Plays a major role in tight junction-specific obliteration of the intercellular space, through calcium-independent cell-adhesion activity. Localizes to tight junctions in epithelial cells. Isoform A1.1: Expressed in lung (PubMed:11585919). Isoform A1.2: Expressed in lung (PubMed:11585919). Isoform A2.1: Expressed in stomach (PubMed:11585919). Isoform A2.2: Expressed in stomach (PubMed:11585919). Belongs to the claudin family.