MDCK cells. Coloured scanning electron micrograph (SEM) of cultured MDCK (Madin-Darby canine kidney) epithelial cells on filter paper (fibres). The MDCK cell line originated in 1958 when it was derived by S. H. Madin and N. B. Darby from the kidney tissue of an adult female cocker spaniel. Since that time, the cells have been widely used to investigate the processing of beta-amyloid precursor protein, as well as the sorting of its proteolytic products. Magnification: x224, when printed 10 centimetres high.