Detection of Entamoeba histolytica antigen in stool samples by enzyme-linked immunosorbent assay using monoclonal antibodies

An enzyme-linked immunosorbent assay (ELISA), using monoclonal antibodies, was applied for the detection of Entamoeba histolytica antigen in stool samples obtained from 148 patients with gastrointestinal symptoms, and the results are compared with microscopic findings. Ninety nine positives by microscopy generally had high ELISA OD values. Ninety one stool samples of asymptomatic cyst passers were also investigated by ELISA, and most were found to be positive. Although false positives were observed in both symptomatic and asymptomatic cases, the ELISA appears to be useful for the detection of amoebic antigen(s). However, our results suggest that both immunological methods and microscopic examination are needed for an accurate diagnosis of intestinal amoebiasis.

ANALYSIS OF PATHOGENICITY OF ENTAMOEBA HISTOLYTICA BY POLYMERASE CHAIN REACTION / 中国寄生虫学与寄生虫病杂志

DNA from five isolates of Entamoeba histolytica were examined for their pathogenicity by polymerase chain reaction. Three isolates SH-3,SH-6,SH-8 were isolated from patients with acute amoebic dysentery, whereas SH-5 and SH-7 were isolated from asymptomatic cyst passers. Gel electrophoresis of PCR products showed that primers P11 , P12 for pathogenic strains could amplify genomic DNA extracted from SH-8 , and primers P13, P14 for non-pathogenic strains could amplify genomic DNA extracted from SH-3, SH-5, SH-6 and SH-7. Furthermore, zymodeme analysis and the reactivity of McAb 4G6, which recognizes the 30 kDa antigen of pathogenic E. histolytica indicated that only SH-8 was pathogenic, while the others were nonpathogenic. The results of the genotypic analysis by PCR were in accord with the phenotypic properties.It is suggested that there are differences in genomic DNA between pathogenic and non-pathogenic strains. PCR is a highly sensitive and specific method for genomic DNA analysis of E. histolytica.

Screening and Expression of Recombinant Human Monoclonal Antibody Fab Fragments Specific to Entamoeba histolytica / 中国寄生虫学与寄生虫病杂志

Objective To prepare recombinant human monoclonal antibody Fab fragments specific to the surface antigen of Entamoeba histolytica. Methods Total RNA was isolated from lymphocytes which were separated from an asymptomatic E. histolytica cyst carrier. The genes of IgG light chain and Fd region of heavy chain were amplified by a reverse transcriptase PCR and ligated with a plasmid vector. After the genes were introduced into Escherichia coli, the clones expressing Fab fragments specific to the surface antigen of E. histolytica were screened and the product was purified. Results Thirty thousand clones were screened and one of them was proved positive to the surface antigen of E. histolytica. Conclusion This study demonstrated that the bacterial system can be used to produce recombinant human monoclonal antibody Fab fragments specific to the surface antigen of E. histolytica and they may be applicable for the future diagnosis and treatment of the infection.