Corneal epithelial-specific cytokeratin 3 is an autoantigen in Wegener's granulomatosis associated peripheral ulcerative keratitis

PURPOSE. In a previous investigation it was demonstrated that circulating a ntibodies to a 66-kDa corneal epithelial antigen (BCEA-A) are associated wi th peripheral ulcerative keratitis (PUK) in patients with Wegener's granulo matosis (WG). The aim of this study was to identify BCEA-A. METHODS. The 66-kDa antigen was purified from a bovine corneal epithelial p rotein extract, using DE52 ion exchange chromatography. Purified protein wa s used to raise rabbit polyclonal antibodies. These antibodies were used to screen a bovine corneal epithelial cDNA expression library. Positive clone s were purified and sequenced. Clones were identified by DNA sequence homol ogy searches of the GenBank DNA database. RESULTS. A cDNA clone that demonstrated strong binding to both the rabbit p olyclonal antibody and patient sera, showed 85% homology to rabbit cytokera tin 3 (K3). K3 is a basic cytokeratin specific to corneal epithelium. No bo vine DNA sequence for K3 is available. However, bovine K3 is larger than ra bbit K3, with a molecular weight of 66 kDa. Immunofluorescence using both p atient sera and the rabbit antibody demonstrated a cytoplasmic binding patt ern on human corneal epithelium. CONCLUSIONS. This evidence suggests that the 66-kDa autoantigen (BCEA-A) as sociated with PUK in WG is cytokeratin 3, and this may form the basis of a diagnostic/prognostic test.