The peripheral vesicles gather multivesicular bodies with different behavior during the Giardia intestinalis life cycle.

Giardia intestinalis presents an intriguing endomembrane system, which includes endoplasmic reticulum and peripheral vesicles (PVs). The PVs have previously been considered to be organelles that display early and late endosomal and lysosomal properties. Some of these vesicles accumulate macromolecules ingested by the protozoan and show acid phosphatase activity. It has been previously shown that the parasite releases microvesicles, which contribute to giardiasis pathogenesis; however, the vesicles' origin and the way in which they are released by the parasite still remain unclear. In this study, we induced the parasites to encyst in vitro and analyzed these events using advanced electron microscopy techniques, including focused ion beam and electron microscopy tomography followed by three-dimensional reconstruction, in order to better understand protozoal multivesicular body (MVB) biogenesis. In addition, we performed an ultrastructural analysis of phosphatase activity during differentiation. We demonstrated that some vegetative trophozoites' PVs exhibited morphological characteristics of MVBs with a mean diameter of 50 nm, containing intraluminal vesicles (ILVs).