Detection of Entamoeba histolytica antigens in stool in amebiasis.

BACKGROUND: Stool microscopy, the conventional method of diagnosing intestinal amebiasis, fails to detect Entamoeba histolytica in more than 30-40% of clinically suspected cases. Demonstration of parasite products in clinical specimens has been suggested as an alternative. However, the usefulness of demonstrating amebic antigen in the stools of clinical cases needs to be assessed. METHODS: A double-antibody sandwich enzyme linked immunosorbent assay (ELISA) using anti-trophozoite antibodies to capture E histolytica specific coproantigen(s) was carried out on stools obtained from 31 patients with microscopically confirmed non-dysenteric amebic colitis, 18 patients with intestinal parasites other than E histolytica and 41 apparently healthy subjects. RESULTS: The assay detected E histolytica specific coproantigen(s) in stools of 23 (74.2%) of 31 subjects with non-dysenteric amebic colitis, none of 18 with other parasitic infections and 1 (2.4%) of 41 apparently healthy subjects. CONCLUSION: Our results provide evidence for the presence of E histolytica specific coproantigen(s) in stool eluates from patients with amebic infection; this finding can be exploited for confirming ongoing amebic infection. However, the sensitivity of the assay needs to be improved by the use of relevant monospecific/monoclonal antibodies.

Isolation & immunochemical characterization of diagnostically relevant antigens of Echinococcus granulosus.

Two hydatid specific polypeptides with molecular masses of 8 kDa and 116 kDa have been successfully isolated from E. granulosus hydatid cyst fluid using affinity chromatography. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and western immunoblot analysis under reducing and denaturing conditions indicated the 116 kDa purified antigen to be a hetero-tetramer consisting of 45 kDa, 66 kDa, 75 kDa and 116 kDa subunits linked by disulphide bonds while the 8 kDa purified antigen was found to be a monomer polypeptide. Affinity purified 116 kDa molecule was heat-labile, sensitive to treatment with pronase, trypsin and pepsin and its immunoreactivity as assessed in enzyme linked immunosorbent assay remained unaltered on treatment with sodium metaperiodate. The affinity purified 8 kDa molecule was heat-stable, sensitive to proteolytic enzymes and also sodium metaperiodate oxidation. Lectin binding studies revealed that the 8 kDa molecule specifically bound Concanavalin A and Triticum vulgaris, and thus had varies; is directly proportional to-D-glucose and N-acetyl D-glucosamine sugar moieties. The immunoreactivity of both the antigens remained unaltered on treatment with lipase. However, biochemical estimation of total lipid content revealed the affinity purified 116 kDa antigen to contain 6.25 per cent total lipids suggesting it to be lipoproteinic in nature. The 8 kDa antigen had no detectable total lipids biochemically. All sera from patients confirmed to have hydatidosis recognised the 8 kDa and 116 kDa polypeptides. However, sera from seven subjects with other parasitic infections also recognised the 116 kDa antigen though not the 8 kDa antigen. The data suggested that the recognition of 8 kDa antigen of E. granulosus has potential for specific immunodiagnosis of hydatidosis.