CLDN1 and periodontitis: The periodontitis-affected gingival epithelium highly expressed tight junction genes claudin-1 (CLDN1) and E-cadherin (CDH1) (p < 0.001), while the average expression of occludin (OCLN) was also elevated, although this was not statistically significant (Figures 5A–C) (Fernandez-Lainez et al., 2023; Wen et al., 2024).