Amyloid P protein in pseudoexfoliative fibrillopathy

Amyloid P protein was demonstrated by immunostaining in all 14 samples of ocular and conjunctival pseudoexfoliative (PSX) material studied, although amyloid was not found by Congo red staining or ultrastructurally. Immunostaining of PSX aggregates for other common amyloid proteins, including amyloid A, prealbumin, and immunoglobulin light chains, was negative in most cases. In three eyes with advanced neovascular glaucoma there was irregular immunostaining of the PSX aggregates for 2-4 of these other amyloid proteins, besides diffuse staining of the iris and vitreous. Control cases of neovascular glaucoma without PSX disease showed minimal amyloid P, but similar tissue staining for prealbumin and immunoglobulin light chains, consistent with an origin from vascular leakage. The presence of amyloid P protein, a minor serum component, in PSX aggregates in all cases with or without evidence of vascular leakage, indicated a more specific association. Ultrastructural localization of the protein on the periphery of PSX fibers suggest it is not an intrinsic fiber component. Since PSX material has an immunological relation to elastic tissue, we propose that PSX fibers have peripheral binding sites for amyloid P protein, similar to those present on normal elastic fibers.