Experimentally Induced Eosinophilic Polyps in Rabbit Sinuses

Abstract

Nasal polyps are one of the most common findings of physical examination in the otolaryngology area and the experimental model of nasal polyps in the rabbit maxillary sinus is helpful for clarifying the mechanism of polyp formation. Several protocols have been reported for this model, but most of them involved infectious polyps without eosinophil infiltration. We have attempted to establish a novel rabbit model of polyps associated with eosinophil infiltration. Rabbits were either untreated (group A) or sensitized with ovalbumin (OVA; groups B-D). After repeated exposure to OVA, some animals further received valine-glycine-serine-glutamine (group C) or poly-L-arginine (group D) in their maxillary sinuses for 4 weeks. Subsequently, sinus tissues were dissected and subjected to histological analysis. The changes in mRNA expression were analyzed by DNA microarray. Remarkable histological changes were observed in groups C and D but not in group B in eosinophil number in the maxillary sinus mucosa, the width of the lamina propria, and polyp scoring. These changes in group D were greater than those in group C. DNA microarray analysis revealed that up-regulated genes in group D included those related to inflammation and extracellular matrix metabolism. On the other hand, down-regulated genes in group D involved those related to anti-inflammation. Our results indicate that treatment with inflammatory agents, in combination with an antigen-dependent immune response, could induce nasal polyp formation associated with eosinophil infiltration and mucosal hypertrophy. The gene expression profile supported the clinical relevance of this model.