Proteinases resistant to sodium dodecyl sulfate-induced autoproteolysis of Entamoeba histolytica HK9 trophozoites

Amebic cysteine proteinase 2 (EhCP2) plays either a minor or no role in tissue damage in acute experimental amebic liver abscess in hamsters

Amebic cysteine protease 2 (EhCP2) was purified from ethyl ether extracts of axenically grown trophozoites of Entamoeba histolytica strain HM1-IMSS. The purification procedure involved molecular filtration and electroelution. Sequence analysis of the purified product revealed EhCP2 and ubiquitin(s). Electrophoretic migration patterns, isoelectric point determination and Western blot studies failed to reveal other EhCP molecules. Polyclonal antibodies against the purified EhCP2 prepared in rabbits either stabilized or enhanced the enzyme activity in a dose-response manner. Purified EhCP2 was enclosed within inert resin microspheres (22-44 microm in diameter) and injected into the portal vein of normal hamsters. In the liver, the microspheres caused mild acute inflammation and occasional minimal necrosis of short duration. Sections of the liver were immunohistochemically stained with the anti-EhCP2 antibody and the microspheres were positive for only a very short period (1 h) after injection. Sections of experimental acute (1 day, 5 days) amebic liver abscess produced in hamsters were also stained with the anti-EhCP2 antibody; and amebas were intensely positive but no staining was observed at any time in the surrounding necrotic structures. It is suggested that EhCP2 plays either a minor or no role in the causation of tissue damage in experimental acute liver amebiasis.

Immunodulation of rat serum and mucosal antibody responses to Entamoeba histolytica trophozoites by beta-1,3-glucan and cholera toxin

Systemic and mucosal and immune responses can be manipulated with immunomodulators. Here we show the modulatory effects of cholera toxin (CT) and beta-1,3-glucan (GLU) on the rat antiamebic serum and fecal antibody responses to one or four intraperitoneal (IP) or intragastric (IG) doses of glutaraldehyde-fixed Entamoeba histolytica trophozoites (GFT). One IP dose of GFT maximized serum IgM and IgG antiamebic antibodies on days 4 and 9, respectively; CT coadministration increased IgM antibodies, whereas IgG titers increased with CT or GLU; coproantibodies were undetectable after GFT alone or coadministered with GLU, whereas CT coadministration maximized fecal IgA antibodies on day 6. One IG dose of GFT alone increased serum IgM and IgG antibodies 2.5 times and no further increases were detected using GLU, whereas CT doubled serum IgG antibodies; GFT did not affect the coproantibody responses, whereas GLU coadministration maximized IgG coproantibody levels on day 6 and CT increased IgG and IgA coproantibody levels on the same day. On the other hand, four IG doses of GFT alone or with GLU induced tolerance, whereas GFT alone via the IP route increased serum antibodies slightly and GLU coadministration increased serum IgG antibody titers 300-fold. CT coadministration by both routes increased IgA coproantibodies, and simultaneous CT+GLU coadministration induced lower responses than either CT or GLU. Different antiamebic immune responses might therefore be attained through the use of different immunization routes and immunomodulators to induce protective immunity against intestinal or extraintestinal amebiasis.

Electron probe analysis and biochemical characterization of electron-dense granules secreted by Entamoeba histolytica

The interaction of Entamoeba histolytica with collagen induces the intracellular formation and release of electron-dense granules (EDGs) containing collagenase activity which are important in the pathogenicity of this parasite. Purified EDGs contain at least 25 polypeptides with acidic pIs, nine gelatinase activities, small molecules, including inorganic phosphate (Pi), pyrophosphate (PP) and other elements, including Na, Mg, S, Cl, K, Ca and Fe as measured by scanning transmission electron microscopy. Six of these polypeptides with apparent molecular weights of 108, 106, 104, 97, 68 and 59 kDa and two protease activities with apparent molecular weights of 40 and 85 kDa were detected exclusively in the EDGs and were not observed in total trophozoite extracts. Actin was also detected in the EDGs. Therefore, EDGs are a complex of mainly cationic proteins, which contains numerous proteolytic activities, actin and small molecules such as P(i), PP and cations.

Intragastric immunization of rats with Entamoeba histolytica trophozoites induces cecal mucosal IgE, eosinophilic infiltration, and type I hypersensitivity

We have investigated the role of IgE in the local immunity of intestinal amebiasis, a parasitic infection known to induce specific antibody-forming cells (AFC) and IgA antibodies in rodents and humans. We found that intragastric immunization of rats with glutaraldehyde-fixed Entamoeba histolytica trophozoites significantly increased antiameba AFC in the Peyer's patches and spleen and that the lamina propria of the cecum from immunized animals was infiltrated by eosinophils armed with IgE antibodies. Morphometric analysis showed that IgE-containing cells and eosinophils were nearly three times more abundant in the cecum of immunized rats. Antigenic challenge with amebal lysates provoked an increase in the short-circuit current and in the transepithelial potential difference in Ussing-chambered cecum preparations from immunized rats. Although eosinophilia and the increase of IgE are common consequences of infection by parasitic worms, our results indicate that local immunity in intestinal amebiasis also involves IgE deposition, eosinophil infiltration, and type I hypersensitivity, which may explain some symptoms of amebic dysentery such as colic, abdominal tension, tenesmus, and bloody stools.