Expression of toll-like receptor 9 in lungs of pigs, dogs and cattle.

Toll-like receptors (TLRs) are important components of the innate immune system. Compared with other TLRs such as TLR4, there is less data on the expression and function of TLR9, which binds to unmethylated DNA. Because there is no data on the cell-specific protein expression of TLR9 in lungs of cattle, dog and pigs, and pulmonary diseases are the major cause of economic losses, we studied TLR9 expression in lungs using Western blotting, immunohistology and immuno-electron microscopy. We characterized a mouse TLR9 antibody to detect TLR9 in lung extracts from pigs, dogs, and cattle. The TLR9 peptide used to raise the mouse TLR9 antibody had significant homology with TLR9 amino acid sequences from these species. Light and electron microscopic immunostaining localized TLR9 in airway epithelium, vascular endothelium, alveolar macrophages, and pulmonary intravascular monocytes/macrophages in all three species. These data are of potential importance for the understanding of pulmonary immune responses in these veterinary species.