Murine monoclonal antibody to mitochondria reacts with the 72 kD antigen of primary biliary cirrhosis.

BALB/c mice were immunized with canine gastric mucosal cells enriched to 70% for parietal cells, to produce monoclonal antibodies (MoAb). Three MoAb, FMM-4C5, FMM-4C9 and FMM-2B2, were obtained which reacted by indirect immunofluorescence with gastric parietal cells and kidney tubules, predominantly distal kidney tubules, with a pattern similar to that of the M2 autoantibodies of primary biliary cirrhosis (PBC). The antibodies also reacted with tissues from rabbit, rat, pig, human and with rod-shaped structures in acetone-fixed monolayer cultures of human fibroblasts and HEp 2 cells. FMM-4C9 and FMM-2B2 reacted with tissues from BALB/c mice but FMM-4C5 did not. Immunoblots of FMM-4C5 with mitochondrial fractions showed that the antibody recognized a 63 kD antigen from dog stomach, rat kidney and rat liver, and a 72 kD antigen from human placenta; mouse preparations were not reactive. The antigen co-migrated with that recognized by serum from cases of PBC and some cases of progressive systemic sclerosis. Absorption of the mitochondrial fraction with PBC sera removed reactivity by immunoblotting with the murine autoantibody and vice versa. Two dimension immunoblots showed that the murine and human antibodies recognized an identical series of paired 'spots'. FMM-4C5 also reacted by immunoblotting with a rat recombinant mitochondrial polypeptide which has disease-specific reactivity with PBC sera. Absorption with recombinant polypeptide removed anti-mitochondrial activity by immunoblotting and immunofluorescence. These observations suggest that the MoAb FMM-4C5 recognizes part of the same 72 kD molecule recognized by human PBC sera. The murine monoclonal antibodies should be useful probes for further studies of the structure, function and possible pathogenicity of the 72 kD autoantigen.