Autoantibodies of sera from patients with primary biliary cirrhosis recognize the alpha subunit of the decarboxylase component of human branched-chain 2-oxo acid dehydrogenase complex.
OBJECTIVE
The major antigens for anti-mitochondrial autoantibodies in primary biliary cirrhosis (PBC) are the lipoyl-containing components of 2-oxo acid dehydrogenase complexes. Autoantibodies against the E1alpha subunit of the pyruvate dehydrogenase complex (PDH) also have been found, but those against the E1alpha subunit of branched-chain 2-oxo acid dehydrogenase complex (BCKADH) have not been detected. We investigated the occurrence of BCKADH-E1alpha-specific autoantibodies by employing the purified human antigen.


METHODS
The reactivities of PBC sera against purified antigens were assessed by ELISA and by immunoblotting analysis. The specificity of immunoreactivity was confirmed by absorption tests and affinity-purified antibodies.


RESULTS
Fourteen out of 27 PBC sera reacted with BCKADH-E1alpha, and these same sera also reacted with BCKADH-E2. No PBC sera reacted with BCKADH-E1beta. The reactivity of PBC sera with BCKADH-E1alpha was removed only when the sera were pre-absorbed with this antigen. However, reactivities to BCKADH-E2 and PDH-E1alpha were retained. Affinity-purified antibodies to BCKADH-E1alpha reacted with BCKADH-E1alpha, but not PDH-E1alpha. Thus, it was confirmed that anti-BCKADH-Elalpha did not cross-react with either BCKADH-E2 or PDH-E1alpha.


CONCLUSIONS
BCKADH-E1alpha-specific autoantibodies were found in the sera of PBC patients. The antibodies seem to occur subsequent to the anti-BCKADH-E2 antibody production, supporting the concept of intermolecular determinant spreading.
Mori
T
T
Department of Biochemistry, Fukushima Medical University, Japan.
Ono
K
K
Hakozaki
M
M
Kasukawa
R
R
Kochi
H
H
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000818:Animals; D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood* / Q000302:isolation & purification; D001324:Autoantigens / Q000737:chemistry; D016022:Case-Control Studies; D002417:Cattle; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D015151:Immunoblotting; D007658:Ketone Oxidoreductases / Q000737:chemistry / Q000276:immunology*; D008105:Liver Cirrhosis, Biliary / Q000201:enzymology* / Q000276:immunology*; D008930:Mitochondria, Liver / Q000201:enzymology / Q000276:immunology; D009097:Multienzyme Complexes / Q000737:chemistry / Q000276:immunology*; D021122:Protein Subunits; D011768:Pyruvate Dehydrogenase Complex / Q000737:chemistry / Q000276:immunology
D001323:Autoantibodies; D001324:Autoantigens; D009097:Multienzyme Complexes; D021122:Protein Subunits; D011768:Pyruvate Dehydrogenase Complex; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)