Transcriptomic and proteomic analyses of Giardia intestinalis: Intestinal epithelial cell interactions.

Giardia intestinalis is a unicellular protozoan parasite that infects the small intestines of humans and animals. Giardiasis, the disease caused by the parasite, occurs globally across socioeconomic boundaries but is mainly endemic in developing countries and particularly within young children, where pronounced effects manifests in a failure to thrive condition. The molecular pathogenesis of Giardia has been studied using in vitro models of human and rat intestinal epithelial cells (IECs) and parasites from the two major human genotypes or assemblages (A and B). High-quality, genome sequencing of representative isolates from assemblages A (WB) and B (GS) has enabled exploration of these host-parasite models using 'omics' technologies, allowing deep and quantitative analyses of global gene expression changes in IECs and parasites during their interactions, cross-talk and competition. These include a major up-regulation of immune-related genes in the IECs early after the start of interactions, as well as competition between host cells and parasites for nutrients like sugars, amino acids and lipids, which is also reflected in their secretome interactions. Unique parasite proteins dominate these interactions, with many major up-regulated genes being either hypothetical proteins or members of Giardia-specific gene families like the high-cysteine-rich membrane proteins (HCMPs), variable surface proteins (VSPs), alpha-giardins and cysteine proteases. Furthermore, these proteins also dominate in the secretomes, suggesting that they are important virulence factors in Giardia and crucial molecular effectors at the host-parasite interface.