Appearance of a stage-specific immunodominant glycoprotein in encysting Entamoeba invadens

The appearance of cyst-specific proteins in encysting Entamoeba invadens an d their immunogenicity were examined by sodium dodecyl sulfate-polyacrylami de gel electrophoresis and immunoblotting using an axenic encystation syste m in vitro. A rabbit antiserum against trophozoites of E. invadens reacted with a number of proteins of cysts after 1-4 days of incubation. Thus, a nu mber of cyst proteins remained antigenically unchanged as common antigens o f the two forms after transformation from trophozoites to cysts. A rabbit a ntiserum against cysts also reacted with the trophozoite proteins as well a s the cyst proteins. The most interesting result was that the rabbit anticy st serum reacted predominantly with an 88-kDa protein of cysts after 1 day of incubation. The 88-kDa protein reacted with the anticyst serum absorbed with trophozoite proteins and was thus cyst-specific. The reactivity of the 88-kDa protein of cysts with the absorbed anticyst serum decreased as ency station proceeded. When soluble and particulate fractions prepared from cys ts after 1 day of incubation were examined by electrophoresis and immunoblo tting, the 88-kDa protein that had reacted with the absorbed anticyst serum was found to be present in the particulate fraction, which was rich in cel l-wall fragments, and stained with periodic acid-Schiff's reagent, indicati ng that it is a glycoprotein. The results indicate that encystation is acco mpanied by appearance of the cyst-specific 88-kDa glycoprotein, which is im munodominant and most abundantly expressed in cysts after 1 day of incubati on and appears to be associated with the cyst wall.