Claudins are a family of proteins that are the most important components of tight junctions, where they establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium. They are small (20-27 kDa) proteins with similar structures. They have four transmembrane domains, with the N- and C-termini in the cytoplasm. This antibody is specifically against Claudin 4. Claudin 4 is overexpressed in a variety of cancers. It can be used as a predictor of recurrent malignant pleural effusion in patients with advanced non-small cell lung cancer (PMID: 38629624). Claudin 4 is the receptor for B. fragilis toxin (BFT), an important oncogenic protein. Blocking the interaction between BFT and Claudin-4 can inhibit the cleavage of the substrate E-cadherin by BFT and reverse the tissue damage induced by BFT in mice (PMID: 42020735).