Keratoepithelin in secondary corneal amyloidosis

Amyloid is found in several corneal dystrophies, including distinct lattice corneal dystrophies (LCD) and Avellino corneal dystrophy. Recently, point mutations in the transforming growth factor-beta-induced gene (TGFBI) encoding for keratoepithelin (KE) have been demonstrated in these corneal disease entities. We intended to investigate if KE was also a component of the rarely seen secondary corneal amyloid deposits. Immunohistochemical staining with a polyclonal antibody against KE was performed on formalin-fixed paraffin-embedded tissue of five corneal buttons with secondary amyloid obtained after keratoplasty. Secondary amyloidosis was due to Fuchs' endothelial dystrophy (FED) with bullous keratopathy and/or recurrent erosions in all cases. The diagnosis had been established by light microscopy using Congo red staining. Two cases of LCD type I served as positive controls and three corneas with FED and one with keratoconus without amyloid served as negative controls. All corneas with secondary amyloidosis as well as LCD type I revealed positive staining in the respective amyloid deposits. KE was localized in the subepithelial pannus and in the anterior stroma in the corneas with secondary amyloidosis. In the specimens with LCD type I it was distributed in the amyloid deposits located in the anterior and mid-stroma. Staining for KE showed a granular appearance in all cases. The intensity of staining was variable among the specimens. KE is found not only in primary amyloid deposits of hereditary corneal dystrophies, but also in secondary amyloidosis of the cornea of diverse ethiologies.