Regulation of VSP 5G8 protein expression during Giardia lamblia infection and in vitro interaction with epithelial cells

Variant-specific surface proteins (VSPs) participate in antigenic variation; therefore, it is important to better understand their functions and the mechanisms regulating their expression. The expression of the highly immunogenic VSP 5G8 in Giardia lamblia was evaluated both in vivo and in vitro. Meriones unguiculatus were infected with 2 × 10⁶ GS-5G8(+) trophozoites, and parasites were recovered from the small intestine 14 days post-infection (dpi) for analysis of 5G8 expression. Moreover, 5G8 modulation was analyzed after co-culturing GS-5G8(+) trophozoites with the human intestinal epithelial cells Caco-2, and a Transwell system was used to assay 5G8 translocation across the epithelial barrier. Results indicate that, at 14 dpi, G. lamblia trophozoites expressing VSP 5G8 on their cell surface decreased from 35 % to 5 %. Intracellular fluorescence-activated cell sorting (FACS) analysis showed the VSP 5G8(+) population declined from 62 % to 23 %. End-point RT-PCR and western blot analyses detected 5G8 mRNA and protein translation. At 12 h of in vitro co-culture with Caco-2 cells, the percentage of trophozoites expressing 5G8 on their surface decreased from 75 % to 42 %. Furthermore, Giardia induced permeability of the epithelial barrier, demonstrating that it facilitates 5G8 translocation across the epithelial barrier. Overall, these findings suggest that regulation of 5G8 expression may depend on Giardia-host interactions and provide a basis for further investigation into the mechanisms underlying VSP modulation.