Detection of Anti-mitochondrial Antibodies by ELISA and Western-blot Techniques and Identification by One and Two-dimensional Gel Electrophoresis of M2 Target Antigens

Seven hundred and eleven sera were simultaneously studied by immunofluorescence (IF), complement fixation test (CFT) and ELISA for the detection of anti-mitochondrial antibodies (AMA). One hundred and nineteen of these sera were also studied by Western-blot techniques, while some of them were examined by two-dimensional gel electrophoresis so as to identify the polypeptides recognized by M2 antibodies. The results indicated that: (1) ELISA is a more sensitive technique for detecting type M2 AMA (27 scored positive in 27 primary biliary cirrhosis (PBC), as compared to 21/27 by IF and 16/27 by CFT). (2) Although ELISA appeared to be a promising screening method, some false positive results were observed that necessitated a double confirmation of positive sera by another technique. (3) Western-blot experiments with rat mitochondrial purified preparation indicated that sera from AMA type 2 could recognize eight different polypeptides and that most of them identified 63-60, 48, 44, and 35-33 kD polypeptides, whereas the 54 and 27 kD were less frequently recognized. A trypsin treatment of antigens confirmed the enzyme sensitivity of most of these antigens. These results suggested some heterogeneity among M2 AMA, though this series of PBC was not large enough to relate the heterogeneous pattern noticed in Western-blot to the clinical and histological patterns observed in PBC.