OCLN and chronic kidney disease: Interestingly, in the CKD and ESKD groups, we observed a gradient of occludin immunostaining positivity along the length of the villi, from crypt to tip; occludin expression was maintained in the crypts and basal portion of the villi, and was reduced in the middle part of the villi in both groups, CKD and ESKD (p < 0.001, p < 0.01, respectively), while greater loss of its expression was observed at the tip (p < 0.001, respectively) (Table 4).