Keratins as Markers of Epithelial Cells

Epithelial tissues, whether protective (such as skin or gut), or secretory (glandular linings) are required to withstand both physical and chemical stress, while at the same time maintaining normal tissue turnover. Much of this stress resistance is provided by a specialized cytoskeleton formed, as in all human cells, from three types of cytoplasmic filaments: actin filaments, microtubules, and intermediate filaments. The actin cytoskeleton is responsible for changes in cell shape and motility, the tubulin cytoskeleton for orientation and cytoplasmic polarization, and the intermediate filament cytoskeleton provides structural resilience (1 ). Intermediate filaments are 10-nm diameter cytoplasmic structures that, unlike the other two classes, show tissue-specific expression. The five main groups are the keratin filaments (epithelia), vimentin filaments (mesenchyma), desmin filaments (muscle), glial filaments (astrocytes), and neurofilaments (nerve).