Alveolar epithelial cells (AECs), fibroblasts and fibrocytes all express Toll-like receptor-9. AECs, fibroblasts, fibrocytes and whole lungs were isolated from Balb/c, mice and total RNA prepared and analyzed for TLR-9 expression. The data were normalized to the expression level of TLR-9 in dendritic cells, which was set to 1 (n = 3/group). No TLR-9 message was amplified in cells from TLR-9-/- mice. (B, C) Immunohistochemistry was performed on paraffin wax-embedded whole-lung tissue from normal Balb/c mice. (B) Control staining with secondary antibody only; (C) diffuse TLR-9 staining, with notable staining in the bronchial epithelium, at the alveolar junctions and the interstitium. Fibroblasts (E) and AECs (G) were isolated from Balb/c mice and fixed. Immunofluorescence staining for TLR-9 shows that both cell types expressed TLR-9. The control slides with secondary antibody alone (D and F) did not show any auto-fluorescence or non-specific staining.