Unique Features of Entamoeba Sulfur Metabolism; Compartmentalization, Physiological Roles of Terminal Products, Evolution and Pharmaceutical Exploitation

Sulfur metabolism is essential for all living organisms. Recently, unique features of the Entamoeba metabolic pathway for sulfated biomolecules have been described. Entamoeba is a genus in the phylum Amoebozoa and includes the causative agent for amoebiasis, a global public health problem. This review gives an overview of the general features of the synthesis and degradation of sulfated biomolecules, and then highlights the characteristics that are unique to Entamoeba. Future biological and pharmaceutical perspectives are also discussed.

An NAD+-dependent novel transcription factor controls stage conversion in Entamoeba

Developmental switching between life-cycle stages is a common feature among parasitic pathogens to facilitate disease transmission and pathogenesis. The protozoan parasite Entamoeba switches between invasive trophozoites and dormant cysts, but the encystation process remains poorly understood despite being central to amoebic biology. We identify a transcription factor, Encystation Regulatory Motif-Binding Protein (ERM-BP), that regulates encystation. Down-regulation of ERM-BP decreases encystation efficiency resulting in abnormal cysts with defective cyst walls. We demonstrate that direct binding of NAD+ to ERM-BP affects ERM-BP conformation and facilitates its binding to promoter DNA. Additionally, cellular NAD+ levels increase during encystation and exogenous NAD+ enhances encystation consistent with the role of carbon source depletion in triggering Entamoeba encystation. Furthermore, ERM-BP catalyzes conversion of nicotinamide to nicotinic acid, which might have second messenger effects on stage conversion. Our findings link the metabolic cofactors nicotinamide and NAD+ to transcriptional regulation via ERM-BP and provide the first mechanistic insights into Entamoeba encystation.

Homologous Recombination Occurs in Entamoeba and Is Enhanced during Growth Stress and Stage Conversion

Homologous recombination (HR) has not been demonstrated in the parasitic protists Entamoeba histolytica or Entamoeba invadens, as no convenient method is available to measure it. However, HR must exist to ensure genome integrity, and possible genetic exchange, especially during stage conversion from trophozoite to cyst. Here we show the up regulation of mitotic and meiotic HR genes in Entamoeba during serum starvation, and encystation. To directly demonstrate HR we use a simple PCR-based method involving inverted repeats, which gives a reliable read out, as the recombination junctions can be determined by sequencing the amplicons. Using this read out, we demonstrate enhanced HR under growth stress in E. histolytica, and during encystation in E. invadens. We also demonstrate recombination between chromosomal inverted repeats. This is the first experimental demonstration of HR in Entamoeba and will help future investigations into this process, and to explore the possibility of meiosis in Entamoeba.

Transcriptome analysis of encystation in Entamoeba invadens

Encystation is an essential differentiation process for the completion of the life cycle of a group of intestinal protozoa including Entamoeba histolytica, the causative agent of intestinal and extraintestinal amebiasis. However, regulation of gene expression during encystation is poorly understood. To comprehensively understand the process at the molecular level, the transcriptomic profiles of E. invadens, which is a related reptilian species that causes an invasive disease similar to that of E. histolytica, was investigated during encystation. Using a custom-generated Affymetrix platform microarray, we performed time course (0.5, 2, 8, 24, 48, and 120 h) gene expression analysis of encysting E. invadens. ANOVA analysis revealed that a total of 1,528 genes showed ≥3 fold up-regulation at one or more time points, relative to the trophozoite stage. Of these modulated genes, 8% (116 genes) were up-regulated at the early time points (0.5, 2 and 8h), while 63% (962 genes) were up-regulated at the later time points (24, 48, and 120 h). Twenty nine percent (450 genes) are either up-regulated at 2 to 5 time points or constitutively up-regulated in both early and late stages. Among the up-regulated genes are the genes encoding transporters, cytoskeletal proteins, proteins involved in vesicular trafficking (small GTPases), Myb transcription factors, cysteine proteases, components of the proteasome, and enzymes for chitin biosynthesis. This study represents the first kinetic analysis of gene expression during differentiation from the invasive trophozoite to the dormant, infective cyst stage in Entamoeba. Functional analysis on individual genes and their encoded products that are modulated during encystation may lead to the discovery of targets for the development of new chemotherapeutics that interfere with stage conversion of the parasite.

Growth of Entamoeba invadens in sediments with metabolically repressed bacteria leads to multicellularity and redefinition of the amoebic cell system

Extracellular signaling and mechanisms of cell differentiation in Entamoeba are misunderstood. The main reason is the popular use of axenic media, which do not correspond to the natural habitats of Entamoeba. The axenic environment lacks the exogenous activators and repressors provided by natural habitats. Absent bacterial commensals understanding of the development of the amoebic cell system remains deficient. The present Aa(Sm) culture method using mixed sediments of antibiotically repressed Aerobacter aerogens and amoebae was developed to model in vitro extracellular signaling that induce multicellularity in cultures of E. invadens. Repressed oxygen consuming sediment bacteria supply E. invadens the hypoxic environment needed for differentiation and development. The amoebae themselves alter the environment by consuming the bacteria by phagocytosis thus reversing hypoxia. Exogenous activators are in this manner down regulated and suppressed. This feedback effect controls amoebic development and differentiation. Co-existing cell types and cell fractions with different life spans and cell cycle length could be identified. Aa(Sm) long term cultures contain continuous and non-continuous self renewing cell lines producing quiescent and terminally differentiated daughter cells (precysts) by asymmetric division. This culturing method helps to understand the intimate relationship between hypoxic environments and the multicellular behaviour of E. invadens and the interrelations existing between the distinct cell types.

Metabolic profiling of the protozoan parasite Entamoeba invadens revealed activation of unpredicted pathway during encystation

Encystation, which is cellular differentiation from the motile, proliferative, labile trophozoite form to the dormant, resistant cyst form, is a crucial process found in parasitic and free-living protozoa such as Entamoeba, Giardia, Acanthamoeba, and Balamuthia. Since encystation is an essential process to deal with the adverse external environmental changes during the life cycle, and often integral to the transmission of the diseases, biochemical understanding of the process potentially provides useful measures against the infections caused by this group of protozoa. In this study, we investigated metabolic and transcriptomic changes that occur during encystation in Entamoeba invadens, the reptilian sibling of mammal-infecting E. histolytica, using capillary electrophoresis-tandem mass spectrometry-based metabolite profiling and DNA microarray-based expression profiling. As the encystation progressed, the levels of majority of metabolites involved in glycolysis and nucleotides drastically decreased, indicating energy generation is ceased. Furthermore, the flux of glycolysis was redirected toward chitin wall biosynthesis. We found remarkable temporal increases in biogenic amines such as isoamylamine, isobutylamine, and cadaverine, during the early period of encystation, when the trophozoites form large multicellular aggregates (precyst). We also found remarkable induction of γ-aminobutyric acid (GABA) during encystation. This study has unveiled for the first time the dynamics of the transcriptional and metabolic regulatory networks during encystation, and should help in better understanding of the process in pathogenic eukaryotes, and further development of measures controlling infections they cause.

Compounds of the upper gastrointestinal tract induce rapid and efficient excystation of Entamoeba invadens

The infective stage of Entamoeba parasites is an encysted form. This stage can be readily generated in vitro, which has allowed identification of stimuli that trigger the differentiation of the parasite trophozoite stage into the cyst stage. Studies of the second differentiation event, emergence of the parasite from the cyst upon infection of a host, have been hampered by the lack of an efficient means to excyst the parasite and complete the life cycle in vitro. We have determined that a combination of exposures to water, bicarbonate and bile induces rapid excystment of Entamoeba invadens cysts. The high efficiency of this method has allowed the visualization of the dynamics of the process by electron and confocal microscopy, and should permit the analysis of stage-specific gene expression and high-throughput screening of inhibitory compounds.

Entamoeba shows reversible variation in ploidy under different growth conditions and between life cycle phases

Under axenic growth conditions, trophozoites of Entamoeba histolytica contain heterogenous amounts of DNA due to the presence of both multiple nuclei and different amounts of DNA in individual nuclei. In order to establish if the DNA content and the observed heterogeneity is maintained during different growth conditions, we have compared E. histolytica cells growing in xenic and axenic cultures. Our results show that the nuclear DNA content of E. histolytica trophozoites growing in axenic cultures is at least 10 fold higher than in xenic cultures. Re-association of axenic cultures with their bacterial flora led to a reduction of DNA content to the original xenic values. Thus switching between xenic and axenic growth conditions was accompanied by significant changes in the nuclear DNA content of this parasite. Changes in DNA content during encystation-excystation were studied in the related reptilian parasite E. invadens. During excystation of E. invadens cysts, it was observed that the nuclear DNA content increased approximately 40 fold following emergence of trophozoites in axenic cultures. Based on the observed large changes in nuclear size and DNA content, and the minor differences in relative abundance of representative protein coding sequences, rDNA and tRNA sequences, it appears that gain or loss of whole genome copies may be occurring during changes in the growth conditions. Our studies demonstrate the inherent plasticity and dynamic nature of the Entamoeba genome in at least two species.

In contrast to the perception that DNA content of an organism is stable and maintained during different conditions and life cycle stages, new evidence shows that many organisms display changes in their DNA content at different stages of their life cycle. We have earlier identified intra-cellular and inter-cellular differences in DNA content of the protist pathogen Entamoeba histolytica and established that this organism can tolerate large variations in DNA content during axenic culture. In this study we have made an important advancement in the understanding of amoeba biology where we have shown that changes in growth conditions and life cycle stages are accompanied by large differences in DNA content involving gain or loss of whole genome copies. This property may well regulate the outcome of infection and subsequently the disease.

The use of the antifungal agent miconazole as an inhibitor of Blastocystis hominis growth in Entamoeba histolytica/E. dispar cultures

In regions with high prevalence, Blastocystis hominis is frequently found in association with Entamoeba histolytica/E. dispar in xenic cultures. Its exacerbated growth is often superimposed on the growth of amebas, thus impeding the continuation of the amebas in the culture, within a few generations. The present study reports on the excellent efficacy (100%) of the antifungal agent miconazole in eliminating B. hominis from cultures of E. histolytica/E. dispar, thereby maintaining the integrity of the trophozoites of the amebas. Nystatin presented low efficacy (33.3%).

Pathogenicity of Entamoeba dispar under xenic and monoxenic cultivation compared to a virulent E. histolytica

Two xenic isolates and cloned cultures of Entamoeba dispar were submitted to monoxenization using Crithidia fasciculata as the associated organism. Growth in monoxenic cultivation and ability of xenic and monoxenic trophozoites to destroy VERO cells and produce lesions in hamster livers were compared to those of a virulent E. histolytica. Parental and cloned E. dispar under monoxenic cultivation showed a remarkable lower growth than the monoxenic E. histolytica and were avirulent in both in vivo and in vitro tests. When xenically cultured, trophozoites of E. dispar showed a moderate lytic activity against VERO cells (1.5 to 41.8% of destruction) but caused severe hepatic lesions in hamsters as those caused by the virulent E. histolytica (29 to 100% in prevalence and 0.86 to 4.00 in lesion degree). Although E. dispar has not been associated with invasive disease in men, the ability of xenic trophozoites to produce prominent tissue damage in experimental conditions has indicated that some strains have a considerable pathogenic potential when in presence of bacteria.

Growth-promoting effect on iron-sulfur proteins on axenic cultures ofEntamoeba dispar

A growth-promoting factor (GPF) that promotes the growth of Entamoeba dispar under axenic culture conditions was found in fractions of mitochondria (Mt), hydrogenosomes (Hg) and chloroplasts (Cp) obtained from cells of six different protozoan, mammalian and plant species. We were able to extract the GPF from the Cp-rich leaf cells of a plant (spiderwort: Commelina communis L.) in an acetone-soluble fraction as a complex of chlorophyll with low molecular weight proteins (molecular weight [MW] approximately 4,600). We also found that on treatment with 0.6% complexes of 2-mercapthoethanol (2ME), complexes of chlorophyll-a with iron-sulphur (Fe-S) proteins (e.g., ferredoxins [Fd] from spinach and Clostridium pasteurianum) and noncomplex rubredoxin (Rd) from C. posteurianum have a growth-promoting effect on E. dispar. These findings suggest that E. dispar may lack a sufficient quantity of some essential components of Fe-S proteins, such as Fe-S center.

DNA methylation and targeting of LINE retrotransposons in Entamoeba histolytica and Entamoeba invadens

In this study, we have isolated by affinity chromatography, using anti-m5C antibody as a ligand, a DNA encoding reverse transcriptase of LINE retrotransposon (RT LINE) in both Entamoeba invadens and Entamoeba histolytica. RT LINE transcripts were detected in E. histolytica but were absent from E. invadens. The methylation status of genomic copies of E. invadens RT LINE was confirmed by bisulfite analysis. In contrast, all the genomic copies of the E. histolytica RT LINE analyzed in this study were not methylated. Many of these genomic copies diverge from the RT LINE isolated by m5C affinity chromatography by a number of mutations that includes conversion of C to T and G to A. These mutations are reminiscent of the conversion of C to T (and G to A on the complementary DNA strand) that occurred during primate evolution in Alu elements following accelerated deamination of methylated cytosines. E. invadens and E. histolytica RT LINEs isolated by affinity chromatography were cloned in a pEhAct Neo vector, amplified in E. coli GM2163 (dam-dcm) and transformed into E. histolytica. Bisulfite analysis of transfected amoeba showed the presence of m5C in E. invadens RT LINE replicated in E. histolytica, but not in E. histolytica RT LINE or in the neomycine phosphotransferase gene, which is also carried by the pEhAct Neo vector. These results suggest the existence of a specific mechanism based on DNA methylation that controls retrotransposons in these parasites.

Effect of artificial gastrointestinal fluids on the excystation and metacystic development of Entamoeba invadens

The effect of artificial gastric fluid (AGF), containing 0.5% pepsin and 0.6% hydrochloric acid, pH 1.8, in distilled water, on the excystation and metacystic development of Entamoeba invadens was examined. Excystation, which was assessed by counting the number of metacystic amoebae after inducing excystation, was enhanced by pretreatment of cysts with AGF for 30 to 60 min at 37 degrees C but not 26 degrees C. Longer exposure of cysts to AGF significantly reduced their viability. Significant enhancement of excystation was observed by pretreatment of cysts with distilled water only at 37 degrees C. In addition, 0.6% hydrochloric acid had a comparable enhancing effect on excystation to AGF. Metacystic development, when determined by the number of nuclei in amoeba, was slightly enhanced by pretreatment with AGF. An artificial intestinal fluid (AIF), containing 1% pancreatin, 1% sodium bicarbonate, and 5% ox bile, pH 8.0, in distilled water, had a significant toxic effect on cysts, where 1% pancreatin had neither an enhancing effect on excystation nor a toxic effect on cysts, whereas 5% ox bile had a toxic effect on cysts. Pretreatment of cysts with AGF followed by AIF had a similar toxic effect on cysts to that by AIF only. These results suggest that gastric fluid but not intestinal fluid at 37 degrees C contributes to enhancing excystation for Entamoeba infection.

Entamoeba invadens: in vitro axenic encystation with a serum substitute

The current media for axenic cultivation of Entamoeba histolytica and Entamoeba invadens are supplemented with bovine or equine serum, which provides several essential nutrients to amoebas. Serum has also been considered an essential component in encystation media for E. invadens. A substitute of serum, PACSR has been described as an alternative for growth of E. histolytica and also maintains growth of E. invadens. When PACSR was used instead of serum for encystation of E. invadens the efficiency was the same as for serum. Our present data show that PACSR can support the growth and induction of encystation of E. invadens strain IP-1.

Entamoeba invadens contains the components of a classical adrenergic signaling system

Epinephrine (Epi) was previously found to bypass the need for galactose ligands during early steps in the initiation of Entamoeba encystment. Epinephrine is presumed to act on amoebae through a classical adrenergic signaling pathway that results in the increased production of cyclic adenosine monophosphate (cAMP). The object of this study was to verify the existence of an adrenergic like pathway and its response to Epi in both whole Entamoeba trophozoites and purified plasma membrane preparations. Whole trophozoite and purified membrane preparations from Entamoeba invadens responded to the presence of Epi by increasing the production of cAMP. The modulators of heterotrimeric G protein signaling, forskolin (FK), pertussis toxin (PTX) and cholera toxin (CTX), also increased cAMP levels in whole cells and membrane fragments. All of these increases in cAMP were inhibited by specific inhibitors of adenylyl cyclase (AC). Treatment of membrane fragments with epinephrine caused an increased binding of non-hydrolysable GTP analogs. Entamoeba trophozoites therefore appear to contain G-protein-regulated adenylyl cyclase that functions downstream of an adrenergic ligand receptor.

AXENIC CULTIVATION OF ENTAMOEBA DISPAR IN NEWLY DESIGNED YEAST EXTRACT–IRON–GLUCONIC ACID–DIHYRDOXYACETONE–SERUM MEDIUM

Yeast extract-iron-gluconic acid-dihydroxyacetone-serum medium that allows axenic cultivation of Entamoeba dispar was designed based on casein-free yeast extract-iron-serum (YI-S) medium, and the usefulness of the medium was assessed. The main differences from YI-S medium are replacement of glucose by gluconic acid, addition of dihydroxyacetone and D-galacturonic acid monohydrate, and sterilization by filtration. This medium promoted the axenic growth of 5 strains of E. dispar (2 strains of nonhuman primate isolates and 3 strains of human isolates). In addition, to clarify the biological basis for the growth of E. dispar in this medium, analyses of relevant enzymes on the glycolytic pathway of the amoebae as well as of the protozoans that are the best culture supplement for amoebae are being performed.

Entamoeba invadens: cysteine protease inhibitors block excystation and metacystic development

We examined the effects of six cysteine protease inhibitors on the excystation and metacystic development of Entamoeba invadens. Excystation, which was assessed by counting the number of metacystic amoebae after the induction of excystation, was inhibited by the cysteine protease inhibitors Z-Phe-Ala-DMK and E-64d in a concentration-dependent manner during incubation compared to the controls. Neither inhibitor had a significant effect on cyst viability; thus, their inhibitory effects were not due to the toxic effect on cysts. Metacystic development, when determined by the number of nuclei in amoeba, was also inhibited by these protease inhibitors, because the percentage of 4-nucleate amoebae was higher than in the controls on Day 3 of incubation. Although other cysteine protease inhibitors, Z-Phe-Phe-DMK, E-64, ALLM, and cathepsin inhibitor III, had a weak or little effect on the excystation, they inhibited cysteine protease activity in the lysates of E. invadens cysts. Broad bands with gelatinase activity of metacystic amoebae, as well as cysts and trophozoites, were detected in the gelatin substrate gel electrophores and were inhibited by Z-Phe-Ala-DMK. There was a difference in the protease composition between cysts and trophozoites, and the protease composition of metacystic amoebae changed from cyst-type to trophozoite-type during development. These results strongly suggest that cysteine proteases contribute to the excystation and metacystic development of E. invadens, which leads to successful infection.

Colonic short-chain fatty acids inhibit encystation of Entamoeba invadens

Entamoeba parasites multiply as trophozoites in the layer of mucus that overlies the colonic epithelium. In response to stimuli that are not understood, trophozoites stop multiplying and differentiate into cysts that are released to infect another host. In the colon, Entamoeba trophozoites are exposed to the large variety of biochemicals that are carried into or are produced within this organ. The normal bacterial population of the colon releases large amounts of short-chain fatty acids (SCFAs). These compounds have effects on the growth, differentiation and repair of the colonic epithelium that correlate with de-creased activity of a Class I/II histone deacetylase (HDAC). We found that the formation of cysts, but not the growth of trophozoite-stage Entamoeba invadens parasites, was inhibited by physiologic concentrations of SCFAs. Variable levels of cyst formation did occur if SCFA concentrations were lowered. Specific inhibitors of Class I/II-type HDACs also prevented encystation, and trophozoites exposed to these compounds had increased levels of acetylation of histone H4 and other nuclear proteins. These results suggest that production of the infectious cyst stage of Entamoeba parasites is regulated in part by the levels of SCFAs made by the bacterial population of the colon.

Characterization of Chitin Synthases from Entamoeba

A major component of the Entamoeba cyst wall is chitin, a homopolymer of beta-(1,4)-linked N-acetyl-D-glucosamine. Polymerization of chitin requires the presence of active chitin synthases (CHS), a group of enzymes belonging to the family of beta-glycosyl transferases. CHS have been described for fungi, insects, and nematodes; however, information is lacking about the structure and expression of this class of enzymes in protozoons such as Entamoeba. In this study, the primary structures of two putative E. histolytica CHS (EhCHS-1 and EhCHS-2) were determined by gene cloning and homologous proteins were identified in databases from E. dispar and the reptilian parasite E. invadens. The latter constitutes the widely used model organism for the study of Entamoeba cyst development. The two ameba enzymes revealed between 23% and 33% sequence similarity to CHS from other organisms with full conservation of all residues critically important for CHS activity. Interestingly, EhCHS-1 and EhCHS-2 differed substantially in their predicted molecular weights (73 kD vs. 114 kD) as well as in their isoelectric points (5.04 vs. 8.05), and homology was restricted to a central stretch of about 400 amino acid residues containing the catalytic domain. Outside the catalytic domain, EhCHS-1 was predicted to have seven transmembrane helices (TMH) of which the majority is located within the C-terminal part, resembling the situation found in yeast; whereas, EhCHS-2 is structurally related to nematode or insect chitin synthases, as it contained 17 predicted TMHs of which the majority is located within the N-terminal part of the molecule. Northern blot analysis revealed that genes corresponding to CHS-1 and CHS-2 are not expressed in Entamoeba trophozoites, but substantial amounts of CHS-1 and CHS-2 RNA were present 4 to 8 hours after induction of cyst formation by glucose deprivation of E. invadens. The time-courses of expression differed slightly between the two ameba CHS genes, as in contrast to CHS-1 RNA, expression of CHS-2 RNA was more transient and no plateau was observed between 8 and 16 hours of encystation. However, both CHS RNAs were no longer detectable after 48 hours when most of the cells had been transformed into mature cysts.

Different effects of cytochalasins on the growth and differentiation of Entamoeba invadens

The effect of five different cytochalasins on the growth, encystation and excystation of Entamoeba invadens was examined. At 10 microM, cytochalasins B, D, E and dihydrocytochalasin B markedly inhibited growth. Encystation was inhibited by cytochalasin D at 1 microM but not by other cytochalasins at the same concentration, whereas it was inhibited by 10 microM of cytochalasins B, E and dihydrocytochalasin B as well as cytochalasin D. Excystation, which was assessed by counting the number of metacystic amoebae after inducing excystation, was markedly enhanced by cytochalasin D as previously demonstrated, whereas the enhancing effect of cytochalasins A, B and dihydrocytochalasin B was weak. In contrast, cytochalasin E at 10 microM inhibited excystation and metacystic development. These results indicate that there is a difference in the effect of different cytochalasins on the growth and differentiation of E. invadens, depending on differences in their chemical structure.

Involvement of signaling through protein kinase C and phosphatidylinositol 3-kinase in the excystation and metacystic development of Entamoeba invadens

Using an axenic excystation system in vitro, we examined the effect of protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K), which are signaling molecules responsible for numerous cellular responses, on the excystation and metacystic development of Entamoeba invadens. Excystation, which was assessed by counting the number of metacystic amoebae after the induction of excystation, was inhibited by the PKC inhibitors staurosporine, chelerythrine chloride and calphostin C in a concentration-dependent manner during incubation, compared with the controls. As cyst viability was not affected by these inhibitors, reduced excystation was not due to their direct toxic effects on cysts. Metacystic development, when determined by the number of nuclei in the amoebae, was delayed by these PKC inhibitors, because the percentage of 1-nucleate amoebae was lower than in controls at day 3 of incubation. Wortmannin, a potent inhibitor of PI3K, also inhibited excystation and metacystic development of E. invadens in a concentration-dependent manner, compared with the controls. These results indicate that signaling through PKC and PI3K contributes to the excystation and metacystic development of E. invadens.

Laboratory diagnosis of amebiasis

The detection of Entamoeba histolytica, the causative agent of amebiasis, is an important goal of the clinical microbiology laboratory. To assess the scope of E. histolytica infection, it is necessary to utilize accurate diagnostic tools. As more is discovered about the molecular and cell biology of E. histolytica, there is great potential for further understanding the pathogenesis of amebiasis. Molecular biology-based diagnosis may become the technique of choice in the future because establishment of these protozoa in culture is still not a routine clinical laboratory process. In all cases, combination of serologic tests with detection of the parasite (by antigen detection or PCR) offers the best approach to diagnosis, while PCR techniques remain impractical in many developing country settings. The detection of amebic markers in serum in patients with amebic colitis and liver abscess appears promising but is still only a research tool. On the other hand, stool antigen detection tests offer a practical, sensitive, and specific way for the clinical laboratory to detect intestinal E. histolytica. All the current tests suffer from the fact that the antigens detected are denatured by fixation of the stool specimen, limiting testing to fresh or frozen samples.

[Studies on the continuous culture and the growth of Entamoeba gingivalis]

AIM

To establish a method for continuous culture of Entamoeba gingivalis(E. g.).

METHODS

The culture conditions of E. g. were compared by observing its size and survival time at room temperature.

RESULTS

The growth of E. g. under different culture conditions including culture medium, temperature and pH were compared. The accompanying bacteria associate with E. g. FJ4 were isolated and identified. The average size of E. g. was 13.19 microns-49.93 microns x 9.88 microns-30.74 microns. The optimal culture conditions of E. g. were: modified LES or YES medium, pH 6.4-6.7, nutritional liquids such as Locke's solution or yolk liquid with 20% bovine serum, penicillin, streptomycin and rice flour at 35 degrees C. Reproduction of E. g. peaked at the fourth day of incubation, and the survival time of E. g. was 120 h-168 h.

CONCLUSION

E. g. could be continuously cultured in modified LES or YES medium by inoculating once every four days.

Effectiveness of peptone-yeast extract (P-Y) medium in the cultivation and isolation of Entamoeba histolytica/Entamoeba dispar in Turkish patients

Amebiasis is a common protozoan infection worldwide, causing serious health problems in both children and adults. Today, almost 10% of the world population is infected with Entamoeba histolytica/Entamoeba dispar. The aims of this study were both the comparison of the reproduction rates and densities of E. histolytica/E. dispar in Robinson, Dobell-Laidlaw and P-Y culture media and isolation of E. histolytica/E. dispar from stool samples in Peptone-Yeast (P-Y) medium. Trophozoites and cysts of E. histolytica/E. dispar, maintained in Robinson medium, and stool samples of patients with amebiasis were inoculated into P-Y, Robinson and Dobell-Laidlaw culture media. Reproduction rates reached their peak levels 48 h after the inoculation in all culture media. Reproduction rates in P-Y and Robinson media were found similar; however, they were higher than the reproduction rate in Dobell-Laidlaw medium (p < 0.01); there was no statistically significant difference between the reproduction rates of P-Y and Robinson media (p > 0.05). Twelve isolates from 12 patients were cultivated in P-Y medium and checked for reproduction everyday for 7 days. Twelve of the 12 (100%) isolates were cultivated in P-Y medium, indicating that the P-Y was an effective medium for the isolation of E. histolytica/E. dispar in stool samples. According to these results, P-Y medium could be preferred in immunologic, serologic and molecular studies and, thus the definitive diagnosis of amebiasis due to its low cost and simple formula.

Inhibition of excystation and metacystic development of Entamoeba invadens by the dinitroaniline herbicide oryzalin

The effect of oryzalin on excystation and metacystic development of Entamoeba invadens strain IP-1 was examined by transfer of cysts to a growth medium containing the drug. Excystation, which was assessed by counting the number of metacystic amoebae after induction of excystation, was inhibited by oryzalin in a concentration-dependent manner. Metacystic development, which was determined by the number of nuclei in metacystic amoebae, was also inhibited by oryzalin because the percentage of 4-nucleate amoebae at day 1 remained unchanged at day 3. The addition of oryzalin after the induction of excystation decreased the number of metacystic amoebae, compared with control cultures. When cysts were incubated for 1 day in growth medium plus oryzalin, little increase in the number of metacystic amoebae was observed after removal of the drug. Excystation and metacystic development were further inhibited when the cysts were incubated for 30 min in encystation medium containing oryzalin before transfer to growth medium with the drug. When cysts were incubated for 30 min in encystation medium before transfer to growth medium without the drug, metacystic amoebae decreased in number. Pretreatment of cysts with oryzalin for 30 min in phosphate-buffered saline markedly reduced viability and prevented excystation in growth medium with or without the drug. The results indicate that oryzalin inhibits excystation and metacystic development of E. invadens, suggesting that it may be an inhibitor of Entamoeba infection.

Possible role of calcium ions, calcium channels and calmodulin in excystation and metacystic development of Entamoeba invadens

The effect of calcium ions (Ca(2+)) and calmodulin (CaM) on the excystation and metacystic development of Entamoeba invadens was examined by transfer of cysts to a growth medium containing calcium antagonists and CaM inhibitors. Excystation, which was assessed by counting the number of metacystic amoebae after induction of excystation, was inhibited by the calcium chelators ethyleneglycol bis (beta-aminoethyl ether)- N,N'-tetraacetate (EGTA) and ethylene-diaminetetraacetate (EDTA), with EDTA being more potent than EGTA. The inhibitory effect of higher concentrations of these chelators on excystation was associated with reduced viability of cysts. Metacystic development, when determined by the number of nuclei in an amoeba, was delayed by EGTA, because the percentage of four-nucleate amoebae was higher than in controls at day 3 of incubation. EDTA made metacystic development unusual by producing a large number of metacystic amoebae with more than ten nuclei. The inhibition of excystation by these chelators was partially abrogated by their removal. A putative antagonist of intracellular calcium flux, 8-( N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8) also inhibited the excystation and metacystic development, but had little effect on cyst viability. The slow Na(+)-Ca(2+) channel blocker bepridil but not verapamil inhibited the excystation and metacystic development, associating with reduced cyst viability at higher concentrations. The inhibitory effect of bepridil on excystation was abrogated by removal of the drug. The CaM inhibitor trifIuoperazine (TFP) but not W-7 [ N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide] inhibited the excystation and metacystic development. The inhibitory effect of TFP on excystation was also abrogated by removal of the drug. These results indicate that extracellular calcium ions, amoebic intracellular calcium flux, calcium channels, and a CaM-dependent process contribute to the excystation and metacystic development of E. invadens.

Effect of proteasome inhibitors on the growth, encystation, and excystation of Entamoeba histolytica and Entamoeba invadens

The effect of three proteasome inhibitors, lactacystin, clasto-lactacystin beta-lactone, and MG-132, on the growth, encystation, and excystation of Entamoeba histolytica and Entamoeba invadens was examined. All of these drugs blocked E. histolytica growth in a concentration-dependent manner; lactacystin was most potent for the inhibition and MG-132 showed the inhibitory effect only at higher concentrations. E. invadens was more resistant to these drugs than E. histolytica. Encystation of E. invadens was also inhibited and was more sensitive to the drugs than was growth. Beta-lactone was the most potent encystation inhibitor. The inhibitory effect of lactacystin and the beta-lactone on encystation was slightly and little abrogated by the removal of the drug, respectively. Multinucleation occurred in E. histolytica trophozoites treated with these drugs, being most marked with lactacystin. In contrast, no multinucleation was observed in E. invadens treated with the drugs. Electron microscopy revealed that the treatment of E. histolytica trophozoites with lactacystin led to an increase in the number of cells with many glycogen granules in the cytoplasm. Lactacystin, beta-lactone and MG-132 had no or little effect on the excystation and metacystic development of E. invadens. These results suggest that proteasome function plays an important role for Entamoeba growth and encystation, but has no obvious effect on excystation or metacystic development.

The enteric parasite Entamoeba uses an autocrine catecholamine system during differentiation into the infectious cyst stage

Enteric amoebae of the genus Entamoeba travel from host to host in an encysted form. We previously showed that in vitro cyst development of Entamoeba invadens requires the addition of defined amounts of multivalent galactose-terminated molecules, such as mucin, to the cultures. The amoeba surface lectin that binds mucin is presumed to convey transmembrane signals when clustered by the ligand, but the signaling molecules that function downstream of the lectin are not known. We report here that Entamoeba encystation was induced in the absence of galactose ligand when catecholamines were added to the encystation medium. Micromolar amounts of both epinephrine and norepinephrine induced encystation. Of a variety of synthetic catecholamine agonists tested, only beta(1)-adrenergic receptor agonists supported encystation, whereas alpha- and beta(2)-adrenergic receptor agonists did not. Only beta(1)-adrenergic receptor antagonists inhibited encystation, and did so even when exogenous catecholamines were not added, indicating that catecholamine binding is required for encystation and suggesting an endogenous source of the ligand. High performance liquid chromatography analysis of Entamoeba extracts showed that the amoebae themselves contain catecholamines and at least one of these is released when the cells are stimulated to encyst with galactose-terminated ligands. The presence of catecholamine binding sites on the surface of amoeba trophozoites was confirmed using radiolabeled catecholamine antagonist. Amoeba encystment was inhibited by addition of beta(1)-adrenergic receptor antagonist to cells that were stimulated to differentiate with either galactose ligand or catecholamines, but not with dibutyryl cAMP. This suggests that the amoeba catecholamine receptor functions downstream of the galactose lectin and upstream of adenylyl cyclase. This enteric protozoan parasite, therefore, contains the components of an autocrine catecholamine ligand-receptor system that may act in conjunction with a galactose lectin to regulate differentiation into the infectious cyst stage.

Biological aspects of a Brazilian strain of Entamoeba dispar

A strain of Entamoeba dispar was characterized by clinical diagnosis, serological and electrophoretical isoenzyme analysis and by the polymorphism of a 482 bp genomic fragment analysis. The pathogenesis and virulence of this strain was investigated considering the experimental infection in hamster livers in association with the original intestinal microbiota. Liver lesions were observed in hamsters experimentally infected with trophozoites from xenic cultures, but not from the monoxenic cultures. Moreover, clones obtained from re-isolated strain Wil1R1 showed a distinct biological behavior. In fact, animals inoculated with Wil1R1ClB3 showed an intense acute inflammatory reaction with destructive focal hepatic lesions. These lesions were characterized as amebic abscesses. The association between bacteria and ameba has been fairly well studied because it affects the pathogenicity of the amebas and has important therapeutic implications. In this study, we demonstrated that E. dispar in association with the original microbiota is able to produce lesions in hamster liver in spite of its having been considered to be non-pathogenic in the hamster model. Based on these results we suggest that diagnosis of amebiasis needs to be made with more care and that clinical and therapeutical procedures need to be revised.

Effect of calcium antagonists, calcium channel blockers and calmodulin inhibitors on the growth and encystation of Entamoeba histolytica and E. invadens

The effects of calcium antagonists, calcium channel blockers, and calmodulin inhibitors on the growth of Entamoeba histolytica and the growth and encystation of Entamoeba invadens were examined. Calcium chelators ethyleneglycol bis (beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) and ethylene-diaminetetraacetate (EDTA) inhibited the growth of both Entamoeba and also the encystation of E. invadens in a dose-dependent manner, with EDTA being more effective than EGTA. A putative antagonist of intracellular calcium flux, 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8) also inhibited both growth and encystation, with the E. histolytica being more sensitive than E. invadens, and with the growth of E. invadens being more sensitive than encystation. The slow Na+-Ca2+ channel blockers bepridil and verapamil inhibited both growth and encystation. Bepridil was more effective than verapamil. The calmodulin (CaM) inhibitors, W-7 (N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide) and trifluoperazine (TFP), were also inhibitory for both the growth and encystation; TFP was more effective than W-7, and encystation was more sensitive than growth in E. invadens. These results indicate that extracellular calcium ions, amebic intracellular calcium flux, calcium channels, and a CaM-dependent process contribute to the growth and encystation of Entamoeba.

Encystation in parasitic protozoa

Giardia and Entamoeba parasites encase themselves in a carbohydrate-rich cyst for travel from host to host. Both parasites upregulate their Golgi apparatus during this process, yielding organelles that are now found to be similar to those of higher eukaryotes. In fact, unusual enzymes and structural proteins used for cyst wall synthesis, the complexity of the secretory pathways used to transport materials to the developing cyst walls, as well as unexpected mechanisms of gene regulation and parasite-host and parasite-parasite information exchange, are revealing a high level of sophistication in these organisms that occupy low branch points in the eukaryotic lineage.

Entamoeba invadens: enhancement of excystation and metacystic development by cytochalasin D

Effects of three actin-modifying drugs, cytochalasin D, latrunculin A, and jasplakinolide, on the excystation and metacystic development in vitro of Entamoeba invadens were examined by transfer of the cysts to growth medium with the drugs. Cytochalasin D unexpectedly increased the number of metacystic amoebae of E. invadens strain IP-1 during incubation. Metacystic development, which was determined by the number of nuclei of metacystic amoebae, was faster in the culture with cytochalasin D than in the culture without the drug. These results suggest that cytochalasin D enhances the excystation and metacystic development. In contrast, latrunculin A and jasplakinolide inhibited these process. No excystation occurred in encystation medium even in the presence of cytochalasin D, suggesting that growth medium is essential for excystation. Excystation was further enhanced when the cysts were incubated with cytochalasin D before culture in growth medium with the drug. The enhancing effect of cytochalasin D on the excystation and metacystic development was abrogated by jasplakinolide. Thus, the results indicate that cytochalasin D, unlike latrunculin A and jasplakinolide, caused enhancement of the excystation and metacystic development of this parasite.

Effect of jasplakinolide on the growth, encystation, and actin cytoskeleton of Entamoeba histolytica and Entamoeba invadens

The effect of jasplakinolide. an actin-polymerizing and filament-stabilizing drug, on the growth, encystation, and actin cytoskeleton of Entamoeba histolytica and Entamoeba invadens was examined. Jasplakinolide inhibited the growth of E. histolytica strain HM-1:IMSS and E. invadens strain IP-1 in a concentration-dependent manner, the latter being more resistant to the drug. The inhibitory effect of jasplakinolide on the growth of E. histolytica trophozoites was reversed by removal of the drug after exposure to 1 microM for 1 day. Encystation of E. invadens as induced in vitro was also inhibited by jasplakinolide. Trophozoites exposed to jasplakinolide in encystation medium for 1 day did not encyst after removal of the drug, whereas those exposed to the drug in growth medium for 7 days did encyst without the drug. The process of cyst maturation was unaffected by jasplakinolide. Large round structures were formed in trophozoites of both amoebae grown with jasplakinolide; these were identified as F-actin aggregates by staining with fluorescent phalloidin. Accumulation in trophozoites of both amoebae of actin aggregates was observed after culture in jasplakinolide. Also, E. invadens cysts formed from trophozoites treated with jasplakinolide contained the actin aggregate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis revealed that the jasplakinolide treatment led to an increase in the proportion of F-actin associated with formation of the aggregate. The results suggest that aggregates are formed from the cortical flow of F-actin filaments, and that these filaments would normally be depolymerized but are artificially stabilized by jasplakinolide binding.

Genetic Variation among Human Isolates of Uninucleated Cyst-Producing Entamoeba Species

Twelve human infections with Entamoeba spp. producing uninucleated cysts were studied. DNA was extracted from infected feces and used to amplify part of the ameba small-subunit rRNA gene. Sequence analysis identified four distinct types of Entamoeba, all of which are related to Entamoeba polecki and E. chattoni and two of which have not been reported previously. Whether these genetic types represent different species is unclear. We propose that the agent of all human infections with uninucleated cyst-producing Entamoeba species be reported as "E. polecki-like."

The cell cycle of Entamoeba invadens during vegetative growth and differentiation

The cell division cycle of Entamoeba invadens was studied during vegetative growth of trophozoites and during their differentiation into cysts. During vegetative growth of trophozoites, it was observed that DNA synthesis typically continued after one genome content had been duplicated. During encystation, DNA synthesis was arrested after 4n genome content had been synthesised. Using multi-parameter flow cytometry, the light scattering properties of cysts and trophozoites were studied. The cytoplasmic granularity, reflected by the side scatter of light, was proportional to DNA content of trophozoites, whereas cysts with similar DNA contents showed heterogeneity in their cytoplasmic granularity. Dynamic changes in the intracellular calcium pools were observed during differentiation of trophozoites to cysts. Comparison of E. invadens and Entamoeba histolytica cell cycles suggest that both organisms may have similar regulatory processes during cell division and differentiation. Since E. histolytica cannot be induced to encyst in axenic culture, analysis of the E. invadens cell cycle during encystation may be useful for identifying homologous processes in E.histolytica.

A role for a galactose lectin and its ligands during encystment of Entamoeba

In the life cycle of Entamoeba parasites alternate between the colon-dwelling trophozoite and the infectious cyst forms. The physiologic stimuli that trigger differentiation of trophozoites into cysts remain undefined. On the surface of the human-infecting Entamoeba, parasites express a galactose/N-acetylgatactosamine (gal/galNAc)-binding lectin, which plays demonstrated roles in contact-dependent lysis of target cells and resistance to host complement. Using a reptilian parasite, Entamoeba invadens, to study cyst formation in vitro, we found that efficient encystation was dependent on the presence of gal-terminated ligands in the induction medium. Precise concentration ranges of several gal-terminated ligands, such as asialofetuin, gal-bovine serum albumin (gal-BSA), and mucin, functioned in encystation medium to stimulate differentiation. Greater than 10 mM levels of free gal inhibited the amoeba aggregation that precedes encystation and prevented formation of mature cysts. Inhibitory levels of gal also prevented the up-regulation of genes which normally occurs at 24 h of encystation. The surface of Entamoeba invadens was found to express a gal lectin which has a heterodimeric structure similar to that of Entamoeba histolytica. The 30 kDa light subunit (LGL) of the E. invadens lectin is similar in overall size and sequence to the LGL of E. histolytica. The heavy subunits, however, differ in size, have an identical spacing of cysteines in their extracellular domains, and have highly conserved C-terminal transmembrane and cytoplasmic domains. These results suggest a new role for the Entamoeba gal lectins in monitoring the concentrations of gal ligands in the colon and contributing to stimuli that induce encystment.

Effect of the antitubulin drug oryzalin on the encystation of Entamoeba invadens

We have recently demonstrated that the antimicrotubule drug oryzalin inhibits the growth of Entamoeba invadens as well as E. histolytica, the former being more resistant to the drug than the latter, and that effective doses of oryzalin are higher for Entamoeba than for the other parasitic protozoa examined thus far. The aim of the present study was to examine the effect of oryzalin on the encystation of E. invadens using an axenic encystation system in vitro. Oryzalin inhibited the encystation of E. invadens strain IP-1 in a dose-dependent manner. The addition of oryzalin after the induction of encystation was also inhibitory for encystation and cyst maturation. Trophozoites incubated for 1 day in encystation medium with oryzalin did not encyst after removal of the drug. Although trophozoites grown in the presence of 300 microM oryzalin for 2 days did not encyst after their transfer to encystation medium containing the same concentration of drug, a number of trophozoites survived for at least 3 days. In contrast, trophozoites grown in the absence of oryzalin neither survived nor encysted after their transfer to encystation medium supplemented with the drug, which suggests that pretreatment of trophozoites with oryzalin contributes to their continued survival as trophozoites, i.e., without their transforming into cysts, in encystation medium. Trophozoites grown with oryzalin did encyst after their transfer to encystation medium without the drug. Accumulation of trophozoites in the mitotic phase was observed after culture with oryzalin. When cysts prepared at day 1 of encystation, most of which were mononucleate, were reincubated in the presence of oryzalin for an additional 2 days, inhibition of their maturation was observed. Thus, oryzalin is a potent mitotic-phase inhibitor of E. invadens and may become a useful tool for studies on the relationship between the cell cycle and encystation of this parasite.

Effect of cytochalasin D on the growth, encystation, and multinucleation of Entamoeba invadens

The effect of cytochalasin D, a specific inhibitor of microfilaments, on the growth, encystation, and multinucleation of Entamoeba invadens was examined. Cytochalasin D blocked the growth of axenic E. invadens strain IP-1 in a dose-dependent manner, which suggests that the drug is effective against this species of Entamoeba as well as against E. histolytica strain HM1: IMSS as previously demonstrated. Encystation of E. invadens as induced in vitro was also inhibited by cytochalasin D. This is the first evidence of the participation of microfilaments in the encystation process. Concentrations of cytochalasin D effective for the inhibition of encystation were lower than those effective for the inhibition of growth. Trophozoites grown with cytochalasin D became multinucleate; more than three nuclei per cell were observed in 71% of trophozoites grown in the presence of the drug as opposed to only 5% of those grown in the absence of the drug. Also, trophozoites grown with cytochalasin D produced multinucleate cysts following their transfer to encystation medium. Encystation with cytochalasin D was more strongly inhibited among trophozoites grown in the presence of the drug than among those grown in the absence of the drug. Also, encystation without cytochalasin D was less frequently observed among trophozoites grown in the presence of the drug than among those grown in the absence of the drug. Thus, the multinucleation of trophozoites induced by cytochalasin D had an inhibitory effect on their encystation.

Effect of dinitroaniline herbicides on the growth of Entamoeba histolytica

The effect of the dinitroaniline herbicides oryzalin and trifluralin on the growth of Entamoeba histolytica was examined. Oryzalin inhibited the growth of E. histolytica strain HM-1:IMSS. Trifluralin was less effective than oryzalin for this parasite. Entamoeba histolytica was more resistant to these dinitroanilines than other parasitic protozoa examined so far, including Leishmania spp., Trypanosoma brucei, Plasmodium falciparum, Toxoplasma gondii, and Cryptosporidium parvum. Colchicine, a potent microtubule inhibitor of animal cells, was much less effective for E. histolytica, even at very high concentrations. A reptilian parasite, Entamoeba invadens strain IP-1, examined for comparison, was more resistant to these dinitroanilines than E. histolytica. Accumulation of E. histolytica trophozoites in mitosis was observed after culture in 100 microM oryzalin. The inhibitory effect of oryzalin on the growth of E. histolytica trophozoites was abrogated by removal of the drug after exposure to 100 microM for 2 days. In parallel to the recovery of growth after removal of the drug, the percentage of trophozoites in mitosis was reduced to a normal level. The results indicate that treatment of trophozoites with oryzalin arrests mitosis and that its effect is reversible. Therefore, oryzalin is a useful tool for studies relating to the cell cycle of this parasite.

Differentiation of Entamoeba histolytica and Entamoeba dispar cysts using polymerase chain reaction on DNA isolated from faeces with spin columns

Since Entamoeba histolytica and Entamoeba dispar were formally recognized as two different species at the World Health Organization (WHO)/Pan American Health Organization (PAHO)/United Nations Educational, Scientific and Cultural Organization (UNESCO) meeting in Mexico City in 1997, the specific differentiation of the two morphologically identical species would seem relevant in clinical diagnosis. Several polymerase chain reaction (PCR)-based methods have been described and used successfully, but methods for DNA isolation from cysts in stool samples are time-consuming and problematic due to inhibitory factors in faeces. The use of the slightly modified QIAamp tissue method (Qiagen, Germany) for DNA isolation was evaluated in 657 unpreserved faecal samples from cases of suspected Entamoeba histolytica/Entamoeba dispar infection. In only 1.7% of the cases was PCR hampered by inhibitors present in the faeces. The DNA isolation procedure was found to be rapid, simple and one that could easily be implemented in a routine diagnostic setting. In 98.8% of Entamoeba histolytica/Entamoeba dispar cyst-positive faecal samples, the true identity of the cysts could be determined using PCR specific for Entamoeba histolytica and Entamoeba dispar, respectively.

[Studies on the continuous culture and pathogenicity of Entamoeba gingivalis]

OBJECTIVE

To establish a method for continuous culture of Entamoeba gingivalis (E. g.) and study the pathogenicity of E. g..

METHODS

The culture conditions of E. g. were compared by observing its growth and reproduction. The pathogenicity of E. g. was studied by investigating its infection rate in humans and observing the relationship between E. g. infection and periodontal abscess in rats and the in vitro effect of some drugs.

RESULTS

The optimal culture condition of E. g. was modified LES medium containing Locke's solution with 20% bovine serum, penicillin, streptomycin and rice starch. Reproduction of E. g. peaked at the fourth day of incubatoin, E. g. could live continuously for 120 to 168 h. The infection rate of E. g. was higher in patients with periondontal diseases than in healthy groups. The animal test showed that E. g. could cause periondontal abscess in rats. The levels of acid phosphatase and MDA were higher in patients with E. g.-positive periondontal disease than in healthy individuals. Metronidazole and SBF are effective against E. g..

CONCLUSION

E. g. could grow very well in modified LES medium, and cause periondontal abscess in patients with low immunity.

Appearance of a stage-specific immunodominant glycoprotein in encysting Entamoeba invadens

The appearance of cyst-specific proteins in encysting Entamoeba invadens and their immunogenicity were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting using an axenic encystation system in vitro. A rabbit antiserum against trophozoites of E. invadens reacted with a number of proteins of cysts after 1-4 days of incubation. Thus, a number of cyst proteins remained antigenically unchanged as common antigens of the two forms after transformation from trophozoites to cysts. A rabbit antiserum against cysts also reacted with the trophozoite proteins as well as the cyst proteins. The most interesting result was that the rabbit anticyst serum reacted predominantly with an 88-kDa protein of cysts after 1 day of incubation. The 88-kDa protein reacted with the anticyst serum absorbed with trophozoite proteins and was thus cyst-specific. The reactivity of the 88-kDa protein of cysts with the absorbed anticyst serum decreased as encystation proceeded. When soluble and particulate fractions prepared from cysts after 1 day of incubation were examined by electrophoresis and immunoblotting, the 88-kDa protein that had reacted with the absorbed anticyst serum was found to be present in the particulate fraction, which was rich in cell-wall fragments, and stained with periodic acid-Schiff's reagent, indicating that it is a glycoprotein. The results indicate that encystation is accompanied by appearance of the cyst-specific 88-kDa glycoprotein, which is immunodominant and most abundantly expressed in cysts after 1 day of incubation and appears to be associated with the cyst wall.