Transcriptional changes in Giardia during host-parasite interactions.

Giardia intestinalis is one of the major causes of parasite-induced diarrhea. The disease, giardiasis, is caused by trophozoites attaching to the intestinal epithelium, resulting in apoptosis of intestinal epithelial cells, disrupted epithelial barrier function and malabsorption. Microarray studies have detected extensive gene expression changes in intestinal epithelial cells (IECs) during interaction with Giardia trophozoites in vitro. In the present study, we examined this host-parasite interaction further by transcriptional profiling of interacting trophozoites using Giardia microarrays. A total of 200 Giardia transcripts were significantly changed due to the interaction, lasting up to 18 h in complete growth medium. Quantitative reverse transcriptase PCR confirmed the changes in all 12 genes tested using mRNA isolated in separate experiments. Genes encoding proteins previously suggested to be important during host-parasite interactions such as arginine deiminase, enolase and cysteine proteinases were up-regulated early but down-regulated later during the interaction. Cell division and attachment genes were down-regulated in the late time-points of interaction. The most highly up-regulated genes encode oxygen defense proteins and several members of the high cysteine membrane protein (HCMp) and Gly-rich repeat (GRREAT) families. Putative small RNAs were up-regulated, whereas the 5S rRNA was slightly down-regulated during the interaction with IECs. Thus, there are extensive gene expression changes in Giardia trophozoites and IECs during host-parasite interactions which can be important for establishment of infection and the induction of giardiasis.