AbstractThe genus Megalocytivirus, belonging to the family Iridoviridae, is one of the most detrimental virus groups to fish aquaculture. Megalocytivirus creates a virus-mock basement membrane (VMBM) on the surface of infected cells. This membrane provides attachment sites for lymphatic endothelial cells (LECs), disrupting fish's endothelial cell-extracellular matrix system. This disruption triggers injury to the vascular system and can result in death. Exploring the VMBM-cell interaction mechanism is crucial for uncovering the pathogenesis of Megalocytivirus and identifying therapeutic targets. Claudins, a class of tetra transmembrane proteins, play a key role in creating tight junctions between endothelial or epithelial cells. In this study, we demonstrated that the expression of Claudin2, a member of the Claudin family in fish, was significantly up-regulated by Megalocytivirus infection. Claudin2 was found in LECs attached to the surface of infected cells. It interacted with the VMBM viral components VP23R, VP08R, and VP33L at multiple binding sites through its two extracellular loops. However, it did not interact with the host basement membrane’s nidogen. Therefore, Claudin2 is involved in the interaction of LEC with VMBM and plays a role in the disturbed distribution of extracellular matrix and endothelial cells in Megalocytivirus-infected fish tissues. This study aims to uncover the molecular mechanisms by which Megalocytivirus infection leads to pathological changes in the vascular system.