Strategy for the characterization of autoantigens in autoimmune diseases. Investigation of the target antigens of antimitochondrial antibodies by radioimmunoassay, immunoblotting, monoclonal antibodies and affinity chromatography.

We present a strategy to characterize specific antigen/autoantibody systems using polyclonal sera from patients as a probe and crude antigenic preparations such as mitoplasts. Sera from patients with primary biliary cirrhosis (PBC) are characterized by at least one of two specific subtypes of antimitochondrial antibodies (AMA), anti-p48 or anti-p62. Immunoblotting of such sera with mitoplast preparations derived from human, rat and rabbit livers revealed three proteins of approximately 27, 48 and 68 kDa as target antigens. On the basis of the molecular weight of these antigens we were able to purify them by elution from preparative SDS gels. Immunization of NZB mice with the high molecular weight component (the 68 kDa antigen from human liver mitoplasts) elicited a monoclonal antibody. The 68 kDa protein was then isolated by affinity chromatography and may well represent the prime target antigen of anti-p62 antimitochondrial antibodies. This experimental approach could be applied to protein target antigens of other autoantibodies.