Novel hemagglutinating, hemolytic and cytotoxic activities of the intermediate subunit of Entamoeba histolytica lectin

Entamoeba histolytica: Membrane and Non-Membrane Protein Structure, Function, Immune Response Interaction, and Vaccine Development

Entamoeba histolytica is a protozoan parasite that is the causative agent of amoebiasis. This parasite has caused widespread infection in India, Africa, Mexico, and Central and South America, and results in 100,000 deaths yearly. An immune response is a body's mechanism for eradicating and fighting against substances it sees as harmful or foreign. E. histolytica biological membranes are considered foreign and immunogenic to the human body, thereby initiating the body's immune responses. Understanding immune response and antigen interaction are essential for vaccine development. Thus, this review aims to identify and understand the protein structure, function, and interaction of the biological membrane with the immune response, which could contribute to vaccine development. Furthermore, the current trend of vaccine development studies to combat amoebiasis is also reviewed.

Identification of Multiple Domains of Entamoeba histolytica Intermediate Subunit Lectin-1 with Hemolytic and Cytotoxic Activities

Galactose and N-acetyl-D-galactosamine-inhibitable lectin of Entamoeba histolytica have roles in the pathogenicity of intestinal amoebiasis. Igl1, the intermediate subunit lectin-1 of E. histolytica, has been shown to have both hemolytic and cytotoxic activities that reside in the C-terminus of the protein. To identify the amino acid regions responsible for these activities, recombinant proteins were prepared and used in hemolytic and cytotoxic assays. The results revealed that Igl1 has multiple domains with hemolytic and cytotoxic activities and that amino acids 787-846, 968-1028 and 1029-1088 are involved in these activities. The hemolytic activities of the fragments were partly inhibited by mannose, galactose and N-acetylgalactosamine, and glucose showed lower or negligible inhibitory effects for the activities. This is the first report of a protozoan protein with hemolytic and cytotoxic activities in multiple domains.

Production of a monoclonal antibody against a galactose-binding protein of Acanthamoeba castellanii and its cytotoxicity

In this study, it was confirmed whether the galactose-binding protein (GBP) was present in Acanthamoeba castellanii, and its function on a target cell was confirmed by production of an antibody against the GBP. Since the genes for GBP have not yet been identified at all, the purification of GBP was done using galactose-beads from amoebial lysates, and monoclonal antibodies were produced using cell fusion. GBP was confirmed to have a size of about 35 kDa. After the third immunization with purified GBP in BALB/c mice, monoclonal antibody production was analyzed. The clone cultured before limiting dilution was named 2AB2 and showed the highest antibody titer in the culture supernatant of a 24-well plate. AF6 clone cultured after limiting dilution showed an antibody titer of 0.259 in a 75-T flask. Antibodies generated by collecting ascites by injecting monoclonal colonies into the abdominal cavity of mice were confirmed through gel analysis and were observed to belong to the isotype of the IgM having kappa chains. Since the cytotoxicity of A. castellanii was inhibited by about 26% by the monoclonal antibody against GBP, it was confirmed that the antibody against GBP had an inhibitory effect on cytotoxicity. This study was the first report on GBP isolated and purified from A. castellanii, and similarly to a mannose-binding protein (MBP), its involvement in contact-dependent cytotoxicity was demonstrated with monoclonal antibody production.

Development of a sensitive immunochromatographic kit using fluorescent silica nanoparticles for rapid serodiagnosis of amebiasis

We have previously shown that the C-terminal region of the intermediate subunit of Entamoeba histolytica galactose- and N-acetyl-D-galactosamine-inhibitable lectin (C-Igl) is a useful antigen for serodiagnosis of amebiasis. An immunochromatographic kit was developed using fluorescent silica nanoparticles coated with C-Igl prepared in Escherichia coli. Samples for examination were added to the freeze-dried particles and then applied to the immunochromatographic device, in which a test line on the membrane was also coated with C-Igl. Fluorescent intensity was measured using a hand-held reader. In an evaluation of the kit using a human monoclonal antibody, the minimum amount of C-Igl specific antibody showing positive results was 100 pg. In the evaluation of serum samples with different antibody titers in indirect immunofluorescent antibody tests in the kit, 20 µL of serum was sufficient to obtain positive results at 30 min. Serum samples from symptomatic patients with amebic colitis and amebic liver abscess and those from asymptomatic E. histolytica-cyst carriers showed positive results in the kit. Based on evaluation using sera from healthy controls and patients with other infectious diseases, the sensitivity and specificity of the kit were 100 and 97.6%, respectively. Therefore, we conclude that the newly developed kit is useful for rapid serodiagnosis of amebiasis.

Comparison of hemolytic activity of the intermediate subunit of Entamoeba histolytica and Entamoeba dispar lectins

Galactose and N-acetyl-D-galactosamine-inhibitable lectin of Entamoeba histolytica has roles in pathogenicity and induction of protective immunity in rodent models of amoebiasis. Recently, the intermediate subunit of the lectin, Igl1, of E. histolytica has been shown to have hemolytic activity. However, the corresponding lectin is also expressed in a non-virulent species, Entamoeba dispar, and another subunit, Igl2, is expressed in the protozoa. Therefore, in this study, we compared the activities of Igl1 and Igl2 subunits from E. histolytica and E. dispar using various regions of recombinant Igl proteins expressed in Escherichia coli. The recombinant E. dispar Igl proteins had comparable hemolytic activities with those of E. histolytica Igl proteins. Furthermore, Igl1 gene-silenced E. histolytica trophozoites showed less hemolytic activity compared with vector-transfected trophozoites, indicating that the expression level of Igl1 protein influences the activity. These results suggest that the lower hemolytic activity in E. dispar compared with E. histolytica reflects the lower expression level of Igl1 in the E. dispar parasite.