This antibody recognizes the alpha-smooth muscle isoform of actin. It shows no crossreaction with actin from fibroblasts (beta- and gamma-cytoplasmic), striated muscle (alpha-sarcomeric), and myocardium (alpha-myocardial). Its epitope is composed of the acetyl group and the first 4 amino acids on the N-terminal end of the peptidic chain of alpha-smooth actin. BIOCARE’s 1A4 MAb stains smooth muscle cells in vessel walls, gut wall, and myometrium. Myoepithelial cells in breast and salivary glands are also stained as they also contain actin. This MAb is reportedly useful for identifying tumors arising from smooth muscle and myoepithelial cells.