Abstract
Following the unilateral implantation of metal ear tags in female Crl:CD(SD)BR-rats, chronic inflammatory lesions were observed in both auricles in 7% and 24% of the animals after 30 and 60 weeks, respectively. Involvement of the collateral auricles was identified only after diffuse inflammation of the ear tag-marked pinnae had developed. Histological examination revealed a multifocal granulomatous chondritis, characterized by progressive destruction of the cartilaginous plate and excessive regeneration of cartilaginous tissue. IgG and complement deposits were present in the matrix of the marginal area of regenerating cartilage and at the destruction sites of autochthonous cartilage. It is likely that the pinally-restricted chondritis was due to an autoimmune response initiated by a chronic inflammatory process at the insertion site of the ear tag. Since the respone was not due to immunity to type II collagen, this pathologic phenomenon in rats may provide a useful animal model to study autoimmunity involving other cartilaginous matrix molecules.