Correlative Microscopy on the Mechanism of Attachment of the Intestinal Protozoan, Giardia: Observations Using Immunofluorescence, Interference Reflection, Phase, and Video Microscopy Together with Tem and High-Resolution SEM.

Abstract

The intestinal protozoan Giardia has evolved a mechanism for adherence of trophozoites to the intestinal epithelium by means of a holdfast or attachment organelle called the ventral adhesion disc. The ventral adhesion disc is formed by a monolayer of microtubules bound to one another and to the ventral plasmalemma by cross links, and each microtubule has a dorsal ribbon-like extension, composed of giardin. These dorsal ribbons are cross-linked with one another, and project from each microtubule into the overlying cytoplasm (1, 2). The peripheral margin of the ventral disc is named the lateral crest. SEM and TEM studies have shown that the monolayer of microtubules forms an overlapping spiral, which externally is visible as a spiral ridge resembling the figure six. Using immunofluorescence, the ventral adhesion disc has been shown to contain contractile proteins distributed in the lateral crest which composes the peripheral margin of the disc (3). The presence of microtubules/contractile proteins and evidence for the adhesion disc attaching to the microvillous border of epithelial cells suggests a contractile mechanism for trophozoite attachment (4, 5).