Abstract: The intestinal protozoan parasite Giardia lamblia is one of the most common causes of diarrhoea and undergoes antigenic variation. In pathogenic microorganisms, antigenic variation is often described as a mechanism to evade the host immune system, resulting in chronic and/or recurrent infections. In the recent years, significant advances in the knowledge of the antigen switching process have been achieved. Here we review the principal knowledge on the mechanisms that regulate this process, including genomic organization, post-tanscriptional gene silencing, expressional modifications, and processing and turnover of VSPs.

Key words: Giardia lamblia, Variant-specific surface protein, Antigenic variation, Post-tanscriptional gene silencing （PTGS）