Immunoreactivity to cytokeratin 8/18 in patients with soluble liver antigen (SLA) positive autoimmune hepatitis (AIH type 3) is not sufficient for diagnostic use.

"Soluble liver antigen" (SLA) has been reported to be an infrequent but in certain cases a unique marker of autoimmune hepatitis, with cytokeratins 8 and 18 as major antigenic components. Using precharacterized sera, we could confirm trypsin sensitivity and a molecular weight of approximately 50 kD of the reactive protein. However, the reaction differed from that of cytokeratins 8 and 18 by molecular weight and a pI of 7.5. A significant reactivity to cytokeratin 8 and 18 preparations was seen in only 1/12 patients. Immunoscreening of a human liver expression gene bank yielded no clones with sequence homology to cytokeratins. We conclude that reactivity in SLA positive sera is not mainly directed against cytokeratins 8/18 and recommend native antigen preparations for diagnostic use until the exact molecular nature of the 52 kD SLA antigen has been elucidated.