Figure 7. In this double-labelled section of canine mammary gland, polyclonal anti-keratin antibody labels the surface epithelium brown (DAB), and anti-calponin monoclonal antibody binds with the marginal myoepithelial cells (BCIP purple). Calponin, a smooth muscle related protein, is also expressed in stromal myofibroblasts in invasive breast carcinomas. Methyl green counterstain. IHC by P.J. Fisher for Dr. B. Summers, Dept. Biomedical Sciences.