The Madin-Darby canine kidney (MDCK) cell line was initiated in the late 1950s by S. H. Madin and N. B. Darby from the renal tissue of an adult female cocker spaniel. The cells, which stain positive for keratin, exhibit many of the typical characteristics of epithelial cells. The MDCK line has been employed for a variety of studies and has been especially important in research focusing on the processing of beta-amyloid precursor protein and its proteolytic products. MDCK cells are susceptible to an array of viruses, including infectious canine hepatitis, reoviruses 2 and 3, coxsackievirus B5, adenoviruses 4 and 5, vesicular stomatitis (Indiana strain), vesicular exanthema of swine, and vaccinia. They demonstrate resistance to poliovirus 2 and coxsackieviruses B3 and B4.

In the body, epithelial cells are organized into contiguous sheets. Specialized junctions known as tight junctions bind the cells closely together and allow them to collectively serve as a barrier that prevents the diffusion of most molecules. Epithelial cells function in a variety of other ways as well, including secretion, absorption, and protection from abrasion. The specific tasks carried out by particular cells are somewhat dependent on their location in the body. Epithelial cells in the kidneys, for instance, are involved in the storage and secretion of bodily wastes.

In mammalian mitochondria, the oxidative phosphorylation (often abbreviated as oxphos) process is catalyzed by five large membrane-bound protein complexes that are the targets of a wide variety of monoclonal antibodies. The adherent monolayer culture of Madin-Darby canine kidney cells illustrated above was immunofluorescently labeled with a primary mouse anti-oxphos complex V inhibitor protein antibody, followed by goat anti-mouse Fab fragments conjugated to fluorescein. The culture was subsequently stained with Alexa Fluor 568 conjugated to phalloidin to reveal details of the filamentous actin network, and DAPI for DNA in the nucleus. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.