An immunohistochemical investigation of canine idiopathic granulomatous scleritis.

The clinical, histopathologic and immunohistochemical findings in three dogs with granulomatous scleritis are reported. The lesions of granulomatous scleritis were characterized by vasculitis, collagenolysis, granulomatous inflammation and perivascular lymphoplasmacytic aggregation. There was evidence of vascular immune complex deposition, and the inflammatory aggregates contained T lymphocytes, IgG plasma cells and macrophages expressing class II molecules of the major histocompatibility complex (MHC). There was no evidence for an infectious etiology in any case, and one of the dogs subsequently developed cutaneous vascular disease consistent with a systemic immune-mediated disorder. Canine granulomatous scleritis has an immunopathogenesis likely involving primary type IV hypersensitivity, with a probable underlying type III involvement.