Immunosorbent Assay for Serodiagnosis of Invasive Amebiasis

An immunoscreening approach was used to isolate a strongly positive cDNA clone from an Entamoeba histo-lytica HK-9 cDNA expression library in the phage vector l ZAP-II. The 1.85-kb cDNA insert was found to be truncated and encoded the cysteine-rich, immunodominant domain of the antigenic 170-kDa subunit of the amebal galactose–N-acetylgalactosamine binding lectin. This domain was expressed as a glutathione S-trans-ferase fusion protein in Escherichia coli. Inclusion bodies of the recombinant protein were solubilized with Sarkosyl, and the protein was enriched from the crude bacterial extract by thiol-affinity chromatography. The recombinant protein was used to develop a rapid, sensitive, and specific avidin-biotin microtiter enzyme-linked immunosorbent assay (ELISA) for invasive amebiasis. Sera from 38 individuals suffering from invasive amebiasis, 12 individuals with noninvasive amebiasis, 44 individuals with other infections, and 27 healthy subjects were screened by the recombinant antigen-based ELISA. The sensitivity and specificity of the assay were 90.4 and 94.3%, respectively, which correlated well with those of an ELISA developed with crude amebal antigen (r 5 0.94; P < 0.0001), as well as with those of a commercially available serodiagnostic ELISA (r 5 0.92; P < 0.0001). Thus, the bacterially expressed recombinant lectin can replace the crude amebal extract as an antigen in the serodiagnosis of invasive amebiasis by using avidin-biotin microtiter ELISA. Human infection caused by the intestinal protozoan parasit