Production and characterization of monoclonal antibodies against a highly immunogenic fraction of Entamoeba histolytica (NIH:200) and their application in the detection of current amoebic infection

A monoclonal antibody against a Leishmania mexicana COX-like enzymatic activity also recognizes similar proteins in different protozoa of clinical importance

In Leishmania mexicana, the protease gp63 has been documented as the protein responsible for cyclooxygenase (COX) activity. The present work aimed to obtain a monoclonal antibody capable of recognizing this protein without blocking the COX-like enzymatic activity. The antibody produced by the selected hybridoma was named D12 mAb. The antigen recognized by the D12 mAb was characterized by the determination of COX activity associated with immune complexes in the presence of exogenous arachidonic acid (AA) using the commercial Activity Assay Abcam kit. LSM-SMS analysis validated the identity of the antigen associated with the D12 mAb as the L. mexicana protease gp63. Confocal microscopy assays with the D12 mAb detected, by cross-recognition, similar proteins in other protozoan parasites. COX-like molecules are located in vesicular structures, homogeneously distributed throughout the cytoplasm in amastigotes (intracellular infectious phase) and promastigotes of L. mexicana, and trophozoites of Entamoeba histolytica, Acanthamoeba castellanii, and Naegleria fowleri. However, in Giardia duodenalis trophozoites, the distribution of the COX-like molecule was also in perinuclear areas. In comparison, in Trypanosoma cruzi trypomastigotes, the distribution was mainly observed in the plasma membrane. Structural analyses of COX-2-like antigens revealed continuous and discontinuous epitopes for B cells, which could be relevant in the cross-reaction of D12 mAb with the analyzed parasites. These results indicate that the D12 mAb against the L. mexicana gp63 also recognizes a COX-like molecule in several protozoan parasites, suggesting that this D12 mAb could potentially be used in combined therapies against infectious diseases.

The 29-kilodalton thiol-dependent peroxidase of Entamoeba histolytica is a factor involved in pathogenesis and survival of the parasite during oxidative stress

The 29-kDa surface antigen (thiol-dependent peroxidase; Eh29) of Entamoeba histolytica exhibits peroxidative and protective antioxidant activities. During tissue invasion, the trophozoites are exposed to oxidative stress and need to deal with highly toxic reactive oxygen species (ROS). In this investigation, attempts have been made to understand the role of the 29-kDa peroxidase gene in parasite survival and pathogenesis. Inhibition of eh29 gene expression by antisense RNA technology has shown approximately 55% inhibition in eh29 expression, maximum ROS accumulation, and significantly lower viability in 29-kDa downregulated trophozoites during oxidative stress. The cytopathic and cytotoxic activities were also found to decrease effectively in the 29-kDa downregulated trophozoites. Size of liver abscesses was substantially lower in hamsters inoculated with 29-kDa downregulated trophozoites compared to the normal HM1:IMSS. These findings clearly suggest that the 29-kDa protein of E. histolytica has a role in both survival of trophozoites in the presence of ROS and pathogenesis of amoebiasis.

Genes induced by a high-oxygen environment in Entamoeba histolytica

Entamoeba histolytica, although a microaerophilic protozoan parasite, encounters a high-oxygen environment, during invasive amoebiasis. The parasite requires specific regulation of certain proteins to maintain its physiological functions to survive in the more oxygenated condition. Our endeavor was to know how does amoeba adapt itself in a high-oxygen environment. Reactive oxygen species (ROS) was found to accumulate in an increasing concentration within the stressed trophozoites in a time-dependent manner. Increased cytopathic activity was detected at 2h in high-oxygen-exposed E. histolytica lysate compared to lysate of normal E. histolytica trophozoites by Ussing chamber assay. The differential display and semi-quantitative polymerase chain reaction showed overexpression in the mRNA levels of thiol-dependent peroxidase (Eh29), superoxide dismutase (SOD), EhCP5, G protein, HSP70, and peptidylprolyl isomerase at different time periods of oxidative stressed trophozoites compared to normally cultured E. histolytica. Analyses of the up-regulated genes that are associated with stress response, viz., signal transduction, tissue destruction, and oxidative stress management, including enhanced expression of a 29-kDa Eh29, suggest that this organism has several protective mechanisms to deal with oxidative stress during invasion.

Entamoeba histolytica: monoclonal antibody against the beta1 integrin-like molecule (140 kDa) inhibits cell adhesion to extracellular matrix components

We describe a monoclonal antibody (3C10) against the beta1 integrin-like molecule which immunoprecipitates two polypeptides of 140 and 155 kDa from detergent-soluble extract of Entamoeba histolytica. The 140-kDa polypeptide has been described as a beta subunit of the amoebic fibronectin receptor as it is recognized by an anti-integrin beta1 (human) monoclonal antibody in immunoblot assay. The receptor molecules were localized with the 3C10 monoclonal antibody in intracellular and surface membranes of E. histolytica trophozoites by immunofluorescence and immunogold labeling methods. Significant inhibitions of cell adhesion on extracellular matrix proteins such as fibronectin (56%) (P < 0.001) and collagen (50%) (P < 0.001) and partial inhibition on laminin (23%) (P > 0.1) were achieved by the monoclonal antibody.

PCR detection of Giardia lamblia in stool: targeting intergenic spacer region of multicopy rRNA gene

A PCR based detection that amplifies the 552-bp intergenic spacer (IGS) region of multicopy rRNA gene of Giardia lamblia and 320-bp internal sequences to first PCR product has been used in diagnosis of giardiasis in stool sample. The primers were found highly specific to Giardia spp. only, because no amplification was observed with DNAs from other enteric pathogens like Escherichia coli, Shigella dysenteriae and Entamoeba histolytica. The test could detect even less than 2 pg of genomic DNA from Giardia trophozoites. In direct diagnosis of Giardia lamblia in stool samples, it was observed that PCR amplification of IGS followed by nested PCR could enhance the sensitivity and specificity of the tests manifold and the system was able to detect as low as 10 parasites in 100 microl of stool. The comparative evaluation of the present system with conventional microscopy, CIEP and ELISA in the diagnosis of giardiasis from diarrhoeic stool samples and control subjects demonstrated a 100% correlation among nested PCR, microscopic examination and ELISA in patients suggestive of giardiasis (Group I) and control subjects (Group II). In Group I cases (patients suffering from other than giardiasis), CIEP, ELISA and nested PCR showed better results than microscopic examination. However, among them, PCR was found most sensitive and specific because 20% positivity was noticed by PCR whereas CIEP and ELISA showed only 7.14% and 12.85%, respectively. Break-up results showed that all the samples which were positive by CIEP or ELISA, also found positive by PCR. The present observation clearly suggests the use of PCR that amplifies the intergenic spacer region of multicopy rRNA gene of Giardia lamblia followed by nested PCR for routine, quick and reliable detection of Giardia lamblia in stool samples.

Antigens of diagnostic and prophylactic importance inEntamoeba histolytica

Amoebiasis, caused by an enteric protozoanEntamoeba histolytica, is one of the major parasitic diseases of mankind. Current estimate suggests that the parasite infects about 10% of the world population at any given time. There is an urgent need to characterize the antigenic molecules ofE. histolytica, and find out antigens which have both immunodiagnostic and prophylactic potential against amoebiasis. The results of somatic antigen analysis, using sera from immune or infected individuals, indicated that the wholeE. histolytica trophozoites, are highly complex and heterogeneous in nature and both immunodiagnostic and immuno prophylaxis activity remain mainly in a surface associated 29 kDa glycoprotein ofE. histolytica. Future studies at molecular level particularly, genes responsible for expression of this protein, their homology with other proteins and structure analysis will give better understanding about this polypeptide. Studies on excretory secretory antigens, clearly demonstrated thatE. histolytica like many organisms, also liberates certain antigenic moieties into the culture medium during in vitro cultivation and this antigen has similar diagnostic values like the conventional somatic antigens. It is important that the ESA should be prepared from the supernatant after collecting the cell and use for immunodiagnosis of amoebiasis. This is an additional source of antigen which will help in carrying out more tests using the same reagents. Further studies are needed to clarify the location of these molecules on the parasite, along with detailed biochemical and immunological characterization and their relation with the pathogenesis.

Differentiation of Entamoeba histolytica and Entamoeba dispar in cyst-passers by immunoblot

Differentiation of invasive strains of Entamoeba histolytica according to their pathogenicity has been a topic of long debate, but now the pathogenic species only is regarded as E. histolytica while the non pathogenic species is E. dispar. The present study applied immunoblot to differentiate infections of the two species among microscopically-detected cyst-passers in Korea. The crude extract of E. histolytica separated in 5.20% gradient gels, revealed many fractions of 94, 81, 71, 50, 44, 38.5, 37.5, 29, 19, and 18 kDa when the cysteine proteinase inhibitor, E64, was supplemented. The scrum IgG antibody of 3 proven E, histolytica cases reacted with the antigenic fractions of 117, 110, 99, 68, 66, 60, 54, 52, 46, and 45 kDa. Sera of PCR confirmed 3 cases of E. dispar reacted only to the 117 kDa fraction of the E. histolytica crude extract which was regarded as non-specific. To the antigen of monoxenic E. dispar, sera of E. dispar and E. histolytica cases showed the same immunoblot reactions. The serum IgA antibody reacted with several antigenic fractions of both E. histolytica and E. dispar, but IgM and IgE antibodies showed no reaction to either antigen. Sera of 24 symptomless amebic cyst passers were screened with the E. histolytica antigen; two were found to be infected by E. histolytica and 22 were by E. dispar. The present findings suggest that in Korea most of asymptomatic cyst passers of E. histolytica are carriers of E. dispar. Immunoblot using E. histolytica antigen is a good technique for the differentiation of E. histolytica and E. dispar infections.

Entamoeba histolytica: fecal antigen capture immunoassay for the diagnosis of enteric amebiasis by a monoclonal antibody

Amebiasis continues to be of epidemiological importance in underdeveloped countries. Clinical diagnosis and epidemiological setting in a region are based on the fecal microscopic identification of cysts or trophozoites. This procedure requires well trained personnel, is laborious, of low sensitivity and frequently yields false-positives results. The present study was designed to develop an immunoenzymatic fecal 96 kDa antigen capture test (COPROELISA-Eh) more sensitive and specific than microscopic diagnosis of amebiasis. Triplicates of 177 stool samples processed by the formol-ether concentration method, were defined as positive or negative by three experienced microscopic observers. Another aliquot was submitted to the antigen capture test by a monoclonal antibody against a specific membrane antigen of pathogenic strains of Entamoeba histolytica. Optical densities were interpreted as positive when they exceeded the mean value of negative samples plus two standard deviations. COPROELISA-Eh showed a 94.4% sensitivity, 98.3% specificity, 96.2% positive predictive value and 97.6% negative predictive value for the detection of E. histolytica in feces. COPROELISA-Eh is more sensitive and specific than microscopic examination, does not require specially trained personnel and allows the simultaneous processing of a large number of samples.