Our preliminary findings that anti-M2/PDC-activity could not be significantly absorbed with any of the linear 167-184 peptides or with peptide 25 or 29 (data not shown), fit to this concept. Based upon molecular modeling of antibodies reacting with antigens, over 90% of B-cell epitopes are thought to be conformational[41,42]. Attempts to map B-cell epitopes have, therefore, kinase inhibitor Alisertib met with mixed success depending largely on the system under investigation. Since there are so many different types of autoepitopes, linear, conformational, cryptic, etc.[43], no universally applicable method is available that allows for the identification of all autoepitopes. Performing those analyses one has, therefore, to be aware of the techniques�� advantages and disadvantages.
Peptide scan as used in the present study does not allow determining conformational epitopes but it has the advantage that even cryptic epitopes can be detected. This method has been proven useful in the identification of immunodominant epitopes of several autoantigens for instance in collagen disorders[43]; and considering the concept of ��epitope-spreading�� it is not unlikely that the multiple immunoreactivity towards several linear and conformational epitopes in an autoimmune disease starts with cross-reactivity to a single (linear) peptide which may lead us to the initiating agent. In conclusion, we have firmly documented that PBC sera react preferentially with peptides of the catalytic domain of PDC-E2. However, it still has to be proven whether this catalytic domain is also targeted by T-cells.
Furthermore, the data again underline the importance of conformational epitopes for AMA-reactivity in PBC. COMMENTS Background Antimitochondrial antibodies (AMA) reacting with the 2-oxo acid dehydrogenase complex of the inner mitochondrial membrane are highly specific for the serological diagnosis of primary biliary cirrhosis (PBC), a chronic cholestatic liver disorder of unknown etiology. Research frontiers The M2-antigen consists of five components which have been identified as subunits of the 2-oxo acid dehydrogenase complex: the pyruvate dehydrogenase complex (PDC), the 2-oxoglutarate dehydrogenase complex and the branched-chain 2-oxo acid dehydrogenase complexes. Each complex comprises multiple copies of three component enzymes termed E1, E2, and E3.
The major M2-antigen which is recognized by nearly 90% of PBC sera is the E2 component Batimastat of PDC. Innovations and breakthroughs Within PDC-E2 an immunodominant epitope has been identified which is associated with the inner lipoyl domain (aa 167-184) wherein a lysine residue (K173) binds the lipoic cofactor for the enzyme. Binding of lipoic acid cofactor to K173 has been discussed to be necessary for antibody reaction. Replacement of this lipoic acid by 2-octynoic acid seemed even to enhance antibody binding.