Ultrastructural study of unidentified inclusions in the cornea and iridocorneal angle of dogs with pannus.

The corneas and/or the iridocorneal angles of 13 dogs were examined morphologically by use of transmission electron microscopy. Virologic identification techniques also were used for tissue from 2 dogs. Four dogs had clinical signs of chronic superficial keratitis or pannus, 9 dogs had normal eyes. In the tissue from 7 dogs (4 German Shepherd Dogs with chronic superficial keratitis; 2 German Shepherd Dogs and 1 mixed-breed dog with normal eyes) we found unusual cytoplasmic inclusions. Inclusions were not found in dogs of other breeds with normal eyes. The inclusions were observed in corneal fibroblasts, vascular endothelial cells, and macrophages, as well as in trabecular cells and fibroblasts of the iridocorneal angle. They were often grouped within the rough endoplasmic reticulum or found free in the cytoplasm. The cylindrical particles had a helical substructure, measuring 20 nm in diameter and up to 400 nm long, with a distance of 10 nm for the repeating turns. Results of virologic culturing on canine and seal kidney cells were negative, as was staining with fluorescein isothiocyanate-labeled antibodies against canine distemper virus, canine herpesvirus, canine parvovirus, and canine adenovirus. Relevance of the inclusion bodies described is discussed. Because our results seem to hint at a correlation between presence of the rod shaped particles and German Shepherd Dogs with pannus, we suggest that an etiologic or pathogenic connection exists that merits further examination.