Plasmalemmal modifications of Entamoeba histolytica in vivo.

We used electron microscopy to study Entamoeba histolytica trophyozoites in rectal and liver lesions. The amebal surface had bleblike structures. Also noted were subplasmalemmal vacuoles and plasmalemmal extensions generally similar to the "surface lysosome" and "trigger" previously described. We found on serial sections that the plasmalemmal extensions were dendritic complexes enfolding the membrane of the subplasmalemmal vacuole and extending to contact host tissue. We postulate that membrane-bound cytotoxic hydrolases enter the plasmalemmal extension via the translocation of the subplasmalemmal vacuole membrane and thus are available to act at contact sites. The small blebs may provide an alternate method for membrane-bound hydrolase activity.