Contact-dependent transfer of the galactose-specific lectin of Entamoeba histolytica to the lateral surface of enterocytes in culture.

In a study to investigate early interactions of Entamoeba histolytica with epithelial cell monolayers, we found that a monoclonal antibody (MAb), CD6, against an ameba surface antigen recognized the lateral surface of epithelial cells after coculture with trophozoites. Display of the CD6 antigen on the epithelial cells necessitated contact with active trophozoites. It was found neither at 4 degrees C, nor with prefixed trophozoites, nor with trophozoite-conditioned media, nor when a filter prevented direct contact. Monolayers exposed to amebic sonicates or detergent lysates showed random immunostaining. Access to the antigenic site was limited, as immunostaining occurred predominantly with subconfluent monolayers. CD6 epithelial cell binding was first observed after 5 min of coculture; trophozoite-mediated target cell lysis was not detected until 15 min following coculture. Epithelial cell immunostaining occurred with some other ameba-specific antibodies but not with MAbs raised against the 170-kDa subunit of the galactose-N-acetylgalactosamine (Gal/GalNAc)-specific lectin. The CD6 MAb as well as some other ameba-specific antibodies immunoprecipitated from trophozoite lysates the same bands as the MAbs against the cysteine-rich domain of the 170-kDa subunit of the Gal/GalNAc-specific lectin. Why the latter MAbs failed to stain epithelial cells in the vicinity of attached trophozoites is presently unknown. We concluded that E. histolytica trophozoites transferred the intact amebic Gal/GalNAc-specific lectin or a portion of it to the lateral surface of epithelial cells. This juxtacrine transfer preceded killing of target cells.