Type 1, liver kidney microsomal
autoantibodies (LKM-1) are associated with a subgroup of idiopathic autoimmune type,
chronic active hepatitis (CAH). The
antigenic specificity of
LKM-1 autoantibodies from 13 patients was investigated by immunoblot analysis of human liver microsomal
proteins.
Polypeptides of 50, 55, and 64 kD were detected with these
antisera. A high titer
LKM-1 serum was selected to screen a human liver lambda gt11
cDNA expression library, resulting in the isolation of several complementary (c)
DNA clones.
Autoantibodies affinity purified from
proteins expressed by two of the immunopositive
cDNA clones, HLD8.2 and HLD13.2, specifically react with a 50-kD
protein of human liver microsomes and display immunofluorescence staining of the proximal renal tubular epithelia characteristic of
LKM-1 sera. Determination of the sequence of HLD8.2 revealed that it encodes a recently described
cytochrome P450db1. A bacterial fusion
protein constructed from HLD8.2 proved to be a specific and sensitive diagnostic
reagent. All sera from patients with
LKM-1 positive
liver disease react with this fusion
protein. No reaction was seen, however, for sera from patients with other types of autoimmune
liver diseases, viral
hepatitis, systemic immunological disorders, or healthy controls.