Antigenic variation in Giardia lamblia and Giardia muris trophozoites

ANDREA RÓPOLO; ALICIA SAURA; PEDRO CARRANZA; HUGO DANIEL LUJÁN

Mendoza- Argentina

Congreso; VII Congreso Argentino de Protozoología y Enfermedades Parasitarias; 2005

Giardia lamblia undergoes antigenic variation, a process that might allow the parasite to evade the host?s immune response and adapt to different environments and involves variant-specific surface proteins (VSPs). Giardia muris, which infects mice but not humans, has been used as a model of giardiasis but its use has been limited by the poor knowledge of its biology. To investigate the presence of VSPs in G. muris, PCR assays were performed with generic primers for G. lamblia VSPs and G. muris DNA. Sequence analysis of the PCR products showed characteristic VSP signature motifs and aligment of the deduced amino acid sequences showed a high degree of similarity among PCR products from G. muris and G. lamblia VSPs. Northern blot analysis using the conserved VSP region indicated that VSPs are expressed in G. muris. Also, monoclonal antibodies (MAbs) for G. lamblia and G. muris trophozoites were generated. Many of them labeled the surface of a fraction of G. muris trophozoites in a pattern similar to that seen with MAbs directed to VSPs of G. lamblia. To demonstrate that MAbs recognize G. muris VSPs, we performed Western blot analysis on recombinant VSPs expressed in Escherichia coli. We found that only MAb 2D10 was able to recognize one of the VSPs previously identified in this parasite. Moreover, the frequency of particular VSPs recognized by the MAbs was highly variable in G. muris trophozoites isolated from infected rats or at different time points during infection, suggesting that G. muris undergoes antigenic variation similar to that of G. lamblia. These results suggests G. muris undergoes antigenic variation and indicates it may be a characteristic of all Giardia species. Increased knowledge of the biology of G. muris allows for a better understanding and rational use of the parasite in model infections in mice.