as long as observed, 14 days after inoculation. Fluences of ultraviolet irradiation can therefore be determined which allow infection of cells but prevent trophozoite proliferation.

Animals↗
PubMed1995

Differences exist in the immunoblotting profiles of cyst and trophozoite antigens of Pneumocystis carinii.

The antigenic profiles of Pneumocystis carinii trophozoites and cysts were compared by immunoblotting with hyperimmune rat sera against cyst and trophozoite antigens. Strong bands corresponding to proteins of 50-60 kDa and 104 kDa were demonstrated in cyst and trophozoite antigens by all antisera. Additional prominent proteins of 81 and 63 kDa and less prominent proteins of 88, 73, 69 and 37 kDa were found only in trophozoite antigen. The latter proteins were recognised by anti-trophozoite and anti-cyst antisera but the 81- and 63-kDa proteins were associated specifically with trophozoites. With cyst-rich antigen, antibodies to the 50-60-kDa protein were detected in only two of 14 sera from P. carinii pneumonia (PCP)-positive rats. With trophozoite-rich antigen, 11 of 24 rats with PCP and one of 18 PCP-negative animals had antibodies to both the 50-60 kDa and 104-kDa antigens. Antibodies to the 81- or 63-kDa antigens were demonstrated in 15 of 24 PCP-positive animals and none of the PCP-negative animals. The use of trophozoites rather than cysts increased the sensitivity of immunoblotting. As trophozoites predominate in PCP, antibody to trophozoite-specific antigens rather than common cyst and trophozoite antigens is likely to be a more useful marker of current infection.

Animals↗
PubMed1989

Generation and characterization of monoclonal antibodies against Giardia muris trophozoites.

Mouse monoclonal antibodies (mAb) were produced against Giardia muris trophozoite surface antigens. To generate B-cell hybridomas, P3/NS1/1-Ag4-1 myeloma cells were fused with splenic lymphocytes from BALB/c mice that had been immunized parenterally with G. muris trophozoites. Hybridoma culture supernatants were screened for mAb by flow cytometry of G. muris trophozoites incubated with culture supernatant followed by fluorescein-conjugated anti-mouse IgG and IgM. Flow cytometry showed three types of trophozoite staining by mAb: (i) bright staining of greater than 90% of trophozoites, with aggregation of the organisms; (ii) bright staining of approximately 90% of trophozoites, with little or no aggregation; (iii) dull staining of approximately 20% of trophozoites, without aggregation. Western blotting of mAb on G. muris trophozoite antigens separated by polyacrylamide gel electrophoresis showed that a mAb exhibiting the third of these flow cytometry staining patterns recognized trophozoite antigens of MW approximately 31,000 and 35,000. Immunoprecipitation studies indicated that the same mAb specifically precipitated two 125I-labelled trophozoite surface antigens of MW approximately 30,000. Monoclonal antibodies generated in this study may facilitate the purification and biochemical characterization of trophozoite antigens that are targets for protective intestinal antibody in G. muris-infected mice.

Animals↗
PubMed1988

Biology of Giardia lamblia. Detection of N-acetyl-D-glucosamine as the only surface saccharide moiety and identification of two distinct subsets of trophozoites by lectin binding.

Lectins and glycosidases of known sugar specificity were used as probes to analyze the surface carbohydrate moieties of G. lamblia trophozoites and in particular to determine whether chitin or oligomeric D-GlcNAc is present in the trophozoite form of the parasite as well as on the cyst. Of 13 lectins with varying sugar specificity, only D-GlcNAc-specific lectins bound specifically to the trophozoite surface as determined by light microscopy and EM. A striking finding was the identification of two distinct subsets of trophozoites, distinguished by reactivity with WGA and detected by light microscopy and EM as well as by flow cytometry. Unlike the cyst wall, the trophozoite D-GlcNAc residues were resistant to chitinase treatment. In contrast N-acetyl-beta-D-glucosaminidase abolished WGA binding suggesting that the lectin binds to terminal beta-linked D-GlcNAc residues. These residues were identified as being present on surface glycoproteins by Western blotting of parasite membrane proteins using WGA as a probe. This study identifies D-GlcNAc as the only saccharide moiety detectable by lectin binding on the surface of G. lamblia trophozoites and demonstrates that in contrast to the cyst, chitin is not present in the trophozoite. In addition two distinct subsets of trophozoites were identified based on reactivity with WGA and may represent varying stages of differentiation from trophozoite to cyst.

Acetylglucosamine↗
PubMed1989

Respiration in the cysts and trophozoites of Giardia muris.

Cysts and trophozoites of the parasitic protozoon Giardia muris both showed respiratory activity but respiration in cysts was only 10 to 20% that of trophozoites. The O2 dependence of respiration in cysts and trophozoites showed O2 maxima above which respiration decreased. The O2 concentration at which the respiration rate was greatest was higher for cysts than trophozoites. The effects of various inhibitors on cyst and trophozoite respiration suggested that flavoproteins and quinones play some role in respiration. The substrate specificities and the effects of inhibitors on G. muris trophozoites were similar to those observed for Giardia lamblia. Metronidazole, the drug most commonly used in the treatment of giardiasis completely inhibited respiration and motility in trophozoites; however, it had no effect on either respiration or viability in cysts. Menadione, a redox cycling naphthoquinone, stimulated then completely inhibited respiration in cysts and trophozoites; a complete loss of cyst viability or trophozoite motility was also observed. The effects of menadione on G. muris may indicate that redox cycling compounds have potential as chemotherapeutic agents for the treatment of giardiasis.

Animals↗
PubMedDate not supplied

Oxygen uptake in cysts and trophozoites of Giardia lamblia.

Oxygen uptake in cysts and trophozoites of the parasitic protozoan Giardia lamblia was examined. Both showed oxygen uptake activity, but that of cysts was only 10% to 20% that of trophozoites. Oxygen dependence of oxygen uptake in cysts and trophozoites showed oxygen maxima above which oxygen uptake decreased. The oxygen concentration at which the oxygen uptake rate was greatest was higher for trophozoites than for cysts. The effect of various inhibitors on cyst and trophozoite oxygen uptake suggested that flavoproteins and quinones play some role in oxygen uptake. The substrate specificities and the effect of inhibitors on G. lamblia trophozoites were similar to those observed for G. muris. Metronidazole, the drug most commonly used in treatment of giardiasis, inhibited oxygen uptake and motility in trophozoites; however, it had no obvious effect on either oxygen uptake or excystation in cysts. Menadione, a redox cycling naphthaquinone, first stimulated, then completely inhibited, oxygen uptake in cysts and trophozoites; a complete loss of cyst viability and trophozoite motility was also observed. The effect of menadione on G. lamblia may indicate that redox cycling compounds have potential as chemotherapeutic agents for the treatment of giardiasis.

Animals↗
PubMed1985

Entamoeba histolytica trophozoites in the lumen and mucus blanket of rat colons studied in vivo.

Trophozoites of Entamoeba histolytica HM-1 were cultivated axenically in TYI-S medium. The amoebae were then transferred into this medium lacking serum (TYI) and inoculated into in vivo colon loops of adult Sprague-Dawley rats. The trophozoites were rapidly absorbed by the mucus, and few were found free in the luminal fluid by 1 h. By 4 h, the amoebae began to reappear in the lumen, aggregated in sloughed mucus blanket fragments. The colon was examined histologically and by scanning electron microscopy. There was no evidence of invasion or even brush-border attachment by the trophozoites within 4 h. In TYI, trophozoite motility was low. Exposure to the colonic lumen environment for 5 min in this medium significantly increased motility. However, as the trophozoites became absorbed to mucus fragments, their observed motility virtually ceased despite some morphological evidence of pseudopod extension. Erythrophagocytosis was not significantly affected by either exposing trophozoites to TYI washings of the colonic lumen, or by the more complete medium, TYI-S, in which the amoebae were significantly more motile. Two major mucus glycoprotein oligosaccharide end-group sugars, L-fucose and N-acetyl-neuraminic acid, were tested for their effects on trophozoite motility in both TYI and TYI-S. L-Fucose reduced motility; the sialic acid increased motility. It is concluded that the intestinal lumen contains several compartments, including the luminal fluid and the mucus blanket, and that Entamoeba trophozoites exist in a highly motile state in the former and a low motility state in the latter. The mucus blanket provided a significant barrier to trophozoite access to intestinal epithelium target tissue.

Amebiasis↗
PubMed2005

Ultrastructural localization of antigenic determinants conserved during Perkinsus atlanticus trophozoite to prezoosporangium differentiation.

Trophozoite, prezoosporangium and zoospore are the 3 main developmental stages that form the life cycle of protozoa of the genus Perkinsus. Several studies have shown that the differentiation of Perkinsus species from the trophozoite to the prezoosporangium stage involves a substantial modification of the antigenic characteristics of these molluscan parasites. With the aim of determining the presence and distribution of antigenic determinants conserved during trophozoite to prezoosporangium differentiation, a polyclonal serum was raised against trophozoites of P. atlanticus purified from parasitized gills of the clam Tapes semidecussatus. Immunocytochemical analyses showed that the serum generated against P. atlanticus trophozoites strongly cross-reacted with the prezoosporangium stage. Immunogold electron microscopy studies revealed that the granular component of the nucleolus, chromatin, cell wall, plasmalemma, lomasomes and vacuolar membrane are the main subcellular structures where the immunodominant epitopes consistently expressed by trophozoites and prezoosporangia are located. Furthermore, analysis of the immunogold staining pattern revealed that the labelling density obtained for prezoosporangia in the nucleolus, cell wall, plasmalemma and lomasomes was significantly higher than that obtained for trophozoites. The most immunoreactive structure in trophozoites was the granular component of the nucleolus, whereas in prezoosporangia it was the lomasome. Interestingly, the main antigenic compartment of P. atlanticus, considering both developmental stages, was the lomasome of the prezoosporangium. These findings show that P. atlanticus trophozoite to prezoosporangium differentiation is accompanied by significant qualitative and quantitative changes in the ultrastructural distribution of the immunodominant antigens shared by these 2 developmental stages.

Animals↗
PubMed1992

Relative susceptibility of Giardia muris trophozoites to killing by mouse antibodies of different isotypes.

The aim of this work was to examine the ability of mouse IgA, IgG, and IgM anti-Giardia antibodies to kill Giardia muris trophozoites in the presence and absence of complement. Using a 2-color flow cytometry assay, binding of antibody to trophozoites was assessed with fluorescein-conjugated anti-mouse immunoglobulin, and percentages of killed trophozoites were quantified by staining with propidium iodide. Trophozoites were killed in the presence of complement by IgG3 and IgM anti-trophozoite monoclonal antibodies. Anti-trophozoite IgA, obtained from the intestinal lumen of G. muris-infected BALB/c mice, became bound to trophozoites in vitro but did not kill these organisms in the presence or absence of complement. The results suggest that clearance of G. muris infection by intestinal IgA directed against G. muris trophozoites does not involve antibody-dependent killing of trophozoites in the intestinal lumen.

Animals↗
PubMed1989

Assessment of human natural killer and lymphokine-activated killer cell cytotoxicity against Toxoplasma gondii trophozoites and brain cysts.

Because previous work has suggested that NK cells may be important in host resistance against the intracellular parasite Toxoplasma gondii we examined whether human NK cells and lymphokine-activated killer (LAK) cells have activity against trophozoites and cysts of this organism in vitro. A method to radiolabel Toxoplasma trophozoites with 51Cr was developed and direct cytotoxic activity was determined by using modifications of the standard 51Cr release assay. Viability of 51Cr-labeled trophozoites assessed by both methylene blue staining and trypan blue exclusion was greater than 90%. Significantly more 51Cr was released by anti-Toxoplasma antibody and C than by antibody in the absence of C. Incubation of trophozoites with freshly isolated human NK cells or NK cells activated with either rIL-2 or rIFN-alpha did not result in significant release of 51Cr (specific lysis was 0 to 2.3%). In contrast, the average specific lysis of radiolabeled trophozoites by LAK cells was significant (specific lysis was 7.8% +/- 1.1, p less than 0.01). In a series of separate experiments, preincubation of radiolabeled trophozoites with heat-inactivated normal or Toxoplasma antibody-positive human serum increased the cytotoxicity of LAK cells from a mean specific lysis of 15% +/- 4.5 to 39% +/- 8.5, respectively (p less than 0.05), as assessed by 51Cr release. Because previous work has shown that radioisotope release from parasites may be nonspecific, separate experiments were performed to determine the cytotoxicity of LAK cells against antibody-coated trophozoites by using ethidium bromide-acridine orange staining to assess effector cell damage. LAK cells had a mean specific lysis of 51% against antibody-coated trophozoites by ethidium bromide-acridine orange staining. Preincubation with heat-inactivated Toxoplasma-antibody positive human serum did not increase activity of rIL-2-activated NK cells against 51CR-labeled trophozoites. Neither human NK cells (freshly isolated or activated by rIL-2 or rIFN-alpha) nor LAK cells were cytotoxic for purified preparations of cysts of Toxoplasma isolated from the brains of chronically infected mice.

Acridine Orange↗
PubMed1989

Plasmodium falciparum: inhibitors of lysosomal cysteine proteinases inhibit a trophozoite proteinase and block parasite development.

Trophozoites of Plasmodium falciparum obtain free amino acids for protein synthesis by degrading host erythrocyte hemoglobin in an acidic food vacuole. We previously reported that leupeptin and L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane (E-64), two inhibitors of the cysteine class of proteinases, blocked hemoglobin degradation in the trophozoite food vacuole, and we identified a 28-kDa trophozoite cysteine proteinase as a potential food vacuole hemoglobinase. We now report that the biochemical properties of the trophozoite cysteine proteinase closely resembled those of the lysosomal cysteine proteinases cathepsin B and cathepsin L. The trophozoite proteinase had a pH optimum of 5.5-6.0, near that of both lysosomal proteinases, and it was efficiently inhibited by highly specific diazomethylketone and fluoromethylketone inhibitors of cathepsin B and cathepsin L. The trophozoite proteinase preferred peptide substrates with arginine adjacent to hydrophobic amino acids, as does cathepsin L. Micromolar concentrations of the fluoromethylketone inhibitor Z-Phe-Ala-Ch2F blocked the degradation of hemoglobin in the trophozoite food vacuole and prevented parasite multiplication. In previous studies much higher concentrations of the inhibitor were not toxic for mice. Our results provide additional evidence that the 28-kDa trophozoite proteinase is a food vacuole hemoglobinase and suggest that specific inhibitors of the enzyme may have potential as antimalarial drugs.

Animals↗
PubMed1990

N-acetyl-D-glucosamine is present in cysts and trophozoites of Giardia lamblia and serves as receptor for wheatgerm agglutinin.

Previously, on the basis of lectin binding and glycosidase digestion assays, we have suggested that N-acetyl-D-glucosamine residues (GlcNAc) are major structural components of both trophozoites and in vivo cysts of the intestinal parasite Giardia lamblia. In this report we confirm that GlcNAc is present both in trophozoites and in vitro cysts as assessed by lectin binding and glycosidase digestion assays, galactosyltransferase labeling, immunochemical analysis using antibodies specific for GlcNAc and its beta 1-4 oligomers, and by gas chromatography/mass spectrometry (GC/MS). The results show that wheatgerm agglutinin (WGA) binds specifically to intact trophozoites and in vitro cysts as well as to SDS-PAGE separated proteins. WGA binding to the separated proteins was markedly reduced after their digestion with N-acetyl-beta-D-glucosaminidase, supporting the conclusion that WGA is reacting with terminal beta-linked GlcNAc residues. Labeling of trophozoites and cysts by 3H-exogalactosylation with galactosyltransferase further confirmed the presence of terminal GlcNAc in both surface and intracellular glycoproteins. The presence of GlcNAc is also supported by microfluorometric analysis using antibodies to (GlcNAc)1, (GlcNAc)2, and (GlcNAc)3, which revealed a sugar-inhibitable binding of the antibody to live trophozoites. Finally, the presence of GlcNAc in both cysts and trophozoites was unequivocally confirmed by GC/MS analysis of detergent-extracted membranes and of glycoproteins isolated by affinity chromatography on WGA-agarose. GC/MS analysis also revealed mannose (Man), N-acetyl-D-galactosamine (GalNAc), fucose (Fuc), galactose (Gal), glucose (Glc) and N-acetylneuraminic acid (NANA) to be present in cysts. All these sugars were also present in trophozoites, except for GalNAc. The glycoproteins isolated by WGA affinity chromatography were 5- to 40-fold enriched in GlcNAc, further supporting the conclusion that WGA reacts with GlcNAc in Giardia. In summary, the data presented here provide biological and chemical evidence for GlcNAc in both cysts and trophozoites of G. lamblia and are consistent with previously published results from this and other laboratories.

Acetylglucosamine↗
PubMed1996

Luminal bacteria and proteases together decrease adherence of Entamoeba histolytica trophozoites to Chinese hamster ovary epithelial cells: a novel host defence against an enteric pathogen.

BACKGROUND: Factors that prevent colonic mucosal invasion by pathogenic Entamoeba histolytica are not understood. A key initial step in pathogenesis of injury induced by amoeba is adherence to target cells mediated by a surface glycoprotein lectin on E histolytica. Mucin degrading bacteria normally present in the colon lumen produce glycosidases that degrade soluble or cell surface glycoconjugates. AIM: To determine whether glycosidases produced by mucin degrading bacteria, alone or in combination with proteases present in colon lumen, can decrease E histolytica adherence to target epithelial cells by degrading E histolytica adherence lectin. METHODS: The effects of exposure of E histolytica trophozoites strains HM1:IMSS and 200:NIH to faecal culture supernatant fluids, culture supernatant preparations of mucin degrading bacteria, and luminal proteases on their adherence to Chinese hamster ovary (CHO) cells were determined. The amount of surface adherence lectin on E histolytica trophozoites before and after treatment with glycosidases and proteases was determined by immunofluorescence. The effect of glycosidases and proteases on purified E histolytica lectin was determined by gel electrophoresis. RESULTS: Incubation of E histolytica with culture supernatant preparations or proteases alone did not modify their CHO cell adherence. However, 24 hour incubation of trophozoites with culture supernatant preparations together with pancreatic proteases decreased CHO cell adherence of HM1:IMSS strain by 71.1% (p < 0.001) and of 200: NIH strain by 95% (p < 0.05). Incubation of trophozoites for 24 hours with faecal extracts which contain bacterial and host hydrolases decreased the adherence of the HM1:IMSS strain by 69.2% (p < 0.01) and of the 200: NIH strain by 83.0%. Reduction of trophozoite adherence to CHO cells by hydrolases was promoted by 7.5 mM cycloheximide, and was reversible on incubation in an enzyme free medium. Decrease in CHO cell adherence of trophozoites was associated with decreased lectin on trophozoites as determined by immunofluorescence using a monoclonal antibody to the lectin. Purified lectin was degraded by the mixture of faecal culture supernant preparations and proteases, but not by either alone. CONCLUSIONS: Mucin degrading bacterial glycosidases and colonic luminal proteases together, but not alone, degrade the key adherence lectin on E histolytica trophozoites resulting in decreased epithelial cell adherence. These in vitro findings suggest a potential novel host defence mechanism in the human colon wherein the invasiveness of a pathogen could be curtailed by the combined actions of bacterial and host hydrolases. This mechanism may be responsible for preventing mucosal invasion by pathogenic E histolytica.

Animals↗
PubMed2001

Effect of steroids on Acanthamoeba cysts and trophozoites.

PURPOSE: Topical steroids are frequently used to control corneal inflammation and uveitis or is administered after surgery, to prevent corneal graft rejection. This study was undertaken to determine whether steroids could affect the pathogenicity of Acanthamoeba castellanii. METHODS: The effect of dexamethasone phosphate on excystment, proliferation, and encystment of trophozoites and cysts of A. castellanii was examined in vitro. Cytolysis capacity of steroid-treated Acanthamoeba was quantified by a spectrophotometric assay, and plasminogen activators were measured by a fibrinolysis assay. The influence of steroid treatment on corneal infection in a Chinese hamster model of Acanthamoeba keratitis was examined in vivo. RESULTS: Treatment of Acanthamoeba cysts with dexamethasone induced 4- to 10-fold increases in the number of trophozoites compared with untreated control cultures. Acceleration of trophozoite proliferation was observed when trophozoites were treated with dexamethasone. However, dexamethasone treatment did not affect encystment of Acanthamoeba trophozoites. Dexamethasone-treated trophozoites or cysts induced a significant cytopathic effect on corneal epithelial cells compared with untreated organisms. Supernatants collected from either dexamethasone-treated or untreated organisms failed to lyse corneal epithelial cells. Treatment of organisms with dexamethasone had no effect on production of plasminogen activators by Acanthamoeba trophozoites. Intramuscular injection of dexamethasone had a profound effect on the incidence, severity, and chronicity of keratitis. Keratitis in dexamethasone-treated hamsters was significantly more severe at all time points than in untreated animals (P < 0.05). CONCLUSIONS: These findings indicate that exposure of Acanthamoeba trophozoites and cysts to dexamethasone increases the pathogenicity of the organisms. The results emphasize the importance of maintaining adequate amebicidal therapy if a topical steroid is used in the management of Acanthamoeba keratitis.

Acanthamoeba↗
PubMed1981

Isolation and purification of Giardia trophozoites from rat intestine.

A method for the isolation of Giardia trophozoites based on their ability to attach to warm surfaces has been developed. Mucosal scrapings were obtained from the small intestine of rats infected with Giardia and suspended in Hanks' balanced salt solution (HBSS). Trophozoites were concentrated by centrifugation and allowed to attach to the surfaces of polystyrene petri dishes incubated at 37 C. Incubation temperature significantly affected the recovery of trophozoites. After attachment at 37 C, trophozoites were separated from contaminating intestinal debris by incubation at cold temperature. The trophozoites detach at 4 C, whereas the intestinal debris remain adherent. Then the detached trophozoites were isolated by reattachment at 37 C. Examination by scanning electron microscopy revealed a marked reduction in contamination of attached trophozoites and dish surfaces after the use of cold temperature detachment and reattachment at 37 C. Viability of trophozoites as measured by erythrosin-B dye exclusion, remained above 90% up to 120 min after isolation. This method of isolation facilitates the recovery of this protozoan directly from small intestine for morphological and experimental study.

Animals↗
PubMed1987

Low susceptibility of trophozoites of virulent Entamoeba histolytica to cellular and antibody-dependent cellular cytotoxicity by guinea-pig effector cells.

Cytotoxic potentialities of lymphocytes and macrophages were determined against trophozoites of virulent and avirulent sublines of Entamoeba histolytica in vitro. Guinea-pigs were immunized with antigens of both sublines to obtain stimulated effector cells and antiamoebic antibodies. Trophozoites of an avirulent/attenuated subline of E. histolytica (NIH200) were significantly more susceptible to killing by lymphocytes and macrophages through cellular and antibody-dependent cellular cytotoxic mechanisms. The resistance of virulent trophozoites to killing was attributed to their higher phagocytic ability and virulence characteristics. Electron microscopic studies of the interactions showed that contact between the effector cells and the trophozoites was essential for the cytolytic event which resulted in disintegration of the trophozoites. Antigens of trophozoites of the virulence subline of E. histolytica (NIH200 V) were effective in inducing cytotoxicity against both virulent and avirulent trophozoites: however, the reverse was not true.

Animals↗