Specific demonstration of myoepithelial cells by anti-alpha smooth muscle actin antibody.

The myoepithelial cells of the sweat, mammary, tracheobronchial, and salivary glands are specifically identified by monoclonal antibody alpha-SM-1, which recognizes alpha smooth muscle actin and not the other actin isoforms. Basal or "reserve" cells in the stratified epithelia and excretory ducts of the salivary glands are negative, as well as all other epithelial cells in various organs. The reaction can be performed in routinely fixed and embedded tissues and is of practical interest in diagnostic histopathology. In immunoelectron cytochemistry, alpha-SM-1 antibody binds to the microfilament bundles in myoepithelial cells of the breast, but does not stain luminal cells and occasional basally located epithelial cells. These basal cells are morphologically and immunocytochemically distinct from the myoepithelial cells, and their nature and significance remain to be clarified.