Entamoeba histolytica is a protozoan parasite that can invade the intestinal mucosa. Infection induces production of secretory immunoglobulin A (SIgA) antibodies that can diminish the adhesion between E. histolytica trophozoites and epithelial cells in vitro and reduce the rate of new infections in children. SIgA antibodies produced by asymptomatic cyst carriers could play a protective role against the damage caused by E. histolytica. To identify membrane antigens capable of inducing SIgA response in E. histolytica cyst carriers, salivary SIgA antibodies were confronted with blotted plasma membrane proteins from amebae. A surface 115-kDa ameba protein was recognized by 62% of the human SIgA antibodies tested. The 115-kDa protein is not a mannose-containing glycoprotein and has no protease activity. Rabbit anti–115-kDa protein antibodies were capable of reducing erythrophagocytosis but were unable to protect culture cells from the cytopathic damage caused by E. histolytica. However, anti–115-kDa protein antibodies induced surface receptor redistribution.

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