Representational difference analysis identifies specific genes in the interaction of Giardia duodenalis with the...

Giardia duodenalis is a re-emerging protozoan parasite that causes diarrhoea in humans, significantly affecting the health of many people globally. To date, little is known about the genetic events underpinning the establishment of infection in host cells; however, the parasite's ventral disc, proteases and variable surface proteins (VSPs) are recognised as important pathogenic factors. In this study, representational difference analysis (RDA) was used to identify differentially expressed genes in four different Giardia isolates (WB, P-1, NF and GS/M) during the first 2h of in vitro interaction with the rat intestinal epithelial cell line, IEC-6. RDA showed that more than 40 genes were differentially expressed in each of the four Giardia isolates upon IEC-6 cells infection. Most of the up-regulated genes were common to the four isolates except for those encoding proteins possibly involved in immune evasion such as VSPs, high cysteine membrane proteins (HCMp), hypothetical proteins, and oxygen defence proteins (e.g., thioredoxin, peroxiredoxin 1). Differences in the expressed VSPs and HCMp may account for the variation in symptoms during giardiasis. Interestingly, the NF isolate solely expressed genes involved in encystation during interaction with IEC-6 (e.g., glucosamine 6-phosphate isomerase, dynamin, acid sphingomyelinase-like phosphodiesterase) suggesting that encystation signals could be different for this isolate. Common to the four isolates, transcripts for genes involved in glycolysis (e.g., glucose-6-phosphate dehydrogenase, fructose bisphosphate aldolase, enolase), attachment (γ and α1 giardins) and cysteine proteases were frequently detected. Genes involved in transcription, translation, signalling and cell cycle control were also up-regulated. This study shows that the RDA technique has selectively isolated genes involved in host-parasite interactions and complements previous microarray data. Some of the detected genes are also discussed as potential virulence factors and treatment targets in giardiasis.