Identification of variant-specific of proteins in Giardia muris trophozoites

ANDREA ROPOLO; ALICIA SAURA; PEDRO G CARRANZA; THEODORO NASH; HUGO D LUJAN

Woods Hole

Congreso; XIII Molecular Parasitology Meeting; 2003

Marine Biological Laboratory

One characteristic of Giardia lamblia is its ability to undergo surface antigenic variation by switching the expression of variant-specific surface. Giardia muris, which infects mice but not humans, has been used as a model of giardiasis and the development of immunity, but its use has been limited by inability to culture the parasite in vitro and the poor knowledge of its biology. Whether G. muris undergoes surface antigenic variation is unknown, although a fragment of one putative G. muris VSP homologue was earlier identified (Nash and Heyworth, unpublished). To determine if G. muris undergoes antigenic variation and has homologous proteins to VSPs, PCR products obtained after amplification using generic G. lamblia VSP primers and G. muris DNA were sequenced. These amplicons showed high homology to different G. lamblia VSPs, including the presence of the highly conserved carboxy-terminal domain and a high cysteine content in the N-terminal variable region mostly consisting of CXXC motifs. Interestingly, one G. muris VSP is highly homologous to VSP GS/H7 of G. lamblia. Northern blot analysis using the conserved VSP region indicated that VSPs are expressed in G. muris. Finally, we produced monoclonal antibodies against G. muris membranes and found that many of them label the surface of some trophozoites in a pattern identical to that seen with VSPs of G. lamblia. The presence of homologous VSPs in G. muris suggests it undergoes antigenic variation and indicates that 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.