Figure 2.

Isolate comparison and dose dependency. We analyzed the effects of Giardia colonization of epithelial monolayers on TEER using the Caco-2 clone bbe, since it is reportedly more homogeneous than other clones or its parental line (Sambuy et al., 2005; Liévin-Le Moal, 2013; Srinivasan et al., 2015). Although, Caco-2 cells have been derived from a human colon cancer patient, a 21-day phase of confluent incubation ensures their differentiation toward a polarized small intestinal enterocyte-like cell type, considered as a model for the small intestinal epithelial barrier (ibid.). In this setup, we tested 11 different G. duodenalis isolates at MOIs of 20, including 5 reference strains WB6, NF, S2 (assemblage AI), GS (assemblage B), P15 (assemblage E) and 6 newly established clinical isolates (1 assemblage AII and 5 assemblage B). Data is relative to measurements before infection. Uninfected controls (CTRL-) were sham treated, monolayers with induced apoptosis using 1 μM staurosporine served as positive (leaky) controls (CTRL+). Each point represents the mean of 3 independent experiments with 3 monolayers per condition per experiment. Error bars indicate standard deviation. No evidence for parasite-induced decreases in TEER was found. In contrast, all tested isolates led consistently to a dose-dependent TEER-increase, without significant differences between isolates or assemblages.