Figure 4 Fas ligand (FasL) expression occurs only at the luminal surface of hyperplastic polyps. (A) Immunoperoxidase staining was performed in paraffin wax embedded hyperplastic polyp sections using a FasL specific polyclonal antibody. Slides were counterstained with haematoxylin. FasL positive immunohistochemical staining (brown) is shown in a representative hyperplastic polyp. The pattern of FasL immunoreactivity was similar to that seen in normal epithelium, with FasL expression occurring in epithelial cells at the luminal surface, but being absent from the crypt base. (B) Detection of FasL positivity in luminal epithelium illustrated at higher magnification. (C) FasL negative crypt epithelium illustrated at higher magnification. These results are representative of 10 hyperplastic polyps.