Pattern-recognition receptor mRNA expression and function in canine monocyte/macrophages and relevance to canine anal furunuclosis.

Pattern-recognition receptors (PRRs) are important components of the innate immune system, enabling early detection of infection. Defective PRR function has been implicated in several infectious and immune-mediated diseases of human beings, including Crohn's disease (CD). Anal furunculosis (AF) is an immune-mediated disease which primarily occurs in German shepherd dogs (GSD) and could result from a similar type of PRR dysfunction. The aim of the current study was to investigate canine PRR responses in vitro and to test the hypothesis that these were altered in AF-affected GSD. The pattern-recognition receptors TLR1, TLR2, TLR4, TLR6, TLR9, NOD1 (nucleotide-binding oligomerisation domain) and NOD2 were evaluated in the DH82 canine monocyte/macrophage cell line. These cells were found to express mRNA for all the selected PRRs with TLR2 mRNA the most and TLR5 mRNA the least abundant. A similar pattern of expression was found in canine blood-derived monocyte/macrophages. Stimulation of DH82 cells and blood-derived monocyte/macrophages using specific PRR-ligands, resulted in expression of pro-inflammatory cytokine mRNA. Quantification of TNFalpha mRNA and protein secretion from stimulated cells demonstrated variable responses with lipopolysaccharide (TLR4 ligand) and PAM(3)CSK4 (TLR1/2 ligand) proving to be the most potent and CpG DNA (TLR9 ligand) the least potent. Comparing PRR responses in blood-derived monocyte/macrophages from healthy blood-donor dogs with those from AF-affected GSD showed a deficiency in the latter in response to LD-MDP (NOD2 ligand) at the mRNA level but not at the protein level. It is possible that dysfunctional NOD2 responses by cells of the monocyte/macrophage lineage are involved in the pathogenesis of AF.