MDCK cells (Madin-Darby Canine Kidney cells) are a well-established epithelial cell line used extensively in cell biology research. They form polarized monolayers with tight junctions, making them a valuable model for studying epithelial transport, cell polarity, and virus-cell interactions., MDCK cells are commonly used in drug permeability assays, viral infectivity studies, and investigations of epithelial barrier function. They are typically cultured in DMEM supplemented with serum and antibiotics. The cells' ability to form tight junctions and polarized monolayers depends on culture conditions and cell density. The quantity is often around 10^6 cells/mL.