Giardia-induced downregulation of mRNA and protein expressions of TJ proteins (claudin-1, claudin-4, occludin, and ZO-1) and NO production in Caco-2 cells could be significantly reversed by application of 3-MA rather than CQ (Figures 2D–F), revealing a tight link between early-stage autophagy occurrence and Giardia infection-related TJ/NO downregulation. Here, CLDN1 is linked to giardiasis.