The median body of Giardia lamblia: an ultrastructural study.

Giardia lamblia is an intestinal parasite of several mammals. The most striking feature of Giardia is the presence of a complex and unique cytoskeleton, and among its components the median body (MB) is the least defined microtubular structure. In the present study, we used a technique that allowed the removal of the plasma membrane and observation of cytoskeletal structures by both routine scanning electron microscopy (SEM) and field emission high resolution SEM. This technique permitted new observations such as details and insights of the median bodies, not previously described or controversial in the literature. Light microscopy after Panotic staining, immunofluorescence microscopy using several antibodies, and thin sections were also used to better characterized the Giardia MB. The new observations concerning the median bodies were : (1) they are not one or two structures, but varied in number, shape and position ; (2) they were found in mitotic and interphasic trophozoites, in disagreement with previous works ; (3) they were present in about 80 % of the cells, and not in 50 % of the cells, as previously described ; (4) they could be connected either to the plasma membrane, to the adhesive disc, and caudal flagella, and thus they are not completely free in the cells, as published before ; (5) they can protrude the cell surface ; (6) their microtubules react with several anti-tubulin and -beta giardin antibodies. These observations add new data on the scarce literature and to this largely understudied cell structure.