Antigenic variation in the intestinal parasite Giardia lamblia

Abstract

Giardia lamblia trophozoites undergo antigenic variation, whereone member of the Variant-specific Surface Protein (VSP)family is expressed on the surface of proliferating trophozoitesand periodically replaced by another one. Two main questionshave challenged researchers since antigenic switching wasdiscovered in Giardia: What are the mechanisms involved?How are they influenced by other cellular processes or by theenvironment? Two molecular mechanisms have beenproposed, both involving small non-coding RNAs. Here wepostulate that (a) chromatin remodeling, triggered byenvironmental factors, also plays an important role in selectingthe VSP that will be expressed and (b) the particular VSPstructure may not only protect the parasite in the small intestinebut also signal the need to exchange the existing VSP foranother.