Keratins are a family of water-insoluble proteins that form monofilaments, which together comprise one of the primary classes of intermediate filaments in the epidermis and various other epithelial tissues. Typically in epithelial cells, keratin filaments are located throughout the entire cytoplasmic region. Along the cell periphery, the filaments interact with cell matrix and cell-to-cell adhesion complexes. Keratin filament networks function chiefly in the endowment of epithelial cells with the resilience to withstand the mechanical stress that they may incur incidentally. This fact is evidenced by inherited skin fragility disorders, which are linked to mutations in keratins.

The culture of pig kidney epithelial cells featured in the digital image above was immunofluorescently labeled with anti-cytokeratin (pan) mouse monoclonal primary antibodies followed by goat anti-mouse Fab fragments conjugated to Pacific Blue. The specimen was subsequently stained with MitoTracker Red CMXRos and SYTOX Green to label the mitochondrial network and nuclear DNA, respectively. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.