Altered keratan sulfate epitopes in keratoconus.

Extracts of normal and keratoconus human corneas were assayed for keratan sulfate (KS) and for the protein core of corneal keratan sulfate proteoglycan (KSPG), using a solid-phase immunoassay. Aliquots from guanidine-HCl extracts of four to six pooled corneas were adsorbed to nitrocellulose membrane and assayed for binding of a monoclonal antibody against KS or of an affinity-purified rabbit polyclonal antibody against the KSPG protein core using 125I-labeled secondary antibodies. The amount of antigen in the extracts was estimated from standard curves with purified bovine KSPG. Extracts from keratoconus corneas contained only an average of 48% as much (P less than 0.001) KS-antigen as normal corneal extracts when assayed with anti-KS monoclonal antibody. There was no significant difference in the amount of KSPG core protein antigens in keratoconus and normal corneal extracts. These results suggest that corneas with keratoconus contain a form of KSPG that contains fewer keratan sulfate chains or in which the keratan sulfate has a modified structure.