Journal
CELLULAR MICROBIOLOGY
Volume 11, Issue 12, Pages 1706-1715Publisher
WILEY-BLACKWELL
DOI: 10.1111/j.1462-5822.2009.01367.x
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Funding
- National Council for Science and Technology (CONICET)
- National Agency for Advancement of Science and Technology (ANPCYT)
- Catholic University of Cordoba, Argentina
- Howard Hughes Medical Institute (HHMI) of the USA
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Giardia lamblia undergoes antigenic variation, both in vitro and within the intestines of infected individuals. Variant-specific surface proteins (VSPs) cover the entire surface of the trophozoites and are the main antigens recognized by the host. Only 1 of about 200 VSP genes encoded by the Giardia genome is expressed on the surface of individual Giardia cells at any time; however, VSP antigen switching occurs spontaneously. In the recent year, significant advances in the knowledge of the antigen switching process have been achieved, which strongly suggests that antigenic variation in Giardia is regulated at the post-transcriptional level by a mechanism similar to RNA interference (RNAi). Several enzymes of the RNAi pathway are directly involved in VSP mRNA silencing and/or translational repression. Although several questions remain regarding how individual VSP antigens are selected for expression on the parasite surface, it is clear that an epigenetic mechanism is involved. In this review, we summarize the characteristics of this fascinating mechanism, analyse conflicting information regarding the structure of VSPs as it relates to the host's immune response, and highlight the major issues that need to be resolved to fully understand antigenic variation in this important pathogen.
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