TLR9 immunoreactivity in the nasal mucosa. Immunohistochemical localization of TLR9 in biopsies of nasal mucosa is depicted in (B-F) whereas (A) illustrates a representative picture of a control slide. A) No immunoreactivity was observed in control sections where an isotype-matched control antibody was used. B) In an adjacent section, immunoreactivity for TLR9 is seen in the apical part of the epithelial lining, in scattered intra- and subepithelial leukocytes and in elongated fibroblast-like cells in the subepithelial tissue (arrow). The epithelial TLR9 immunoreactivity varied from being foremost present within the apical region of the epithelium (B) to a more even distribution (C). D) A distinct TLR9 immunoreactivity was also present in endothelial cells (arrowhead). E) Bright field micrographs demonstrating TLR9-positive large non-granulated mononuclear cells (arrowhead) and mast cells (inset). F) TLR9-positive intraepithelial lymphocytes (arrows E-F). Scale bars: A-C = 50 μm, D-E = 20 μm, and F = 350 μm.