An Entamoeba histolytica antigen devoid of enzymatic activity, but endowed with immunogenic and protective properties

One of the most relevant features of Entamoeba histolytica extracts is their great enzymatic activity. The consequence of this peculiarity is that these extracts digest not only extrinsic proteins but also those within the parasite, causing instability during extract preparation which makes their characterization more difficult and hinders their use in immunoprophylaxis. This report presents evidence which indicates that treatment of E. histolytica extracts with a pH2 acid shock for 30 min at 37 degrees C irreversibly, as shown through its reactivity with polyclonal E. histolytica antisera and through its capacity to induce antibody formation and to protect against intrahepatic challenge with E. histolytica. Among the foremost activities in the field of immunoparasitology are the identification, isolation, purification and characterization of parasite antigens, particularly because of their potential use in immunoprophylaxis. Given the world wide distribution of amebiasis, particularly in undeveloped countries, various researchers have given special importance to the antigenic characterization of the causal agent, Entamoeba histolytica, and to its ability to induce protective immunity in several animal models. Initial studies demonstrated that the parasite produces a variety of proteolytic enzymes which play an important role in the immune response and pathogenesis of the infected host. Additionally, these enzymes cause autodegradation of the amebic extracts, their use in immunoprophylaxis, since proteins germane in inducing protection could be degraded. Even though enzymatic activity may be abolished through specific inhibitors, these are very toxic and therefore not adequate for biological material to be tried on humans.(ABSTRACT TRUNCATED AT 250 WORDS)