Spontaneous development and characterization of an endothelial-like cell line from mandarin fish Siniperca chuatsi.

Infectious spleen and kidney necrosis virus (ISKNV), the type species of genus Megalocytivirus within Iridoviridae family, stands as a leading causative agent of viral diseases in diverse teleost fish globally. Previous study has demonstrated that lymphatic endothelial cells exhibit specific adhesion to virus-mock basement membranes (VMBMs) formed outside ISKNV-infected cells, underscoring the critical role of this interaction in the ISKNV infection process. However, the lack of a dedicated endothelial cell line has significantly hindered in vitro investigations into ISKNV pathogenesis. Here, we developed and characterized an endothelial-like cell line, designated as MEC, derived from the heart tissue of mandarin fish (Siniperca chuatsi). The MEC cell line has been stably sub-cultured for over 80 passages and displays typical endothelial-like features, including a classical polygonal "pavement-like" morphology, the ability to form tube structures in vitro, and robust phagocytic activity toward latex beads. Susceptibility assays, including cytopathic effect observation, fluorescent tracing of GFP-labeled ISKNV, Western blotting, qRT-PCR, and transmission electron microscopy (TEM), confirmed efficient replication of ISKNV in MEC cells. Temporal gene expression analysis revealed that ISKNV dynamically modulates the transcription of host genes involved in viral invasion, such as vascular endothelial growth factor, antiviral genes, immune pathway-associated genes, interferon regulatory factors, cytokines, chemokines, and their receptors. These findings provide mechanistic insights into how ISKNV subverts host immunity through endothelial cell attachment. Collectively, the MEC cell line establishes a valuable in vitro model for dissecting the role of endothelial cells in Megalocytivirus infection and advancing our understanding of immune regulation in mandarin fish.