Studies of Giardia-host interactions: role of cysteine-rich surface proteins.

Giardia intestinalis is a eukaryotic parasite that colonizes the small intestine of humans and animals causing the diarrheal disease known as giardiasis. This parasite is not invasive and does not internalize into host cells but it rather attaches to the brush border surface of the small intestine disrupting the epithelial barrier. Giardia causes around 280 million symptomatic infections in humans every year, while it can also cause chronic and asymptomatic infections. Giardiasis is a multifactorial disease but only few factors that directly contribute in the pathogenesis and virulence of the disease have been identified. G. intestinalis has eight genetic groups, but only two of them (A and B) are known to infect humans. In this thesis, whole genome sequencing was performed for two human assemblage A isolates (AS175 and AS98) and were compared to assemblage A isolate WB genome (Paper I). Genome-wide variations were identified among the three isolates including isolate-specific coding sequences and high level of nucleotide diversity of multi-gene families such as VSPs and HCMPs. We further used an in vitro model for parasite interaction with host intestinal epithelial cells (IECs) to study the interplay between Giardia and the human host. We have identified the major Giardia excretory-secretory products (ESPs) released by two Giardia isolates (WB and GS) when they interact with the Caco-2 IECs (Paper II). Wide changes in the transcriptome (Paper III) and the proteome (Paper IV) of the parasite (WB isolate) and the host IECs have been studied giving us a further understanding of the parasite-host interactions. An understudied gene family (HCMPs) was studied and further characterized during interactions in both RNA and protein level (Paper III, IV). In conclusion, the thesis has provided a further understanding of Giardia-host interactions in vitro and the molecular mechanisms involved